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4.0L Jeep Six: Cylinder #1 Misfire Trouble Code


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My TJ has an occasional cylinder 1 misfire indicated by the check engine light and an occasional lurch at highway speed.  I have noticed the misfire when cruising at highway speed after driving about 20 minutes and feeling a sudden lurch, or when sitting at a red light idling.  The engine runs fine aside from the occasional lurch and running rough at idle.  I suspected a sticky lifter so I ran Sea Foam in the oil for about 2k miles and then changed the oil and filled with 10w-40.  I never noticed a misfire on the highway after this, but it idles rough at stop lights and the check engine light came back on at a stoplight.  It will probably turn off if I drive the highway a few times.  Wondering if there's an interim fix to get by another 6 months or year without getting stranded by this thing.  It's a 1998 with 250k miles on it, but I'm trying to put off replacing the engine due to the expense and I'm not sure it's worth it on a vehicle this "used".  Is there any chance an even heavier weight oil is a temporary fix?  Or is this engine shot and needs overhaul or replacement? 

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Hi, JJ, and welcome to the forums!  The #1 misfire could be a variety of things.  Since you did ask about engine longevity and whether the engine is at the end of its duty cycle, I'll start with a suggestion:  Begin with a compression test, or better yet, a cylinder leak down test.  Any internal combustion engine needs four things to be "right", I talk about these basics in each of my books.  My mantra for basic engine condition:

 

1) Normal compression or cylinder seal, I prefer a leak down test for this reason.

2) Normal oil pressure and flow, since the bearings and lubricated parts must remain in reliable condition.

3) Normal valve timing, which means the timing chain and sprockets are in good condition.

4) Normal valve lift, which means that the camshaft lobes, lifters and rocker assemblies are in good condition.

 

Once you get past these concerns, any engine problems are either vacuum leaks, "tune" related or engine management (fuel/spark) issues. 

 

Your TJ 4.0L engine uses an ignition distributor for the high tension spark delivery alongside an MPI fuel system.  The distributor spark timing is fully controlled by the PCM (computer) and its sensor readings.  The PCM also controls fuel flow through the injectors.  A check light or 'MIL' with a consistent "#1 Cylinder Misfire" could be relative to either fuel flow or the spark at that cylinder. 

 

Spark wise, this could be a weak spark lead, worn distributor cap and rotor, the spark plug itself, or engine troubles like low compression or a leaky valve.  A misfire can also be fuel related.  Poor fuel pressure/supply can be the issue.  (See the Mopar EFI comments in the threads from the CJ forum:  Mopar EFI Conversion starving for fuel.) 

 

The injector for #1 cylinder can be clogged, too.  Or, there may be an unrelated device to consider, like the throttle position sensor (TPS) or the oxygen sensor (upstream sensor).  Sometimes, these other components will not send their own signal, yet they contribute to something like the #1 misfire.  I don't recommend replacing a number of parts randomly, JJ, I'm just calling attention to related trouble spots...

 

After ruling out the overall engine condition, I'd check the fuel pressure at the injector rail.  This should be around 49.2 PSI +/- 2 to 5 PSI.  That test can be revealing.  The #1 spark wire lead should also be tested for ohms-resistance, and spark to the #1 plug should  appear consistent. 

 

Spark plug and other ignition issues should be ruled out.  The #1 injector is more likely to be consistently faulty—not likely to be intermittently faulty.  This is still a possibility, though, so don't rule out a defective injector.

 

For additional troubleshooting guidelines, see these two articles at the magazine, covering tune and troubleshooting on Jeep MPI fuel-and-spark management like yours, JJ:

 

http://www.4wdmechanix.com/Jeep-Multi-Point-Injection-Operation-and-Troubleshooting.html

 

http://www.4wdmechanix.com/Jeep-TBI-&-MPI-Advanced-Troubleshooting.html

 

Let the forum community know what you turn up.  I'm certain other forum members will benefit from this exchange, JJ, your questions are thoughtful! 

 

I'm here for more discussion...

 

Moses

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Hi Moses,

 

Thanks for the reply.  I really appreciate your use of fundamentals when troubleshooting.  Our family has a busy summer ahead, so I'll try and post some results when I can.  Probably not for at least a couple weeks.  I need to scare up a leak down tester.  I saw a video http://www.youtube.com/watch?v=GvG22YMOzUI on how to do it that looked pretty good. 

 

I suspect #1 - cylinder seal - may be a problem because of the high mileage.  I was hoping 10W40 might help extend the engine a bit here? 

I suspect #4 - valvetrain wear - may also be a problem due to high mileage. 

Based on the oil pressure gage in the instrument cluster, #2 seems OK as oil pressure runs where it has been for 15 years. 

I'll have to check past repair slips, but I think for #3 the timing chain and sprockets and water pump were replaced in the last five years. 

I hear and smell exhaust under the hood when the engine is running.  The engine used to have the standard ticking of the tappets, but now it makes a putt-putt sound like an old tractor.  I'm still running the stock header after all these years, so perhaps it is cracked or maybe the gasket between the header and head has failed?  Any reason to believe this would relate to a misfire? 

Adding to my puzzlement is the fact that this engine consumes no measureable amount of oil and has good power.  The dipstick reads full even when I'm ready for the 3k-5k oil change. 

 

Thanks again

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JJ...I understand your time constraints and family commitments.  Family takes precedence...I'll respond to your questions then open a new, follow-up topic about why I recommend the use of a leak down tester compared to a compression gauge...First, your questions and my answers:

 

Q: I suspect cylinder seal may be a problem because of the high mileage.  I was hoping 10W-40 might help extend the engine life a bit here? 

A: Yes, we're attempting to rule out a cylinder seal problem.  There are two entirely different ways to look at cylinder seal: 1) adequate spinning compression to produce sufficient combustion, and 2) true cylinder seal that will prevent seepage under load and resist blow-by. 10W-40 instead of 5W-30 will not compensate much for wear; however, it will help alleviate nuisance rear main or timing cover seal seepage (will not stop an actual leak), and it may reduce oil consumption from valve guide, guide seal or ring blow-by issues.  The wear we're concerned about in terms of leak down is at the valves, rings and head gasket—and casting leaks in the worst case scenario, like a cracked cylinder head from severe overheating.

 

Q: I suspect valvetrain wear may also be a problem due to high mileage. 

A: This can be a problem, and we'll get right down to the bottom of that issue in my follow-up topic on the leak down test! If you mean valvetrain wear in terms of valve lift error, valve lift can be measured with a dial indicator at the rocker arms (valve cover removed). You do need proper valve timing and correct valve lift.  Valve lift corresponds to the camshaft lobe shape, lifter function, valve/lifter clearance and rocker arm function.

 

Q: Based on the oil pressure gauge in the instrument cluster, oil pressure runs where it has been for 15 years. 

A: This is a good sign, helpful in terms of bearing life expectancy if you do make other repairs.  If pressure did read low, you might want to make major repairs rather than spending money on a patch repair.  Avoid the proverbial "good money after bad" scenario... 

 

Q: I'll have to check past repair slips, but I think the timing chain and sprockets and water pump were replaced in the last five years. 

A: That's helpful and would eliminate or reduce the likelihood of having a valve timing problem.  Had the valve timing not been set properly, you would have experienced trouble immediately, as the PCM receives both a crankshaft position and camshaft position reading from your TJ 4.0L inline six.  If out of sync too much, the PCM would throw a trouble code.

 

Q: I hear and smell exhaust under the hood when the engine is running.  The engine used to have the standard ticking of the tappets, but now it makes a putt-putt sound like an old tractor.  I'm still running the stock header after all these years, so perhaps it is cracked or maybe the gasket between the header and head has failed?  Any reason to believe this would relate to a misfire? 

A: The sound of an exhaust leak could very well be a cracked OEM header, it's amazing that your header lasted this long if original!  Sounds like a leak from the exhaust manifold gasket area or a cracked exhaust manifold/header.  This would not be the "cause" of the misfire, however, an exhaust leak near the head is dangerous in terms of valve warp risk.  Under extreme conditions, if colder air drafts back into the engine (at the exhaust port or ports) when the engine shuts off, an exhaust valve can warp.  Valve warp like this is unlikely, and the leak down test will reveal that kind of problem.  (See my leak down tester follow-up topic post.)

 

Q: Adding to my puzzlement is the fact that this engine consumes no measureable amount of oil and has good power.  The dipstick reads full even when I'm ready for the 3k-5k oil change.

A: Let's not rule out the possibility that the engine is still viable and functions okay!  In my follow-up on the leak down test, I will explain how oil consumption does not always occur when there is engine wear.  An engine can have oil ring seal without compression ring seal; in the extreme, this can be an engine with inadequate compression or cylinder seal, yet an engine that still resists oil blow-by and oil burning—or "consumption". 

 

Keep in mind, JJ, we're simply trying to rule out an engine condition issue, separating engine "long block" problems from vacuum leaks, fuel flow issues and spark misfire.  If the basic engine tests okay, the tune-related problems can be sorted out and fixed.

 

Please see the leak down test explanation at my follow-up leak down test post...

 

Moses   

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Hi Moses,

 

I have a small update on my cylinder 1 misfire on my 1998 TJ with 250k miles (and counting). 

 

I stopped by the auto parts store to shop for a cylinder leak down tester.  I've read what you wrote about how to do the cylinder leak down test and I was making a list of what I'll need:

 

Leak down tester

air compressor (I only have a small tire/ball inflator)

Looks like about a 3/4" bolt to turn the crankshaft to TDC (I have basic wrenches and sockets)

A spark plug wire boot puller because the one on cylinder #1 is tough to remove because of the AC plumbing

 

More to the point, while I was there I thought it would be good to borrow their OBDII scan tool and check the recent codes just to see if any other cylinders are misfiring.  Every time I've checked it (until today), I get P0301 Cylinder 1 misfire detected. 

 

Today I got three codes - maybe this gives some more valuable clues as to why my engine is misfiring...  With the engine off, I plugged in the scan tool, turned the key to on (engine not running), and here's today's codes:

 

P0201 Injector circuit open cylinder 1

P0123 TPS/Pedal position sensor A circuit high input

P0301 Cylinder 1 misfire

 

I still like your approach of checking the health of the engine with the cylinder leak down test to tell its viability.  Armed with additional OBDII codes, does this now suggest the more immediate problem is in the electronics?  Should I be replacing the TPS sensor (throttle position sensor, I believe)?  NAPA had one for $60.  I have not yet looked at my Haynes manual to see what's involved.  I am interested in your feedback. 

 

I've enjoyed reading some of the other posts and the magazine.  I have a few more topics for future posts I can add later just to stir up some conversation.  For instance this Jeep of mine has been without 3rd gear (AX-15 5 speed manual) for a year or so (I just wind up 2nd gear and skip to 4th).  Also my airbag light is on and my cruise control no longer works (related?  clock spring?).  And it's got a bit of death wobble despite replacing a very worn out front track bar.  And lastly, I thought I read you were planning a write up about air conditioning - I've added refrigerant to mine in summer's past, but it doesn't last as long as it used to - looking forward to your future articles! 

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Sounds like you've been busy and committed to a solution, JJ!  I like your pursuit of a leak down tester; this will demystify the engine's condition and seek out a possible compression loss that could cause a misfire.  Trust the tool will pay for itself on this engine work and other projects.  I've had my Snap-On MT324 for decades and am always pleased with its pinpoint diagnosis.

 

Your new codes do hint of a TPS switch problem.  I had a specific TPS switch issue/code around 110K miles on our XJ Cherokee.  I purchased an aftermarket Brand-X replacement, and it worked for a short time before causing a misfire string that resembled a short or burned wiring from the crankshaft position sensor.  Anyway, I sourced a second TPS from AutoZone on a Sunday, their own "brand", installed it, and no trace of a problem since. 

 

Some offshore stuff works, sometimes not.  As just one example, let's consider the oxygen sensor.  For Jeep and other Chrysler products, I specifically recommend genuine Mopar or at least ND brand as a direct crossover.  Denso was the OEM supplier to Chrysler, and oxygen sensors have very sensitive ohms feedback, heating functions and such.  See my article, this also applies to other electronic components in the fuel-and-spark management system: http://www.4wdmechanix.com/Use-OEM-Mopar-Oxygen-Sensors!.html.

 

I'd try a TPS, even though I'm set against "parts replacing" experiments.  The TPS is a wear item and prone to fail long before your 250K miles on the TJ Wrangler.  This would be the first order of business to see if the other two codes clear as well.  You'll find the TPS easy to replace; think of it as a spring loaded voltage rheostat or potentiometer.  The TPS fits one way with a slight tension as you install the switch and rotate it into position.

 

Your TPS does not require a voltage calibration, it's a straightforward replacement.  Exercise precaution with the aging plug connector.  Make sure the O-ring seats properly.  I use automotive dielectric grease on the plug connector contacts for a moisture barrier.  Considering how many issues can begin with a defective TPS, this is a good place to start.

 

It's actually good that you don't have several cylinders randomly showing misfire codes or acting up. That kind of issue is usually the PCM itself.  In any case, let's go a step at a time.  You might also run a continuity and voltage drop test on the injector plug at this nemesis #1 injector.  See this Geo Tracker post and my reply for more details on voltage drop tests and electrical circuit testing:  http://www.4wdmechanix.com/forums/topic/115-geo-tracker-sending-torque-converter-clutch-solenoid-code/.  Use a good quality digital volt-ohmmeter for these tests.

 

This approach will get results.  I would also disconnect the plugs at the PCM carefully, inspect the contacts and clean them only as needed, using electrical contact cleaner. Use automotive dielectric grease for a moisture and corrosion barrier when reconnecting these plugs.  Take your time with old connector clips and fragile lock release connections.  Protect these plastic parts. 

 

Let us know how this progresses.  I'm curious about the cylinder leak down results, too!

 

Moses

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I called the local Jeep dealer yesterday for a Mopar TPS.  It arrived today and my wife was gracious enough to stop by and pick it up for me.  It was $106 plus tax.  The auto parts store wanted $60 for a TPS - not sure what their brand was, but I was hoping with the new OBDII codes I wrote about last time, that a new TPS would alleviate the trouble, so I didn't want to mess around with a potentially flakey off brand sensor to save $40. 

 

I installed the sensor this evening.  One of the screws was a bugger to get out.  I did use a bit of liquid wrench and I tapped on the screw and after a time it finally worked loose.  I didn't want to strip out the small torx head.  It went just as you said, Moses, it kind of plugs in and rotates into place with just a little spring resistance.  I followed your recommendation and put a little dielectric grease on the rubber seal on the plug.  It seems like a pretty good seal design because the old plug was filthy on the outside, but clean on the inside. 

 

After installing the new TPS, I let the Jeep idle for a while in the driveway and then took the Jeep for a spin.  After more idling in the driveway, I am encouraged to report there has been no check engine light.  Normally idling at a stoplight would cause the engine to stumble and the check engine light would come on with the cylinder 1 misfire code. 

 

We'll see how tomorrow's drive to work goes.  But early indications are good that the TPS was causing me a lot of grief! 

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JJ, this is good news...Trust tomorrow's drive will prove equally productive. 

 

The TPS should be considered a "perishable" wear item.  Think of the duty cycle and how many times that stem has wound up and down the tension and voltage curve in 250K miles.  In my own experience, the TPS and the wire from the crankshaft position sensor to the engine harness can deteriorate over time and create "gremlin" issues like you experienced. 

 

Another issue on engines with rear main seal seepage is engine oil on the toothed ring for the crank position sensor or on the sensor pickup itself.  Each can cause erratic error messages that often dance around the actual problem.

 

We're awaiting your update and optimistic.  It certainly was productive to change this TPS, and your Mopar parts choice assures accurate calibration of the new TPS.

 

Please share the follow-up!

 

Moses

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Day 2 with the new TPS.  After some idling in the driveway yesterday and the check engine light did come back on.  I don't own an OBD2 scan tool (yet), so I haven't been able to see what the current codes are indicating.  I did take the opportunity to clean up the battery connections since I disconnected the negative terminal to swap the TPS.  When I reconnected the battery I did notice that the negative terminal is not as tight as I'd like to see it.  It's the original factory terminal and cable, and after about 3 batteries and a few cleanings over the years, it's a bit worn out.  It's not going to come off, but I can wiggle it.  I don't suspect that it's causing any electrical problems, but I thought I'd mention it in case the forum thought otherwise.  A quick internet search seemed to indicate that purchasing replacement battery cables for a Jeep is not a straightforward thing to do.  Might make for an interesting topic/article, Moses.  I'm going to submit one under tools to see which OBD2 scan tool people like. 

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JJ, sounds like that new Mopar TPS made a huge difference...Good news! 

 

The battery cable is very important, actually both negative and positive cables must be in good shape, as this is a D.C. system where both "hot" and "ground" circuits need the same amperage carrying capacity.

 

You need a consistent 12.4V or higher (12.6V or higher is a fully charged battery) for the PCM to be happy.  A bad cell in the battery or an open at a battery cable can stop the engine from running—even if the alternator still functions properly.  We experienced this with an intermittent 10.5-volt reading on the XJ Cherokee's battery.  The engine would barely keep running.  A replacement battery immediately eliminated the issue.

 

Looking forward to your posts, JJ!

 

Moses

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Just back from a good week at Scout camp with my son and his troop.  Based on Moses's feedback about battery voltage and battery cables, I spent a few minutes poking around my Jeep with a multi-meter just to try and rule some things in or out as the cause of the cylinder 1 misfire I'm having. 

 

These readings were all taken with the engine off. 

12.25 V probing from positive battery post to negative battery post

12.22 V probing from positive battery post to alternator housing

12.22 V probing from positive battery post to engine block negative battery cable terminal

2.3 ohms probing from injector 1 red wire connector to negative battery post (the cylinder that is misfiring)

2.3 ohms probing from injector 4 red wire connector to negative battery post (just a random other cylinder for resistance comparison)

 

With the engine running:

13.80 V probing from positive battery post to negative battery post

 

In short:

  • According to Moses' guidance, my battery is showing signs of wear (12.25 V I have is lower than desired 12.4 V), but I assume it's not enough to cause a cylinder 1 misfire. 
  • Battery voltage reads 13.8 V steadily with engine running - no issue there? 
  • Battery Cables don't look corroded, but they are covered with insulation and the OEM terminal, so can't really tell
  • Resistance of the one injector wire (ground I assume?) looked fine compared to cylinder that is not misfiring
  • Check engine light is on - haven't scanned the codes yet.  I'm assuming (and hoping) this will reveal a great deal more with a new TPS installed.  I don't have a scan tool (I borrow the one Napa loans out at their store) - started another post under tool and equipment sources to see which OBD2 scan tools people like and why as I'd like to pick one up. 
  • Cylinder leak down test - no progress yet - busy summer

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JJ_Jeep...Glad you had some camp time with the troop and your son!  I read your findings, and the battery sounds shot.  After running, it should have from 12.6V (full state of charge) to 12.8V (common voltage for a freshly charged, newer battery).  12.2V is below par.  Not sure when you checked it, right after running, after setting a while, overnight?  This makes a difference.  If low after setting overnight and the battery case is very dirty, voltage can leak off the sides of the battery case or from post to post (a grounding discharge) and slowly discharge the battery.  Or you might have a slight drain from an accessory or whatever.

 

The best way I can illustrate this is to share a quick story about my wife Donna driving off with the XJ Cherokee after a sluggish engine crank over. (Most unusual, we wrote this off to the door being left open with the interior light on.)  Donna came home shortly thereafter, quite irritated, sharing that while she was at a stop sign, the engine died (again, most unusual!).  When she did get it going, the engine misfired and lacked power.  This is unheard of around our place because I do "preventive maintenance", a habit from my truck fleet mechanic days over forty years ago...

 

Anyway, I quickly checked the charging circuit, it read much like your findings.  I checked the battery immediately after shut-off, and the battery voltage was 12.7V.  Seemed okay, so I ran a simple load test.  AutoZone, NAPA and others will do this for free, in or out of the chassis.  In my case, I did a basic approach: turning on the headlamps with the engine off. 

 

Under this headlamp load, the voltage at the battery read 10-volts with the headlamps on just a few seconds.  Cranking would have dropped the voltage even lower. 

 

Try this with your volt-ohmmeter and headlamps on, picking up a voltage reading away from the battery to prevent sparks that might ignite a defective battery under load.  (Heavy battery lead contact at the starter motor is a good point, or even the alternator battery terminal.)  If your voltage drops to 10 or so, you've found what occurred in the Cherokee: a battery with a dead cell.

 

Now, if you do have a dead cell in the battery, it's possible that your engine will run erratically, just like our properly tuned Cherokee 4.0L did.  A dead cell is like an open, and regardless of the normal output from the alternator, the battery itself is not a reliable conductor of voltage to the PCM—or anywhere else.

 

I replaced the battery with new, and the problem immediately disappeared.  In your case, since I'm not comfortable with spending your money, try the load test with the headlamps on for a minute or so.  Or better yet, let AutoZone, NAPA, O'Reilly's or a similar "free test" outlet do a bona fide load test on your battery.

 

Replacing the battery is not a guarantee that your #1 misfire code will go away.  However, you can be assured that a defective battery will raise havoc with your engine's performance and reliability.  With the new TPS, I'm curious to know what code(s) the engine is now throwing. 

 

Read the stored codes before disconnecting the battery.  Deal with the battery and see if solving the battery issue cures any MIL or code problems...The ohms resistance from the injectors (red lead) to battery negative requires some thought.  The injector pulse width is a function of grounding at the PCM, not positive current switching.  We can discuss this further after you retrieve the codes.

 

We'll keep at this JJ!

 

Moses

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More good advice...  shopping for a scan tool to get the codes. 

Meanwhile, I took some more voltage readings... 

 

Lights and engine off

12.27 V alternator housing to alternator battery terminal

 

Headlights on, engine off

11.88 V alternator housing to alternator battery terminal

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JJ, I would have the battery load tested, which simulates the cranking amperage draw.  To put this in perspective, a drained battery (still intact) will read 12V.  12.3V is 50% charged.  12.6V is 100% charged.  These are approximations.  Your battery is less than 50% state of charge at best, and below fully drained voltage with any kind of load.

 

This sounds like a "bad battery".  Load testing will confirm.  You're getting consistent 12.27V, so the battery seems to peak there.  The PCM likes 12.4V minimum, so this is a marginal situation.

 

How old is this battery?  Do you have aftermarket accessories or possible drains on the battery when static?  Assuming no draining down, and with daytime running to fully charge the battery, this battery is not in good condition. 

 

Did you catch my comments about a clean battery case?  We're all expecting better terminal connections soon.  Next stop: a load test, likely followed by replacing that battery.

 

Moses

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Should be able to check codes, then load test battery Friday with a stop at Napa.  Really curious about the latest codes.  Still thinking about the scan tool options for reading codes at home.  And the battery cables...  I might try a new terminal on the old ground cable to save cost until I know where I'm at with this misfire.  Battery is 6 years old - where did 6 years go?  No accessories, but it did sit for a couple weeks while we were gone to camp.  I re-read your comment about the clean battery case.  I've kept the battery blanket that came on the battery from the factory so it covers the case.  I'll check it out when I replace the battery. 

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Six years on a Jeep battery is quite a while.  I use a Battery Tender in the winter on both of our magazine vehicles.  We also use a block heater, plugged in the night before starting the engine, in cold weather (below 45-degrees F and down to zero or lower in our neighborhood).  This is a necessity for the Cummins, as our traditional use of 15W-40 oil is daunting in cold weather.  I'm looking into alternatives here...

 

The Dodge Ram with Cummins engine should, by all accounts, eat up both batteries at around five years.  Due to the steady use of the Battery Tender, all winter and in other seasons when the vehicle sets for up to a week without a start-up, we have gotten nearly nine years out of the OEM batteries and they're still okay.  I've topped off with distilled water only twice in that timeframe.  (No complaints about OEM Mopar batteries here!)  I do expect replacement within a year; ten years for a diesel engine is amazing.

 

Our Cherokee, much like your Wrangler, does get battery use.  There's a winch that relies on a single 800 CCA battery, two Spal electric fans set to run after engine shutdown, and then there's the steady air conditioner use in the summer.  All tolled, five years of battery life is just fine here...

 

Let us know what you discover about your battery.  The terminal fix is a must.  Consider a Battery Tender, the best investment we have made in extending battery life!

 

Moses

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Six years on a Jeep battery is quite a while.  I use a Battery Tender in the winter on both of our magazine vehicles.  We also use a block heater, plugged in the night before starting the engine, in cold weather (below 45-degrees F and down to zero or lower in our neighborhood).  This is a necessity for the Cummins, as our traditional use of 15W-40 oil is daunting in cold weather.  I'm looking into alternatives here...

 

The Dodge Ram with Cummins engine should, by all accounts, eat up both batteries at around five years.  Due to the steady use of the Battery Tender, all winter and in other seasons when the vehicle sets for up to a week without a start-up, we have gotten nearly nine years out of the OEM batteries and they're still okay.  I've topped off with distilled water only twice in that timeframe.  (No complaints about OEM Mopar batteries here!)  I do expect replacement within a year; ten years for a diesel engine is amazing.

 

Our Cherokee, much like your Wrangler, does get battery use.  There's a winch that relies on a single 800 CCA battery, two Spal electric fans set to run after engine shutdown, and then there's the steady air conditioner use in the summer.  All tolled, five years of battery life is just fine here...

 

Let us know what you discover about your battery.  The terminal fix is a must.  Consider a Battery Tender, the best investment we have made in extending battery life!

 

Moses

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Okay, I feel like we have a little more progress. OBD2 codes were reduced to a single code:  my friend the P0301 (cylinder 1 misfire).  The TPS code and injector code were not present. 

 

Battery checked out fine at NAPA - the store clerk came outside and connected their battery tester to my Jeep and he checked it with the engine off, on and on with headlights and HVAC fan on.  This surprised me after the lower voltage readings I got.  Must have been because the Jeep sat for a couple weeks before I measured the battery voltages?  I checked some voltages again today and got 12.66 V off, 13.74 V engine running, and 13.45 V running w/lights and fan.  Perhaps, Moses, as you mentioned a dirty case is bleeding off some voltage as it sits?  Not denying that I should get a new battery, but really desiring to understand what costs are in front of me to keep this Jeep running another year before I commit. 

 

There were no family plans for the weekend, so I've been tinkering and I think, Moses, I proved your point about the ground terminal replacement being a must.  Here's what I did:

 

1)  Disconnect neg batt cable from batt

2)  Connect a jumper cable to the neg batt cable so the jaw of the jumper had a nice, tight grip on the neg batt cable terminal

3)  Connect the other end of the jumper cable to the neg batt post (carefully keeping this birds nest away from the pos batt post and the engine belts and fan)

4)  Start the Jeep and let it idle with scan tool monitoring for codes (borrowed a scan tool from a friend at work)

 

Results - idled several minutes with no check engine light!  I am cautiously optimistic, because this is how things looked after idling with the new TPS several minutes, until the code returned the next day.  But I don't dare drive the thing around with dangling jumpers connected to the battery. 

 

Could we conclude from this, that a slightly loose negative battery terminal can cause a cylinder 1 misfire?  You recommended last post, that a neg terminal replacement is a must, and might resolve this misfire issue? 

 

Incidentally, a quick call to the Jeep dealer parts dept revealed battery cables are no longer "supported" for the 1998 Jeep Wrangler.  So apparently factory cables can't be sourced from the dealers. 

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This is great, JJ_Jeep!  The battery is at least bringing normal readings, and the negative battery terminal has been a problem all along.  Whether this "cures" the #1 Misfire code or not, you needed to do this as a place to start, since you cannot get accurate readings or consistent performance any other way.

 

As for the #1 Misfire code, if this occurs again, there's an inexpensive way to test the #1 injector.  Try swapping the injectors.  Move #1 injector to any other cylinder (pick an easy injector to reach), and place that cylinder's injector in the #1 position.  With injectors swapped, clear the code(s), run the engine, and see if you throw a new code.  Drive the Jeep and see if you throw a code.

 

If you throw a #1 Misfire code, the original injector was not at fault.  If you throw a code for the cylinder where you placed the #1 injector, you know for sure that the problem is the original #1 injector itself (replace that injector!).  This is a fairly failsafe test and often a dealership troubleshooting technique.  Swapping injectors is not very difficult when compared to other troubleshooting steps.

 

Before swapping the injectors, try the terminal fix, and go from there.  You're making progress!

 

Moses

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After the jumper cable experiment showed some promise, I made a quick trip to the auto parts store and with Biggman's suggestion, picked up the marine terminal add-ons for the battery post and a couple copper crimps.  I wanted to try a quick and dirty fix to see if this battery terminal has been the issue all along. 

 

After a lot of idling in the driveway and a couple test drives, there was no check engine light! I was optimistic. 

 

I attached a picture of the cable.  Once I cut the 1998 factory battery terminal off and stripped some insulation, one cable had a little green here and there, but the other cable (the factory terminal has two cables - one for the firewall and one for the block) was heavily corroded.  Minnesota winters and road salt are probably the culprit here.  I stripped both cables back to clean copper, tried to "tin" them the best I could with the small solder iron I have, and crimp the copper terminals on (the other attached picture shows the two terminals attached to the marine battery terminal and the battery post. 

 

 post-27-0-33812400-1376189520_thumb.jpg post-27-0-10006600-1376188517_thumb.jpg

 

Admittedly, it's a hack job.  The terminals were maybe a 1/16" big for the cable and, a neighbor crimped it for me with a tool slightly undersized for the job.  The guy at the auto parts did mention that they actually will make battery cables for me.  They have the "one-ought" cable and the $300 crimp tool and shrink tubing to do it.  But I wanted to complete a low cost fix first just to see if the misfire was an electrical problem or something more foreboding (read expensive) like engine wear requiring an overhaul. 

 

More to come...  but at present, that looks like new battery cables.  Expect an update. 

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The menacing P0301 cylinder 1 misfire came back.  But not to be deterred, I tinkered with the injectors a bit and found some odd behavior.  My neighbor saw the hood up and came over and asked what it does if you unplug injector number 1.  We did and nothing noticeable happened.  Hmmm, that doesn't seem right.  So we confirmed by unplugging injector #4 instead, and then the engine stumbled MORE.  I checked the codes and you get a P0201 or P0204 depending on which injector you unplug. 

 

Moses, you suggested swapping injectors.  I would like to do this and just double confirm that replacing the injector is the fix (versus say replacing the electrical connection to the injector if the problem stays with cylinder 1 for instance).  Is it best to have the proper O rings on hand for putting these injectors back in place?  Or do they come out and go back in pretty easily? 

 

I've read the procedure for doing it - in rough outline, you relieve pressure in the fuel rail, then unbolt the fuel rail and pull the rail and injectors from the manifold.  At that point I can swap #1 with one of the others and repeat the procedure in reverse...  Any tips here for avoiding creation of new problems? 

 

In the event that the problem follows the injector indicating the injector is bad, I see various options for dealing with it.  Is there "better" logic to one of these options over another? 

1)  Replace the bad injector and move on with life. 

2)  Replace all 6 injectors (are injectors an item where it's recommended to replace all together, rather than just one?)

3)  Replace all 6 injectors with the higher pressure injectors for the potential stroker build some time in the future.  Do the injectors recommended for strokers perform fine with a stock (albeit old) 4.0 L? 

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It would pay to have some correct O-rings on hand, as they do not cost that much, and you anticipate stroker injectors in the future, anyway.  Since you do anticipate the stroker build at some point, I would just replace the one injector, if defective, with a stock 4.0L rebuilt type.  They are readily available from GB and others, through your local auto supply and outlets like AutoZone.

 

Replacing with "stroker" injectors at this point would be ill advised.  You are not sure of the engine's condition, but the engine has high mileage.  Compression and cylinder seal are still uncertain, so higher flow injectors would certainly not help.  In fact, the fuel enrichment could shorten the remaining service life of the stock engine.

 

Do the injector swapping that I suggested and see the results.  This is the quickest approach and could lead to, at most, a new injector that you know is needed.  As for the injector wiring harness, connectors and all of that, you'll narrow the trouble with the injector swap.

 

This has become a popular topic and replies.  I'm glad to offer further help.  Let us know the outcome... 

 

Moses

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The fuel rail is kind of a pain in the neck to wrestle off and on.  After considering the prospect of doing it twice (once to swap injector #1 to another cylinder, and then a second time to swap in a new injector), I was thinking I would prefer doing it once.  I stopped by the auto parts store and they had the injector in stock, so I made the $70 bet that the injector was the problem and bought it.  I finished swapping the new injector onto cyl #1 tonight. 

 

After the TPS and the new ground battery cable terminal looked good for a day, and then weren't the final fix, I don't want to jinx the injector!  So we'll see how it runs through the weekend, but suffice it to say the light is not currently on. 

 

For the uninitiated, swapping an injector was a doable task for a novice. 

I followed the Haynes manual which advised disconnecting the neg batt terminal, opening the fuel cap, and relieving the fuel pressure from the fuel rail at the Schrader valve into a rag.  There's a good amount of fuel that comes out, so I left this rag outside to air out.  Note that later, as you remove injectors to replace the O-rings, there is more fuel in the fuel rail that can spill out.  Keep lots of old socks handy. 

The air intake comes off fairly easily - it helped me to remove the air filter cover end of the intake and then rotate and pull the intake at the throttle body. 

Next the throttle cable bracket comes off.  I tucked the cables under the rod that goes from the grill to the firewall and that pretty much kept them out of the way. 

Four bolts hold the fuel rail on the intake manifold.  The one by the firewall also held a sensor in place, so there's a nut to remove first. 

The fuel rail takes some patience and elbow grease to pull it free from the intake.  I must admit my wife had the brilliant suggestion of shooting a little WD-40 on the injectors at the air intake to help wiggle them free. 

Once the rail was loose, I left the fuel line attached since it's flexible hose and I just flipped the fuel rail and tied it in place so I could remove the injectors.  I cleaned up the injectors with WD-40 and a rag and put new O-rings on them and swapped the offending injector from cylinder 1.  I lubed the O-rings with WD-40 to put the injectors back in the fuel rail. 

Everything goes back together in reverse order. 

When done, I did take the precaution to turn the key to "on" to run the fuel pump and pump up the fuel rail and checked under the hood for fuel leaks.  I thought I'd rather discover a leak before I started the engine.  There were no leaks, but thought I'd pass this along. 

Drove it around a bit.  Seems less prone to burbling and backfiring when I get out of the throttle. 

More to come... 

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I almost suggested that you change the #1 injector rather than do the job twice.  However, I was reluctant to spend your money.  At the engine's mileage, the original set of injectors has been thoroughly worked.  Your description of the task involved builds a good case for simply replacing the #1 injector.

 

This is a valuable "how-to" for those needing to change an injector, JJ_Jeep.  Thanks much for taking time to share in detail.  Looking forward to this weekend's test driving and results, an update on whether this ends the misfire code.  If so, credit to Chrysler/Jeep and OBDII for an accurate DTC (Diagnostic Trouble Code) reading!

 

Was there anything "suspicious" about the look of the old #1 injector when compared to the others?  Did you see anything unusual at the nozzle end?  If so, could you please attach a photo of that injector's nozzle?

 

There are many followers of your topic, and it's been a good opportunity to air the issues around injector codes and defects.  Thanks, JJ_Jeep!

 

Moses

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Well, so far, so good.  After replacing injector #1, I have not seen a check engine light. 

 

The injector nozzle end didn't look suspicious to me.  I do wonder about the other end - is there a screen in there that can clog?  I'll try to get a couple pictures of the bum injector at work.  And we'll see if the check engine light stays away! 

 

Still thinking about that cylinder leak down test.  I'd like to know the health of this engine before I move on down the list of other work this Jeep needs.  The link you provided has the lowest price I've found.  And OTC seems to be the best "entry level" model out there.  Summit Racing has a nice package that comes with a stethoscope and a compression tester, but was quite a bit more money.  Other brands seem to be limited in the pressure they can use or read. 

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JJ_Jeep, this is good news!  If the MIL stays out, you have a single-part cure here!   OBD-II, in this case, has narrowed your diagnostics and proven cost-effective.  That was the original aim of the Federal mandate for OBD-II, which opened up dealership, proprietary engine diagnostics to independent shops and, eventually, hands-on consumers. 

 

The simplicity and standardization of tester plugs, with common DTCs (diagnostic trouble codes), makes even a $30 aftermarket code reader or $100 real-time scan tool a place to start.  Today, the "real time" functionality of inexpensive scan tools makes powertrain device troubleshooting much easier and places diagnostics in the hands of consumers and smaller shops—often short of the need for a $6,000 tool. 

 

Sure, there are limits to the code readers and basic scan tools, but in your case, the trouble was specific and identifiable with just a reader.  To the point, a "#1 Cylinder Misfire" was the code read, and not surprisingly, you wound up with a defective injector.  The reader narrowed the field to either a wiring issue or as you apparently have found, the likely trouble:  a misfiring injector.

 

So, if this is the cure, OBD-II did its job.  Sometimes, the DTC (diagnostic trouble code) is a generalized reference to the trouble, but in the case of a #1 Cylinder Misfire, the read is more explicit.  Still, it paid to do some checks and tests before replacing any parts, and that's true mechanics, and not just being a "parts replacer".  Thanks for going along with the process, JJ_Jeep!

 

You asked if there is a filter or screen in the injector, and yes, there is one.  Here is a generic injector illustration from Wiki that helps explain the injector firing process.  You'll find the animated illustration helpful:

 

http://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gif

 

As for assessing the overall engine condition, the OTC leakdown tester would be a good investment.  Your volume of usage for the tool may not justify buying one, though.  For that reason, I'm posting a topic on how to make a very inexpensive home use tool, and I'll explain its usage.  Again, we're after affordable solutions, and this is one I'll post at the "How-to Tips" forum category.  I'll also post comments on the use of a vacuum gauge as a simple, overall engine tester.

 

Keep us posted on your MIL/check light and the engine's performance.  On that note, is the 4.0L engine running "better"?  If the engine runs noticeably better, please share with us the actual difference and how a #1 Cylinder Misfire impacted performance.  What was the "before and after" effect of replacing that #1 injector?

 

As a footnote, it's great to fix an engine and extend its service life a bit.  Every day you drive the TJ prior to rebuilding the high mileage engine is money in your pocket.  As long as the vehicle is safe, reliable, reasonably fuel-efficient and there's no risk of damaging the engine in a way that would prevent rebuilding it (like, say, running the engine with bad crankshaft bearings and chucking a connecting rod through the side of the block!),  you're ahead of the game—and without a $500 a month payment for a new vehicle.  $70 for a single injector?  If this is the cure, it sounds like a bargain!

 

Moses

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