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bmorris57

1993 Jeep Wrangler Sahara 4.0L Troubleshooting OBD Code 27

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I have recently purchased a 1993 Jeep YJ with a 4.0. The jeep recently started running and idling rough. The Check Engine Light (CEL) was not lit nor did it illuminate when the key was turned ON.

 

After further investigation I found the CEL bulb was removed and found shards of glass in the socket. I removed the socket and added a new bulb. Upon further investigation I found the PCM is storing the following codes:

 

12 ==> Battery disconnected (accurate) I just did a head light upgrade and added relays.

27 ==> I have found a few listed on-line...

  • Code 27 -Injector control circuit-bank output driver stage does not respond properly to the control signal.
  • Code 27-Injectors No. 1, 2, or 3 control circuit and peak current not reached.

Then followed by the closing code 55

 

I am not sure where to start troubleshooting this...

 

Thanks in advance!

 

Bruce

 

 

 

 

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Hi, bmorris57...Welcome to the forums! The Code 27 on a 60-pin PCM system is just as you describe—vague and global. 

 

When you have a global injector issue on a YJ 4.0L engine, the cause can be as simple as a vacuum hose leak to the fuel pressure regulator.  I'd start with simpler vacuum hose checks.  Look for hoses that connect to the intake manifold, fuel pressure regulator and the throttle body.  You're trying to locate a damaged or split hose that's sending a poor vacuum signal.  Check these circuits, especially the MAP, EVAP and, most likely, the fuel pressure regulator:

 

  YJ Wrangler 4.0L Vacuum Circuits.pdf

 

Try this first.  A vacuum leak or damaged hose has an easy remedy.  We can go from there...Code 55 is simply the end code after an engine diagnostic check.  12, as you observed, is a disconnected battery.  Always suspect when the MIL/CEL Engine Check lamp is either broken or disconnected!

 

Moses

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Moses - Thanks... the diagram certainly helps...

 

It makes the mind wonder when you see this critical lamp removed and fragments left in the socket. 

 

That said, I really enjoy the jeep and the challenges it provides...

 

I assume it's easiest to test for vacuum leaks with the engine running to here the leak or observe the impact as you manipulate the vacuum line?

 

I'll get an update soon...

 

Bruce

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bmorris57...Usually, given age and engine heat, the hose leaks are easy to locate.  Look for brittle or cracked hose.

 

There are machines for "smoking" a vacuum circuit and watching for leaks.  (I have such a VacuTech that does this with smoking peanut oil or equivalent and a black light.)  A low volatility spray, kept away from heat sources or spark, or even pure water in a spray bottle, can help detect a vacuum leak.  When picked up by the idling engine's vacuum, the engine speed will momentarily change.

 

Otherwise, visual checks or the use of a vacuum hand pump can help.  If you have a vacuum hand pump, try testing vacuum circuits between known points that normally seal at the opposite end (like the circuit to the MAP sensor or fuel pressure regulator).  This can also turn up defective vacuum devices and leaky diaphragms...You can get an idea which circuits are sealed from the diagrams.  A vacuum hand pump/pressure gauge is a valuable diagnostic tool. 

 

Let us know what you find, members are here to assist further!

 

Moses

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Moses and team, sorry it took so long to get back to this problem. I had a locked front brake to deal with.

So Moses the diagram was easy enough to follow... The Jeep is easy to get around, that's for sure. With no background in troubleshooting a vacuum problem, I decided to build a smoker. Took about 30 minutes to build. After a few cycles I could find no vacuum leaks, which frankly was a surprise. Injectors, all lines everything looked fine.

What to do next? I priced the Fuel Regulator Valve... $59.00 and decided I will not shotgun parts, if I can help it.

I decided to simply follow your instructions... I removed and inspected the vacuum lines from the MAP sensor, the Fuel Regulator Valve and the Evap line. Everything looked good with one exception: The connection to the fuel regulator seemed to be cracked as you suggested. The problem was compounded by the fact that these vacuum lines seem to be custom made. There is a small boot on the valve end and a normal size boot on the Intake manifold.

I decided to buy a regular vacuum line to fit the smallest adapter and try to get it over the Intake nipple.

$.69 for a 1 foot line. Started the Jeep.... No CEL... Hmmm

Took it for a couple mile loop.... Got the engine warmed up, then climbed a hill in 4th gear.... Accelerated... No lugging or missing.

I was shocked these fine cracks could cause this problem.... More testing is needed will keep you posted.

Although the smoker was not needed, I I have better confidence I don't have a more pervasive issue with these lines.

Do I need to try to order a direct fit vacuum line? Any other preventative suggestions? Should I replace other lines?

Thanks in advance!

Bruce

Thanks for all the help...

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Bruce, the symptoms did sound fuel pressure regulator related, you did a great follow-up, let's watch this success unfold!  Vacuum lines can be as difficult to troubleshoot as wiring issues.  This one was simpler.

 

The factory vacuum line may not be available, you can check with a local Jeep dealer.  This could be an item that gets replaced with vacuum hose as you did.  I suggest that if you're getting a good vacuum seal now, make sure the vacuum hose is higher grade and reasonably heat resistant.  (Route carefully, away from high heat.)  There are various grades and qualities of hose available.  NAPA and others offer traditional, heavy-duty vacuum replacement hose.  As long as the seal at connections is good and the hose will not become brittle and crack prematurely, this can work.

 

Congrats on the smoker!  Glad you took the time to be innovative and troubleshoot at this level.  If you ever suspect that the pressure regulator is defective, the regulator can be tested for a diaphragm leak using a vacuum hand pump/gauge.  Better to invest in a vacuum hand pump with gauge than to replace parts that are not defective.

 

Keep us posted!

 

Moses

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Moses and team,

I replaced the exhaust manifold on my jeep and the rear main seal.  A few days after that I took the jeep for a long drive... about 10 to 15 minutes into my drive my Check engine light lit up. Code 27 again. Next time I drove the jeep it was a short trip, no light. I have now been able to recreate the error condition only after about 10 to 15 minutes of driving. It appears to be Heat related. Another thing I have noticed is that the engine does not bog down as severely as before. I borrowed a fuel pressure gauge from O'Reilly's, I bought a Haynes manual and they recommend checking the Fuel regulator valve by reading the fuel pressure at around 31 PSI at normal idle, then removing the vacuum line from the regulator and you should see the fuel pressure rise 8 to 10 PSI.

 

You had recommended using a vacuum gauge to test this... is the vacuum gauge a more reliable test? How much vacuum should you pull? I assume the point is to pull the vacuum and make sure it holds... if not, the diaphragm in the regulator has a small leak.  

 

Is the temperature component of this significant or a red herring?

 

Sorry to reopen this issue... thought it was resolved... thanks in advance for advise.

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I just took a fuel pressure reading from the Test port on the fuel rail. My fuel pressure is 65 PSI and steady. I removed the vacuum line from the fuel pressure regulator and there was no change.

 

Could the fuel pressure regulator be stuck closed so it never opens the return line to keep the pressure at 31 psi? The Haynes manual says to pinch the return line and the pressure should rise to about 95 psi... if I am at 65 psi constantly does that mean the return line is partially closed? 

 

How do I verify the pressure regulator is functioning and how do I test the return line.

 

Any help is much appreciated.

 

Bruce

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Bruce...On your two-rail EFI/MPI system, you could have a restriction on the return line to the tank or a regulator defect.  The regulator sticking closed is, frankly, unusual, but this could happen.  It's far more likely that lines are either crossed or restricted to the tank.  Check for flow through the return line.  The return line goes into the fuel pump module and could be tested at the module if necessary.

 

There should be no restriction on the return line, hose or the tube into the module.  Be sure pipes and hoses are routed correctly.  Eliminate any restriction before testing the regulator or the rail pressure.  65 psi at the fuel rail is high. 

 

For testing the return flow, I would disconnect the return line or hose at a safe and accessible place, away from heat.  Make sure your hands and eyes are protected.  Make sure you have a relief hose to a safe can or vessel while cycling the key and activating the pump.  Cycle the key on and off.  There should be an intermittent but distinct flow of fuel at the return line.  If you have compressed air, try very gently blowing through the return line from the engine toward the tank and be sure there are no restrictions.  You may need to drop the fuel tank and remove the fuel pump/gauge module to confirm free return flow all the way into the tank.

 

Re-test the regulator and fuel rail readings after clearing the return line.  Let us know what you find... 

 

Moses

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Moses, Sorry for the long delay. I have not had much time for the jeep lately. I took it out the other day for a spin and I smelled Fuel fumes. Pulled it in the garage and found the rubber hose from the return line split open. This hose is the one that is behind the fuel filer and goes between the Frame and the chassis.

 

I removed the tank and am replacing all of the rubber hoses, I am also replacing the sending unit and fuel pump while it's out.  

 

I have hit one snag... it appears that over time the grommets that set between the body and the frame have compressed. I have lubricated the folding piece of rubber and have been unable to get any of the lines out. 

 

  1. Are there any tricks for removing these?
  2. What about reinstalling them?
  3. Should I replace the grommets? or add a body lift? (the jeep came with 31's and rub when turned hard)

Even though I didn't have time before, I have enjoyed this project.

 

Any advice.recommendations are much appreciated... 

 

Bruce

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bmorrris57...Since rubber and solvents don't mix, be sure that you are replacing these body mounts before applying penetrant or lube to hardware.  These bolts were installed with air tools and come out best with the use of a pneumatic air wrench/gun that puts out good torque.  If you reinstall the bolts, use Loctite 242 (blue) on the threads.  It's both a thread locker and rust preventive measure.  Avoid spinning the nuts loose in the frame or body pads.  This is a challenge, and in my experience, pneumatic tools applying torque in spurts get better results than use of a hand breaker bar and sockets.

 

There are aftermarket urethane body mounts available.  If you replace the body mounts with urethane, a mild body lift is possible, or you can simply restore the original height.  I have never been a fan of body lifts, as there is trickledown effect from one end of the vehicle to the other when spacing with taller body lifts.  My preference would be restoration or a very mild lift.  Be careful about the durometer of urethane mounts.  Too firm is rough on sheet metal pads and ride quality, too soft will crush quickly and not hold up.  Most body grommet replacement kits come with hardware.  Torque to specification and use supplied fasteners plus Loctite on threads as I suggest.

 

Moses

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Thanks Moses... I'll get after it. I will keep it stock on your recommendation.

So I should be looking for urethane mounts? Is there a name brand you have grown to trust?

I appreciate the help...

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I've used Energy Suspension products for decades.  There are other respected brands like Daystar.  See what's available, we can discuss the options you like...Durometer is crucial.  Color is your preference!

 

Moses

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Moses,

Thanks for the quick response and the suppliers... what do you mean by "Durometer is crucial"? Is there a range?  

 

I called Daystar, they do not publish this number...   they stated it had a hardness of 88. I have read that the stock rubber bushings were around 40 to 45.

 

What are the recommendations?  Is 88 in the acceptable range?

 

Thanks in advance...

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Daystar and Energy Suspension both know what works.  I would roll with their "findings".  As you note, you're already firmer than stock. 

 

Usually, the quality kits have a steel spacer sleeve/bushing through the cushion to prevent crushing the mount.  (Let me know what the "kits" include.)  The sleeve prevents squeezing or compressing the bushing too tightly.  It also allows the cushion to yield under body flex and not act like a solid puck.  Body sheet metal prefers some yield at the cushion, so does the seat of your pants!

 

Moses

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Moses,

I know what you are referring to, I did see this as part of the kits for other Jeep models, however, not for my YJ. Here is the link to Daystar...  http://www.daystarweb.com/productdetail.php?productID=313

 

The only difference I saw was the Energy suspension kits comes with the washers...  I did see kits for other models that had this bushing sleeve and the 1 inch lift comes with the bushing sleeve as well as all associated Hardware.

 

The standard kits (no lift) from these two suppliers come with no hardware, with the exception of the washers in the Energy Suspension kit.

 

I made the assumption for my Jeep model, with no lift, it did not need the additional support of the sleeve...

 

Would I be better served with a 1" body lift and a complete Hardware package? I have 31" tires on the Jeep now and they rub at full turn. I do not see that as a big deal though.

 

Your thoughts?

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I'd prefer the 1" and hardware approach...This is not excessive and should not compromise pipes, hoses, radiator location, steering column space or other concerns.  You'd have a bit more clearance at the fender wells, nothing huge.  Sounds better conceived. 

 

Snag a photo of the kit you're considering, post it here, and we'll make an assessment...

 

Moses

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Moses,

Thanks for the response... here is the image files. I could not get the images to cut and paste so I had to attach them.

 

I look forward to comments.

 

Regards,

 

Bruce

 

post-416-0-44910500-1438613194_thumb.jpg

 

post-416-0-23747600-1438613213_thumb.jpg

 

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Moses,

I noticed on the Energy Suspension Installation guide that the kit was made for 97-2000, Jeeps,  I called their Tech Support and found out that the Web-Site and even the Amazon site had misinformation. According to the Tech Support person I spoke to, Energy Suspension did not make a 1" lift kit for the Jeep YJ.

 

I found that very hard to believe... I also found that the Daystar replacement body mounts (no lift) have the metal bushings built into the mounts and also come with the same washers as the Energy Suspension kit.

 

So the only hardware I would need to buy would be replacement bolts and any Nuts needed should I sheer any bolts off.

 

Based on this new information... Is there value in lifting? Other than the radiator shrowd, are there other hidden gotcha's?

 

I appreciate you input.

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Bruce, both kits look good, too bad the Energy Suspension kit is not for a Jeep YJ Wrangler...1" lift should not be dramatic.  More radical body lifts raise concerns about the radiator/shroud, the brake lines from the master cylinder, the steering column, shift linkages, fuel hoses and such.  Daystar's instructions might be worth reading before you plunge.  They'd likely furnish a PDF or perhaps offer a download PDF at their website.  Daystar looks complete.  Presumably, you use Loctite on the bolt threads, there are no lock washers for the large bolts?  These large bolts would be the mount-to-body through bolts, which should take care of hardware needs.

 

The rectangular plate is some kind of offset and included in both kits.  The gear shifter needs attention with some chassis lift kits, see if this kit takes a similar approach.

 

Unless the lift is needed or you prefer more hose and other clearance between the Jeep's body and frame, stock mounts hold up very well.  There are aftermarket suppliers that likely offer OEM replacement rubber body cushions.  Have you checked Omix-ADA listings, they furnish OE replacement pieces for the utility Jeep models. 

 

Moses

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