Sabueso

Jeep 1990 YJ 2.5L drives 35 minutes well then stalls

32 posts in this topic

Hello All,

This is my first post and hope for the best.  My 1990 YJ Wrangler Jeep 2.5 TBI starts well in the morning, heats up to temp and can ride for about 35 minutes.  After which it starts to act as if it wants to turn off.  If I step on the gas it kind of coughs.  What I do is pull over and while in neutral it turns off by itself.  I wait about 10 minutes, turn it on and we’re almost back to normal, just enough to make it home.  If I wait longer it turns on and drives well.  

     Thanks for your help.

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Sabueso...Welcome to the forums, we're a helpful bunch and glad to offer some ideas...In the search box, type "TBI troubleshooting".  You'll find several long threads on 2.5L TBI problems that should be useful.  One example would be:  

There are several other topic threads that will help.  Try this one:  

You will benefit from reading these topics on 2.5L TBI troubleshooting.  We've covered a lot of ground, I'm glad to comment once you've become oriented and perhaps checked over a few of the trouble spots like fuel pressure and volume.  You'll find crosslinks to additional coverage, too.  We've chased a lot of gremlins on the 2.5L TBI engine.  I also cover it in depth at the magazine site, do a search under 2.5L TBI.  This is a key link: http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1.

See if you find a troubleshooting angle and cure, and if not, glad to add more information as needed!  As a place to start, have you changed the paper fuel filter lately?  Just one watery tank of gas can clog the filter.

Moses

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Thanks Moses.  I'm familiar with your Tuning-troubleshooting article since I have it as "Favorite" on my browser.  I've been using it to tune-up the YJ for over a year now :D

 And yes I just changed the fuel filter this weekend.  The old one threw out some muddy looking fuel from the un-filtered side so I hope this will relieve my symptoms.  But before I can test it (which would be to drive for at least an hour) I need to resolve a drive-shaft issue due to my 3" lift.  

In reading some of the posts you've directed me to I believe I have a fuel pressure problem.  So I'm gonna need the fuel pressure testing tool if you can direct me to one.

Also, my ISA motor is definately bad as it won't extend all the way.  I'm read up on your articles on testing it.  I would also need a ISA exercisor or a way to do the test without it.  I can't find the tool anywhere on the internet.

I will be troubleshooting maybe on the weekend so I'll provide feedback at a later time.

Thanks for the posts!

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I tried the Jeep after changing the fuel filter.  There was definitely an improvement but after 40 minutes I could feel the fish bites.  I hit the gas but it would not respond smoothly so I pulled over.  The only way I could describe how it acts is that it revs up and down until it dies.  It won't idle.  I stop giving gas and it goes up to 1100rpm then drops below 900rpm every second while decreasing rpms each cycle.  Then it turns off.  Except this time I didn't have to wait more than 3 minutes before I started up and continued home with no problems.  So the fuel filter did help.

I know I definitely need to buy an IAC motor (or ISA?) because Its not helping during startup like it used to.  I'm going to check fuel pressure and all the important sensors/relays in-between.  So I'll be going thru all the posts you mentioned earlier.

I'll provide more info after I try these remedies.  Thanks again Moses.

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Sabueso...Looking forward to your pressure test results...Problems after full warm-up can sometimes be electronic, like the ECU or bad ignition coil, but don't start replacing parts without first pinpointing the area of trouble.

Start with the fuel pressure and ISA.  We'll go from there...Also, check your grounds, we've covered this with other Jeep 2.5L TBI YJ Wrangler models like yours, they are notorious for poor grounds, and when warm under the hood, resistance increases.  One troublesome ground in particular is between the body and engine, look for that cable near the dipstick...Clean up terminals, attachment screws and painted or corroded surfaces.

Moses

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Thanks Moses.  I'm shopping the Pressure tester.  I've never checked my ECU connections and I know they are hard to get to because at one time I removed the whole dash board and everything in-between to cure a rain water leak into the cabin.  I found the ECU on the passenger side between the glove box and vent apparatus.  Very difficult!  I remember removing two nuts from the firewall near the battery area to get it loose.  I thought the water leak might have affected it but it was in great condition inside and out.  I sealed the leak and really don't wanna remove my dash.

As far as ground since I did an engine rebuild I already had taken that particular ground near the dipstick and scraped all paint and rust from the nut, wires and engine block in that area and tightened the nut on the wires.   Are there other grounds I can check?  I know there is one from the firewall to the block which I will double check.

Here is a fuel pressure tool I'm looking at:

https://www.amazon.com/gp/product/B00QL8O3G2/ref=ox_sc_sfl_title_1?ie=UTF8&psc=1&smid=A1UMBRA5ZTBCX8

I've removed my tank about 3 times to fix the sender and once replaced the electric fuel pump and sock.  But I never did a tank cleaning (Jeep is now almost 28 years old).  I didn't actually want to remove the tank again until I could afford a new sender unit as my old one is very jumpy.  I can read the fuel gauge when the jeep is still but while riding it just goes up and down.

I guess we'll have to wait for the fuel pressure tester.

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Just got the Fuel Tester Gauge.  Only it doesn't have a fitting that fits in the TBI test port.  Anyone know where to find an adapter for this fitting or can I test pressure from where the fuel filter connects?  I need options, thanks.

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Sabueso...The test port on the TBI unit is regulated pressure, which is what you need to read.  Toward the fuel tank at the fuel filter would be the fuel pump output pressure.  You may want to test that also, but for your TBI concerns, you want a regulated pressure reading at the TBI unit.

You're also concerned about the volume of fuel available at the test port.  A "T" in the tester line and a hose to direct fuel into a safe metal container will test for fuel flow volume.  You can have normal regulated pressure and still not have enough fuel volume.  You need correct pressure plus normal fuel flow volume.

Do you have a NAPA or CarQuest store nearby, or AutoZone?  Any automotive motor supply or even a hardware store should have an assortment of brass fittings.  Simply match the thread size of the TBI test port plug.  If you need to adapt that fitting to the hose, you should be able to find a fitting to do so.

Moses

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Great.  We have Autozone and Pepboys mainly on the Island.  I'll try to get and adapter or maybe even luckier at the hardware store.  Thanks Moses!

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Finally got an adaptor for my Fuel Pressure tool.  I went to a specialized hydraulics shop who had all kinds of adapters.  My Jeep clocks at 14.5 PSI and very steady.  So following ideas from another post I replaced my Fuel Pressure regulator.  It ran great but again starts to sputter and kick after driving for 20 minutes.  It used to las 30!

I can quickly turn it on by keep my foot on the peddle and continue home for another 7 minutes before it starts kicking again.  I'm kind of pissed because the Fuel Regulator kit was $52 (someone here got it for $30 from the same ebay store).  I've tested all my sensors and the ISA.  All within specs.  I cleaned the CPS.  The peculiar thing is that every morning it fires up fine with no trouble.  You can hear the fuel pump engage with key on, and it starts with little Cranking.  It warms up nice and idles at about 10000-900rpms.  But at idle, once warm, it will go up and down in rpms slightly.  I can even drive like I said for at least 20 minutes.

Something seems to fail after some time of driving.  Grounds? fuel return line?  Injector?  Fuel pump plugged up?  Something in the tank gets near the sock and causes it to suck less fuel?

What could it be?  Its keeping me from enjoying the Jeep.  Before buying more parts I'm going to bring down the tank and look for obstructions.  I definately need a new ISA (rock auto $56) because it's the original and noisy.  The idle goes up and down.

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I like your thoroughness, Sabueso!  You're on the proven track toward a solution.  The ISA motor will affect the idle stability and has been an issue with many owners.  I would expect a more stable idle but not a fix for the sputter and kick.

A discussion with Sinisterwillys1940 turned away from the fuel system.  He has a problem with his 2.5L TBI engine's run state when the engine warms up, and he seems to think it gets triggered by humidity.  You're in a humid climate, too...Our discussion turned toward the ignition spark wires being worn with too much resistance.  I thought first of an open in a connection related to engine bay heat or ambient air and humidity.  When he tested the spark plug leads, however, trouble immediately turned up.

If you have an ohms/resistance meter, check the spark plug wires and see our exchange at the forums.  Sinisterwillys1940 also tested the coil at my suggestion.  He offers ohms readings for the coil.  His plug wires are bad.  The first lead I always test on a distributor type ignition is the coil-to-distributor cap wire.

Spark is a possibility outside of the fuel system...See our exchange, especially the last week's discussion:

Moses

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I just finished cleaning/scraping the firewall ground just in case.  It's a braided cable that goes from a screw on the firewall (near the MAP) to a screw/nut from the engine block.  Since we talk a lot about ground problems.  As I mentioned before the ground cables near the oil dip stick I totally cleaned up a while ago since my motor is rebuilt and super clean.  But I can also double check those too.

So right now I'm going to review the Sinisterwillys1940 post and see if it might help me out.

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Sounds like a good idea.  I just need the "how to" test leads and the ICM. 

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I did some inspecting on my wires and found some with very rusty connectors.  The coil to cap wire was defenitly rusty.  I haven't bought any yet because i want to research the type and brand I should use.  Autozone has kit for $21 but lately its all chinese like buying stuff from Walmart.

If this is my issue I'll be jumping for joy.  If not, at least I will put in some quality wires.  I re-did my motor and I'm shocked at the condition of the wires.  It means one of two things for which I can't remember.  1) I probably looked at the wires and they looked clean enough to re-use or 2) I bought a cheap kit from Pepboys.  I know for sure that I put in new spark plugs with the rebuilt motor.

I have my doubts regarding climate because it was never an issue in the past 22 years.   And I've been out in some really bad rain on the island.  One time the Jeep stalled and turned off because I went through too many flooded areas.  Water went into the Distr. cap.  But I sprayed some WD-40 that day and was on my way when it stopped raining.

Right now I just need to know exactly "how" to test my coil and ICM.  The one in the jeep is not factory/original.  I bought that one a few years back thinking I could enhance performance.  According to some people on the internet a coil can test good and still leave you stranded.  

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Glad we pursued this prospect...The spark wires sound ready for replacement...There's a practical test for the ICM and coil:  Consider the inexpensive Lisle spark tester with adjustable spark gap.  If/when the engine acts up, do a spark test at a convenient spark plug wire while parts are still warm.  This is a simple, useful test of the coil.  Ideally, you're looking for a sharp, snapping blue spark.  At least snapping, even if orange-ish!

The ICM, like the ECU and other electronic devices, generally works or it doesn't.  The connectors can corrode, and resistance increases as the engine bay warms.  You ruled out humidity.  Temperature can also affect wiring connections, a module like the ICM or a coil.

Moses 

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Its bedtime and I just came back from a road test.  I got my new spark plug wires and ISA Motor.  But nothing changed.  It starts up great with the exception that I havent done the ISA adjustment (I've got your PDF handy).  So at start it kind of wants turn off so I hold a little gas until the ISA kicks in.  It warms up well and drives great.  Then after about 15 minutes it starts to kick and eventually not want to drive anymore and turn off.  I wait 5 minutes to turn on and go home.

Next time a get a break I'll be doing the ICM and coil test.  

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If fuel flow is still adequate during the "kick" and "turn off" symptoms, this sounds electronic.  Modules are notorious for faulting when warmed up.  Cool down, and the engine runs.  Ford ignition modules during the '70s and early '80s were notorious for this kind of behavior.  The ICM/coil test will be productive, optimally when the trouble occurs.  Then there's the ECU...One step at a time.

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I think it might be good to share some history with this issue.  It goes back about 4 years (2013/2014).  I used to work as an inspector for AT&T mobility installs. This means I needed a vehicle to reach remote areas of Puerto Rico where their antenna towers are located. It gave my 4wd a lot of use due to the improvised roads.  Anyway, everytime I traveled for more than 2 hours and turn off the jeep it would not immediately start back up.  It would take about 20 minutes and start backup and drive normal. As time went on it began not wanting to go more than 1 hour before the problem returned.  Last summer I did a motor overhaul because of noisy piston rods and 400k miles of good use.  The problem went from 45 minutes last summer to now 20 minutes.

So something has surely died slowly.  I'm going to search for a new Coil to see what costs are.  The ICM is newer than the original which I still have. But I will do some tests.

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Smart approach...Something is warming up and shorting or opening.  The behavior is like a coil or module.  Since the problem is consistent and can be replicated, you could use a spark tester (inexpensive Lisle spark plug wire test tool would do); when the engine fails to start, check the cranking spark at the spark tester.  A weak spark could indicate why the engine is not starting.  Also, when you have this no-start condition, listen for the fuel pump as you attempt a restart. 

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I found my old ICM.  the original Bendix brand made in France.  I installed it just to see if it does the same thing so I can rule out the ICM.  It turned on as usual and had great power and idled fine.  But I couldnt do a long drive because it was too late at night (Bed time).  I will test with the old ICM and write here again.  If it stalls after high temperature then all points to the ignition coil, right?

I also pulled the MAT sensor because its the only original sensor on the Jeep.  Been there since 1990 and it didn't look bad except for dirt/grime.  I cleaned it with Brake cleaner which probably finished off  :D.  I'm planning to get a new one which are hard to find.

Do you think a bad MAT can cause this kick/sputter/stall problem?

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BTW - Here's one I found on Amazon.  The part number doesn't match the ones listed from another member's post regarding Jeep YJ MAT but Amazon had it as a related item.

https://www.amazon.com/Delphi-Packard-Temperature-25036751-Connector/dp/B00E5PLAVO/ref=pd_sbs_263_3?_encoding=UTF8&pd_rd_i=B00E5PLAVO&pd_rd_r=AMMT2W7QC6G15HFD6WMC&pd_rd_w=BAEtw&pd_rd_wg=hw6pP&psc=1&refRID=AMMT2W7QC6G15HFD6WMC

 

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MAT could cause issues, and your problem occurs with a fully warmed engine.  You'll know when the new one is in place, which you need anyway.  MAT does indicate incoming air density, which would affect A/F ratios.

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Justed tested a long ride with old ICM installed. Same kick/stall.  Ive got 2 ICMs.  I dont think both are identically  bad.  You mentioned ICMs or ECUs work or they don't.   I'm betting on the coil.  But I might get the MAT first or both.

My next item is testing the coil spark.

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Test coil spark with the coil hot from operation, ideally during the engine's stumble and stall mode.  Thanks for sharing, Sabueso!

Moses

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Update!  Rather than buy yet another tool for testing I bought a new coil.  Ran great for 20 minutes.  Then spit and stall.  Waited 10 minutes and started.  Ran another 10 minutes before stalling.  Since it stopped in front of the vegetable store i bought some lemons, started the Jeep and made it home (5 minutes).

So new spark plug wires, new coil, new fuel pressure regulator.  I really need to get this right.  I'm not buying the coil/ICM problem since the jeep reacts exactly the same with 2 different ICMs and the new coil and wires.  The weather where I leave is not that humid/hot.  I live close to the hills where the temperature is bearable.  And this Jeep has always been on the cool side.  I have a larger aluminum radiator installed and the engine stays between 195 and 200 F.  

It seems to be a time syndrome.  I get 20 minutes per ride before it cuts out.  Could it be a fuel pump relay get tired after a while?  Should I go back to checking fuel problems?  I've never changed the injector because it behaves great for a while.  But I might as well test it.

Bye the way, I got the wrong MAT in the mail.  Looks exact but the thread is bigger than my original.  Any idea what my thread measurement is for the MAT?  

Frustrated!

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Understand the frustration!  Relays and other devices can be an issue, try swapping the relays around, using the same amperage relays for your swaps.  I like your fuel pump relay concern and don't discount the possibility of the fuel pump itself acting up after operating for a while, though it shouldn't get hot with a steady fuel flow through the pump.  A relay or the ECU can be an issue when hot.  I have a periodic turn signal relay issue with our '99 XJ Cherokee, it starts making a "ratchety" noise when it begins to act up.

Something is being triggered by "time" and possibly heat.  Have you dealt with the emissions timer?  I addressed this uniquely Jeep YJ 2.5L issue in this discussion:

Use a caliper and thread gauge to confirm the MAT thread size.  If you can remove the MAT sensor without a hassle, measure the thread diameter and thread pitch or have a local hardware/parts source measure the thread size.

Hang in there!

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Actually I eliminated the emissions timer many years ago.  At the time I found it very inconvenient to have a timer that can't be reset and its only purpose is to let you know to check your emissions.  At a cost of $120!  I never had a problem without the timer for many years.  Whenever I suspect the O2 sensor I replace it and the Jeep immediately performs much better.

Because of work and my weekend job (My band Gigs every weekend :D), I barely get time to deal with the Jeep.  I may take a day off just for that.  I'm going to try the Relay switching and maybe buy a new one, and I'm going to check everything regarding the fuel tank. I read on another forum that the return line can sometimes be the culprit if it gets blocked somehow.  I will also do the connections at the ECU with contact cleaner and any other contacts that might need cleaning.  And of course the injector.  Been meaning to test the spray pattern.

Thanks for the info on the MAT.  I think I found one based on part number everyone mentions on the internet.  I bought it on Amazon and they agreed to the return.  But one thing about the old MAT - I removed it after my last test and put it aside.  It got cold really quick cause the tip is plastic so I measured for Ohms and I got almost 4K!  But since the motor was still hot after the drive I screwed the MAT back in by hand and checked the ohms.  I watched it go down to .683 ohms!  That's a good reading for the MAT with a warm engine right?

Frustrating yes, but I'm not giving up!  Thanks Moses.

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Sabueso...The return line can be a problem for fuel systems.  If clogged it will raise the fuel pressure by acting like a regulator.  The TBI/EFI pressure regulator can be functioning properly, but if the fuel return line is clogged, the fuel pressure can soar as high as the actual fuel pump pressure.  Whether you have this problem or not, you should make sure the return is unclogged and unrestricted.

Your list of troubleshooting steps sounds good!  Cleaning ECU and other contacts can't hurt and could help.  A TBI spray pattern is useful as a diagnostic step.

In this PDF you will find the MAT readings by temperature.  If you have a temp infrared tester and the ohmmeter, you can pinpoint the function.  I also included some additional sensor and ECU connector pinout information for your "Model 81" Jeep YJ Wrangler 2.5L.  This will help with diagnostics.  Note the importance of chassis grounds with your 2.5L TBI system, many of the sensors and devices complete the ground at the ECU:

Jeep YJ 2.5L TBI Sensors and Pinout.pdf

This should provide some ideas and tools for troubleshooting...

Moses

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Another update.  I've done a lot of searching on the forums looking for someone with a similar issue.  Finally found someone which made sense.  I don't have the link, but since this person had the same stall issue after only 30 minutes or so.  In fact he stated he could set his watch to the problem.  It would act up after 30 minutes of driving.  Turned out to be his CPS even though it was a Cherokee, but the CPS was the same as mine.  I did more reading and found that a CPS can develop "thermal failure".  They can test good and turn on when cold but will leave you stranded down the road from heat or vibration.

Can you elaborate more on this Moses?  Does it sound logical?  I've only replaced mine once and then it was because my cables got cut when I repaired the tranny.  But I kept the original.  

So yesterday I spliced and soldered the cables from my old one to the connector of the replacement.  Went for a test but it acted the same after 30 minutes.  I think both are bad - my original is pretty old from 1990.  The replacement is just Pepboys type that might not be the best and it's over 5 years old.  I really think this could be it.  The Jeep drives so well for the first 25 minutes.  When I installed my original CPS and tested I could actually feel a stronger performance.  It was doing 3rd gear going uphill!

According to a video, testing ohms at connections B & C should produce NO resistance.  On both CPS' I did get some resistance (.209 and .241).  Bottom line, I'm gonna buy a new one.

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Sabueso...The CPS (crankshaft position sensor), like any other electronic device or sensor, can be affected by heat.  I'll buy that reasoning.  A new CPS based upon the resistance test readings also makes sense.

While we're on the subject of the CPS, do you have any oil leaking onto the CPS or the flywheel notches (hall effect)?  A leaking rear main seal can raise havoc with any CPS that signals from the flywheel or flexplate.  Excess resistance is trouble-making resistance, regardless of the cause...

Moses

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No oil leaks yet.  I re-did the motor last summer and haven't driven much due to these problems.  But my driveway is oil-free!  Having the Jeep since 1990 I've experienced leaking rear main seals a few times.  Right now everything in there is super clean.

And even with a leaky main seal the Jeep always ran for good long time.  In the PDF you sent me before I could see the CPS test.  I'll try that test with a warm engine.  Thanks again Moses.  I'm feeling closer everytime.

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Sabueso...Sensible to test the CPS when the fault occurs.  If you have a surface temp infrared tool handy, you might also test the temperature of the CPS when it faults...

Moses

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