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Wrangler YJ, TJ, and LJ (1987 - 2006) Technical forum for the Wrangler YJ, TJ, and LJ Unlimited.

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  #1  
Old February 9th, 2019, 21:07
Cwburrell Cwburrell is offline
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Extremely cold natured YJ

I have an 89 wrangler YJ TBI with 2.5 liter 4 cylinder that is hard to start when itís cold. It will fire rather quickly but immediately dies. Sometimes it takes 15 or 20 tries to keep it running. Once it warms up, it runs well. I noticed the electric fuel pump stays running almost constantly when the key is turned to the run position. Should it only run for a few seconds until it pressures up and then kick off? Any suggestions would be appreciated.
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  #2  
Old February 10th, 2019, 16:47
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Ecomike Ecomike is offline
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Re: 2.5 L TBI 89 cold start issues

Being a 2.5 L TBI, that was part GM stuff and part Chrysler stuff, I would track down some folks familiar with it. I thought at one time they MPI, but they may well have some differences I know noting about. Nick at nickintime on youtube, or here, may know a little about them, as his new REM scanners can now access the 2.5 L, 4 banger ECUs as well as the 4.0.

Maybe the main difference is just one injector??? If so, I could help some.

Oh, and it also sounds like the FPR is bad reading the first post here (or relay is stuck??). Unless the TBI had a lower pressure, and different pump and FPR from the 4.0s ??? I worked on an 84 once and it had an old style mechanical pump that ran off CAM.
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Old February 10th, 2019, 16:50
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Re: Extremely cold natured YJ

Since it is temp related I would check the MAP Vacuum line and ends for any weakness/leaking at all.

Check the IAT air temp sensor in the Intake and clean it. Test it for proper resistance at cold temps.

Check the TPS voltage when cold and warmed up. And for sure clean up the sensor ground contacts surfaces!!!
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old February 10th, 2019, 21:52
Cwburrell Cwburrell is offline
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Re: Extremely cold natured YJ

MAP Iím assuming is manifold air pressure? Iíve checked all vacuum lines but Iíll go over everything again just to be sure.

I replaced both the IAT and TPS early on in the troubleshooting but it didnít change anything.
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Old February 28th, 2020, 20:15
Cwburrell Cwburrell is offline
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Re: Extremely cold natured YJ

I’ve finally narrowed this issue down to what we (myself and a very knowledgeable mechanic who has had my jeep at his shop for over a month now) believe is the ECM. Can anyone tell me where to find one? All my searches turn up plenty for the 6 cylinder but nothing for the 2.5 liter 4 cylinder.
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Old February 29th, 2020, 11:38
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Re: Extremely cold natured YJ

Unless warning up the ECU with a hot air dryer solves the hard to start when cold problem I would find a new mechanic. That is based on what is in the this post so far.

Is that a Renix ECU in that beast or a GM? 89 TBI injection sounds like GM, but I am not sure.

Disclaimer: I have yet to find a mechanic in 50 years that I trust
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old February 29th, 2020, 20:18
Cwburrell Cwburrell is offline
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Re: Extremely cold natured YJ

I used my timing light when trying to start it so I could see what the spark was doing. The spark would quit and then the engine would die so I decided it was related to the ignition system and not fuel related. My mechanic acquired some data ( I don’t know where from and I’m only getting this information second hand from the lady behind the front desk when she called me with an update) that detailed the proper output of the crankshaft position sensor and the ECM. Using what she thought he said was an oscilloscope he determined the output from the crankshaft position sensor to the ECM was good but the output from the ECM to the ignition module was not correct. There have been times that it would not fire at all. Using my timing light I determined that there was no spark so I decided to change the ignition module. Upon returning from the parts house with the new module I decided to try it again before installing the new module and it fired right up. I went ahead and put the new module in but it didn’t seem to change anything. Why it’s worse when it’s cold I have no idea unless something is breaking down inside the ECM and it’s affected by colder temps contracting something. At this point I’m willing to try a new ECM assuming I can find one.
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Old February 29th, 2020, 20:25
Cwburrell Cwburrell is offline
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Re: Extremely cold natured YJ

And to answer your question I don’t know if it’s a renix or GM ECU/ECM. I would have to pull it out and look at it but the jeep is still at the mechanic shop. These guys have been the best in our area for years and have put a lot of effort and research into figuring this thing out. But just like me they’ve discovered that there just isn’t much information out there on this particular year model.
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Old March 1st, 2020, 11:27
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Re: Extremely cold natured YJ

If it was me, I would refresh and clean all the connections on the ECU and harness, and then if needed open up the ECU and look for signs of loose connections, cold solder joints, over heated parts with signs of burning, and try to repair it.

Look up Nickintime here and on Facebook. He might be able to help you find one or repairs yours.

Have you checked Ebay and the online Junk yard searches?

Usually the CPS is the bad part (at least on the 4.0's), works one minute and not the next, comes and goes. Or the voltage output to the ECU is just a little too weak for the ECU to see it all the time. They use a magnet in the tip that looses its field strength with age and the peak voltage signal gets too low for the ECU to read through old weak contacts in the harness connections
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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