?upstream oxygen sensor?


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I believe it was replaced when the engine was replaced because they had issues getting it to run in the shop after changing the engine. I'll check it nonetheless though. Thanks for the input!

 

Welcome to the Forum Cae08,

Here's a link to a thread about a somewhat similar problem. Read through the whole thread and see if anything sounds familiar. Make sure to read the #15 post. I'd offer the same suggestion to you.

Won't Start when engine warm

Hi, So about 2 weeks ago when I was attaching my plow since snow season is upon us and my jeep just died, at first I thought I just stalled it so I tried to start it and it did start but as soon as it start it would rev up to 1500 RPMs and then just die. I tried to start it multiple times but it...

www.wranglerforum.com

Good Luck, L.M.

 

This is a huge help. The coil is going to be the next thing I try. I also downloaded all of the maintenance manuals. Definitely sifting through those.

There's a local Jeep Guru who used to be the foreman for a Chrysler dealership and now only works on 2006 and earlier Jeeps in his spare time. He seems to think it's purely electrical, as if the ecm is cycling through its startup routine repeatedly. However, he hasn't had time to really look at it yet, so I'm seeing if I can figure it out before he gets time for me to drop it at his front door. That being said, the coil sounds promising. Thanks!

 

So I have narrowed the field to the Charging Circuit.

Note that I have installed an external voltage regulator, but these issues were present before I installed it.

I found that when I unplug the voltage regulator, which keeps the battery from charging, the issue goes away.
If I plug in the the regulator, reinserting the alternator into the charging circuit, the issue starts back up.
I changed the alternator today, and it did not fix the problem, but disconnecting the voltage regulator while the vehicle was running stopped the issue instantly. I found this by accident but have no idea what direction to go. Literally there are 5 wires on this circuit.

1. Battery Positive to alternator
2. Ground to alternator
3. Ground to regulator
3. Field positive from alternator to regulator
4. Field negative from alternator to regulator

When I disconnect Field Positive, the problem goes away, but the alternator also stops charging the battery. The problem only happens when the engine is at operating temp.

Any advice is much appreciated.

 

Isn't the voltage regulator part of the ECM?
Can you reconnect it?

 

The voltage regulator is part of the ECM stock, but they are known to go bad on the YJ's. There are several companies that make external voltage regulators, such as Quick Start, specifically to bypass the one in the ECM so that you can still charge your battery without having to replace the ECM. That is what I did. Everybody has success with them as a whole, so I don't think my issue is the external regulator.

 

It sounds like there may be an issue within your PCM (computer). The voltage on your 1995 is controlled by the PCM. Since you state that the issue was going on prior to installing the external voltage regulator and it goes away with the regulator disconnected that's where I'd start looking.

Why did you install the external voltage regulator? Did you take any shortcuts when installing the regulator?
Have you had your alternator tested?
Since you're using an external regulator, your check engine light is likely lit all the time. Is that the case? (The check engine light wants to tell you that it's not getting power from the alternator).

Since the issue only happens at operating temp, perhaps there's an internal short between the temp section of the PCM and the charging part of the PCM. If you suspect the PCM, you can contact Wranglerfix and ask if they can repair it. Wranglerfix is a Vendor Member of Wrangler Forum.

Let us know what you find and what works (and what doesn't work) as a fix.

Good Luck, L.M.

 

I installed the external regulator because the internal one stopped charging the battery. I had the alternator tested and it tested good (at least it was putting out the right voltage). I didn't take any shortcuts with it according to all of the diagrams. I took off the original connector and wired the regulator to the correct terminals. I'm getting 14.3V to the battery at all times with it connected, so it's charging fine. I just taped up the original connector really well and tied it up away from everything so there wouldn't be any shorts. All of the parts that were also connected to the Alternator are getting voltage from the battery and other points. It appears there are redundancies where all of the sensors and relays get Positive and Ground connections.

The check engine light is on and I know that is because I disconnected the internal regulator. When I do the key trick I don't get any relevant codes.

Your last point makes sense. I feel like it's a wire connection/short somewhere and the temp sensor circuit makes the most sense. I'll look into that more and see. I only question this idea because the alternator and regulator are entirely isolated from the PCM now, so it doesn't make sense to me that a short in the PCM would be cured by disconnecting the external regulator from an unrelated circuit.

I'll keep the thread updated with my progress because I've been chasing this problem for a year now and at this point it's just a challenge.

 

One suggestion is to try a PCM from a Cherokee with the same engine (2.5). It will need to be from an automatic transmission vehicle if you have an automatic transmission in your YJ If you have a standard transmission either a standard or automatic PCM will work, you'll simply have to jump the plug that would normally go to the neutral safety switch on an automatic YJ.
You'll have to reattach your charging system to the way it was prior to installing the external regulator, but if that cures your problem, your CEL will be out after the initial startup flash.
A Cherokee PCM for a 1991-1995 2.5 should be fairly cheap at your local Pick & Pay yard.

I only know about using a Cherokee PCM from reading about it here, so I offer that as a suggestion to try, rather than as an absolute cure. After a year of frustration, I'd be willing to try almost anything.
Perhaps other posters that have used a Cherokee PCM will chime in.

Keep us posted.

Good Luck, L.M.

 

I have a 95 wj 2.5 that had a rough idle, back firing and stalling when it started to warm up. I tried almost everything TPS, MAP, plugs, wires, fuel filter, repaired leaking vacuum hoses, coolant temp switch, air intake temp switch, gas treatment, filled tank with 93 octane, cleaned throttle body to no avail. I had noticed all along it wasnt producing but around 12 volts when running. SO my next effort to repair the rough idle included: New alternator, new O2 sensor and new Idle air control switch (the plunger was stuck all the way out with carbon buildup). Now its Fixed! Runs like a champ. Hope this helps.

 

Update, still not right. Idles up and down from about 400 rpms to 550 rpms. I changed the coil, crank sensor. May have improved a little. I am testing the fuel rail pressure today. At a loss

 

When it is acting up, spray starting fluid around the intake manifold. It may have a leak.

 

When it warms up slightly. I checked the pressure at the fuel rail when running, it was 19lbs and immediately drops to 0 when I shut engine off. The fuel pressure did not increase when I removed the vacuum hose from the fuel regulator nor did it increase with more rpm's. The fuel pump relay is not closing when the key is in the On position. Cant hear fuel pump running at all. It must just run when cranking? I have read that it only runs when cranking and it runs with key on, so I am not sure what it is supposed to do.

 

@tullis After the Jeep has sat for a while (overnight) if you turn the key to "run", you should hear the fuel pump run until it builds up pressure at the regulator. Then if you don't turn the key to "start", the fuel pump will shut off. Once the Jeep is running, naturally the fuel pump is running.

Your issue sounds different than Cae08's issue. Yours sounds more like a fuel pump starting to fail. Perhaps other posters have a more experienced opinion. Have you checked out the flowchart in the Factory Service Manual?

Good Luck, L.M.

 

I will look at that tonight. Thank you for your help.

 

When a Jeep, any Jeep, runs like crap after It warms up...check temp sensor, tire goes flat for no reason, check temp sensor, kids failing in school, check temp sensor, old lady says she's pregnant and you've been away for 12 months...well, maybe check the temp sensor
Then only reason I didn't suggest it sooner was the direction the thread took, may not be the issue, but eliminate the possibility

 

intake air temp sensor and coolant temp sensor have both been replaced

 

Sorry, thought you were the OP, when you hijack someone else thread, you may not get too many responses as when people go to it, they see the older date from the OP and not realize you have a similar but different problem, and you tend to get the wrong advice based on the original post.

 

Sorry, thought you were the OP, when you hijack someone else thread, you may not get too many responses as when people go to it, they see the older date from the OP and not realize you have a similar but different problem, and you tend to get the wrong advice based on the original post.

Happens all the time. It's always best to start a new thread for each issue with as much information as you have about your issue. I often refer new members to this thread.

A better way to get help in the YJ Tech Forum

Originally posted in the General Discussion Forum by NonRubicon in May 2014. It's every bit as relevant today as it was then. ....................................................................................................... I think there are a few things members here can do to help...

www.wranglerforum.com

Most of us join this forum because we need help to keep our old heaps running. The way to keep the forum alive is to follow up in your thread with what worked for each particular issue and to give advice and suggestions to other posters.

Good Luck, L.M.

 

that makes sense. thank you

 

Another thing I was wondering was: Does the PCM immediately respond to the new parts that are installed or does it take a few running cycles to make changes needed?

 

Takes a little while to learn

 

But shouldn't affect runnability, uses pre-set perameters until values determined

 

What coolant temp sensor did you buy, and did you get all the air out of the system burped out-issue with our jeeps

 

1995 YJ 2.5L Update: after getting 19lbs of fuel pressure I decided I would pull the tank and replace the fuel pump. When I removed the pump from the tank I noticed that the pump/motor was not in its saddle and there was a tear in the small fuel hose that is on the FP assembly. I said well ok I found my problem as to why I had low fuel pressure. Re assembled with new pump and screen. Started up fine but I had 100lbs of fuel pressure when running and it was idling up and down about 200 rpms. I remembered my skid plate for the gas tank was dented and that is probably why the fuel pump motor was not in its saddle. Then I realized the return line would be jammed to the bottom of the tank causing a high fuel pressure which caused a hole to be blown into the small gas hose on the FP assembly. So I removed the tank again, cleaned and straightened the skid plate. Removed the assembly from the tank because my return line was still touching the bottom of the tank. I assume the tank had just collapsed over the years. So I took my tubing cutters and cut about 3/8" from the return line (not sure if that was the right thing to do but its all I had come up with). Reassembled and now have 30lbs of fuel pressure while running and it maintains pressure when the key is off. The fuel pump also runs when the key is switched on (it wasn't doing that before with the old pump). The idle is steady and I believe I have finally got it back to normal. In this process of finally getting to this place I think its odd that I found so many bad parts and pieces to never really actually fix the problem. I just wonder if the PCM takes you on a journey of issues when you replace a part/sensor it possibly doesn't know what to do with the new information. Some things improved the problems with rough idle but then it would throw another code. Just kinda strange. Anyway I hope this helps.

 

Thanks for letting the forum know what the final solution was. Your experience is sure to help someone with a similar problem. Glad you had the fortitude to pull the tank a second time.
All too often we don't hear back as to what cured a poster's problem. If anything comes from cutting the return hose, please let us know.

Thanks again and Good Luck, L.M.