1987 XJ 4.0 - Erratic Idle and Dies when Warm

[godenades]

Hey Guys, first and foremost, thank you for the add! I just picked up my new (old) XJ a few weeks ago, and went through and replaced the timing chain, oil seal on the timing cover (it was leaking), water pump (bad bearing) idler pully Bad Bearing), thermostat and housing, alternator and exhaust flange donut. I also went through and did a full tune-up, changing oil, filter, plugs, wires, dist cap and rotor. I was really hoping the tuneup would help the idle when warm issue I am having, but no dice. It certainly runs much smoother and sounds great but I am still having the occasion stall/die when the engine gets to running temp. I am hoping some of you guys have had experience with this and could point me in the right direction, here goes:

As I stated, the engine runs flawlessly except when it dies. I have noticed that it only seems to die when it is up to running temperature (right around 190-200).

I have let it sit and idle for long periods of time to see if it will do it on its own and once in a while it will, after sitting for about 20 minutes yesterday, it just shut off as if someone turned off the key. It didn't stumble or anything, just boom, it was off and the electric fan was running.

I also notice that once i am at running temperature, if I stop at a stoplight, sometimes it will just die. I also noticed that if I am in neutral and just sitting there, the idle will sometimes fluctuate very slightly between maybe 500 and 600. While experimenting, i noticed if I hit the gas and rev it up to around 3k and take my foot off the gas, the idle dips, it sounds like it wants to die and sometimes recovers, other times it dies.

I have also noticed that after it dies, it starts right back up as if it were cold. No difference in starting whatsoever.

I have read that this could be caused by a few things... and I am hoping to get ideas from you guys on where I should start. I have heard the following that seem logical to me:

Engine Temp Sending Unit - Causes the engine to run rich due to the wrong temp hitting the ecu
Crank Shaft Position Sensor - Failing unit may cause no spark, in turn killing the engine
IAC Valve Failure/Dirty - Rapid deceleration (letting foot off the pedal) causes the throttle body to shut completely, starving the engine of air

That is about all I have found that seems relevant... IAC in my opinion would be where i should start because I can easily remove it and clean it to see if it makes a difference... I simply don't know why the temp of the motor would make a difference so I am wondering if maybe it has something to do with that Temp Sending Unit?

What are your experiences with this? Any thoughts on saving me some time in figuring out what my culprit is? :) Thanks guys! I look forward to your help and of course sharing my experiences with you guys for years to come.

Brian

[nickyg]

Did you clean the throttle body and the Idle air control valve? couldn't hurt and it's cheap to do.

[godenades]

I have not, but will probably give it a shot in the next day or so. Would the heat of the engine play a role in the the failure of an IAC?

[nickyg]

Just reread your post sorry.. Yea, I'd start with the IAC. maybe it has something to with when crud gets warm. Any way you gotta have a cleanish IAC for a smooth purring engine any how.

[godenades]

I will certainly give that a try first! Thank you so much for your response and confirming what I was thinking.

[4.3LXJ]

Welcome Brian. You have done some good research, but unfortunately not complete. Good effort so far. There are a couple of items that are neglected with tune ups that everyone does. One is the IAC, it should be cleaned every 100K when tuning up. Another at 100K, but not related to this problem is the crank position sensor. Now on to your problem.

When your engine is cold, the fuel air ratio is rich, similar to how a carburetor choke works. As the engine warms up, the coolant temp sensor signals the ECM and the ECM leans the mixture based on the information the oxygen temp sensor gives it. Unfortunately these things don' last forever. They generate their own electricity and eventually run out of electrons to donate. So they give a false reading to the ECM. So with bad info the mixture ends up being lean or rich. It is a crap shoot which one it will be. But these sensors need to be replaced about every 50K to insure they will function right

[godenades]

Very interesting, while I was aware of the Coolant Temp sensor, I really didn't know the relation between that and the O2 sensor. I will certainly go ahead and replace both of these as they are inexpensive parts which should probably be changed anyway! So you are basically saying that the two sensors work together to keep a happy rich/lean medium, interesting!

I assume this is a fairly common issue then huh? Can't believe I didn't see this in my google searching. :)

[4.3LXJ]

Your coolant temp sensor is probably doing what it is supposed to. Up to you on that one. But new sensors don't hurt. The O2 sensor is the real culprit here, and yes a fairly common problem that people don't diagnose correctly assuming this problem is caused by something more closely related.

[godenades]

Ok, I will see if Autozone has one in stock and I will replace it tonight and get back to you! So this O2 sensor is likely failing, but not enough to cause the "Check Engine" light to go on i suppose. I will go ahead and change the O2 sensor first, test and then replace the Coolant Temp sensor just so that I know what does or does not make a difference. I will also order an OEM Crank Position Sensor from Rock Auto as I would like to be proactive... Don't want my baby dying on me in the desert. Thanks again 4.3XJ, great information!

[4.3LXJ]

Your welcome. Just to add to that, the code for O2 sensor failure is caused when the wires are broken, that is no current coming back at all, or by the failure of the heater in it. As long as it does something, even if it is wrong, the ECM assumes it is functioning correctly

[godenades]

that makes sense! Thanks again for sharing your knowledge, I will replace the O2 sensor and report back with the results!

[godenades]

So I bought a new O2 sensor, old one didn't look bad but replaced it anyway as looks can be deceiving, no change at all. I drove for about 20 minutes and thought it was better but then pulled up to a stop sign by my house and boom, thought someone turned the key off. :( I then pulled out my phone to see if I could get it to die again, tried everything that I thought may be causing it and nothing. I did get a video right after it died and I restarted, you can see it turn off but recover quickly enough in this one... other times it isn't so quick and it just dies. Hope this helps.

1987 Jeep XJ Wagoneer - Idle Issue - Random Stalls: https://youtu.be/ZtHQnJp7EDo

[4.3LXJ]

Did you replace the upstream or downstream sensor. There are two

[godenades]

I replaced the one that is right at the end of the manifold. Didn't have the option to buy another one at autozone, unless they are identical. Is there one near the muffler?

[godenades]

If the O2 sensor was out, would it happen ALL the time when I get to operating temp? Or would it be sporadic like this? I literally tried for 45 minuts last night after the initial failure and couldn't get it to even come close to dying. Haha. No that's frustrating! :)

[Brasscatz]

Here's another question for not only you, but Steve. Could a bad engine ground cause this? Like that flat ground going from the block to the firewall? Just every once in a while whether by vibrations or whatever, the connection is lost long enough to shut the motor off?

[4.3LXJ]

That is a good question. It is possible. However, I think it could only be one other thing, the crank position sensor. This is another common problem. One thing I focused in on was the higher rpm lean type condition. I am sure it probably needed changing anyway. But when crank position sensors become marginal they can give the shutting off and restarting symptoms

[godenades]

Funny you say that... i sat up last night researching again and came across a lot of articles that explain the 1987 cherokee having major grounding flaws... honestly, I wouldn't doubt if that is the cause and I plan on looking at the ground that is mounted near the base of the oil dipstick tonight. I will start the engine and simply wiggle that ground to see if it kills the engine. It is close enough to the engine to where I could see the heat making a difference. Strange thing is that when my jeep is in normal running temp range, it runs perfect! But if it raises 10 degrees is when i seem to experience the issues... like the temp is right at the threshold of allowing whatever it is to work and if it gets slightly higher, its starts failing. I will keep testing to see what else I notice. Symptoms are just as important as the solution so we can help the next guy diagnose it.

Don't worry, i will definitely keep you guys posted. I have come across way too many posts where people help and suggest things, and then the guy disappears and doesn't say what fixed or did not fix the issue. Can't stand reading through 5 pages of forum to find that it is left open like that! haha

[godenades]

4.3XJ, i have never once had any issue whatsoever restarting the jeep. It always takes maybe 3 seconds of turning to start, but it always starts after right around 3 seconds. I don't know if that is a long time for a normal RENIX jeep to start, but that is what mine takes

[godenades]

Are there any smells that I could look for or any other indications that it is running rich or lean at the time of having issues?

[godenades]

So just a quick update, I really haven't changed anything but since I changed the O2 sensor, took it for a test drive, it stalled once and then I tried to repeat it, I haven't been able to. I didn't drive it much, but I did decide to drive it to work today to see if I could get it to die and so far so good, no erratic behavior. I put around 50 miles on it today and will put another 25 miles on my way home.

I checked the grounds where they are supposedly problematic and they look perfect so I didn't mess with it yet. I also checked to see if there was indeed another 02 sensor near the cat/muffler and there was not. I only have one sensor near the flange donut. I researched this online and this seems normal on the Renix engine. Am I wrong there? I have not replaced the coolant temp sending unit, but will do that tonight or tomorrow if I have continuing trouble.

Couple things I have noticed:

My battery seems small for the area in which is sits. I don't know if that makes a difference, but it just seems like the wrong battery.

In relation to the battery, I have gone back to the times that I can remember, and the times that the truck has died, the headlights have been on... I don't know how this could affect the truck, maybe it can, but when the headlights are on, i seem to be pulling around 10V on the volt meter, when they are not, i am around 13V. When i put the windows down or up, if I hold the button, the batter seems to drain down to around 8 and maybe further if I keep holding it but I let it go... does this mean maybe a bad battery?

Also related to the battery, I attached a trickle charger to it last night and it was pulling around 6 Amps, which to me also signifies a bad battery.

Lastly, the battery Positive cable was not very tight... i was able to wiggle it off with my hand. I pushed it on and tightened it as far as I could last night.


If you remember, I noticed that if i got slightly above normal operating temperature, the jeep started stalling at a stop. It started right back up with no issues, but only at those higher temps... is it possible that I am hitting a certain temperature, the electric fan hits a higher speed and pulls more amps and kills the car at low RPM? Just a thought...

All in all, i do think that my battery is bad, regardless of whether or not it is the root of my problem. I will replace it when i get a few spare bucks... money is tight right now...

Thanks for staying tuned!

[nickyg]

Welcome to the world of JEEP! Whenever I address 1 issue I run across 3 more that need attention.
Hence my signature.... one more part and I'll have a new Jeep.

[nickyg]

Welcome to the world of JEEP! Whenever I address 1 issue I run across 3 more that need attention.
Hence my signature.... one more part and I'll have a new Jeep.

[godenades]

Hahaha, so darn true... love that signature.

[4.3LXJ]

It was my mistake on the second O2 sensor. Musta been a brain fart. But don't tell Al Gore, he will get me for greenhouse gas emissions. :D

[godenades]

Agreed! Well, just a slight update, my battery was tested by Autozone and they said it was perfect.

I went through the battery posts and cleaned everything up with light sand paper so that the wires, posts and clamps were all metal-on-metal. There were some random wires that were installed by the brain-dead previous owner that were done half-arsed, which I removed and I also removed a couple of other wires he had run for his fog lights which I removed because they were hideous.

I now have over 13V coming from the battery and when I turn on the lights it doesn't dip like it used to, so that is good news.

I drove her back from work yesterday (25 miles or so) and didn't have any issues, also drove her around town last night running errands and drove her to work today with no stalls. Maybe it was the O2 sensor and it just took some time for the computer to learn what the new sensor was pushing? Maybe it did have something to do with the batter?

Not sure... but I am still not fully convinced, i will give it a few more days as this issue was sporadic in the future, it could just be hiding from me making me feel good. haha.

I do have an engine coolant temp sending unit I picked up, I will install that this weekend just to do it. I also have a new CPS, but it is made by AIRTEX/Wells and i have heard nothing but horror stories about non OEM Jeep sensors bought through Jeep... Is this something I should be worried about when popping this one in? I find it hard to believe they would sell sensors that have a history of not working so often...

Also have almost burned through a full tank of high octane fuel, maybe that has helped something... Who knows... I will keep an eye on this and will certainly keep everyone posted every day or week depending on how often I drive it!

Thanks for all the suggestions, let me know if you think of anything else!

[rv-errr]

godenades I have a 2001 4.0 olds aurora that acted just your like XJ, leave home and at third stop light it would stall then start right back up with no problems the rest of the day,this was intermittent but each time the same stop light.Their were no codes, I took advice given on the AURORA forum and replaced the crankshaft sensors, that cured that problem but just like my 2000 4.0 xj as they say IF IT HAS TITS OR TIRES YOUR GOING TO HAVE PROBLEMS!!! I see they have your level as jeep compass my wife has a 2012 compass raly with 30k that has been trouble free. JUST SAYING

[xj-jake]

This is posted on another forum but it's all relevant Renix information. I referred to this list all the time when I was having issues with my 88. Hope it helps you out.

Cruiser 54's Renix Tips

http://www.jeepforum.com/forum/f140/cruisers-mostly-renix-tips-1304879/

[godenades]

rv-errr: Thank you so much for the tip! I have been driving it all week now and haven't had a single episode. When I bought the car, i didn't know the gas gauge was backwards (full is empty, empty is full) so I was all happy that he left me with a full tank of gas and was driving it up to work when all of a sudden I hit a hill and started losing power and all that... Sure enough I was right near a gas station, so I pulled in and filled up. That was around 1.5 months ago and I didn't drive it more than 10 minutes for the test drive and had no issues... I almost wonder if there was something at the bottom of the tank that got sucked into my fuel system... ugh... its an endless number of things it could be! Either way, I will be replacing the coolant temp sensor and the CPS this weekend (hopefully i have a few hours), once that is done I will feel pretty good. I appreciate you sharing your experience with your Aurora, sounds identical to what I had experienced!

XJ-Jake: thanks for the link! I have actually gone through that one before and that is how I gathered some ideas of what could be wrong. I would absolutely love to print that list out and leave it in my garage... every weekend knock out a few of those items, that would be great! But we will see... This is my desert rig and I just want it to be functional enough to have some fun on the mountains and I will slowly fix her up as I go, so this list is a great road map. I appreciate the share and you taking the time to read through my post here. I really like my Renix, though it had given me some issues, i have become pretty familiar with it fairly quickly so I have a lot of confidence in taking care of this truck for the long haul!

Thanks again for your help you guys! I will keep visiting here and let everyone know how things are going.