Hey all,

I've had this happen twice to me now. Doesn't seem to be any pattern other than its after a moderate to long drive with the AC on. I'll be sitting at an intersection and it'll just shut off. Not stall, just power down, but all my dash lights and things still work. If I turn off the AC it'll start right back up again, but with AC on it cranks but won't start. I think it's some kind of short but figured I would ask the pros.

'99 Jeep cherokee sport 6c 4.0L automatic.

Thanks in advance for any help!

 

This has been brought up many times lately. No one has followed up with a fix (if any).


I wish I knew what the fix was but I don't.


Good luck.


As a side thought it may be the Idle Air Controller, but it's a long shot.

 

I don't know if it's related, (bear with me my mechanical knowledge is limited) but there is a fan driver's side right next to the big engine fan attached to the radiator. I know that mine is really loud/sounds weird. I wonder if there's a problem with that fan's motor that's causing the problem?

 

Doing a lot of digging on google. To be clear when my XJ dies, it's not sputtering out or anything, the engine just stops. All gauges lights all other electronics seem to be working. So I don't think it's throttle/gas related.

 

I HAVE HAD THIS EXACT SAME PROBLEM!! I'm amazed with how little amount of people this has happened to. I unfortunately haven't gotten mine figured out but so far I have cleaned the throttle body, IAC valve, and TPS. Also have cleaned the injectors and redone the AC system. I thought it might've been the alternator because it's pretty old and factory. I'm replacing it for a better one anyways. I'm thinking when I do the neon injectors it will help maybe? I'm not sure. I will update this thread if I get any changes.

 

The electric fan is loud, sounds like a small jet aircraft.
If there are grinding or squealing noises than it could have an issue, but not likely related to the main issue you are having.

 

Have you swapped out the crank sensor? That was one thing google was spitting back to me pretty often, although most people said it didn't seem to help. To me it sounds like something electrical since it's not sputtering or idling rough or anything, it just switches the engine off.

 

If....


With the HVAC Mode Selector to off (O), and the engine is started cold, the RPM initially jumps to around 1200 RPM then settles down to around 1000 RPM until the engine warms up, then settles to around 750 idle RPM, the IAC is responding properly to the PCM targeted steps in its memory. This should eliminate any fault in the IAC stepper motor, its wiring, and the PCM memory.


Now....


With the engine idling at 750 RPM, and the HVAC Mode Selector is moved to an AC setting (AC Compressor engaged) the engine dies, it may mean that the PCM IAC memory control function has failed when AC has been requested.


Try this: With the HVAC Mode selector off (O) and the engine idling, depress the gas pedal enough to get 1000 - 1200 RPM, then select an AC setting on the Mode Selector. If the engine does not die it may mean the PCM is faulty. If the engine does die, there's an electrical issue in the circuits somewhere (TBD). By adjusting the RPM with the gas pedal you have bypassed the IAC.


~~~~~~~~~~~~~~


Here's the PCM/IAC function concerning AC:


IAC A/C Operation


The IAC is used for A/C compressor load control by opening the idle air passage in the TB slightly before the A/C compressor is engaged so that the engine rpm does not dip down when the compressor engages.


A function of the PCM memory program occurs when the A/C request circuit requires that the IAC stepper motor control engine rpm is the recording of the last targeted steps into the memory cell. The PCM can anticipate A/C compressor loads. This is accomplished by delaying compressor operation for approximately 0.5 seconds until the PCM moves the IAC stepper motor to the recorded steps that were loaded into the memory cell. Using this program helps eliminate idle-quality changes as loads change.


~~~~~~~~~~~~~~


If the engine dies when AC is selected (as is the current issue) and the PCM appears to be the fault, you may want to try clearing the PCM adaptive memory and see if the PCM has recovered. If it doesn't recover I would think a replacement PCM may be required.






PCMAdaptive Memory Clearing


After performing this procedure the PCM will re-learn and store into Adaptive Memory your engine's performance characteristics.

This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect both battery terminals and touch them together for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.).
Reconnect the Battery Cables.

The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.

 

Wow CCKen, hell of a response thank you. That sheds a lot more light on things. So each time I've had the engine die, the AC had been on the whole drive, so like an hour and half or so. No change to dial, just died. But, Each time it has happened i had been stuck at an intersection for a while and I'm sure the RPM dipped while sitting there. I'll start it up tonight and play around with the RPM and see if I can make it happen again as you've described. Stay tuned.

 

Yes I have replaced the crank sensor as well. Didn't seem to help and for all that work I wish it did! The thing that helped the most was new plugs (champion) but even that didn't last. Will try the trick he said above^ and get back with that as well.

 

Ken, you have a diagram of engine grounds you could post up?

 

Okay I went out to test this this morning. I couldn't get it to stall. Engine was around 210 temp and it switched on the AC no problem. The last time it did this to me under the hood was super hot. I almost burned my hand opening the damn thing. But the engine temp gauge wasn't abnormally high. Don't think I can recreate that situation without a long drive though.

 

Until we get a ground diagram from CCKen, I'd suggest doing a complete connector refreshing in the engine bat. Unplug every connector one by one, spray them out with contact cleaner, visually inspect the contacts, and then plug them back in. You could have a connector with high resistance which is aggravated by high underhood temps.

 

Connectors for the PCM you mean?

 

Every engine management connector you can find in the engine bay, along with the PCM connector.

And then, you need to refresh the grounds. This doesn't mean just looking at them. It entails remove the bolt/screw, cleaning the terminals til shiny, scraping the paint to bare metal, and then applying OxGard to everything before reattaching everything securely.