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Stalling Problem

M

Mad Steez

NAXJA Forum User
Location
So Cal
I have searched but with no exact matches.

My problem is that my xj is stalling/ loses all power when i go into reverse, hit a bump/hole, and take a turn just right. the jeep has to be warm for it to happen. if i put it in reverse it starts to cut in and out, shake violently, and then dies with all with in about 10 seconds. i found that if i gas it, it some times corrects it self.

when i hit a bump/ hole i lose my engine. the car stays on but the engine cuts. this also happens when i go around a turn just right.

I have checked all of the fuses and relays, as well as some plugs. I replaced the CPS just last week as i thought this was the culprit.

any help would be great


SPECS:
2000 Cherokee Classic 4.0
112000 miles
automatic
242 transfer case
no engine mods
brand new Mopar CPS ( less than 200 miles on it )
2 year old Costco battery
 
Start the engine, then start shaking the harness where it connects to the PCM. See if that makes it cut out.
 
joe_peters said:
Start the engine, then start shaking the harness where it connects to the PCM. See if that makes it cut out.
Click to expand...

I tried that but no luck.

Also, I forgot to mention it does not shift right.
Example: going from first to second, my RPMs go up to 2500, then stays there until i let my foot off the accelerator or it shifts automatically ( which takes about 10-15 seconds ). This problem is more extreme when going from second to third. my RPMs will get well above 3000 before shifting, but it stays in second gear at above 3000 RPMs, before i take my foot off the accelerator or let it shift by itself ( which it does not do some times ).
 
You have a number of things going on.

First, clean the throttle body and IAC port, and clean the pintle on the IAC being careful not to break it.

Second, test the TPS, and replace it if out of specs.

Third, using an external tach--not the one in the instrument panel--measure the idle RPMs in PARK/NEUTRAL, and post that number up.

Fourth, have someone sit in the driver's seat and shift the engine into 1st gear while they hold their foot on the service brake pedal--you need to be observing the engine for excessive shifting under torque. Next, have them shift into reverse--again, while you are watching for excessive shifting of the engine.

Post up what you find.
 
joe_peters said:
Fourth, have someone sit in the driver's seat and shift the engine into 1st gear while they hold their foot on the service brake pedal--you need to be observing the engine for excessive shifting under torque. Next, have them shift into reverse--again, while you are watching for excessive shifting of the engine.
Click to expand...

Like as if my motor mounts were/are broken?
 
Mad Steez said:
Like as if my motor mounts were/are broken?
Click to expand...

Yes, bad mounts and/or broken/missing engine mount bracket bolts--the brackets bolted to the engine block that the engine mounts attach to.
 
joe_peters said:
You have a number of things going on.

First, clean the throttle body and IAC port, and clean the pintle on the IAC being careful not to break it.

Second, test the TPS, and replace it if out of specs.

Third, using an external tach--not the one in the instrument panel--measure the idle RPMs in PARK/NEUTRAL, and post that number up.

Fourth, have someone sit in the driver's seat and shift the engine into 1st gear while they hold their foot on the service brake pedal--you need to be observing the engine for excessive shifting under torque. Next, have them shift into reverse--again, while you are watching for excessive shifting of the engine.

Post up what you find.
Click to expand...

So far i have checked the to see if i had excessive shifting of the engine but it was rock solid.

I don't have access to an external tach, but when I first start my xj up in the morning i have about 900 idle RPMs. once the engine is hot, my RPMs are much lower; about 500 or lower. it is the same when in park and neutral. this probably doesn't help you.

Where is my IAC? is it right next to the TPS? What is the pintle?

All of these problems started at once. is this common?
 
Sounds like your IAC--idle air controller--isn't doing its job. It is a stepper motor that extends and retracts on command from the PCM to control the idle speed of the engine.

Once fully warmed up--both the engine and automatic transmission--after 20 minutes of operation, when you put the gear selector in DRIVE, foot on the service brake pedal, then engine must idle in the 700-750 rpm range. What is happening is that your idle is too low, you put it in gear and it stalls.

IAC:
getimage.php

The pintle is the pointed end that when mounted to the throttle body it extends/retracts on command from the PCM to vary the idle speed.

Get some throttle body safe aerosol cleaner, cotton swabs, and an old toothbrush (M16 cleaning brush is great). Remove the IAC, clean the throttle body, throttle plate, the IAC port where it mounts, and the IAC pintle. Put it back together and see if the idle speed has improved.

Post up your results.
 
My bet would be on a poor ground on the right side of the engine. All signal values to the pcm go to hell without good grounds there resulting in it running the way it does. Check all obvious ground wires while you're at it.
 
just finished cleaning the throttle body. started the xj with the engine temp at about 160*. cycled through all the gears and the RPMs stayed at 750 idling. however the RPM tach is still jumping, although, very little.
 
What about the stalling issue?
 
Ok, the 750 rpm idle--in DRIVE, service brakes applied, after 20 minutes of running? If the 750 rpm is in PARK or NEUTRAL you still don't have enough idle speed.
 
Swing by a salvage yard and grab a couple IACs from XJs--compare IAC part numbers on various late model 4.0s at rockauto.com to get a range of donors.

IACs seldom go bad, but they do become lazy with age. If you pick up a couple the odds are in your favor that you will get a good one.
 
Likely, the PCM/ECU is constantly adjusting the idle with extend/retract signals to the IAC--its a stepper motor--and your idle in PARK and NEUTRAL should be substantially higher than the 700-750 rpm in drive.

Another thing to consider is that part of the IACs job is handling the transition circuit (old carb term); it helps when changing from idle to throttle.

Once you have this issue sorted out if other symptoms persist it will be easier to track them down.

Good luck.
 
Thank you for all of your help Joe. I really appreciate it.

I'm going to try to hit the junk yard in the next few days, and I'll post up what my results are.
 
UPDATE:

I went to the junk yard but all of the xj's were picked over. so i didnt get the IAC or a TPS.

However, I did test my xj. It gave me the P0700 code; transmission control system malfunction. I need to put a few miles on the clock to get more readings, ie: missfires, and other codes.

Also, its been hot these past few days and my xj is hatting life. It has been running even worse. Just the other day I put the jeep in reverse and it was suttering, and the RPMs were jumping. The jeep stalled and once it stopped, it made a pttts sound. Also there was a knocking snound the time before that after it stalled.

what is going on?
 
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