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Stalling/bucking issue

933 views 24 replies 10 participants last post by  ZeeJay1997 
#1 ·
I have read over all the threads on this but I just need to be sure I'm on my way to fixing the problem.
1997 jeep zj and it will randomly stall out at idle and highway speeds. Huge issue when driving in 5 o'clock traffic. No CEL or anything. Hooked up the code reader and the only code it spit out was for ignition module. So I changed the ignition coil. Cranked it up this morning with no issue, thought everything was great, until it started bucking on my way to work. So now I've narrowed it down to 2 things- crank sensor, or ECM. I know by reading here that the crank sensor sometimes won't throw a code, it will just fail. I will test it when I get home today. Is there any way to test the ecm to see if it has gone bad????


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#4 ·
How did you narrow it down to those two things?
 
#7 ·
Had similar issue with the fuel pressure regulator. It would randomly stall and when giving extra gas it would buck because it couldn't get enough fuel to the injectors. Best way to confirm if this is a problem is to use a fuel pressure test gauge. You have a 97, so not sure if you have a vacuum line to the regulator. Pulling the vacuum line will increase the pressure and should cause a change in engine speed for a couple seconds until the pcm adjusts the air/fuel mixuture. If no change then this could be suspect. You might be able to rent a test gauge one at one of the auto shops or buy one for 25 bucks at Harbor Freight.
 
#8 ·
I've checked the fuel pump with a gauge and all seems normal. When it dies, fuel is present just no spark. It's a 50/50 shot if it cranks immediately after stalling. If it doesn't crank right away it takes awhile. Possibly from absence of spark, it could be flooding. I will ohm out the crank sensor tonight. If it is ok I will try the pcm screw trick.


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#9 ·
I've checked the fuel pump with a gauge and all seems normal. When it dies, fuel is present just no spark. It's a 50/50 shot if it cranks immediately after stalling. If it doesn't crank right away it takes awhile. Possibly from absence of spark, it could be flooding. I will ohm out the crank sensor tonight. If it is ok I will try the pcm screw trick.

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Oh ffs.

The screw trick is snake oil. http://www.jeepforum.com/forum/f13/12-things-you-can-do-when-your-zj-stalls-1407423/
 
#11 ·
Ok so update on the issue. I left the battery cable off all night, ran fine but a little rough this morning. Got on the road for work, as soon as I got up to highway speeds it started bucking and cutting off. The code it spit out was P0351 ignition coil primary/secondary circuit. Is this the PCM for sure since no other codes are present?? Don't want to take it to the dealership and don't want to be left on the road either as this is my daily driver.


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#12 ·
What were you expecting to happen by leaving the battery cable off all night?

Have you done any of the tests in the dirty dozen? Have you cleaned the grounds?
 
#13 ·
I left the battery cable off to clear the codes because I could not delete the codes with my code reader. The dirty dozen will get cleaned up today after work. I've got my brake cleaner and contact cleaner. I'm really hoping that will fix the issue. I'm really starting to have buyers remorse over this jeep.


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#14 ·
Never did see anywhere in this thread where you posted what engine you have?

That P0351 code can be thrown for lots of things including coil, cam or crank sensors, PCM, etc... If you do find it's a sensor after testing don't go with anything other than Mopar, especially on the crank sensor, or you'll be sorry.

In cleaning the grounds in addition to spray cleaners having a small wire brush, fine sandpaper/emery cloth, steel wool, etc, come in handy.

As mentioned in the dirty dozen with link in my signature it helps to try the wiggle test of the PCM connectors.

Post your engine size and can point you to your PCM ground location along with some specific tests for it.

PS. believe what Kg is getting at is normally any saved codes are removed from the PCM after disconnecting the neg battery terminal in a matter of minutes.
 
#16 ·
You have the same 97 4.0 that ZeeJay does who wrote the real good dirty dozen. Look at his "grounds" section and click on the photo link which show the PCM ground on one of the coil studs.

Can't stress enough how critical it is to have a good/clean PCM ground. A rusted/oil coated PCM ground on my 96 4.0 took out 2 PCM's and 2 crank sensors to boot on my 96 4.0. It doesn't help the PCM supplies ground to all the engine compartment sensors and I've found the crank sensor is about the 1st to go w/o a good ground. But testing is key before throwing parts at it.

It's easiest to clean that PCM ground from underneath. And you may have to hold the wire eyelets with a pair of pliers/vice-grips so you don't twist them off. There's also a nut in front and behind the connectors while you have to hold both to break the outside nut loose.

I'd also be checking your coil, cam and crank sensor connectors since sometimes they aren't tight or don't make good contact.
 
#17 ·
sacalaitman said:
Ok so update on the issue. I left the battery cable off all night, ran fine but a little rough this morning. Got on the road for work, as soon as I got up to highway speeds it started bucking and cutting off. The code it spit out was P0351 ignition coil primary/secondary circuit. Is this the PCM for sure since no other codes are present?? Don't want to take it to the dealership and don't want to be left on the road either as this is my daily driver. Sent from my iPhone using Tapatalk
I also got the P0351 code. It is not the ignition coil. It is a flakey PCM.

As I posted above, after wasting two weeks thinking I fixed the problem I finally replaced the PCM and it has been fine since then.
 
#18 ·
Yes, as you've posted in every stalling thread since you replaced your PCM. It shouldn't be a difficult concept that multiple things can cause the same symptoms and diagnosing over the internet with anecdotes instead of testing isn't effective.
 
#19 ·
By all means check out Zee's thread on stalling as it was meant to save you money throwing parts at an elusive problem. You will learn some things along the way. Having said that it doesn't hurt to have a spare PCM for the zj . While my next statement is perhaps anecdotal as it is based on reading, a large percentage of P0351 codes are the result of bad solder and flaky coil drivers in the module itself.
 
#21 ·
Update-----
I went through the 12 steps, cleaned grounds and such. I found a few issues
1. The negative battery terminal clamp was heavily corroded. Took it apart and cleaned it well. Found a chunk by the nut side had broken. Fixed all that.

2. Upon investigation of the pcm and connectors, I found that they were loose and some on the harness side were corroded. Cleaned the contacts very well and greased with dielectric grease. Also zip tied the connectors on more snug.

I know it will probably fail again and I am locating a pcm for it. Other than that, it runs much better, hasn't had a hiccup, and hasn't thrown any codes. I am now confident to run around town in it until it fails again. Thanks everyone for all the help in trouble shooting this issue.


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#23 ·
Sounds like you fixed the issue, good job!
 
#24 ·
Sounds like you fixed it. I was also going to add about how the Dirty Dozen are amazing steps to troubleshoot and honestly just should be done when purchasing one of these older vehicles. I personally purchased my ZJ last month and have been wrenching on it ever since (bringing it back to life), but I was expecting to do such from the moment I purchased it. The cleaning ALL of the grounds up really made a HUGE difference.

Idles smoother, voltmeter reads higher (spot on 14), everything seems smoother and even the windows seem to run up and down much smoother and a tad quicker. Overall, taking these vehicles back to basics (DirtyDozen steps) really helps clean everything back up and solves a lot of common issues.

Best of luck to you. Glad to hear you aren't afraid of running it to town or work.
 
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