96 ZJ dying again! - Page 2 - JeepForum.com
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post #16 of 53 Old 01-10-2019, 10:20 PM
peter_zabriskie
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Seems my posts keep disappearing, so again here goes. I have have a ‘97 ZJ and 354000 miles and have been down this road a few times. Most recently after the 3000 mile road trip moving with trailer from NM to MD. The common problem is the Idle Control Valve. It gets dirty or over heated and made in China craps out. Of course making sure the PVC vents are not switched and pouring oil into the air intake makes a big difference, don’t ask how I found that out. Next indeed are plugs, wires, distributor cap/rotor (very important-brass not alumn), then coil. If you have done all these like I did after arriving in MD then it still stalls at highway cruise or unpredictable other like speed up, slow down or stop sign, then the ECU is your problem and at $150 is cheap enough to fix and forget. Autozone rebuild with core. Now I am on to tie-rod ends and probably a new steering box as I have run out of over center adjustment. 🙂


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post #17 of 53 Old 01-10-2019, 10:53 PM
JonS
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It definitely sounds like a PCM problem. With the engine running in Park, wiggle the PCM connector closed to the engine and see if engine sputters or stalls. If so, the PCM is shot.


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post #18 of 53 Old 01-11-2019, 10:41 AM Thread Starter
xtrattitude4u
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So ive been trying to learn what goes wrong with the PCM or the connector, since lot of people seem to have this problem.

A few people say it's the header inside the PCM that gets a loose/cracked solder joint, but after pulling it apart, u couldn't get any if the header pins to show any issue while trying to flex the board. I added a bit of solder to each pin for good measure.

When reinstalling, I unplugged/replugged each PCM connector several times in case there was some corrosion on any of the pins.

Now when it's running, I can't get it to stumble by tapping on the PCM or wiggling the connectors, so it seems like it's fixed for now, but I'm still not sure where the problem was.

I'm leaning toward a bad connection between the connector socket and one of the pins on the PCM, but I can't be sure.

I read somewhere that the PCM isn't completely sealed, and moisture can build up and try to escape through where the connectors plug in, causing some slight corrosion on the pins.

That's what I'm leaning towards, since I couldn't get the header pins to act up.

It drives me crazy not knowing what the actual issue is.
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post #19 of 53 Old 01-11-2019, 11:56 AM
Some_Anchovies
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Quote:
Originally Posted by xtrattitude4u View Post
So ive been trying to learn what goes wrong with the PCM or the connector, since lot of people seem to have this problem.

A few people say it's the header inside the PCM that gets a loose/cracked solder joint, but after pulling it apart, u couldn't get any if the header pins to show any issue while trying to flex the board. I added a bit of solder to each pin for good measure.

When reinstalling, I unplugged/replugged each PCM connector several times in case there was some corrosion on any of the pins.

Now when it's running, I can't get it to stumble by tapping on the PCM or wiggling the connectors, so it seems like it's fixed for now, but I'm still not sure where the problem was.

I'm leaning toward a bad connection between the connector socket and one of the pins on the PCM, but I can't be sure.

I read somewhere that the PCM isn't completely sealed, and moisture can build up and try to escape through where the connectors plug in, causing some slight corrosion on the pins.

That's what I'm leaning towards, since I couldn't get the header pins to act up.

It drives me crazy not knowing what the actual issue is.
Unless you were inspecting each solder joint with a magnifying glass, you won't be able to easily see the breaks in the joint. Enough of a break that heat expansion can be the difference between a good connection and one too spaced out, causing high electrical resistance and voltage drop at the joint.

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post #20 of 53 Old 01-11-2019, 01:28 PM
paulvon
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For me it was my PCM on my 97 ZJ.

I drove it more than I should have. Then one time when it started back up there was a loud explosion.

The muffler less than a year old looked like a watermelon and I twisted my drive shaft.

Replacing the PCM was the easy part of the repair.

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1997 ZJ 4.0 L - Upgraded to heavy 93 sway bar
2004 WJ 4.7 L - 2 1/2" lift
2011 KK 3.7 L
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post #21 of 53 Old 01-14-2019, 06:58 PM
kalpol
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Fifth or sixth PCM opinion chiming in here, and I also blew off my muffler after not fixing it for a while. Usually only failed when hot.

90s solder had issues. If your tach isn't dropping to zero when it dies, it's not the crank sensor. The cam sensor hardly ever goes bad, as it's pretty well protected. Sometime the PCM wire wiggle trick works, sometimes it doesn't. Sometimes baking it in the oven works. But in the end it's a crappy solder that pretty much everyone in the 90s suffered from. O'Reilly has them with lifetime warranties, I got one that lasted about a year then the replacement has been fine for the last 5 years.
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post #22 of 53 Old 01-15-2019, 08:54 PM
RedRiverT
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"a crappy solder that pretty much everyone in the 90s suffered from"

Hmmmm . . . let's see here. George H.W. Bush served from 89-93, during which he worked to increase China's commerce with the U.S., i.e., imports. Clinton began in 93 and of course he was pro-China too, if for no other reason than they gave him millions for his campaign, but also because as governor of Arkansas he had dealt with them a lot trying to get business investment in his state.

Wonder where all that crappy solder came from? How much has it cost Americans?
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post #23 of 53 Old 01-15-2019, 09:17 PM
ZeeJay1997
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Quote:
Originally Posted by RedRiverT View Post
Wonder where all that crappy solder came from? How much has it cost Americans?

Most of the electronics for ZJs were assembled at the Chrysler plant in Huntsville AL. However, they had suppliers from all over the US who, in turn, had there own suppliers.


The plant closed long ago and most of the engineers went into the defense industry. Working in the defense industry myself, I had a chance to talk Chrysler electronics with one of the former quality engineers. My question to him was "What's up with the bad solder joints in 93-98 grand Cherokees?" He said the problem lies in lead free solder. The government mandated that they phase out leaded solder. Their suppliers had to develop new soldering processes using lead free solder. Basically, they learned how to do it when our electronics were being produced.


Now you don't have to wonder


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post #24 of 53 Old 01-16-2019, 12:40 PM
kg6mov
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Yup, the goverment was offering tax breaks to companies who went lead free, whether they knew how to or not.


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post #25 of 53 Old 01-24-2019, 11:46 AM Thread Starter
xtrattitude4u
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So here is where I'm at with the PCM saga.
I took the PCM apart and tried resoldering all the pins on the header.

Even with a 60W iron on full blast for 10 secs, I could not get the pins hot enough to melt solder while the iron is on the pad, due to the aluminum back sucking the heat away. I put some solder on the pad, held it for 10 secs and hoped for the best.

I reinstalled the PCM and I can still easily get it to die wiggling either of the left 2 connectors. 😞

I reinstalled the old PCM I had lying around, and now I cannot get it to die. So it seems it's definitely the PCM, but likely not the header pins.
Maybe the header is broken on the inside.

The old PCM was taken out on suspicion, after the rear O2 sensor wrapped around the driveshaft and blew the PCM fuse. The Jeep was shifting a little weird occasionally and sometimes idling a little rough, but that may be a different problem.

Gonna drive it for awhile and see.

So where is the good place to get a rebuilt PCM?
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post #26 of 53 Old 01-26-2019, 12:55 PM
poor93
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Garage
My jeep dose this at times. My problem is in the wiring next to the battery so i run out jump the starter relay and shake the harness and it fine till i hit a big bump check that

D.K.A
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post #27 of 53 Old 01-27-2019, 07:25 PM Thread Starter
xtrattitude4u
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Well, I did it.
I bit the bullet and reflowed the PCM.
All 126? Pins on the main board.

The 3-4 most outside row of pins for the connectors were obviously cracked, the rest looked fine.

I almost destroyed the little S shaped fuse pulling the compound off of it, but managed to get it back into shape and cover it with nail polish clear coat.

Just put it back in and it fired right up.
Now I can't get any reaction at all wiggling any of the main connectors.

I also took a wire brush and cleaned the two main grounds, on the fender and the block.

As a bonus, I think the mysterious oil pressure gauge dropping to 0 issue might be fixed now too.

Gonna take it for a test drive, fingers crossed!

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post #28 of 53 Old 01-27-2019, 09:48 PM Thread Starter
xtrattitude4u
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Wow.

Here is a list of things that seem to be fixed after reflowing the PCM.

1. Oil pressure gauge randomly dropping to 0 psi
2. Coolant temp sensor fault on the VIC.
3. Random dying
4. Wierd laggy tranny shifting issues
5. Unstable idle issues
6. Brake pedal now resting higher and feeling firmer.

That last one I don't quite understand.
My wife did the test drive but she swears the brakes are significantly better, with the pedal feeling firmer and engaging earlier.

I'm not sure what the PCM has to do with that, maybe engaging the booster or something?

Anyway, this fixed several issues already, and I'm thrilled!

Will update later as the PCM does a re-learn.


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post #29 of 53 Old 01-28-2019, 02:00 AM
Zilliver
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xtrattitude4u, if the engine is running better, the vacuum is better and brake booster works better.

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post #30 of 53 Old 01-28-2019, 08:05 PM Thread Starter
xtrattitude4u
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Quote:
Originally Posted by Zilliver View Post
xtrattitude4u, if the engine is running better, the vacuum is better and brake booster works better.
Ok, but it seems to run just fine until it dies.

Well, just got a call from the wife and it died again, thankfully right as she was pulling into the driveway. It wouldn't start for a minute or two, now it's starting right up again.

Ugh.

Im gonna pull the PCM back out and see if there are any cracked joints somewhere else on it.

I did find a refurb PCM with a lifetime warranty and 60-day money-back guarantee. I have a feeling I'll be ordering that.

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