Anyone ever done business with these folks?

http://www.siaelec.com/index.asp?PageAction=COMPANY

Hope I'm not violating any rules...

 

FWIW, it sounds like the PCM may very well be the issue, BUT!!!!! I had a Jeep ZJ 4x4 4.0L that I fought for a year before finally finding the problem......very similar as you described. Cold starts ( even in relatively warm ambient temps, just engine was at ambient as well ) , starting down his lane, maybe 2 - 3 minutes into the process, it would stumble harsh, act like it would die, and then come out of it if you either romped it down, or waited it out. I finally discovered that the event occurred just as the PCM was going from open loop to closed loop as the O2 sensors came up to temp. When it happened, I could see the voltage on the O2 sensor spike to 5V . The O2 heater would basically short out to the sensor at that point and almost kill the engine. Replacing the O2 sensor fixed it. Sorry for the long story, but after you replace the PCM, if there are still issues, just thought that may be something to look at as well.

 

Haven't used them, but I have used ECUDIRECT.com with quite a lot of sucess. Very quick turnaround time. Kind of a pain with the credit card and core and all, but worth it in the long run.

 

That thought has occurred to me. I'm wondering if a sensor short has taken the PCM out.

I know there's a problem with the PCM because it shuts the engine down if I tap on it while it's cold. i can beat the crap out it when it's hot with no effect.

I drove it for 8 years without any problems. The MIL came on a few years back and i pulled in a auto parts store and they pulled the code while the light was on... O2 sensor, dont remember which one.. it went away the next time i cranked it and never came back.

I found out in the last couple of days that when it stop cutting out by tapping, it still tries to stalls at road speed and leaves no codes.

I'm going to do some more checking. Maybe disconnect the o2 sensors and see if it stalls running in closed loop all the time.

Whatta ya think?

 

It won't ever make it to closed loop with the O2 s unplugged. The Jeep I worked on never would set a code either. I just got lucky and saw it with a scanner while it actually happened.

 

Err... I meant open loop.

It's ran 160 miles in the last two days with no problems.

It's not a major problem to keep running it, so maybe I can catch it in the act. I want to be sure I only have a bad PCM.

I'm going to buy a scan tool and monitor O2 sensors.
I've needed a scan tool for a number of years now. It will work on my truck too

 

Found three bad relays, transmission, ASD, and fuel pump. None were totally inop, just intermittent. I can see how those relays would break down after a while, it so hot in there. Plus, about six months ago, I left the switch on for two days and totally drained the battery. Couldn't have done the relays any good.

I seems like a lot of this model ZJs start going south around 75K.

Still haven't replaced the PCM although I still have my suspicions.

 

Well, I'm still messing with this PCM and I couldn't stand the thought of buying another one without knowing something is wrong with it.

So, I did what any life long electro-mechanic would do, I took it apart.

Figured out that the voltage regulator is mounted on the the inside of the large plate that also serves as front cover. It has an internal connector that separates with the plate/regulator. The main body (the rest of it) has a conformal coating that looks similar to clear silicon. The voltage regulator has a seal around it forming a mold for some more conformal coating that coats the regulator circuits.

The coating on the regulator looks and feels like it has reverted from it's original state.

After getting all the slime off the regulator, I found and cleaned a moderate amount of corrosion around the solder joints where the connector is mounted to the board. I think this is the problem because every time it fails, I lose voltage and the computer resets.

Does anyone know if this coating around the regulator should be solidified or is it supposed to be slimy??

Anyone been into one of these before? It's on a 97 Grand Cherokee.

 

The couple of times I have run into coated electronics circuit boards, the coating was solid.

 

Try searching these sites for help, they are Grand Cherokee specific:

www.mallcrawlin.com
www.nagca.com

 

Sounds like you are on the right track. I think you've just got a simple cold solder joint in the PCM. I've fixed a lot of those successfully over the years, but not on a JTEC PCM like you've got. Those boards are usually sealed up real good, and it's actually pretty rare for them to fail. Most of the few I've replaced were destroyed by failed reflashes and such. Anything's possible after a lot of miles though. I know you want to be sure, but my hunch is that it's simply a PCM problem.

 

From my experiences with Jeeps and 4.0's ill offer this advice.

kbb.com to find trade in value, get to operating temperature, drive to dealer. Drive home in anything but a 4.0. LoL. I love how everyone says "The 4.0 is a bulletproof motor except for....." and the list goes on and on about everything except the core internals.

Just kidding 4.0's jeeps are very commong in junkyards here, why not just try to get another junkayd PCM before going through all this hassle?

You say you're at least getting a MIL light, you can pick up a cheap scantool for $40. Toss that on as soon as you see the light and figure out what the real cause is.

 

I don't think I said I'm getting a MIL light. I really wish I were!

No codes at all. The light flashes whenever it stalls, but does not store a code.

I think corrosion is the problem. Remains to be seen. Thanks to all.