88 Grand Wagoneer power train module question

[markusj68]

Me and my son were out today in the Wagoneer.
It was running fine untill about 20 miles and it lost power...as in the V8 turned into a V6( probably best way to explain it).
It never stalled, and before we could pull over it went back to firing on all 8 cylinders and running normal. A couple miles later it started it again and he pulled over and shut it off. I looked under hood and everything looked ok. Started it and it fired right up and run fine.
We headed for home and it did it one more time while we were moving, then went back normal and run fine rest of the way home. It has never done this except a week ago, I went to move it out of garage and it did it when I fired it up, then went away and run fine.

This Jeep is mostly stock except for the engine which has an Edelbrock intake,cam, and shorty headers. It has always run fine, and starts fine.

It seemed like an ignition issue, and not like a fuel issue as it never stalled or quit running .
Could this be a power train module going out? It appears to be the original one.
As a side note it was hot as Hades here today ( and the past week or so)
I ordered a PCM from TGW, has anyone else had anything like this happen?

[Stuka]

I think what you mean is an ignition module. No FSJ ever has a PCM.

But a malfunctioning ignition module typically just stops working when hot. I would verify the rest of the ignition system looks good.

[tgreese]

You can search for related discussion, and the TSM will help you too.

viewtopic.php?t=17734

Headers will make your under-hood temperature much higher. Could be part of your problem. Not a big fan of headers, for a Jeep in particular - noisy, hot, leaky, fragile, expensive race car tech - otherwise they are great!

[fulsizjeep]

Remove the ignition module from the fender well and flip it over. If the resin inside is soft and gooey, replace it. I had the original on my 88 up until about 10 years ago when I started having misfires and temporary shut downs. The resin was soft and module was hot to the touch after running engine at operating temp for a little while.

[rocklaurence]

Remove the ignition module from the fender well and flip it over. If the resin inside is soft and gooey, replace it. I had the original on my 88 up until about 10 years ago when I started having misfires and temporary shut downs. The resin was soft and module was hot to the touch after running engine at operating temp for a little while.

This is my guess also. Ive parted-out around 30 FSJs and all of them showed signs of previous module meltings [goo on the fender well]. I have HEI on all my FSJs. Also, stay away from TGW--they are horrible regarding customer service. BJ's is Good/Great

[markusj68]

Went out and unbolted the ignition module. It is dark and spongy on the backside with truck sitting overnight.
I also went through and did a quick check of the ignition system. No corrosion under cap, and resistor wire seems ok as when running I have 5.3 V at the coil.
It has never had any starting or running issues untill yesterday. The only thing that has been changed is the fuel tank pickup( to get fuel gauge working) . I really did not like the replacement( looked kinda cheap) but yesterday it never seemed to run out of fuel, and never shut off just lost firing on some cylinders, and then they would come back and engine would run ok.

[tgreese]

Spongy? It should be hard plastic, like a plastic brick.

One option is "Stealth HEI." This is what I'm running in my CJ-6, though I did not use an old Duraspark module to mount the HEI moduls.
https://web.archive.org/web/20110719122 ... HEI01.html

The picture that's missing from this archived page shows the module mounted on a flat piece of copper bridging across the inside of the Duraspark module case (you could use good heavy aluminum too). The ends of the copper are bent at a right angle and screwed securely to the case. A good mechanical connection between the module and the bridge, and the bridge and the case, is important.

The aftermarket GM modules are considered more reliable than the aftermarket Duraspark modules.

[Stuka]

Fuel starvation issues can certainly cause cylinders to miss. Your issue very well could be the ignition module, but since you changed the fuel pickup just before these issues started, it could also be the cause.

[dodgerammit]

Another option is to run a MSD ignition box. I run the most basic. Streetfire. I kept the factory duraspark distributor and paired it with the streetfire box. Did the tfi coil, big cap, and rotor upgrade at the same time.

Also agree to double check for vapor lock. It is still a possibility.

[markusj68]

On the way home satuarday I filled the tank. It was at a half a tank when it started the missing when running. After I filled it never did it from filling station to the house. I'm working nights for the next few days , so I'll take it for a long trip tomorrow morning and see if the problem shows up.
The fuel pick up I installed looked a bit cheap. If it runs fine with a full tank, then that could be it.
A couple months ago I gave the wagoneer to my son for his first car, so it needs to be dependable( and it always has been).
We will see tomorrow how it does.

[letank]

The only thing that has been changed is the fuel tank pickup( to get fuel gauge working) . I really did not like the replacement( looked kinda cheap) but yesterday it never seemed to run out of fuel, and never shut off just lost firing on some cylinders, and then they would come back and engine would run ok.

time to connect a fuel pressure gauge, no need to cut a hole thru the hood like I did some years ago... you can wind a hose thru a hole in the fresh air vent and out thru the cowl opening and secure your gauge on the ribbs... example is for the vacuum gauge



and the hole in the hood for the fuel pressure gauge , being away from the home base required action!


may be the fuel sender has a leaky output weld at the interface cover/tube when it was welded or the hose was pinched between the tank and something, the space is so tight, anything can happen

[fulsizjeep]

Spongy? It should be hard plastic, like a plastic brick.

Yep, spongy, mushy, gooey. I have seen a few like this but only once in one of my own Jeeps. Once I found one in a junk yard that was actually drooling down the fender well.

[dodgerammit]

The fuel pick up I installed looked a bit cheap. If it runs fine with a full tank, then that could be it.

You're on to a good possibility. Pull sender. Measure depth of tank. Measure length of sender. And NO, the 2" sock-type strainer on the end doesn't count. It can suck air before the tank is empty.

[carnuck]

I recall corrosion on the ground inside a Stock distributor Causing a miss too.

Spongy? It should be hard plastic, like a plastic brick.

Yep, spongy, mushy, gooey. I have seen a few like this but only once in one of my own Jeeps. Once I found one in a junk yard that was actually drooling down the fender well.