Very strange ECM trouble

[ThatGuy]

I have been helping a friend of mine that bought a '94 Explorer sport. It's a 5 speed and had just had the engine rebuilt with a cam and the Aerostar heads and some other goodies. It runs pretty good but not as good as we thought it should.

It has a rather odd problem. Anytime it gets below 50 degrees it won't start. Well, not easily.

Above 50---starts first crank

Below 50--can take up to 20 minutes to get it running--has even ran the battery down twice trying to start it.

We changed the IAC, TPS, MAF, coolant temp sensor, and just about every single electrical thing the darn truck has on it.
We changed the fuel filter, spark plugs, wires, fuel pressure regulator, coil, and even more stuff.
Today we talked about it was time to change the fuel pump or at least check the grounds to it.

Then for some reason we came up with the idea to go pull the computer. We pulled it out and brought it inside. Let it sit for about one hour then went and put it back in.

Fired up first crank.
Let it sit for 2 hours outside.
Took about 5 mins or so to get it to fire up.
Pulled the ECM out and took it back inside. Let it sit for a couple of hours.
Fired up first crank.


So the idea is that something is up with the computer that it will only start when the temp is warm?????





Anyone ever heard of anything like this???

 

[ElleShooTiger]

Broken solder joint inside the PCM most likely. The solder starts cracking due to vibrations and after a while it breaks completely, more like microcracks, they're hard to see without a magnifying lens. The "heat" keeps the connection tight, but the cold shrinks the solder and breaks the connection.

 

[Foxracin]

If you need a computer let me know and I will look next time I go the the junkyard here. I know there are a couple manual explorers out there but cant remember if there 91-92 or 93-94.

I have a spare for 91-92 but it wont work.

 

[ThatGuy]

Yeah we put my ecm in it and it ran like ass. Barely idled and no throttle response.

 

[Ranger44]

Yeah we put my ecm in it and it ran like ass. Barely idled and no throttle response.

There are quite a few differences between a 91' & 94' pcm. You're going to have to get the proper pcm. Also pay attention to whether it has a cam position sensor or egr. It'll also make a difference.

+2 on the broken solder. Happens all the time.

Good luck