Alright fellas im new to the forum so any help will be appreciated. Here is the problem. I have a 1988 f250 custom 300 l6 4x4 5speed. I recently acquired this truck off of an old man who was having trouble with it stalling while warm. Long story short it ended up being the fuel tank selector. Now im having a very rough idle accompanied by surging fuel pumps and a bad shaking under acceleration. Getting alot of backfire out of the exhaust between shifts and during down shifting. Sometimes, on rare occasion it will studder backfire loudly and die untill it gets back down to outside temprature. Ive replaced: fuel pressure regulator, intake manifold gaskets, both low and high pressure pumps, fuel tanks, MAP sensor, coolant temp sensor, IAC, fresh cap, rotor, plugs, wires, air filter, fuel filter, and fuel pump relays. There is no check engine light on, and it seems to run alot better when its cool or cold outside. Any help or comments would be awesome.

 

Pulling the codes is the first thing to do in the order of diagnostics.

 

Its not throwing any codes at all. The light will flash one time and thats all it will do

 

Looks like you've done replaced everything that you could! You mention the fuel tank selector, was it replaced? I'm guessing it was.

This is an early Ford EFI on this motor, and had bank injection going on (2 banks of 3 cylinders). There's a lotta fuel flowing through this engine, which is why there is the air pump to help the catalytic convertor burn it all. My '78's donor truck was an 87 and I did some research on it's efi. I went with VEMS instead

Would an Oxygen Sensor trip a code? my '87 mustang had horrible performance when the O2 sensor died.

Check the distributor timing? check the pickups inside of it for anything obvious... check firing order? and read plugs?

hmm... what else... Clogged intake exhaust?

Oh I know, Check Fuel pressure! poke a fuel pressure gauge on the fuel rail nipple thingie and see if it is a fuel issue or not.

Dang it, oldfuelinjection.com is gone... but here check here too Fuel Injection Technical Library

 

Ok. I cant seem to find a pressure guage out here in the boonies but im fairly sure thats not the problem at hand. Yesterday i drove about 15 miles and it died. It did not studder or anything, just acted like i shut the key off. After tinkering on it for an hour i found i had no spark what so ever and the icm was extremely hot. So i replaced it. Got me back home but as i was pulling into the driveway it did the same thing. What else could cause this issue?

 

When you replaced the ICM, did you apply any thermal paste to the back of it or on the plate it is mounted to? If you didn't apply computer grade thermal paste, it will not dissipate heat as it is designed. Also, you could do the same with the old one, if it isn't cracked or damaged. The early EFI trucks and cars had the ICM bolted on the distributor, and that allowed for early fails associated with heat and vibration.

Radio Shack or any computer repair shop will have thermal paste available. Also, do not use dielectric grease in place of thermal paste. It will actually insulate it with heat.

 

I did apply the thermalgrease that came with the new icm when i installed it

 

If it's getting really hot, then perhaps high resistance in the wiring leading to it or away...

I would check all the wiring to and from and ensure that all connections are clean.

May also want to post in the "87-96" forum for a greater audience.