86 ford truck from hell questions


Old 10-12-02, 05:25 AM
tammi ann
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86 ford truck from hell questions

Several questions about my Ford truck

1986 Ford F-250 300 6 cylinder tfi ignition or DI ignition as the Ford guys now call it. The one with the hall effect sensor and th icm module on the side of the distributor. Truck also has a carburator instead of fuel injection.

Truck is in terrible shape, 14 yrs of commercial use, truck has been abused, worked on by non professional "mechanics", pieced back together after some major engine work.

Truck will run now but it runs very sluggishly, the plugs foul up with carbon after about 2 minutes of running, they foul so bad that a timing light will stop working and then the plugs must be taken out and all the fluffy dry carbon must be cleaned from them.

Does anyone know how to troubleshoot the pcm on this truck ??? I have checked the icm and the eec relay and both work and now I wonder if maybe the pcm (computer under dash) is bad. My first thought is to just kill power to the eec relay and this should drop the computer out of the picture, therefore if the computer is bad then if I do this with the motor running there will be no change in engine performance. Would this be correct ???

I have a book and have performed tests on the icm, distributor etc... but the only thing it says can be done to diagnose a bad pcm is to change it out and thn see if it fixes the problem. My book is 10 yrs old and am hoping maybe someone has come up with another way to diagnose.

I dont think on this particular carb that anything is adjustable but if someone thinks I can lean it out a little and help my situation I would be more than happy to hear about it.

The egr on the tuck is completly non funtional as I had to change manifolds and must get around to pe piping the egr to manifold connections so for now I have it blocked off, also the oxygen sensor is not hooked up but it has not been hooked up for over 10 yrs.

I know this is a pretty screwed up post but any comments would be appreciated.
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Old 10-12-02, 08:31 AM
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It sounds in piss poor shape frankly, and doesn't warrant much attention. If the body is rotten, things have been bypassed (you mention the O2 sensor is disconnected, there is the first problem).

Personally, I would have scrapped it a long time ago as it sounds like it is in poor shape. Your choice though ..

1) Check the basics. If the timing is off, has stretch in it, you've got trouble.

2) If a compression test reveals poor results..stop here. Rebuild time or pitch the truck. No cobbling together will help it.

3) The computer can be sent out for testing through any parts store. No real checks you can do except to make sure grounds are good and sound.

4) Reconnect any disconnected sensors. It will never be right with things bypassed. Anyone that bypasses things like that should not repair cars. Things are there for a reason!

5) This carb is pesky and complete junk, but not much can be done about it, except a thorough rebuild of it.

In summary:

1) Any sensors bypassed have an effect on what's happening.

2) If the truck is in poor mechanical shape (bad compression, burns oil, etc), think twice about spending any good money or time at it. A better unit can be purchased for less time and money in the long haul.

3) Go through the basics, and test things. If you're into the truck for the long haul, then I suggest you get a hold of a factory OEM manual either used, or from Helminc.com

4) Need more detail on these "fixes" and bypasses. We're not getting the whole story here.
Old 10-12-02, 06:21 PM
Join Date: Dec 2001
Posts: 2,538
i would say you need to replace or rebuild the carb they are as joe said a common problem and in almost every case will always dump way to much fuel. i wouldnt be replacing the pcm it has very little effect on fuel control in this model, even if your pcm was bad with a good carb it would still not run rich enough to foul the plugs.
next time you check your timing see if it retards when you disconnect spout connector to set base timing and should advance when connector is plugged back in, this will atleast tell you if the electronic advance portion of the pcm is working.

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