Well, I recently replaced the fuel pumps, senders, and filter in my 1990 F-Super Duty (460 MPI) because of a faulty harness. I hoped replacing the pump filter and tanks might resolve the bad off idle and low speed throttle response. It didn't. It almost acts like a vacuum leak but it seems to idle fine in gear. It only seems to happen off idle or low engine speed. Once the truck gets rolling it disappears. Any suggestions would be appreciated... TPS?

Thanks in advance for any help.

 

Just an update, after putting a Snap-On "the brick" scanner on the truck we found that the EEC or computer was not responding to any codes or issues we tried to create. The EEC was junk and it was operarting in limp mode, which explains why it was limping around and could not identify the issue easier.

 

So is it running better now or are you still in the process of finding another PCM for it? You may have made the correct diagnosis anyway because at 24 years old the factory unit probably has leaking or blown electrolytic caps, but just so you know these things aren't that quick to respond to sensor problems.. sometimes it will take several drive cycles before the computer sets a code or the check engine light. And many current scanner type devices will fail to establish communications with the systems in these trucksl, the fall back test for computer sanity is to try to make it flash codes on the check engine light, if that fails and the CE light bulb isn't burned out then there is a good possibility the computer needs replacing.

 

PCM should be delivered today.

After running poorly for so long I never got a dash code even with all the bulbs replaced. I tried to trigger a code by removing the MAP sensor while running, and while i could hear the scanner/sensors clicking and the engine changing RPM after a half dozen attempts I could never get the scanner to complete any test cycle, so i could never get any codes.

I'll update you once i get the new PCM installed.

 

Well, we replaced the computer tonight and no change to the performance and I was still unable to link the old snap-on Brick MT2500 scanner to the system.

Do I need to relearn this computer?

Any idea if this scanner should work or not for vehicles over 8500 GVW?

Any suggestion at all would be great appreciated.

 

I am not familiar with the Snap On Mt2500 tool so I cannot tell you if it is compatible with OBD-I vehicles.

There is no "relearn" for this computers per se. They are not flashable if that is what you are asking about.

In cases like this I suggest to go back to basics. Get a jumper wire then do this: How to run a self test