hesitation/stuttering only when hot

[cochino12]

I'm having an issue with my 00 (classic bosy 5.7) hesitating or stumbling when at operatint temp, but only when its hot outside. I checked fuel lines, exhaust to see if it might be vapor locking but I don't see anything out of the ordinary. Fuel pump has been changed, as well as the fuel filter, wires are new, pulled and cleaned mass air sensor. Also the problem is much more noticeable when the truck is loaded or pulling a trailer

Any other ideas?
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[cochino12]

Nobody

[speedygonzales]

I had the exact same problem. When extremely hot out and go to take off when engine is up to temp, boom fell flat on it's face. I had an MSD 5 ignition box that was causing the problem. Went back to straight and all ok.

In your case it could be the optical sensor in the distributor or the coil or the ICM.

One thing I did discover before removing the MSD was, the ICM is mounted to an aluminum heat sink and the heat sink compound was just about gone. I cleaned it and put new compound between the ICM the heat sink and the bracket.

I had previously used my Vantage to look at the signal coming from the distributor sensor since the problem occurred right after I changed to an aluminum distributor. But the signal was just as pretty and square as you could ever want. So no need to mess with that.

Incidentally, the coil is considered a "tune up" item and should be changed periodically. Look at the insulation on the windings for tell tale white dots showing you were it was arcing to ground. You could even look at it at night to see if it has fireworks.

The funny thing about the problem I was having was the PCM never through a misfire code. I have a reprogrammed PCM from PCMFORLESS and I need to test it by pulling a plug wire to be sure the misfire detection still works.