Okay, so I'm back with some new developments. I decided to start a new thread to ease some confusion. As a recap, I have an '89 Ford L9000 with a Cat 3306B and 8ll trans. When accelerating under heavy throttle, at around 1600-1800 rpm, the engine loses power sometimes to the point of stalling. Shutting the engine off and restarting "fixes" the problem until the next time it's placed under heavy load, rinse and repeat. I discovered this morning that the air/fuel ratio control seems to be the culprit. Engine running with the rear cover of the AFRC removed, I activated (pushed in then released) the plunger. Engine is slow to rev, replicates my on-road no power condition. If I hold the plunger in, like it's receiving boost pressure, engine revs freely and runs good. If engine is started and AFRC isn't activated, it also runs normally. This is the first direct correlation I've found with my problem, so I'm excited to say the least. I'm currently running a new pressure line from manifold to AFRC to eliminate a possible blockage in the original steel line. Anyone familiar with the AFRC operation that could shed some light on this? Thank you!
You could remove the AFRC completely. Block the oil port and purchase a 8N-3799 cover to test your theory. Or, put new o-Rings in the AFRC.
Well, I finally found the smoking gun! New temporary boost line didn't help, so I removed the AFRC and tore it down again; this time I had my shop manual to follow. After some studying, I realized two springs had been swapped around inside the housing! Put it back together correctly, re-installed it on the engine, and now it runs normally. It'll take full throttle all the way up through 7th and 8th gear no problem. Crazy to think it could be something so simple. Thanks to everyone for all of the help, what a great wealth of knowledge on this forum. I learned a lot from this experience.
I'm glad you found it, who was in it before when springs got swapped.
I've owned the truck for less than a year, I bought it early this spring. But the guy I bought it from owned it for 10-12 years, and he experienced the issue too. He thought it was bad fuel filters. I don't think he ever really attempted to fix it. The governor has had hands on it, the wire seals are missing on the back. But it finally runs good now. I fixed a bunch of leaks in the charge air cooler as well, so now it actually makes boost. Can't wait to see what it does now with a good load on it!