...floored, keeps running.

The first time it happened I was running down the freeway, and hadda floor it so it would stay running, and got a huge, puffy cloud of grayish-white smoke in cab. Thing backfired, power way down--in the good ol' days, and in a C$%^&y, it woulda been jumped time from a sloppy timing chain.

Quits if I let it drop below 1,500 RPM. If I didn't know better, I'd say it's running out of gas. Runs fine, then intermittently does its run-outta-gas trick.

Fresh in-tank pump, 65 psig fuel pressure (specs).
Fresh fuel filter.

Truck: '91 F-150
Engine: 4.9L

Codes Read:
(Key On, Engine Off)
334--EGR Valve Closed, Voltage High

(Key On, Engine Running)
311--Thermactor or Air System Fault
538--Insufficient RPM change during KOER Dynamic Response Test
538--(Trucks ONLY): invalid cylinder balance test due to throttle movement during test

After sitting for 3 weeks, it fired right up and drove fine, after which I got those readings.

WTF?

Eddie

 

Sounds like an electrical short. Had one in my 92 f-150 4.9 . My plug wire from the ignition coil to the distrbutor was loose.Corrosion(sp?) built up on the ignition coil causing to truck to backfire and die out but not all the time.