Recently replaced a worn '91 351W non-roller cam in a '91 F150 w/ E4OD, with a roller cam unit out of a '95 F250. Overall, the truck runs great and performs as expected, all but the idle quality.
When cold, computer just connected, the engine "tries" to idle around 800-600 rpm, but just cannot hold it (irradic) and will return to 1000 rpm. It will stay there for several minutes & sits around 900 rpm while in DRIVE and at rest, it will do this all day long and is fine, but it will not idle, EVER, where it should around 600 rpm. I have checked for vacuum leaks, replaced IAC...all gaskets (intake - upper/lower, throttle body, IAC, PCV valve, all hoses/vacuum lines have been replaced and gone through), I'm certain there are no vacuum leaks, it holds around 18" HG when at 900 rpm. When cold, and the IAC is unplugged, the engine will idle at 600 rpm, but when it's warm, it stays about 1000-900 rpm. I have gone through and checked TPS voltage and set it up accordingly, even though it didn't need adjustment. Throttle cable is brand new & not sticking.
I'm all out of ideas as of what to do? Is this the roller cam causing this issue? Or do I need to rewire something? All stock components were reused off of the '91 engine, including the distributor/wiring harness, but with a new steel gear just for the roller cam. This is a speed density system, in case anyone wanted to know.
I can live with the way it runs as of now, but it irritates me to have to deal with this idle issue, if you have any thoughts, please let me know!
The 1st gen lightning block is designed to have a roller cam so all you have to do is get 5.0/5.8 roller lifters, bones and retainer. Then just drill and tap two holes to mount the retainer in the valley and shop for your roller cam of choice.
Yes. The motor is all stock as of yet, including the factory roller lifters and pushrods. The only items I switched over were the accessories from the original motor. Everything else is from the donor, all except the computer. New gaskets were installed at the time the motor was put in.
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or the 95 lightnings
