1992 P30 454 TBI total high end power loss

[Oz]

Thanks! 

[Eyez Open]

It has plenty of power on the low end. Like on the back roads going 45 or 55. It really prevalent on the freeway with cruise control on. Usually I set the cruise control on about 65, I go at about that speed and not slower to keep the tractors from blowing my off the road. When I start pulling a small incline, I'll turn off the cruise control and feather the pedal to keep it from shifting all the way down to 2nd.

I may sound anti tbi/injection here but I can tell you I am not that. Your tbi unit is or should be a Rochester 220. That tbi unit can only deliver 670 CFM, meaning it will have the same equivalency as a 650 carb. I'd would be surprised if that tbi motor builds power past 3500 rpm..The engine cannot breathe enough...

There is not to much you can do about that with your existing setup, one thing that is a real possibility would be high carbon build up in your combustion chamber's/valve area. Under higher rpm you might be experiencing minor detonation which the knock sensors pickup and then retard the timing. You would never be able to hear this but the engine would definitely respond poorly.

A decent engine analyzer would be able to read these knock counts, and if that is what is happening google Sea Foam combustion  cleansing... Snake oil yes but GM once advised using a water drip into the carbs just for this carbon problem...do not use that approach to many people believe more is better. More is very very bad, it destroys engine's.

Most of the old 454's were epa restricted, at the same time GM changed the manner in which they rated HP. Underrated is the first thing that comes to mind. I've seen some of these old engine's be reworked, using modern engine measurements they produce 330 HP and very close to 475 ft lbs of tourqe..that big tourqe number says it all. Induction restrictions along with very retarded timing strategy. Meaning a diesel like engine preformance...low rpm high tourqe preformance...Then adding extremely low gear ratio's, lowered  enough to get these old RV"S moving .

[Rickf1985]

Does this have catalytic converters? If so it sounds like an exhaust restriction. Even if not I have seen exhaust pipes collapse internally, especially at a Y connection. Have someone push hard on the gas while you are at the tailpipe and see if it sounds like a vacuum cleaner. The other thing that comes to mind it that you should NOT have a vented fuel system on an emissions controlled vehicle so you have something wrong in the emissions system and that could be a major contributor to this problem. Clogged charcoal canister, someone plugged the wrong hose thinking they were eliminating the emissions system. ( I have seen that one a LOT!) The emissions hose routing is on the side of the air cleaner, go over it like a hawk and make sure all is correct and Google tests for the canisters.