Problem with new motor

I resently had a motor built, for a 1990 GMC 4x4, the old motor (5.7) died. had this one redone and built to a 383 Stroker, nothing hot, new heads with good rockers, larger valves ,9 to 1 flat tops,little larger than stock cam, steal rod caps and good rods, Edelbrock perform, intake , shortie headers Holley throttle body,just a good strong mildly built motor and a good rebulit strong 700R4 tranny. the problem is, I'm not gettin full power from the motor, (Note* had a custom chip burnt with the specs of the motor, tire size, rear end the works and the motor runs worst) I pulled the return line from the tank and pinched it off and the motor seems to run better. Has anyone had any luck dropping in a 383 Stroker in a truck or car with the EFI? and what was your success? Like I said it seems to be a fuel problem , but could I also have some computer problem, apperciate ya'lls help on this. My wife is now callin the truck a "Problem Child"
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I take it that this is a fuel injected engine. When you closed off the return line you temp boosted fuel psi since this motor is slightly modified and you did a computer remapping, try higher fuel pressure. You may have to install regulator. What does your O2 sensor read, lean or rich?

I agree with Dozzer, you may have to add an aftermarket fuel pressure regulator. You need a computer you can hook up to the engine while its running and see what's going on with O2 sensor and fuel pressure and timing. You may need to find a hot rod shop that tunes computer controlled engines and let them tune it. Have you gotton with Holley Tech? You may need to go over your specs with them and see if they can locate the problem.

I have built a couple 383 TBI engines with stock TBI and did nothing but put a performance chip, and boost fuel pressure. I have never even had to get a custom chip. Most have been about the same engine, so I say get with Holley on their TBI.

This link might be of some help.

http://www.xtremefi.com/

I agree you should hook up and do a full scan of your fuel settings.The basic chip shouldn't have cared that you changed engines, you just needed to add more fuel to compensate for the added inches. Have you made major changes down stream in the exhaust also? Pull your o2 sensor and see if it looks fouled or burnt,might help you figure out which wat to go.

Thanks ya'll, I figured it had to be a fuel problem, now is this why too my custom chip isn't working either, when I have it in , the motor run awful, and when the old stock chip is install, it runs.

Denny, apperciate ya's reply, will give it a try. All of ya I apperciate. Thanks again. Don

OK gentleman, Just an up date on my 1990 GMC Z-71 with the mild built 383 stroker, ya'll nailed it right on the head, Thanks again ya'll. Don
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