TPI Vapor Lock? - Third Generation F-Body Message Boards

nomad350Z · 09-24-2009, 06:11 PM

I'm moving this post from the TPI forum to this one, hopefully somebody out there will be able to give some positive input.

I know its not vapor lock, but thats the way the car is behaving. Sputtering, lacking power, stalling, refusing to start, the whole works. The car will start and run fine when cold, but not when it warms up. I've noticed that the fuel pressure drops considerably when it warms up, but is right at 45psi when cold.

It is an 1988 Iroc-Z, originally a 305 TBI car. I swapped in a TPI system and a 350 using RBob's Dynamic EFI program and by modifying my existing wiring harness. No problems there, everything works as it should. I'll mention that I haven't gotten it tuned yet, I'm using the basic GM 5.7 TPI tune that came with the software.

The car keeps eating up fuel pumps too, this will be my 3rd. I've replaced the fuel pump, pre-pump filter sock, fuel filter, fuel pressure

regulator, IAC valve, TPS, and I'm just about out of ideas. I thought the fuel pump relays may have been different for the 305 TBI to the 350 TPI, but they're not.

One thing worth mentioning is that I do not have the hard metal fuel lines that run from the engine to the flexible lines in the chassis. Instead, I went to a local hydraulics shop and they fabricated some flexible, fuel rated high pressure line.

I've heard people having this issue before, and it was due to to the stock Multec (sp?) injectors. The TPI setup is utilizing the stock 305 injectors. Would this cause and issue? Why? I've heard of issues with the injector electrical resistance, but I don't know of the exact details....

I think this post is long enough, but if you need more info I'll gladly answer. Thanks again guys.

Edit: The engine has some upgrades, ported 113 heads, balanced and forged internals, and a bigger, slightly longer duration and larger lobed cam. Its a Crower cam designed for injected engines, 204/210 duration and .485 in .505 exhaust 113 lsa.

I noticed that there isn't any fuel coming out of the return line when its cold, but I haven't checked it when the car is warmed up. I'll make sure to check it as soon as possible.

How would too much fuel cause the engine to run? Could it be that the injectors are staying open too long, causing a drain in fuel pressure, poor performance and no fuel from the return line?

HELP! Thanks again!

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