TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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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 on the chassis. Instead, I went to a local shop and had them make me some fuel-rated 300 psi flexible lines to complete the link.
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 think this post is long enough, but if you need more info I'll gladly answer. Thanks again guys.
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The 305 injectors are only 19lb I believe the 350s are 24lb.
45psi cold with engine off, or running?
Have you checked for proper voltage drop?
Is the fuel actually returning to the tank?
__________________ 88' IROCZ 388/6.4L TPI Motown 350/4-bolt main stoker, and then some.
I understand that they flow different amounts of fuel, but would there be an issue with different resistances between injectors?
It gets 45psi when its priming itself/running on cold start-up. It drops when it warms up....
I removed the return line to check for any fuel flow, and I did not see any....
And no, I haven't checked for a voltage drop at the tank. What would be the easiest way of doing this? Putting a volt-meter on the fuel pump wires underneath the car?
I'm wondering if the injectors are staying open too long, causing too much fuel in the cylinders and also draining the fuel pressure.....that would explain the lack of pressure and no fuel flow, but would it explain the vapor lock issues? If it was getting too much gas, would it behave as I stated above?
what fuel pump you running, a/c delco dude theyre awesome. and test the ohms of the injectors. if no fuel is going back to the return line then maybe youre looking at the wrong line, like the vapor line. There always should be fuel in the return line, id check the fuel pressure regulator. or if worst comes to worst, possible mix up with fuel rail inlet and outlet fuel lines. ive people mix them up. to test the fuel pump. attach a gauge to the rail, and put 12volts power to the g terminal under the dash by your knees. that diagnostic link. that runs the fuel pump. good luck dropping tanks is a pain in the lower back side, ive change my pump three times in 6 months, over 2 years ago. damn autozone junk pump. i told some people im going to urinate on the assembly line in china. no offense to china
were the injectors you are using left out of a car for any length of time? if when removed from the donor car they weren't stored in a can of gas, they likely corroded and are not working correctly. i'm willing to bet you have a few not working right, and that combined with the injectors being too small for your displacement and programming would definitely cause your engine to stumble and run very lean.
__________________ The only difference between genius and stupidity is that genius has its limits - Albert Einstein
The TPI unit was removed from a donor car, and stored in a dry basement for a few months, completely assembled. The injectors were never removed from the intake manifold, so perhaps thats a start.
I'll check the resistance and let you guys know what I find. From the corvette links above, it looks like you guys have found my problem. Thanks again, I hope we've got it pin-pointed.
The fuel pumps I've used are Walbro 255's, one was a BBK pump, one is a Holley. Both are the same exact pump, same part numbers.
So I checked the resistance today. When cold, 7 of the injectors were between 16.2 and 16.8. One was at 13.2.
When Hot, 7 of the injectors were between 17.1 and 17.8. One was at 7.9. Sounds like I've got one bad injector, but would just one injector cause this kind of problem?
ive people mix them up. to test the fuel pump. attach a gauge to the rail, and put 12volts power to the g terminal under the dash by your knees. that diagnostic link. that runs the fuel pump. good luck dropping tanks is a pain in the lower back side, ive change my pump three times in 6 months, over 2 years ago. damn autozone junk pump. i told some people im going to urinate on the assembly line in china. no offense to china 
