i switched to carb form TBI and purchased a mallory 3 port regulator to bring the pressure down and hook up the return line. I set the pressure when you first turn the key on and you can hear the pump turn on for about 2 sec. When I run the motor the pressure begins to drop off until it goes to zero and the engine dies. Is the pump not staying on? I tried adjusting pressure up while the motor is running and it has no effect? Anyone give me some ideas..

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• 412ci/sb

My Homepage

Anyone?

Sounds like the pump is shutting off. Maybe its looking for something from the ecm. Run a direct key-on hot wire to the middle (I think) terminal on the connector that goes to the tank. See if the pump will run continous.

I am told the only thing the pump looks for is oil pressure. Which I obviously have since it primes itself. What else could it be looking for signal wise? Other people have switched to carb from TBI and have not had the pump shut off to my knowledge after the car is started...

When I made the swap, I had to connect an oil pressure "switch" to my fuel pump relay, since I no longer had much of the original wiring connected. Find your fuel pump relay and make sure it is turning on and staying on when your cars runs. My guess it that it only primes.

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1992 Pontiac Firebird 350/Six Speed
1987 Toyota Pickup 383/500+ HP

Hey Josh, you still at Cat? I just ran a new relay for my fuel pump when I went to carb. I haven't had any problems. Mine had a tan wire that was the power to the pump from the original harness. I redid my harness b/c I dropped the factory oil pressure circuit.



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Joshua Johnston
1991 Z-28
350, T-5, K&N, Ported Vortec heads, Edelbrock RPM, Holley 750 D.P., HEI, 11.07:1 CR, Comp Cams Roller-.510"/.520"-282*/288* dur., Shorty Headers, Dual 2.5 Exhaust, Dynomax Bullet Mufflers, T&R Motorsports custom air intake, Bald tires

Hey johnsjj2, Yes I still work at Cat I survived the intern layoff. How did you know I work there? So I have to change something to make my fuel pump run instead of just prime. I have the factory oil pressure sending unit in and working. Is it normal for the fuel pump to just prime when you switch to carb?

Josh,
I saw your car in Bldg.A lot, and asked Wes if you worked here and he said yes. I have met you before. I work with Dave Montgomery. Anyway, I ran my relay so when I turn the key on, voltage is sent to the pump. It runs whenever the key is on, but not on acc. Is this by chance for your 412? I want to see it when it gets done. If you check the wires going to your pump back by the gas tank, 1 is ground, 1 is power, and 1 is for the gauge I believe. Turn your key on, but not started, get under there with a volt meter, and start checking the wires. If you don't have access to a volt meter, let me know, I will get one for you.



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Joshua Johnston
1991 Z-28
350, T-5, K&N, Ported Vortec heads, Edelbrock RPM, Holley 750 D.P., HEI, 11.07:1 CR, Comp Cams Roller-.510"/.520"-282*/288* dur., Shorty Headers, Dual 2.5 Exhaust, Dynomax Bullet Mufflers, T&R Motorsports custom air intake, Bald tires

Well I just re-read your post. It is normal to prime and shut off, b/c the computer doesn't register either dist. signal, or oil pressure. If you could find out what which wire by the firewall goes to your fuel pump, I will bring in a schematic to wire in a relay.



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Joshua Johnston
1991 Z-28
350, T-5, K&N, Ported Vortec heads, Edelbrock RPM, Holley 750 D.P., HEI, 11.07:1 CR, Comp Cams Roller-.510"/.520"-282*/288* dur., Shorty Headers, Dual 2.5 Exhaust, Dynomax Bullet Mufflers, T&R Motorsports custom air intake, Bald tires

The car normally primed then "shut-off" when I had stock TBI on there. I have a volt meter so I will check some wires. Yes this is my 412 I finally installed. Few bugs to get worked out. need to re-do intake gaskets they are leaking around crossover ports. It is an Edelbrock RPM as well. And it seems I have the famous front oilpan seal leak as well. I hate leaks.

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• 412ci/sb

My Homepage

I think you'll need to rewire the fuel pump relay a little. On my TPI car it only required messing with one wire actually. I just wired a lead over to a certain wire (sorry, I forget the colors and junk) to operate the relay and power the pump whenever the key is on. Did that and just set my Mallory regulator at 5psi and it works fine, no pressure dropoff problems. Just about got to the pump cutting off in your case.

Good luck with the leaks, I went through that myself. I had an especially annoying leak that I finally discovered was the smog pump mounting bolt holes. Didn't leak just idling, and it was all over the bottom front of the engine so I couldn't tell where it was coming from. I didn't put anything in those holes originally, didn't realize they went all the way through the block and were exposed to oil. Finally figured it out. LOL, yes I'm stuipd...

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

[This message has been edited by Ray87Z (edited October 16, 2001).]