fuel pump woes - Team Camaro Tech
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post #1 of 9 (permalink) Old Oct 24th, 02, 06:19 PM Thread Starter
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I believe my fuel pump is dumping gas into the motor. Every few months my oil gets thin and gassy-smelling, I start burning oil, fouling plugs, backfiring, etc.
Given my motor combo (mild 427 - approx. 400 horsepower), what fuel pump would you all recommend? I'm leaning towards an electric pump to avoid this problem in the future, as well as hopefully make the car a little easier to start, but I haven't made up my mind yet.
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post #2 of 9 (permalink) Old Oct 24th, 02, 09:18 PM
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Make sure it's not a bad needle and seat or incorrect float setting in the carb before you condemn the fuel pump. Overly rich jetting can also cause this over time. You didn't mention what kind of fuel pump you're using. Some mechanical race pumps put out as much as 14psi which require a fuel pressure regulator. See if you can borrow a fuel pressure gauge and check it out. Holley's street pump 12-454-11 should be all you need. I put one of these on a big block street Chevelle with an 800 cfm carb and so far so good.

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[This message has been edited by 1 2RUN (edited 10-24-2002).]
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post #3 of 9 (permalink) Old Oct 26th, 02, 07:08 AM Thread Starter
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It's an Edelbrock fuel pump, nothing special.
It does have a regulator on it, and I believe it had around 7 psi or so? I'll have to doublecheck that, though, I'm having trouble remembering.
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post #4 of 9 (permalink) Old Oct 26th, 02, 09:45 PM
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Usually a bad diaphragm will cause a fuel leak out of the fuel pump vent. does your pump have an open vent hole above the diaphragm?

If vent is OK, I'm thinkin' carb too.
David

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post #5 of 9 (permalink) Old Nov 11th, 02, 05:14 PM Thread Starter
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I don't believe it's vented, but I'll look this weekend.
It originally put out around 15 psi and is regulated. Currently 7 psi.
I've got a 6000 RPM 427 with a .540" lift hydraulic cam (228/238 dur at .050) and a Holley 750 (may upgrade to the 830 soon).
How many gallons per hour would you all recommend for this application? Is there a formula to figure what you need?
Also, I'm thinking if I do wind up needing a new fuel pump, I might replace mine with an electric fuel pump. Any suggestions?
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post #6 of 9 (permalink) Old Nov 12th, 02, 09:51 AM
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The Edelbrock mechanical street fuel pump claims 110 gph at 6-7 psi and the Carter street pump claims 120 gph at 6 psi. Either one of these will work fine with the 750-800 cfm carb your engine needs unless you plan to run nitrous. They also eliminate the need for a regulator. The electric pump will require some creative wiring if you want to be safe and who doesn't. An oil pressure switch that turns the fuel pump off in case of a crash is a must if burning to death is a concern. A relay must be used to bypass this feature when you're cranking the engine.

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post #7 of 9 (permalink) Old Nov 18th, 02, 08:06 AM
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I've been running an electric fuel pump with out a safety switch or a relay. I've got my car pretty much stripped down putting in new floors, dashtop and vintage air kit.

I want to wire my fuel pump correctly when I put things back together. I don't think that a relay will be too hard to find, but where can I get an oil pressure switch ? Does it break continuity of the hot wire to the relay ? Another issue is where to put it; I already have a "T" with a mechanical gauge and "OIL" light hooked to it.

Would it matter if the pump didn't run while cranking before the engine starts on an engine with a carburetor ? I'd think that there would be enough gas there to start it. Thanks for any suggestions.
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post #8 of 9 (permalink) Old Nov 18th, 02, 11:19 AM
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The relays are available at most auto parts stores. They are usually used for adding fog or driving lights. Painless sells a kit (50102) that includes the relay, circuit breaker and harness. The oil pressure switch looks like the one for the idiot light except it has three terminals instead of one. I believe this is the one you need if you still want to use the idiot light. If you find a parts store that has an Echlin or Standard master catalog it will have the thread sizes and a breakdown of the contacts in the switches. Mr. Gasket sells one (7872) with three terminals but I'm not sure how the contacts work. Holley also sells one (12-810) that's just a two terminal switch that cuts the power to the pump when the oil pressure drops. If you drive the car on a regular basis you might not need the bypass feature. However if it sits long enough for the fuel bowl to dry out you will have prime the carb or crank it until hopefully the oil pressure comes up enough to start the pump. I'm pretty sure there's a three terminal switch that grounds one terminal for the idiot light when the pressure drops and the other two terminals are independent contacts that close when pressure is present. If you use these contacts to energize the positive side of the relay coil you can run a wire from the start terminal on the starter with an inline diode that will energize the relay when you crank the engine without the starter staying engaged when the pressure comes up. It sounds more complicated than it actually is. If you want I can draw a schematic and send it to you.

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post #9 of 9 (permalink) Old Nov 19th, 02, 07:19 AM
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1 2RUN, thanks for all of the information. I'm going to get one of the Holley 12-810 switches. I found a picture of one on the net; it has 3 connectors. If it won't work with my "OIL" light sender, I guess there won't be any harm in putting a "T" on the "T" that I have now ?

The idea of having a pressure switch never crossed my mind until I read this post. Now, I don't want to drive it again until I put one on. Thanks again, Ron.
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