Replacement Fuel Pump

[SeanC]

Hey guys,

For the past couple of months my car has a hard time starting after it sits for a while. When you turn the key to the on position repetitively before you crank the motor, it starts up better. From what I have read, i'm guessing that my fuel pump is leaking pressure once you shut the car off.

I checked out replacement pumps online at Napa and they were almost $500!! I definitly can't afford that, but then I found a granatelli motor sports replacement electric fuel pump at summit for like $125. Does anyone have any experience with these? It says it flows a higher volume (255 lph), but my car is fairly stock...Is this no good? Any help is really appreciated guys. Thank you!

[Injuneer]

Why "guess" if the fuel system is losing pressure at shutdown. Put a fuel pressure gauge on it.

[Joe 1320]

Why "guess" if the fuel system is losing pressure at shutdown. Put a fuel pressure gauge on it.

And if you don't have a fuel pressure gauge, Autozone will provide a "free" rental. You have to leave a deposit, but you get it back when you return the tool.

[SeanC]

Is there a specific fuel pressure gauge that is needed for the Lt1?

[Injuneer]

Nothing special. Most cars use the "Schrader valve" (-4AN male fitting) to test the fuel pressure. The valve is attached to your fuel lines already. You get a "fuel pressure test gauge", and it will screw directly onto the valve. It has a small pin in the fitting that depresses the valve core in the Schrader valve, and allows the gauge to read the pressure.

Shoebox has a photo of the Schrader valve:

[Wild Willy]

It is easier to do the fuel pump on the f-body cars if you are willing to cut a small hatch under the carpet in the hatch area, above the fuel tank. You can then replace the pump without dropping the tank, which, on older cars, can be pretty difficult-

One link:
http://www.z28.com/forum/showthread.php?t=36676

There are lots more if you do a search-

Haven't had to do mine, yet, but will probably go this route. Toyota has had this feature since the late 70's, maybe by the 5th gen GM will figure it out-

[Joe 1320]

If you plan to cut a trap door, it's a whole lot faster with an air hammer and sheetmetal cutting blade. If you use a dremel, pack a lunch.... you'll be there a while. I drill four small holes in each corner of the panel that I want to cut out, take the air hammer and have at it. 2 minutes tops.

[Blazer]

Dremel has come out with a newer an bigger cutting wheel. Did mine in about 10 min. With 1 wheel.
Blazer

[SeanC]

Hey guys,

I was able to diagnose my loss of fuel pressure a little more while I was home over spring break. Right after the system builds up pressure, it drops immediately. I discovered that there was fuel in the fuel pressure regulator vaccum line (obviously leaking), so I changed it out in hopes of it being the source of the problem. Pressure seems to drop more slowly, but pretty much goes to zero within 5-10 seconds. So I'm guessing there's two other sources: the fuel pump like previously stated, or a leaky fuel injector. How do you test for a leaky injector?

I'm really hoping its not the pump. First, i'm honestly a little scared of creating sparks by the fuel tank, and second, it seems like a fairly difficult job. I just want to be sure the fuel pump is the source of the problem before I take it on. Thanks for the help, I really appreciate it!

[Timbers]

Pump

My fuel pump in my 97TA went at about 55,000. I have 65,000 on the car now.

I ended up purchasing a $125.00 pump and putting it in myself. It was about 7 years ago that I did this and I really didn't take any pictures.

It wasn't too difficult, it was just time consuming. The hardest part of the whole deal was getting the exhaust off so I could drop the tank. That was a pain. I have aftermarket exhaust and I used U clamps to hold it all together. I had to heat the metal up cherry red in order to open the clamped metal up.

As for the fuel pump, the stock fuel pump is located in this plastic housing looking thing. If you get it out of the tank you will see what I am talking about. I had to crack this plastic shell apart carefully with a screw driver blade. Then I took the new aftermarket pump, and put it inside the housing, hooked up the wires, and then used JB Weld to hold the housing together again. I put the whole unit back into the tank and everything ran great.

If I could do it again I probably would have cut the access hole above the tank. Would have saved hours and hours of work...


Not sure what to tell you about your system losing pressure. A bad regulator usually is what I have seen cause things like that.

...Tim

[Injuneer]

Dropping pressure can be due to the check valve in the fuel pump assembly failing. That's what holds the pressure in the system on the supply side. The FPR hold the pressure on the return side.

To check for leaking injectors, unbolt the fuel rails, pull them up with the injectors intact. Turn the key to pressure the system. Don't try to start the engine - very messy. Look for drips from the injectors. If the pressure doesn't build high enough on the first turn of the key, keep turning it until you have at least 40psi.

[SeanC]

Okay I will try that. Also, my fuel pressure was higher with the engine running with my old regulator. I believe it was like 42, and now its 34 psi with the engine running and the vacuum line connected. I can't seem to remember if this is in the acceptable range. Its suppose to be 3-10psi below system pressure while the key is in the "ON" position, correct?

And thank you guys very much for all the help so far!

[Injuneer]

The new FPR is showing a lower pressure because its working correctly. When you test the fuel pressure at idle, remove the vacuum compensation line (cover line with finger to prevent vacuum leak). "Correct" fuel pressure is 43.5psi, but GM accepts anything between 41-47psi. Still idling, connect the vacuum line, and the pressure should drop about 6-8psi below the "no vacuum" value, with a stockish cam. Tape the gauge to the windshield and take it out on the road. At full engine load (max RPM, WOT) the pressure should never go below 40psi.

If the old vacuum diaphragm was ruptured, allowing fuel into the vacuum line, it couldn't pull the fuel pressure down in response to inatke manifold vacuum.

[SeanC]

Thank you very much Injuneer! That makes a lot of sense. I'll have to test my injectors, and if their not the source for the loss of pressure, I guess i'm doing the fuel pump haha. Thank you guys for all the help. I'll keep you updated!