sooperdood3

1996 LT1 here. just installed walbro 255 fuel pump to replace my dying stock pump. stock pump held pressure fine, but wouldnt go over 14 psi. now after the install, the fuel pressure leaks down wont hold pressure while the car is off. pressure does stay up and steady at idle and under throttle.

ive been trying to run some tests to see the source of the pressure loss. here is what i have tried so far:

-looked and smelled under the car for fuel leaks. none to be found
-pulled the vac hose to the FPR and smelled for fuel. no fuel smell.
-pulled the vac hose and ran the car for a few min to check for fuel spitting out of the FPR. no spitting
-clamped the fuel return line and primed the pump. fuel pressure spikes to ~80 then drops to 0 within 45 seconds
-primed pump, then clamped off fuel supply line. fuel pressure drops to 0 within 45 sec.
-removed fuel rail w/injectors, then primed the pump. no leaking from injectors.

whats left to check? im at a loss here. any insight would be appreciated!

Kevin Blown 95 TA

What did you just work on?

There's lots of posts like this and usually it ends up being the clamps on the hose or one guy even had a leaky replacement hose itself that was causing the problem. It is possible the new pump has a leaky check valve or there is dirt in it, but the first cause I listed is what you should look at first, especially since you already eliminated everything else as a cause and that was the last thing you messed with.

Let us know what you find.

sooperdood3

i know, i did a search and ran all the tests the other people did, i made this topic because none of the tests are pointing me in the right direction. the pump was the last thing i worked on. i have double checked the hose and the clamps in there, tightened the clamps as much as i could. also checked the hose for cracks or leaks.

i'm aware it could be a leaky check valve, but i have to be sure before i send it in for warranty. walbro charges $40 plus it takes 4-6 weeks for them to test it.

how do i tell if there is dirt in the system?

but if the problem was on the pump side, wouldn't it hold pressure if i clamp off the supply line after i prime though? i am measuring on the schrader valve on the rail by the way...

Kevin Blown 95 TA

Yes it should, but I'm not so sure you can smash that fuel line enough to completely seal it off though, especially since it is 16 years old - I'd be careful about that or you might end up with another problem. Your troubleshooting sounds good, but I'm not exactly sure how you are measuring supply at the schraeder valve if you clamped the supply line off. I just think you have to be missing something there.

What kind of hose and clamps did you get with your new pump? One guy had a new teflon hose with a pin hole in it. And there are better clamps out there than worm clamps, in case you used those.

sooperdood3

the way i tested it was i had someone prime it from the inside of the car, after the pressure started to drop, i'd clamp it off with vise grips with washers between the jaws. but you're right, it might not have made a perfect seal to hold the pressure.

the hose i got was the flexihose from this site:
Auto Performance Engineering - Walbro fuel pumps and more

it did come with worm gear clamps, and i tightened the crap out of them. what type of clamps do you suggest?

Kevin Blown 95 TA

The worm gear hose clamps are OK, but there are better ones out there - I forget what they're called but you can see them in the photo below. When I did my first fuel pump replacement, I used a hose clamps like everyone else, and it worked just fine. The place where you got the parts is a good shop to buy pumps and parts. I guess I'm not sure what to tell you - there are only a few things that can cause the leak down and we've covered them all. A very tiny leak will lose the pressure in a static fluid system - it's not like a gas where it is really slow. If there is any leak at all, it will just drop off.

ak95ta

Stock fuel pressure regulator? Aftermarket fuel pressure regulators such as aeromotive won't hold fuel pressure while the pump is off. Just something I thought I'd throw out there.

sooperdood3

yes it's a stock FPR. i've decided to just live with it. im afraid if i try to make a warranty claim with walbro they are just gonna tell me there was dirt in the system.

lt11997

I would replace that flex hose with rubber fuel line hose and fuel clamps like in Kevin's post and see what happens.

Lt1son

Ive heard of and have seen first hand walbro pumps bad right out the box. def sounds like bump is bad as stated above---

zmike

I had a brand new pump with teflon hose fail due to a small hole in the Teflon hose. It took a while to find it but when it shipped with the hose installed and bent over it caused it to break near the clamp.

sooperdood3

thanks for the input guys. i'm gonna try the rubber hose thing first. im just nervous about trying a warranty exchange because they charge $40 to test the pump and they state 4-6 weeks for testing.
how do i get the teflon hose without this happening:
Auto Performance Engineering - Walbro fuel pumps install tips

do i need to cut it off?

it will most likely be a couple weeks before i get around to this... my rear just grenaded

sooperdood3

rear fixed.

not trying to be "all over the place," but i noticed there is fuel on the outside of my FPR. any chance that this could be leak in question? the regulator is regulating pressure just fine, and there is no fuel smell in the vac hose, and it doesnt spit fuel if you unplug the hose for a while; its just on the outside of the FPR. is this a non-issue or does my FPR need replacement because of this?

Injuneer

How is the fuel getting on the outside of the FPR? Must be leaking from one of the connections. Only takes a few drops of leakage for the fuel pressure to disappear.