Fuel Pump Question

[4-cam]

Do the fuel pumps have a check valve in them? While trouble shooting a code 55 after changing injectors, I was monitoring the fuel pressure and as soon as I shut it down the fuel pressure drops to "0". I think I have a fuel pump getting flaky as under WOT, about 6000 rpm the car hesitated, the fuel pressure dropped to about 40psi. Then the fuel pressure jumped up to 50, like the 2ndary fuel pump started. Instant power increase, but I think it was running lean already and the code 55 came up. It definitely feels like its starving for fuel and struggles to get up past 6000 rpm. The car was sitting for 3 months before I went for the injector change so the fuel pump may be failing from sitting idle.

Anyone got any Ideas or am i on the right track?

Thanks in advance

[VetteMed]

pressure drop should be slow, perhaps over 20-30 minutes. there is indeed a valve that prevents instant drop in fuel pressure after the key is turned off. Sounds like you are on the right track.

[4-cam]

I checked the running amps on the pump and they are at 9.5 so it seems they are good. I thought I remember a post were someone said the stock clamps in the tank come loose? I think I will pull them and see if that's the issue. If they are loose that could explain erratic pressure and my leak down issue.

[tomtom72]

Yes the stock clamps are the plastic sliding teeth type. The plastic I think becomes softened by the gas over time is my guess, or the hose becomes harder and the clamp has a hard time sealing the connection. I don't which is the more likely culprit.

I just did what everyone else does, use small s/s ideal clamps and new hose.


Tom

[QB93Z]

My first thought for the fuel pressure drop on enging shut off is a leaking injector. The service manual describes how to test for fuel leakdown.

Jim

[Paul Workman]

Originally Posted by 4-cam

Do the fuel pumps have a check valve in them? While trouble shooting a code 55 after changing injectors, I was monitoring the fuel pressure and as soon as I shut it down the fuel pressure drops to "0". I think I have a fuel pump getting flaky as under WOT, about 6000 rpm the car hesitated, the fuel pressure dropped to about 40psi. Then the fuel pressure jumped up to 50, like the 2ndary fuel pump started. Instant power increase, but I think it was running lean already and the code 55 came up. It definitely feels like its starving for fuel and struggles to get up past 6000 rpm. The car was sitting for 3 months before I went for the injector change so the fuel pump may be failing from sitting idle.

Anyone got any Ideas or am i on the right track?

Thanks in advance

They do have check valves, and I discovered that when I had pretty much identical symptoms as you describe, after I installed new pumps - one had a bad check valve out of the box!

With respect to Jim V's comment on the injectors, I would agree. However, in my case I logically dismissed leaking injectors being that 1) there was no hard starting or short term rough idle and 2)the plugs were all dry and 3) I had the luxury of knowing the characteristic behavior of the fuel pressure leak down test, prior to determining one of the pumps was in fact not working, and it held pressure before installing the new (and faulty) pump.

And, BTW, I was able to confirm the pump check valve was bad by blowing (mouth) into the pump outlet while holding it in my hand.

HTH,

P.

PS:

Forgot to mention it, but I changed my fuel filter at the time I changed the pumps. The car had about 42k miles on it, but you should have seen the bottom of the catch pan when I drainded the fule out of the old filter. Boy-howdy!! Was it filthy!!

[4-cam]

Thanks for the reply Paul, I am just going to pull the assembly and check it out. I'm ruling out the injectors as The are brand new and i am lacking fuel pressure upon acceleration. Fuel pressure drops off instead of increasing as the vacuum drops. Pumps amp out OK so i believe I have a leaky hose inside the tank. This would cause the low fuel pressure and leak down of fuel pressure upon shutdown. Ill check her out and most likely replace pumps and strainers. Mileage on the car is about 44k, close to yours.

[4-cam]

So I replaced the fuel pumps.
Under WOT the fuel pressure jumps to about 52 so I was correct in thinking that the fuel pumps were going bad. Still was getting a lean code 55. The spark plugs verified this. I figured maybe a vacuum leak so I pulled he plenum off again and did some further investigation. Couldn't find anything until I looked down the injector housing. Upon closer inspection I see the tip of the injector protruding past the end of the injector housing boss about 1/8 inch on the secondary side. I was able to see part of the O'ring with a small inspection mirror. I noticed there are two slots on the injectors for the fuel injector clip. If the top one is used, the injector is too far down in the housing causing my issue. I moved the injectors up into the fuel rail and now the face of the injector is flush with the end of the injector housing boss. I reassembled the car, and took it for a drive. Idles much better, no vacuum leaks, pulls harder than before all the way to 7000 + rpm and then the code 55 pops back up. Could this be a tuning issue? I don't have a scan tool. Any ideas? BTW these are new injectors

[scottfab]

Originally Posted by 4-cam

So I replaced the fuel pumps.
Under WOT the fuel pressure jumps to about 52 so I was correct in thinking that the fuel pumps were going bad. Still was getting a lean code 55. The spark plugs verified this. I figured maybe a vacuum leak so I pulled he plenum off again and did some further investigation. Couldn't find anything until I looked down the injector housing. Upon closer inspection I see the tip of the injector protruding past the end of the injector housing boss about 1/8 inch on the secondary side. I was able to see part of the O'ring with a small inspection mirror. I noticed there are two slots on the injectors for the fuel injector clip. If the top one is used, the injector is too far down in the housing causing my issue. I moved the injectors up into the fuel rail and now the face of the injector is flush with the end of the injector housing boss. I reassembled the car, and took it for a drive. Idles much better, no vacuum leaks, pulls harder than before all the way to 7000 + rpm and then the code 55 pops back up. Could this be a tuning issue? I don't have a scan tool. Any ideas? BTW these are new injectors

Frustrating I know. Persistence WILL pay off. Keep going.
My first thought would be to put the stock prom back in but....
not sure how all the mods (nixed secondaries and porting) would behave.
I may have missed something.
Did you replace both fuel pumps or just the one?
The reason I ask is that I had a lean code set but only intermittently until finally the pump failed all together. Once I replace BOTH pumps the lean code went away. No amount of pressure testing uncovered this highly intermittent failure.

[GOLDCYLON]

Originally Posted by Paul Workman

I forgot to mention it, but I changed my fuel filter at the time I changed the pumps. The car had about 42k miles on it, but you should have seen the bottom of the catch pan when I drainded the fule out of the old filter. Boy-howdy!! Was it filthy!!

Before you go ANY further did you change the fuel filter?