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.

:cheers:
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]

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]

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]

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?

[4-cam]

Both pumps were replaced, Fuel filter is new, and I have a consistent 52 psi on the fuel rail all the way to 7000 + rpm. As she passes the 7k mark it throws the code. It didn't do this last year with he old injectors and coils, but had the dreaded flywheel knock and a didn't run very strong on the bottom end. Past 4k rpm it took off and ran great. Figured the injectors were toast as they were the originals. The only difference between now and last year is new MSD coils and new Accel injectors. The original prom was reprogrammed so I don't have another one to try.
Corey programmed my prom for the secondary removal so I will contact him to see if he added some fuel to go along with the top end porting.

[tomtom72]

Here is a fwiw on the coils.....and this is based upon all the reading I did after I bought my Jegs Hi-performance coils. Waaay back screamin' deamon coils were the rage, circa 04 & back. Everyone who used them had issues with coil break down fairly quickly & some not so quickly.:o

My take is based on the info at GM. They list two different P/N coils for a waste spark system: ours and all their other cars that used a waste spark system. The specs are the same, so what is the difference? Where the coils live is my conclusion. Ours live in a hostile place for anything electrical. If you cross reference any of the other GM motors that use a waste spark system the aftermarket coil P/N is the same as what they sell for our car.

I bought a real GM LT5 set and took out my Jegs coils after about a year of wondering if I was going to suffer a coil failure due to heat. Okay, all this is JMHO supported by no testing or knowledge what so ever....just looking around at what happened to all the aftermarket coils.:o

:o Yea, if a little juice is okay, then a lot of juice is better? I fell into the trap, and then I did the reading! LOL :o

[4-cam]

Thanks for the info as another opinion is always helpful, but I don't think its the coils. I haven't run the car more than 1/2 tank of gas thru it since the injector / coil install. Definitly a fueling issue. No miss and runs smooth, just lean on all cylinders.

[Starman]

Here are a couple of dumb suggestions:

1) verify that you have the right flow rate injectors for the car. I know one of them is physically unique to the car, but the other one is physically pretty unversal to all cars with port injection. I would note that the ACCEL/DFI online catelog does not list injectors for our cars - I went with the RC myself.

2) It seems like my fading memories recall that these cars had a fuel shutoff feature around 7400 - 7600 rpm. It might be that your tach is lagging a little and you are bumping the fuel shutoff.

3) This is really rusty, but if you have the ability (laptop) take a look at the block learn value and the O2 sensor values. With a lot of mods, you might be slightly lean all the time and need your prom tweaked again.

Best of luck

[4-cam]

No suggestions are dumb and thanks for the reply. The accels's that I used are the same ones that many others have used and Mark H recommends so i am comfortable with the injectors. I just got my cable for some data logging on my laptop, so I will be playing with that this weekend and hopefully post up once I get some data to look at.

Regards

[scottfab]

2) It seems like my fading memories recall that these cars had a fuel shutoff feature around 7400 - 7600 rpm. It might be that your tach is lagging a little and you are bumping the fuel shutoff.



Something familiar about this. I've not often hit the rev limiter (I think stock limit is 7200) but when it hits maybe the side effect is a lean code set?
I just can't remember. Anyone?
I guess I'll just may have to find out again. Good an excuse as any.
"but officer I was testing the rev limit for a friend......"

[tomtom72]

fwiw the stock is around 7200 I think, and as I have hit it in 2nd mostly I have never had a lean code set. And two times at least I have hit the limit in a "hard" fashion....not even realizing I was there, as it just seems to want to go on forever in 2nd, I have run over that limit and thought I had just broken my motor. It's as if the motor shuts off.:o

[scottfab]

fwiw the stock is around 7200 I think, and as I have hit it in 2nd mostly I have never had a lean code set. And two times at least I have hit the limit in a "hard" fashion....not even realizing I was there, as it just seems to want to go on forever in 2nd, I have run over that limit and thought I had just broken my motor. It's as if the motor shuts off.:o

Well there goes my excuse to test it. I guess I'll just have to answer "yes" when I'm asked if I was on my way to a fire ;)

I wonder if maybe one of his new injectors is failing at this high cycle rate?
It's painful but swapping injectors left to right and looking for the lean code to shift would isolate.

[4-cam]

I pulled all the plugs and they looked all the same so I don't feel its one or two injectors. I think I would see the difference in spark plug colors.

Interesting thought, could i be hitting the rev limiter. When it shuts off the fuel do you get a lean code?

Corey did bump up the rev limiter when he programed my prom and last year with the old injectors i did not have this problem. Could be my old injectors were failing and adding more fuel?