99 astro new fuel pump in old module loses pressure after prime

[stoopud]

Any suggestions would be appreciated:

I have a 99 astro that had a definite fuel pump problem (first lous then silent). To save money I bought a replacement pump on e-bay ($60 vs $250)to put in the existing module. Although I have saved alot of money it has caused alot of added work.

1st the internal fuel line popped off (top) had to drop tank and reattach.
2nd the the insternal fuel line popped off (bottom) dropped tank and reattached (clamped both ends). My fault for not claping them right away, but the stock wasn't so I thought it would be OK.

Now the van ran for about a 1/2 hour, then when I went to take it for a test drive it stalled as soon as it started to move and will not restart. I checked the fuel pressure (thinking maybe there was another problem with the hose). I have 60#'s until the pump stops and then it drops to 0 almost instantly. I pinched the return line and the pressure did not change. I found that if I crank the engine during the prime cycle the pressure drops to about 45 psi. If I pinch the line during the prime it still drops.

Anyone have a guess what the problem could be or a good dianosis procedure to avoid removing the plenum (look dificult with dash above). I think it could be a check valve in the pump (maybe I messed it up during pump install 3x), or the regulator or the injectors. Why would it drop to 45 psi while cranking?

Any help would be greatly appreciated. I need to get this thing running and I do not want to waste time chasing the wrong thing (I am working outside int he drive in Cleveland in January - Really F'n Cold)

Thanks

[Blue Bowtie]

Since you've blocked the regulator return line and the symptoms didn't change, that proves the regulator is not leaking through. That doesn't prove that the regulator or line set is not leaking externally, however. If you are pooling fuel in the intake, there may be a leak at the FPR or the line set in the plenum. If it is not flooding (pooling fuel) that doesn't leave much but the filter and pump assembly. If the pump has full voltage, it should be able to generate at least 61 PSIG. The electrical connectors at the tank are always suspect.

If the pressure drops immediately and it is not due to the FPR or line set, that sounds like the pump check valve or short accordian line between the pump and tank outlet may be leaking. If you're replaced the filter, and verified pump operating voltage, there isn't much left.

Yes, removing the upper intake is a bit more difficult in the N-Vans.

[stoopud]

Thanks Blue Bowtie:

I am leaning towards the problem being the pump check valve, just because that is what I have tampered with that could have caused the problem. Plus I think the other items would have likely had a breaking period, and the van ran very well when I first got it running (1-1.5 hours in the drive).

Is the check valve in the pump itself or in the module? I am going to see if I can crimp the supply line during priming and slow the pressure loss. If so it would seem to be the valve. If it is unaffected, that would seem to indicate a leak elsewhere.

Thanks again, any further advice is still appreciated. I will post the results.

[stoopud]

Update:

After more testing, I still cannot determine if it is in the fuel pump or the plenum. I cunducted a crimp test again:

1. When I crimp the return line only the simptoms do not change. Meaning the regulator is not dumping fuel internally.
2. When I crimp the feed line during priming the condition does not change (with or without the return crimped), which would imply the condition is forward of the crimp. However, when the key is turned off and the pump cycles again, I cannot prevent the pressure from going above 30#'s, meaning I have not adequatelly sealed the line.

I find it hard to believe that the problem is in the plenum, because the van ran so good before it died. I would have to believe that other than a catastrophic break, any leak would develop and poor running would be observed. If it were the injectors I would expect a miss, unless all failed at once, which I find unlikely. Thus, I have decided to buy a new module and start at that end. If the pump is not the problem I will be selling a bebuilt module with a new pump installed for a real good price (if anyone is interested) lol.

If anyone sees fault in my logic, please let me know. I cannot buy a pump till tomorrow because the partstore is already closed, so I have time to change my mind. At this point any advise would be appreciated, even psychological.

Thanks,

Chris

[Blue Bowtie]

The pump discharge check valve is installed in the pump itself. The rest of the supply system should remain under constant pressure if the check valve is intact.

The fact that line pressure is dropping while cranking may indicate a voltage problem at the pump. The drop in pressure after pump shutdown is pointing to the pump discharge check valve itself or the accordian line/connections. Since it sounds as if you have already resigned yourself to removing the tank (yet again) inspect the electrical connectors at the top of the tank very closely. The tend to overheat and become resistive.

Always replace the fuel filter after the tank had been disturbed.

I also doubt that the injectors are the culprit, since you would likely detect the raw fuel accumulating in the intake.

[stoopud]

Hi all,

It's running now. It was the connection at the accordian line again. The top of the line was leaking eventhough I clamped it. Guess this is proof of two things. First, the obvious choice no matter how bad you want to deny it is ussually the culprit (really didn't want to give up on that pump and drop the tank a fourth time). Second, trying to save money ussually costs more; the pump bought on e-bay was a genuine GM pump but their is a reason they sell the whole unit.

Thanks for all of the help.

Chris

P.S. If anyone is desperate and needs to save a $150-$200, email me I have a pump i will sell at a real good price (just make sure you do not disconnect or damage the top of your accordian line).