Fuel system loses pressure when off- is my fuel pump bad?

[BuickMike]

Last night I got a little further on my project and tested the fuel system. After the pump turns off the pressure drops slowly over the next few minutes. I verified that it was not a stuck injector or the regulator bleeding pressure back through the return. I also listened inside the tank to make sure that the fuel line from the pump to the pickup tube wasn't leaking.

Isn't the pump supposed to have a 1 way valve in in that holds pressure while the system is off or am I just crazy?

 

[1quick6]

Yes, they do have an internal check valve to hold fuel pressure for a time. If you've already verified the injectors aren't leaking pressure and the fp reg is fine, there isn't much left. How did you verify the regulator and injectors? Clamping the lines appropriately?

 

[BuickMike]

I verified by forst pulling all the spark plugs and checking for gas. Then I clamped the return line to the regulator and no difference. Then I had my wife connect the fuel pump wire by the alternator and I clamped the fuel supply line as soon as I had her disconnect thew wire. The pressure was dropping much slower until I unclamped the supply line.

I fired up the car to break in the motor and it held pressure fine while it was running. It just can't hold it while the car is off. Looks like I'll go buy a Supra pump to replace it.

 

[~JM~]

My car does this also. It had happened once before & the previous owner took the car to the dealership where they replaced the pump. It solved the problem for a few years but has returned. The system loses prime over night & takes about 4 long cranks to get her to start. I have tried to power up the pump with the jumper wire but it still won't build pressure enough to start. I have plans to replace the pump with a Walbro & install the Racetronics Hot-Wire kit. I hope this resolves the problem.

Good luck
~JM~

 

[turbofrank]

Last night I got a little further on my project and tested the fuel system. After the pump turns off the pressure drops slowly over the next few minutes.

Isn't the pump supposed to have a 1 way valve in in that holds pressure while the system is off or am I just crazy?

How far does it drop in the next few minutes?

 

[TurboBuRick]

Not unusual to see this. Also not a real big deal.

 

[BobbyBuick]

should hold steady for 5 minutes

 

[Slow91z]

The check valve in the pump is really just a convenience feature. Instead of being able to hit the key and go straight to start just turn the key to on, give the pump a second to prime and then start the car. Not worth buying a new pump and dropping the tank IMO, but to each his own.

 

[dynoman]

Why do they have a check valve anyways ? Is it just so you don't have to wait the 2 - 3 seconds for pressure to build ? I think it's better for the pump to start with no load on it . It's easier on the relay contacts , wiring , all conections , and the pump itself . Mine doesn't hold pressure & I have no problem with it, just my $.02 Sam

 

[HighMileage]

Why do they have a check valve anyways ? Is it just so you don't have to wait the 2 - 3 seconds for pressure to build ? I think it's better for the pump to start with no load on it . It's easier on the relay contacts , wiring , all conections , and the pump itself . Mine doesn't hold pressure & I have no problem with it, just my $.02 Sam

I agree that it's probably better for a pump to start with no load. Hmmm...I never thought of that.

My stock fuel system used to hold pressure for hours. But now I have a DW-301 pump and an Accufab FPR that's had it's return hole enlarged. Pressure drops to 0psi as soon as the pump stops.

My GN runs well. Just wait those 2-3 seconds when starting.

 

[TurboBuRick]

Put a pressure gauge on and watch what happens when you turn the key on. After 2-3 seconds, the fuel pump will have kicked off and the pressure will have dropped to 0.

I think you need to be a little quicker than that if you want to catch it at the right time.

Just my o2.

 

[~JM~]

With the key OFF, I jumpered my fuel pump to prime the system & it still fails to pressurize. I can hear the pump running but it never seems to catch up & build pressure. What would cause this condition?

Is it safe to jumper the pump with the key in the ON position?

Thank you
~JM~

 

[BuickMike]

It drops to about 10psi after about 30 seconds and was down to 0 a few minutes later. Maybe that's normal. I think that my old Red Armstrong pump would hold pressure for days. I'm not going to worry about it right now. The car runs fine.

 

[S10xGN]

I agree that it's probably better for a pump to start with no load. Hmmm...I never thought of that.

My stock fuel system used to hold pressure for hours. But now I have a DW-301 pump and an Accufab FPR that's had it's return hole enlarged. Pressure drops to 0psi as soon as the pump stops.

My GN runs well. Just wait those 2-3 seconds when starting.

Well, there ya go... Same here. Mine goes to 0 PSI within 3 secs and I did my best to maintain a viable valve seat when I enlarged my return port.

 

[gusszgs]

Worry about what the pump pressure is WITH it powered up/running then when your look'n at it in the garage......KISS

 

[HighMileage]

With the key OFF, I jumpered my fuel pump to prime the system & it still fails to pressurize. I can hear the pump running but it never seems to catch up & build pressure. What would cause this condition?

Is it safe to jumper the pump with the key in the ON position?

Thank you ~JM~

I'll take a stab at this one since there has been no reply since yesterday. ...

I'd clamp off the rubber return hose where it enters the tank. It can be accessed without dropping the tank.

Then I'd jumper the pump again. If the pressure still doesn't go up,I'd definately be looking for a ruptured in-tank hose between the pump and sender,a bad pump,low gas level or a rust hole in the in-tank pipe above the hose.

I've jumpered pumps with key on and off. No problems yet. Not sure if I should be.

 

[~JM~]

I'll take a stab at this one since there has been no reply since yesterday. ...

I'd clamp off the rubber return hose where it enters the tank. It can be accessed without dropping the tank.

Then I'd jumper the pump again. If the pressure still doesn't go up,I'd definately be looking for a ruptured in-tank hose between the pump and sender,a bad pump,low gas level or a rust hole in the in-tank pipe above the hose.

I've jumpered pumps with key on and off. No problems yet. Not sure if I should be.

Thank you for the reply. I will give this a try.

~JM~

 

[Fast4Ward]

putting the key to on should prime that baby to close to 40# in an instant. i've found that if its been sitting for more than a week it will only prime to about 30 or so.
now my pump recentley stopped climbing past 60# on wot. it now barely kisses 50#. I have noticed it loses pressure within 10 mins, before it would be holding close to 20-30 mins. i would just keep a close eye on the throttle response of the pump.
editing...ok so i went and turned the key to on and it primed to 41#, turned it back and primed it again. timed and it took 16 mins for it to go to zero. this is on Walbro pump.

 

[Fast4Ward]

FYI UPDATE ONLY......per my previous post i replaced the failing 169 pump with the Red Armstrong modified pump which i had a feeling was still good and the fuel pressure after over 1 hour was at 5 psi. yep its still good and jumps past 60 in an instant