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Fuel Pump Check Valve

TTA579

TTA579

South Bay TTA "Barn" Find
579 currently isn't holding fuel line pressure. I've replaced every component of the fuel system; pump, filter, injectors, pressure regulator. Running through the service manual troubleshooting process suggests that the fuel pump check valve, part of the sending unit, is bad. Has anyone else had this problem? I haven't read about it anywhere on the TTA or Buick forums.
 
I did and I replaced the fuel pump and all was well after that. It was a while back now but I'm pretty sure that's what I did. I ve never gotten a new sending unit and the fuel pressure is holding above 40 now. I think without the check valve you will have to crank the motor over longer for it to start and that is about the only ill effect I know of resulting for a faulty check valve.
 
jarredsoon said:
I did and I replaced the fuel pump and all was well after that. It was a while back now but I'm pretty sure that's what I did. I ve never gotten a new sending unit and the fuel pressure is holding above 40 now. I think without the check valve you will have to crank the motor over longer for it to start and that is about the only ill effect I know of resulting for a faulty check valve.
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It takes longer to start but also the pressure isn't changing with vacuum/boost.
 
TTA579 said:
Bad FPR is unlikely, it's new. Vacuum leak wouldn't explain the immediate leak down.
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IF boost doesn't rise one to one there are three reasons.

1)too much power for the pump to keep up
2) bad FPR
3) vacuum leak so the FPR doesn't know it should add.

How old is the new one?
 
Quiky One said:
IF boost doesn't rise one to one there are three reasons.

1)too much power for the pump to keep up
2) bad FPR
3) vacuum leak so the FPR doesn't know it should add.

How old is the new one?
Click to expand...

I have tested the vehicle per the service manual (clamped pressure line held pressure) and it's given me either a leaky pump coupling hose or faulty in-tank pump.

Either failure might prohibit the pressure from rising above a point, vacuum or not. It is impossible to test the FPR for an additional issue without resolving this first one.

The fuel pump is two years old, FPR is a couple of months old, injectors are brand new. Oldest fuel system parts only have a 100 miles on them or so.
 
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TTA579 said:
I have tested the vehicle per the service manual (clamped pressure line held pressure) and it's given me either a leaky pump coupling hose or faulty in-tank pump.

Either failure might prohibit the pressure from rising above a point, vacuum or not. It is impossible to test the FPR for an additional issue without resolving this first one.

The fuel pump is two years old, FPR is a couple of months old, injectors are brand new. Oldest fuel system parts only have a 100 miles on them or so.
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Check the hoses leading the fuel pressure regulator.

Question still stands, how OLD is the fuel pressure regulator. If it is a new 1989 one, it is old. The rubber diaphram is in just as bad of shape as any. Miles really don't matter in this instance.

Your check valve is obviously bad in the pump, but your fuel pressure never changing isn't that.
 
Quiky One said:
Check the hoses leading the fuel pressure regulator.

Question still stands, how OLD is the fuel pressure regulator. If it is a new 1989 one, it is old. The rubber diaphram is in just as bad of shape as any. Miles really don't matter in this instance.

Your check valve is obviously bad in the pump, but your fuel pressure never changing isn't that.
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There are no fuel leaks outside the fuel tank. I'll be checking parts inside the tank next. There are no vacuum leaks either, I've tested.

The FPR is new, it's exact build date is unknown to me but I did not purchase a NOS pressure regulator. Replacing old parts with old parts is a waste of my time.

Removing the vacuum line on the FPR causes the pressure to jump momentarily. A significant failure could prevent the pump from building pressure before the FPR.
 
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Is that a Walbro pump you have? They had issues and replaced loads of pumps under warranty due to leakdown ...
 
TTA579 said:
I believe it's a Walbro, i got it from Racetronix.
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I would call them and ask them about it, can't remember exactly when they did have problems with them (I think the guy and fullthrottlespeed.com work with Walbro to get it all sorted for existing customers) ... there's a thread @ tb.com about it all.

Your system should hold pressure for some time when you shut it all off.
 
Jan Larsson said:
I would call them and ask them about it, can't remember exactly when they did have problems with them (I think the guy and fullthrottlespeed.com work with Walbro to get it all sorted for existing customers) ... there's a thread @ tb.com about it all.

Your system should hold pressure for some time when you shut it all off.
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that varies, 45 min to 8 hrs with mine
 
Jan Larsson said:
I would call them and ask them about it, can't remember exactly when they did have problems with them (I think the guy and fullthrottlespeed.com work with Walbro to get it all sorted for existing customers) ... there's a thread @ tb.com about it all.

Your system should hold pressure for some time when you shut it all off.
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It appears the 340M pump that Racetronix sells was not part of the Turbo Buick problem that involved Full Throttle. That doesn't mean it didn't fail, or that the 340Ms couldn't be suspect either. It's a gear pump though, and I'd expect to see little backflow. I expect (hoping for) a loose or damaged coupling hose.

robert lee said:
that varies, 45 min to 8 hrs with mine
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I tested the system per Service Supplement chart A-7. After priming the system with the fuel pump I clamped off the fuel pressure line from the pump and shut off the pump. The pressure held as it should. Chart A-7 suggests the problem is a coupling hose or check valve failure.
 
I had the Walbro 340 with the hotwire kit put on my car last august and no problems yet. I believe the fuel pressure is set at around 43.
Got it from Racetronix also.

You could have got a bad one. I had 2 new 60lb/hr injectors that were bad, the car ran terrible and it was the 2 new injectors that was the problem.

They came from Mike at fullthrottlespeed.com and he replaced them.
 
TTA984 said:
I had the Walbro 340 with the hotwire kit put on my car last august and no problems yet. I believe the fuel pressure is set at around 43.
Got it from Racetronix also.

You could have got a bad one. I had 2 new 60lb/hr injectors that were bad, the car ran terrible and it was the 2 new injectors that was the problem.

They came from Mike at fullthrottlespeed.com and he replaced them.
Click to expand...

It is possible that the fuel pump has gone bad in 2 years. I won't be sure until I can check the coupling hose and replace the pump.
 
TTA579 said:
There are no fuel leaks outside the fuel tank. I'll be checking parts inside the tank next. There are no vacuum leaks either, I've tested.

The FPR is new, it's exact build date is unknown to me but I did not purchase a NOS pressure regulator. Replacing old parts with old parts is a waste of my time.

Removing the vacuum line on the FPR causes the pressure to jump momentarily. A significant failure could prevent the pump from building pressure before the FPR.
Click to expand...
Not fuel leaks, vacuum leaks...

And the check valve is built into the head of the pump.
 
My pump was less than 2 years old and went bad. It wouldn't build over 40psi. I thought it was the hose coupling also, but it ended up being the pump. When I replaced it I also ordered the new in tank wiring kit from Racetronix. Don't ever run the pump dry to test it! I emptied my tank using the fuel pump in the to put fresh fuel in it, and it ran dry for a few seconds. Never worked right again after that.
 
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