Fuel psi leakdown question
Fuel psi leakdown question What keeps the line pressure on a LT1 motor for the fuel lines? Is it a check valve in line somewhere? The fuel pump have one built in? In the rail somewhere? Basically, I have an issue where if the car sits for a while, it starts, stumbles & then dies. But when you crank it back up, it fires and stays running. Now I have tried priming the lines by letting the key sit in the "on" position for a few seconds before cranking just to see if that would help, but it does not seem to matter much. Just curious what it could be...I was thinking fuel pressure was leaking back into the tank out of the lines/rail. Just wanted to see if anyone else had any ideas or suggestions on what it may be.
Thanks for the replies. I don't get to check my computer as often as I would like, sorry for the late response here. The previous owner said he replaced the fuel pump, so I was curious if the check was in there as the new pump should have eliminated the issue then. Once it has been run, it's fine. It's only cold first thing in the morning or after sitting for hours. Also today it spit/sputtered and ran like pooh this afternoon until I moved it, shut it off, and started it up again. But my gas was below 1/8 and I may have a pick up issue as well. I was also curious if the catalytic converter coming apart internally would cause symptoms like this and may possibly be leading me down the fuel path when it is really a restricted exhaust...though it seems to run fine once it is running, so I don't know. I will get a pressure tester on there before I ask too much more here to make sure the psi is right before doing too much else...just asking opinions in the meantime. I appreciate the responses thus far though...thanks again.
Thanks for the replies. I don't get to check my computer as often as I would like, sorry for the late response here. The previous owner said he replaced the fuel pump, so I was curious if the check was in there as the new pump should have eliminated the issue then. Once it has been run, it's fine. It's only cold first thing in the morning or after sitting for hours. Also today it spit/sputtered and ran like pooh this afternoon until I moved it, shut it off, and started it up again. But my gas was below 1/8 and I may have a pick up issue as well. I was also curious if the catalytic converter coming apart internally would cause symptoms like this and may possibly be leading me down the fuel path when it is really a restricted exhaust...though it seems to run fine once it is running, so I don't know. I will get a pressure tester on there before I ask too much more here to make sure the psi is right before doing too much else...just asking opinions in the meantime. I appreciate the responses thus far though...thanks again.
Yea, I finally got a gauge on the rail today. The pressure builds to about 35psi and immediately falls off to 0 once the pump shuts off or the key is turned off. Once it cranks and is running it holds at about 35. When you disconnect the vacuum line to the regulator you get about 42 psi. Again once everything is shut down though it bleeds back off to 0 immediately. I am thinking that even though the pump was replaced, it could have been a cheap reman and the check valve in there is crap or an injector is leaking down. I bought the car from someone who replaced the pump, so i don't know what kind it was or much aside from that I am pretty sure he did replace the pump...aside from that I couldn't tell you. And the pump is a real joy to get to if you don't feel like cutting open the floor of your trunk/interior area for pump access.
Anyway, any substantiation on the leaky injector or bad check valve in the pump...am I heading in the right direction you think?
Anyway, any substantiation on the leaky injector or bad check valve in the pump...am I heading in the right direction you think?
Yea, I finally got a gauge on the rail today. The pressure builds to about 35psi and immediately falls off to 0 once the pump shuts off or the key is turned off. Once it cranks and is running it holds at about 35. When you disconnect the vacuum line to the regulator you get about 42 psi. Again once everything is shut down though it bleeds back off to 0 immediately. I am thinking that even though the pump was replaced, it could have been a cheap reman and the check valve in there is crap or an injector is leaking down. I bought the car from someone who replaced the pump, so i don't know what kind it was or much aside from that I am pretty sure he did replace the pump...aside from that I couldn't tell you. And the pump is a real joy to get to if you don't feel like cutting open the floor of your trunk/interior area for pump access.
Anyway, any substantiation on the leaky injector or bad check valve in the pump...am I heading in the right direction you think?
Anyway, any substantiation on the leaky injector or bad check valve in the pump...am I heading in the right direction you think?
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Yea, that was my plan. I wanted to pull the rail and injectors anyway and at least clean them at my shop as I have a makeshift injector cleaner I can run pressure through and clean/pulse the injectors to clean them up. Especially since the rail appears to come off pretty easily. As far as the trap door, I think I will eventually do that and make a nice cover plate with some rivnuts and button heads so it at least looks good and seal it with a gasket or something. That way it can be accessed from that point on and not look too ghetto. I have a feeling I will be into the pump again before this issue is resolved.
And no, I did not smell any fuel when removing the vacuum line. As far as I could tell, the regulator seems to be working normally. For now I guess I will prime the pump and start it right away before the prime circuit shuts off as the pressure bleeds down so fast until I can clean the injectors and get the trap door. I'm not dropping the tank/rear diff. to change out a pump that works fine in the meantime just yet if it comes down to that being what it is.
I appreciate everything so far guys, the responses have been awesome and helped tremendously. I'll have this wrapped up/repaired pretty soon I think as a result.
And no, I did not smell any fuel when removing the vacuum line. As far as I could tell, the regulator seems to be working normally. For now I guess I will prime the pump and start it right away before the prime circuit shuts off as the pressure bleeds down so fast until I can clean the injectors and get the trap door. I'm not dropping the tank/rear diff. to change out a pump that works fine in the meantime just yet if it comes down to that being what it is.
I appreciate everything so far guys, the responses have been awesome and helped tremendously. I'll have this wrapped up/repaired pretty soon I think as a result.
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