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1993-97 Gen II Small Block V8

Loss of fuel pressure after key is turned off

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Old 02-16-2007, 06:25 PM   #1
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Default Loss of fuel pressure after key is turned off

My car has had this issue and has been undrivable for the past month:

Random missfire code
Only 30PSI fuel pressure
all fuel pressure is lost after the key is turned off


I have replaced the fuel PUMP and REGULATOR and fuel filter......any ideas?
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Old 02-16-2007, 06:49 PM   #2
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Oil pressure switch? also called oil sending unit....?
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Old 02-16-2007, 06:52 PM   #3
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fuel pressure not oil pressure
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Old 02-16-2007, 07:00 PM   #4
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well right off the get go 30 psi is too low. at start up it should be somewhere around 45 psi and like 37 psi when its running. check gas lines, maybe something to do with the evap canister?? i doubt it though just somewhere to look that might directly affect fuel pressure.
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Old 02-16-2007, 07:26 PM   #5
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Does it blow blue smoke out the tailpipe when first starts up?
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Old 02-16-2007, 08:06 PM   #6
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how does it run when its on? possibly bad injectors, if one was stuck open it might make the pressure drop and make it misfire, dont know from experience but sounds like a possiblility
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Old 02-16-2007, 11:14 PM   #7
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Evap canister eh?

How do i test that?
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Old 02-16-2007, 11:29 PM   #8
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I don't see how it could be the evap canister since there are no pressurized fuel lines there. Maybe a stuck open injector as someone else mentioned, but I don't think that would drop your fuel pressure to 30. Maybe a bad wire to the fuel pump?
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Old 02-16-2007, 11:58 PM   #9
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I have replaced the pump once with a Delphi pump. I am banking on the chance that it may have been a bad lemon out of the box, ima order another one tomorro and try that. However if it doesnt work with the new fuel regulator ima hit something.....really really hard
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Old 02-17-2007, 12:18 AM   #10
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pull the fuel rail and turn the key on to pressurize the fuel system. Inspect the injectors to make sure one is not faulty..
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Old 02-17-2007, 08:38 AM   #11
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Is there any way to look at the relay and tell if its broken? I thought that the relay either worked or it didnt since all it does is deliver electricity to the pump
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Old 02-17-2007, 08:43 AM   #12
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ya i could almosst go with a bad injector being that u have a random missfire code that can be the fault of the injectors
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Old 02-17-2007, 07:03 PM   #13
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I said oil pressure switch because the fuel pump does get a reading from the oil sending unit, if you have a faulty oil pressure switch, sending a false signal of low oil pressure, it will cut off fuel pump pressure..... now.... does it make more sense to you?????
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Old 02-17-2007, 11:44 PM   #14
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^^ actually I dont think it works that way. I recall the oil pressure sending unit will allow the fuel pump to continue to be powered if it blows the fuse and the car still sees the car has oil pressure.
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Old 02-18-2007, 07:37 PM   #15
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I understand that it will cut off fuel pump if oil pressure is too low in order to avoid any damage to the engine. So, if its sending a false signal, or if its leaking, it will trigger such action. We fixed a friends car that had a similar problem, he replaced a bunch of stuff, such as fuel pump, relay, opti, module, coil... still his car wouldn't run for too long... untill he replaced the oil sending unit... I am just telling my expierience on a similar situation.
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Old 02-18-2007, 10:40 PM   #16
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^^ maybe it's different on the f-cars, cause it doesnt work that way on the bcars. You can unplug the darn oil pressure sending unit, get the light to show up on the dash, and it will still run..
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Old 02-18-2007, 11:14 PM   #17
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fuel pressure is controlled by the regulator. when you turn the engine off vacum goes to zero which closes the return line. There is a checkvalve in the fuel pump to keep pressure in the rail for the next start up.
Either you have a faulty checkvavle, failed regulator, or leaking injector (s).
you should check the vacum line that attaches to the regulator and see if there is any trace of fuel.
its not electrical so keep your test light in the tool box.
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Old 02-19-2007, 11:00 AM   #18
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I had a similar problem with mine, it ended up being a small hole in the fuel line that runs from the pump to the metal lines in the tank. I found it by pressurizing the pump with it out of the car.
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Old 02-21-2007, 06:40 AM   #19
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change the fuel filter along the underside of the car
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Old 07-21-2008, 12:27 PM   #20
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Did you ever figure out the problem? My car is doing the exact same thing now and I have replaced everything I could think of...
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1993, bad, corvette, diagnosing, dropping, drops, engine, fuel, grand, key, loss, pressure, prix, rail, regulator

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