Fuel pump / pressure question.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 116
Likes: 2
From: Webster Florida
Fuel pump / pressure question.
I've got an 86 corvette with a 5.7 tpi engine.
I've also got a 88 trans am with a 5.0 tpi engine. When I turn the key on the TA I can hear fuel running around the rails and I can hear the fuel pump.
just got the vette and noticed that when I turn the key on I hear nothing... no fuel pump, no fuel running around the rails...
is this the way the 5.7 is supposed to be?
Sorry if this is a silly question but it's something that's bugging me.
thanks in advance,
Robert
I've also got a 88 trans am with a 5.0 tpi engine. When I turn the key on the TA I can hear fuel running around the rails and I can hear the fuel pump.
just got the vette and noticed that when I turn the key on I hear nothing... no fuel pump, no fuel running around the rails...
is this the way the 5.7 is supposed to be?
Sorry if this is a silly question but it's something that's bugging me.
thanks in advance,
Robert
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Check fuel pump relay on firewall.
Could be faulty or have bad wiring at connector ( common )
As with your TA ,the pump will run on the fuel pump oil pressure switch in block once you get 4psi oil pressure when cranking.
Just takes longer cranking to fire
Could be faulty or have bad wiring at connector ( common )
As with your TA ,the pump will run on the fuel pump oil pressure switch in block once you get 4psi oil pressure when cranking.
Just takes longer cranking to fire
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
If the engine starts there is pressure in the system. On my 1985 there is an oilpressure switch just behind the distributor. When the oilpressure is present the switch is on paralelling the fuelpump relay so if the fuel relay breakes during driving the fuelpump continue to work till the engine stops.
But if you listen carefully you should have the fuelpump running for 2-3 seconds just after the ignition is switched on.
If the fuel relay is gone you have to turn the engine several times to let the oilpressure come to the threshold of the oilpressure switch and then it will start. It might also be that all your injectors are good and the engine hold the pressure so long that there is enough to have the engine to start before the oilpressure switch is enabled (this is if the fuelpump does not work).
Good luck
But if you listen carefully you should have the fuelpump running for 2-3 seconds just after the ignition is switched on.
If the fuel relay is gone you have to turn the engine several times to let the oilpressure come to the threshold of the oilpressure switch and then it will start. It might also be that all your injectors are good and the engine hold the pressure so long that there is enough to have the engine to start before the oilpressure switch is enabled (this is if the fuelpump does not work).
Good luck
Safety Car
Joined: Jan 2008
Posts: 3,939
Likes: 1
From: Vero Beach Florida
You should be hearing the pump run and the IAC spin into position, have someone turn the key when you are out of the car with the hood up make sure every thig is off, to listen to pump go to rear of car.
Thread Starter
Instructor
Joined: Jun 2010
Posts: 116
Likes: 2
From: Webster Florida
My guess is the fuel pump relay is bad... I've got an extra from my TA... this makes sense because it will not start like my other TPI... has to crank quite a bit and almost always have to touch the gas pedal which I never have to on the 5.0 TPI.
I knew this from getting the TA running.... but forgot that these two are so similiar. Guess I've been working on my porsche too much :-)
I knew this from getting the TA running.... but forgot that these two are so similiar. Guess I've been working on my porsche too much :-)
Thread Starter
Instructor
Joined: Jun 2010
Posts: 116
Likes: 2
From: Webster Florida
Even with a new Relay I still don't hear anything coming from the tank but it must be working. I don't believe that 2 seconds pass during the very breif fuel noise up at the TPI unit. I swapped the relay with my other TPI unit and the other one still runs as long as the key is on.
I beleive part of the hard starting is due to sitting for a couple of years. Its starting up better now when cold but hot... it's not start well at all. Don't think it's fuel pressure since it' runs fine past Idle.
Checked the plugs, wires, cap rotor and internal ingintion unit yesterday. they have all been replaced recently.
I've found at least 10 wires/plugs within the engine compartment that are not attached to anything... plus the plug is fried on the end of what I beleive to be the cold start injector.
way up front near the drivers side fog light is a plug that looks like it needs a relay.
I've got so many of these I think I'll post some pictures.
thanks in advance,
Robert
I beleive part of the hard starting is due to sitting for a couple of years. Its starting up better now when cold but hot... it's not start well at all. Don't think it's fuel pressure since it' runs fine past Idle.
Checked the plugs, wires, cap rotor and internal ingintion unit yesterday. they have all been replaced recently.
I've found at least 10 wires/plugs within the engine compartment that are not attached to anything... plus the plug is fried on the end of what I beleive to be the cold start injector.
way up front near the drivers side fog light is a plug that looks like it needs a relay.
I've got so many of these I think I'll post some pictures.
thanks in advance,
Robert
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