C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

help new to c4

 
Old 04-14-2019, 09:06 PM
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Tony Patz
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Default help new to c4

Hello everyone, I just purchaced a 94 automatic. It will only kick over for a split second after repedative cranking. Fuel psi gets to 30 but then just drops off to nothing.
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Old 04-14-2019, 09:58 PM
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aklim
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Sounds like a fuel pressure problem. Without more tests, we don't know if it is losing pressure at the regulator, the injectors or the "drain back valve" or all of them.

Crimp off the return line and turn the key to run position and see if it pressurizes up and how long it can keep it at that pressure.
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Old 04-14-2019, 10:39 PM
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Tony Patz
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OK Iíll do that tomorrow and get back with you guys
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Old 04-15-2019, 10:08 AM
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so I crimpped the return an it runs just fine, what do I need to replace? The pump or the regulator?
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Old 04-15-2019, 11:37 AM
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Originally Posted by Tony Patz View Post
so I crimpped the return an it runs just fine, what do I need to replace? The pump or the regulator?
Runs what? Engine was not supposed to be running.
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Old 04-15-2019, 11:39 AM
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Tony Patz
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When I crimp the return line the car started. but I tried to start it again and it wont start.
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Old 04-15-2019, 11:43 AM
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Originally Posted by Tony Patz View Post
When I crimp the return line the car started. but I tried to start it again and it wont start.
Don't care. Turn it on to run to see if the pressure spikes up, to what point and how it holds with the return line crimpped off.
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Old 04-15-2019, 11:46 AM
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Well sounds like fuel pressure issue. Start simple and work through it. 1) fuel filter, is it clogged? 2) regulator, is there gas in the vacuum line? 3) fuel pump, do you know when or if it was ever replaced? Are you getting good voltage to the pump? 4) injectors, any leaking down? are they reading spec resistance?
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Old 04-15-2019, 12:59 PM
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Originally Posted by aklim View Post
Don't care. Turn it on to run to see if the pressure spikes up, to what point and how it holds with the return line crimpped off.
OP, here aklim means turn the ignition to ON but don't crank or start the engine. This will run the fuel pump so you will be able check what is the fuel pressure, if it's holding pressure after shutoff, etc.
If you crimp the return line and the engine runs better, that means to me that the pump is ok but the regulator / diaphragm is faulty. Find the vacuum hose on the diaphragm and if you pull this vacuum line and get fuel coming out, that means the diaphragm is bad. But please don't do this with a hot engine or with the ignition on (pump running) and be sure to have plenty of rags around.

Last edited by DGXR; 04-15-2019 at 01:00 PM.
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Old 04-15-2019, 01:37 PM
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Originally Posted by DGXR View Post
If you crimp the return line and the engine runs better, that means to me that the pump is ok but the regulator / diaphragm is faulty.

Find the vacuum hose on the diaphragm and if you pull this vacuum line and get fuel coming out, that means the diaphragm is bad. But please don't do this with a hot engine or with the ignition on (pump running) and be sure to have plenty of rags around.
I wouldn't go that far. We also need to see that it can deliver the goods at WOT before we say the pump is OK.

I wouldn't do that myself. Would not mind watching someone pull that hose FROM A DISTANCE ON THEIR CAR. Possible Barbecue moment.
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Old 04-15-2019, 03:04 PM
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Tony Patz
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Default Thank you everyone

As soon as I get home from picking up my daughter I will check the pressure with the hose crimped. I know that the pressure goes up to about 35 after I turn the key on and then It drops quickly, this is with the hose not cramped. If anybodyís willing to talk me through it please call me anytime after four at 561-866-8934
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Old 04-15-2019, 05:26 PM
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ok so I installed a fuel psi regulator, no change. the pressure is no effected by crimping the return line.It goes up to 35, with the key turned onand the and stays steady while cranking
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Old 04-15-2019, 08:05 PM
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Originally Posted by Tony Patz View Post
ok so I installed a fuel psi regulator, no change. the pressure is no effected by crimping the return line.It goes up to 35, with the key turned onand the and stays steady while cranking
1. Hook up gauge
2. Turn key to RUN
3. See what pressure it gets
4. Turn key to off
5. Periodically check fuel pressure.

Nothing was said about cranking so not sure why you keep trying to crank and run.

What I am trying to see is what the pump does. With the return line crimpped it should go to at least 43 psi. It should hold pressure for a while. By cranking you change the test parameters.
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Old 04-15-2019, 08:21 PM
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Ok so I took the pump out and some bozo used a peice oh hose tat was too short comming from the pressure line of the pump, so gas was just circulatiing in the tank. I hooked it up right and after a few cranks it started I ran it around the block and it stalled on me comming around the bend. Tomorrow i am replacing the pump with a fresh one....stay tuned. and thaks for all the support.
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Old 04-15-2019, 08:22 PM
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psi was only up to 30 with just the key on
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Old 04-15-2019, 08:34 PM
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correct
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Old 04-15-2019, 08:35 PM
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Originally Posted by Tony Patz View Post
Ok so I took the pump out and some bozo used a peice oh hose tat was too short comming from the pressure line of the pump, so gas was just circulatiing in the tank. I hooked it up right and after a few cranks it started I ran it around the block and it stalled on me comming around the bend. Tomorrow i am replacing the pump with a fresh one....stay tuned. and thaks for all the support.
The pump was replaced before and they used a properly rated fuel hose. Are you saying it was bleeding off pressure? If after you hook it up right and it still doesn't bring up the pressure to 43, I think there is another issue besides that. Get THIS. It comes with the hose that is capable of being submerged. Regular fuel hose is fine with fuel inside but it might destroy it on the outside. You won't have to make multiple trips and you can replace the bolts with the SS bolts which make it easier to remove in the future. You also need the gasket. I really wouldn't reuse.

My only concern is that it still stalls when you have connected it correctly. The hose is the replacement for the pulsator which is known to leak.
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Old 04-16-2019, 11:19 AM
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Tony Patz
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Ok I replaced the fuel pump and its runninig BUT it dies after a few minutes a little hard to start again. runs then dies. I did not replace the fuel filter.

Last edited by Tony Patz; 04-16-2019 at 11:25 AM.
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Old 04-16-2019, 12:12 PM
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Originally Posted by Tony Patz View Post
Ok I replaced the fuel pump and its runninig BUT it dies after a few minutes a little hard to start again. runs then dies. I did not replace the fuel filter.
Pull the vacuum line off the fuel pressure regulator and check for fuel. Any fuel means it has a bad diaphragm. Also if it is a bad FPR then you will need to change your oil after you fix it.


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Old 04-17-2019, 08:26 AM
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Tony Patz
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Default I replaced the Fpr

I did replace the SPR
Originally Posted by 3D-Aircrew View Post
Pull the vacuum line off the fuel pressure regulator and check for fuel. Any fuel means it has a bad diaphragm. Also if it is a bad FPR then you will need to change your oil after you fix it.

I did replace the FPr
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