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Discussion Starter #1
Just picked up an 85 vette. When cold, car will not start until oil pressure builds up to 45-55 pounds. It will start firing when pressure reaches 45-55 and finally starts. You cannot hear fuel pump running when you turn the key. Once fired off it usually fires right up but it has started to die at times after it is warmed up. Sometimes if it is shut off to go in a store and you come right back out it just turns over and won't fire. If I wait a few minutes it then immediately fires up. Today it died twice on the way home. Waited for a couple minutes each time and it would immediately fire and drive for a few minutes again.

when it is hot and won't start, you cannot hear fuel pump then either when you cycle the key on and off. The engine is oil is hot and pressure gauge reads 30 to 40 pounds cranking when it won't start. Can't build pressure to see if that is the reason it won't start when hot. Just weird that it will immediately fire if I wait a few minutes.
 

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Fuel pump oil pressure switch faulty ?
Should close @ 4 psi oil pressure and run the pump
OP switch is a backup to the pump relay should relay fail ; allows motor to start once oil pressure up and keep running.
If relay not working and OP switch intermittent could be cause of your problems

In any case pump should prime for 2 sec when key 1st turned on.
Check fuel pump relay and connector; commonly go bad with age.

To prove a point ; put 12V on terminal G of the ALDL connector.That will run the pump fulltime.
Try starting with pump running and see if anything different
 

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Fuel pump oil pressure switch faulty ?
Should close @ 4 psi oil pressure and run the pump
OP switch is a backup to the pump relay should relay fail ; allows motor to start once oil pressure up and keep running.
If relay not working and OP switch intermittent could be cause of your problems

In any case pump should prime for 2 sec when key 1st turned on.
Check fuel pump relay and connector; commonly go bad with age.

To prove a point ; put 12V on terminal G of the ALDL connector.That will run the pump fulltime.
Try starting with pump running and see if anything different
I think he knows his sh*t:agree:
 

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Discussion Starter #7
85

I'll start with the pressure switch and check out relay - car was just out of shop before they brought to me and they were planning on purchasing a new or used ECM for it. Since I traded, I have not heard back on whether it has shipped or not. Would like to make sure it isn't something else. The hot stalling business is like the fuel just shuts itself off. If I open the hood, it tends to fire back up a little faster.
 

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Discussion Starter #10
More Info

OK, went out today and got code off vette - it has a code 54 - low voltage fuel pump - I also thought I would do the A and G ground to force pump to run and it did not make the pump run. I'll go back through the info you gave me and do more checks tomorrow. Thanks for help so far
 

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OK, went out today and got code off vette - it has a code 54 - low voltage fuel pump - I also thought I would do the A and G ground to force pump to run and it did not make the pump run.
Check /replace fuel pump relay first
Power to terminal G assumes the relay is in it's static state and passing power.
If the contacts are worn / faulty it may not be supplying power to pump in test mode





As you can see from above diagram ,if you disconnect the relay connector and jumper [email protected] E to [email protected]
then you have bypassed all electrics and are supplying 12V to pump.
 

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Discussion Starter #12
More tests

Ok, next phase of testing - no fuel pressure turning on the key, pump not functioning - no pressure grounding out the aldl testing ports a and g pump does not come on - pulled oil pressure switch by distributor and used a test wire to connect the two wires, pump came on immediately. Pressure was at 38 pounds. Turned key and vette started to fire here and there and then finally caught and ran. While running pressure was at 30 pounds. As soon as I pulled the test wire the car will start stumbling as pressure drops and then die. Leakdown test was not good as within a minute after turning off car it dropped to 18 pounds from 30 and 5 minutes later was down to 10 pounds. 20 minutes down to 5 pounds. Also just checked A and E on the fuel pump relay and fuel pump kicked right on up to 38 pounds. Thanks for ideas so far.
 

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pulled oil pressure switch by distributor and used a test wire to connect the two wires, pump came on immediately. Pressure was at 38 pounds. Also checked A and E on the fuel pump relay and fuel pump kicked right on up to 38 pounds.
So pump is OK (ish)
Low pressure could be blocked filter , pump on way out or regulator leaking.There are further tests you can do to check out

First problem is getting pump to actually run as it should
I would try and get some DVM test leads on the OP switch terminals and see if it closes @ 4psi when cranking as it should If not replace.

At the relay connector ;see if you get 12V @ terminal C when key first turned on ( only for 2 sec ) .That confirms ECM is trying to operate the relay
In any case I think relay replacement would be justified based on age alone
 

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Discussion Starter #14
Fuel Pump

Fuel pump does not come on with turning key on - fuel pump relay is replaced and there is no signal from the computer at C on the relay to start the fuel pump.
 

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if you have a electrical "poke tester" (it allows you to punch into a wire)-- check behind the connector for volts about 6 inches back on wire going into C -- from computer. our years are notorious for bad wiring and busted connectors.
remember this signal will only apear for about 5 seconds and there has to be significant time off between cycles for it to manifest the voltage. in lay terms you have to wait about 3 minutes between checking for volts at c. and don't be concerned with proper volts just use a check light to verify something is coming out of the wire first

if volts are present you'll need to replace the connector obviously.

if your car runs when the oil presure electrodes are jumpered buy a new pressure switch-- about $15 at autozone. kid of a bear to change-- much easier removing the wiper motor first.

Lets get it running first then we'll move onto the leak down test-- it's too easy to get off on tangents with trouble shooting
 

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Discussion Starter #16
Terminal C

I have jumpered from e to c, 12 volts to c, and tested with poker on a test light and turned on key and nothing has happened. I was told if I jumped 12 volts to the relay with key off on C, the pump would start or if it did not then the ground was bad? I spend the day cleaning up the ground connections from the battery, installed a new battery, connected and cleaned ground connections at the block and frame rail. Used a battery ground cable to run from transmission to engine bolt to the frame. They had grounds connected on the inspection plate instead of the bolt to hold the transmission to engine.
 

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Discussion Starter #17
Poke

I gave it a poke, turned key, did not light test light. So no ground for relay - somewhere I should look to clean up a ground? ECU or ECM bad?
 

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I gave it a poke, turned key, did not light test light. So no ground for relay - somewhere I should look to clean up a ground? ECU or ECM bad?
your test light should go to separate ground when performing this test
 

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Discussion Starter #19
more info

your test light should go to separate ground when performing this test

it was grounded to battery

Currently I am replacing oil pressure switch with new one in hopes it will keep the car running until I find out why the relay will not run the pump. This may cure the hot stalling problem also since as the oil heats up the pressure drops and the pressure switch may no longer be running the pump.
 

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ECU or ECM bad?
I think we have already established on the other forum that you have a ECM fault because ECM will not send power to the relay in any situation ; initial key on or while engine running
The bad ground on the relay is just another complication

That said;
replacing the faulty oil pressure switch as I suggested over there will allow you to start ( will crank a little longer ) and run engine while you sort out the other problems
 
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