MBE111

I was driving the car all day and it ran fine. I shut it off for a minute and would not restart. There was no fuel pressure when I checked at the fuel rail. I had replaced the fuel pump with a new GM earlier in the day because the old one growled and sounded like its life time was near the end.
I removed the new pump and tested/jumped it from a battery and it ran fine. So tested the wires for power at the fuel tank and find what seems to be the problem. No electricity.
I swapped the two relays on the firewall thinking that maybe one was bad but that did not change anything.
So then I jumped the lower left hand post of the ALCL under the dash and I can hear the relay trip on the firewall and then I have power at the connection at the fuel tank.
My car is an 86 and the fuse panel does not have a slot marked F/P for the fuel pump fuse. What do I look for so that the fuel pump runs with the key turned to on so that the pump runs for the approximate 2 seconds. Is there an inline fuse somewhere? I have a Haynes manual and have not found anything in it to help me figure out my problem.

Thanks for your help

rodj

Would only have power to pump for 2 sec

Putting power to the ALDL pin still puts power through the FP fuse so you know wiring circuit is good to the pump.

Do you have 12V on the Org power wire to the relay? Has a inline fusible link on feed wire in engine bay.
Disconnect the relay and jumper the pump relay connector (pins A-E ) and see if pump runs.
The early style plugs are bad for faults and shorts due to age

FP fuse should be bottom row ; RH side of fuse panel
10A

gerardvg

Hi
Check your oil pressure switch, you have a oil pressure sender behind and to right of distributor and below that the oil pressure switch. It faces toward the driver side.

Check the connector has not come of, The fuel pump will run when your ignition is turned on / starting the engine for a few secs then stop if there is no oil pressure (at the oil pressure switch)

You can bypass the switch for a test , closes when there is oil pressure.

rodj

Is no connection between the switch and relay.

Pump should still run from ECM through relay when engine cranks over and ECM see pulses from the dist.

The OP switch is wired in parallel to the pump relay and works independently as a backup only device.
Allows you to start engine by cranking IF relay goes bad.

If the fusible link I mentioned above is blown ;neither will supply power to pump as both are fed from the same fuse.

pmihaltian

Rod is right. I had the very same problem with my 86 when I changed out my pump a few years back. It turned out to be the connector plug at the top of the gas cap inlet area. I cleaned it up with WD40 & contact cleaner, added some dilectric grease and made sure the wires were seated snugly in the plug - problem solved.

Also, the fuel pump fuse is on the bottom row of the fuse panel, all the way to the right (toward fire wall). Mine is marked FR, It is a 10 amp fuse.

AGENT 86

With that and these links, you should be able to diagnose.

From my 86 FSM

http://dankai.shawwebspace.ca/asset/...l_delivery.pdf

http://members.shaw.ca/agent86/Fuse%20Block.pdf

http://members.shaw.ca/corvette86/En...ButWontRun.pdf

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf

http://members.shaw.ca/corvette86/Co...0View%2086.pdf

stoydido

gerard; have you verified that the FP on your car shuts off if oil switch is out of circuit? try it and let us know. it isn't supposed to work that way. if the engineers designed it that way they are dumber than I had thought. a car that has "passed all the tests" will shut down if the switch fails.

after reading the thread by the C4 engineer who has no clue how to restart a stored vehicle, I can see why there are so many design issues with the C4!

MBE111

OK, Thanks for all of the help so far.
When I jumper wired the A and E posts on the fuel pump relay (after removing the relay) I have 12 volt power at the connection to the fuel pump at the fuel tank.

When I jumped 12 volts to the fuel pump post on the ALCL I had 12 volt power at the connection to the fuel pump at the fuel tank.

The fuse panel on my car is designated F/R for some reason instead of F/P as the rest of the cars are marked. It is a 10 amp fuse and the fuse is good.

I think my next step is to put the fuel pump back in the gas tank and leave the pressure hose off to look for pressure there. My assumption that no fuel pressure at the schrader valve on the fuel rail was because the fuel pump wasn't running may not have been correct. However it is unlikely that the fuel filter would have plugged so quickly that the car is running fine, I shut it off and it does not restart.
Or am I still missing something here?
When you turn the key on and the fuel pump runs for two seconds, I assume that is to build pressure in the system for the injectors to work/spray and the engine to fire and run. The fuel pump must have constant power though and continue to pump fuel based on the consumption of the engine and maintaining the approximate 45 pounds pressure at the fuel rails.

I will put the pump back in and check back here for more ideas.
Thanks again

MBE111

I put the fuel pump back in and left the main gas hose off. A spurt of gas came out of the pump, not enough to overflow the flange of the mounting plate for the pump. Certainly not enough to build 45 pounds pressure to satisfy the fuel injectors.
I checked for power at the connection and found none.

Agent 86 sent a link to his service manual, and I find something about the VAT system. I see something called a vats decoder module that says "cranking fuel enable" is this my problem? If so how do I fix it or bypass it?

stoydido

if I'm following correctly, the pump will not show voltage when key is turned to on except for the 2 secs, unless ecm sees pulses from the distributor while cranking..

MBE111

So you are thinking that the fuel pump won't pump unless I am cranking the engine?

stoydido

it is on for 2 secs if key is turned. it stays on if dist is pulsing and ecm sees them. yes.

I checked mine several times, 91, at the fuse, and the fuse had voltage for 2 secs, then did not. Think about it.

if you use the G terminal I suppose it will stay on as long as...

jc

MBE111

Well, I jumped the fuel pump to build pressure and started the engine, then disconnected the jumper wire and it kept running! Surprise!
I have shut it off and restarted it many times and it seems like it runs as it should. I do not have a fuel pressure gauge to check at the rail for proper fuel pressure but will do that before I trust it to drive it anywhere.
I will report back the final status.
Thanks for the help

rodj

So you have confirmed you have power on the pump circuit and it is getting to the pump.
You may have had a intermittent fault that "may " reappear.
From the above tests , now know that you problem is with the relay itself, the control wire from the ECM or the relay ground wire ; something causing the relay not to operate correctly


If you didn't reinstall the relay then pump would be getting power from the backup system through OP switch as noted above

Completely seperate item.
VATS makes the ECM not pulse ( turn on ) the injectors so even if you have perfect fuel pressure , engine will not start if VATS is activated