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SmokinVette.com Forums : Corvette Forums : C4 Corvette Forums : C4 Tech & Performance : '90 ZR1 no fuel pressure
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Old 02-05-2013, 02:29 PM   #1
joekc135
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Default '90 ZR1 no fuel pressure

I think I have a bad fuel pump or relay. I have checked the fuel pressure with the key on and it is 0. All fuses have been checked and are good. I have seen diagrams showing where the relays are on this car but cannot see them under the right or left dashboard. Do you have to take the car apart to access the fuel pump relays? Any help would be appreciated. The car is stuck in a lower level parking garage that cannot be reached by a tow truck.
Thanks!
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Old 02-06-2013, 02:10 AM   #2
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I assume the Z is wired the same as reg C4's

Putting 12V to terminal G of the ALDL connector under the dash will make the pump ( if it is working) run full time bypassing the relays
IIRC , on my '90 the panel under the dash has to come off to access the relays
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Old 02-06-2013, 10:37 AM   #3
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Quote:
Originally Posted by joekc135 View Post
I think I have a bad fuel pump or relay. I have checked the fuel pressure with the key on and it is 0. All fuses have been checked and are good. I have seen diagrams showing where the relays are on this car but cannot see them under the right or left dashboard. Do you have to take the car apart to access the fuel pump relays? Any help would be appreciated. The car is stuck in a lower level parking garage that cannot be reached by a tow truck.
Thanks!

You can force the pump to run by bypassing the relay and hooking a temporary hot wire directly to the fuel pump's hot wire. Then you can at least get it out of the parking garage and back home where you can troubleshoot it in your leisure.

Although I have an '82 I added an 18-gauge wire to my fuel pump's hot wire then dropped it down alongside my spare tire (with a wire nut on the end of it) so I could power up my fuel pump with a trickle charger so I could run my pump even with my engine not running.
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Old 02-07-2013, 10:39 AM   #4
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Try banging on the fuel tank with a mallet or something soft so you don't dent it. This will "jar" the pump and hopefully get it off the flat spot on the pump motor's commutator. After you bang the tank , turn the key and listen for a buzzing noise, that is the pump prime , it will only last for two to three seconds. If you don't hear it, turn the key off and repeat above procedure until you hear the pump prime. Once you hear the pump prime turn the key to start the engine and git 'er home. This only works once so get the car home immediately. If you shut the car off it might not start again.
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Old 02-07-2013, 03:39 PM   #5
joekc135
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Quote:
Originally Posted by vetteoz View Post
I assume the Z is wired the same as reg C4's

Putting 12V to terminal G of the ALDL connector under the dash will make the pump ( if it is working) run full time bypassing the relays
IIRC , on my '90 the panel under the dash has to come off to access the relays
Thanks, I will give that a try, is there a 12v source in the connector where you can just jump with a piece of wire?
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Old 02-07-2013, 03:43 PM   #6
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Thanks, I wouldn't have thought of that but I will give it a try. I ordered a new fuel pump from Lingenfelter as it was the only one anywhere on the internet. If I can get it running and get it home it doesn't look like too difficult of a job. Thanks again for the advice.
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Old 02-09-2013, 04:21 PM   #7
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Quote:
Originally Posted by joekc135 View Post
I think I have a bad fuel pump or relay. I have checked the fuel pressure with the key on and it is 0. All fuses have been checked and are good. I have seen diagrams showing where the relays are on this car but cannot see them under the right or left dashboard. Do you have to take the car apart to access the fuel pump relays? Any help would be appreciated. The car is stuck in a lower level parking garage that cannot be reached by a tow truck.
Thanks!

Are you sure someone hasn't come along and siphoned all of it's gas out?
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Old 02-10-2013, 07:05 AM   #8
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Yes, the tank is full and its "Chevron with Techron".
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Old 02-10-2013, 12:32 PM   #9
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The connector under the dash does not have any labels so there's no way to tell which one is the G connector. Also, I have battery voltage at the fuel pump connector between the black (ground) wire and the purple wire but not between the black wire and the white or green wires. I have negative battery voltage between the purple wire and either the white or green wires. Do you think this means the pump is grounded out? It is a 2 stage fuel pump so not sure which wires should be hot at start. Thanks for your help if you have any ideas....
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Old 02-10-2013, 09:51 PM   #10
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Originally Posted by joekc135 View Post
I have battery voltage at the fuel pump connector between the black (ground) wire and the purple wire but not between the black wire and the white or green wires.
the purple is probably the fuel gauge wire

OK.
The ZR1 is wired different to std cars , but you still have the pump prime point under the hood . A heavy red wire with a black connector on the end (by brake booster on std cars)
If you supply 12V there the pump should run ( see pump circuit diagram below )
You have checked the pump fuses?

Also unless you supply 12V to the system as detailed above. the pump will only run for 2 sec to pressurize the rails when the key is turned on ,
then shut off which could account for you seeing no power at the tank

90 FSM shows a gray and a Dk green / white as the pump wires at tank (the tan/ white shown from #2 relay turns into Dk green/ white at tank , the gray from #1 relay is continuous )


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Last edited by vetteoz; 02-10-2013 at 09:58 PM.
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