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Discussion Starter · #1 ·
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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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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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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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. :seeya:
 

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Discussion Starter · #5 ·
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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Discussion Starter · #6 ·
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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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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Discussion Starter · #9 ·
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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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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Discussion Starter · #11 ·
Thanks for the info, I will check the prime point. I tested the system with a fuel pressure guage, the pressure is 0 with the key on and the circuit breakers are all good. The only thing I haven't tested are the relays since you have to take the dash apart to get at them.
 

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Discussion Starter · #12 ·
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 )



I tried the pump prime connector with no results. It appears from the wiring diagram the prime circuit runs thru the fuel pump relays so if they are bad there will still be no voltage to the pump. If anyone has any other ideas on troubleshooting, I would appreciate hearing them. Thanks!
 

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I tried the pump prime connector with no results. If anyone has any other ideas on troubleshooting,
Only alternative I see now is to power up the pump directly through the connector under the filler flap and see if the pump runs
If it does then highly likely the relay is at fault
 

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Just make up a 12 foot wire with alligator clips on each end. Connect one end to either the battery or hot post on the alternator and the other end directly to the fuel pump's input wire. Or you can connect it to the relay's output-to-fuel-pump wire.

And yes, the connection at the relay or the relay is probably bad. The relays usually last 150,000 miles or more but they can fail earlier. And you can always take it's cover off and sand the points to remove the little buildup of carbon that has built up. Just use a little piece of 600 grit wet-or-dry sandpaper, fold it in half, then drag it thru the points about 10 times; that'll clean both of them at the same time. Then put the cover back on.
 

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Problem is;
to date he hasn't wanted to go under the dash to find the pump relays


I had read that but forgot about it. Sorry. But I still think the easiest way is to provide external power to the fuel pump's hot wire with a long jumper wire with two alligator clips on it; connecting it to either the battery or alternator HOT post.

I would think a couple of strong guys could easily push the car out of it's parking place and out into the open where a tow truck could get to it. But without any picture I don't know what he's dealing with.
 

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As long as you can open your doors fully where it's parked it's not that hard to access the relays. one is on the passenger side behind the glove compartment and the other behind driver gauges. using the diagrams OZ provided, you can feel for them. On the drivers side you will have to remove screws from the left side end of the dash and more along the bottom ( the carpet part )then you should be able to get your hand and feel for the proper relay.
 

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As long as you can open your doors fully where it's parked it's not that hard to access the relays. one is on the passenger side behind the glove compartment and the other behind driver gauges. using the diagrams OZ provided, you can feel for them. On the drivers side you will have to remove screws from the left side end of the dash and more along the bottom ( the carpet part )then you should be able to get your hand and feel for the proper relay.

All of the earlier C4's had two ways of providing power to the relay; the first being the ECM for the first 2 seconds then by the oil pressure sender once oil pressure rose about 5 psi. It's possible a mouse chewed thru the wires where they attach to the top of the oil pressure sender. And that is also another place where you can power your relay by simply adding a jumper wire from the alternator's hot post (or battery's hot post) to the wire that goes to the relay.
 

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Discussion Starter · #19 ·
Nothing seemed to work so I installed a new fuel pump and lo and behold, the engine started and ran...for about 5 minutes & then quit. After that it would only run for a few seconds & then quit. It appears the secondary fuel pump is not coming on for some reason. Anyone experienced this before?
 
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