When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello y’all I recently picked up an 85 corvette with 97k miles. I guess I will get into it. The car was running great until about two days ago would not start. The car turns over but i’ve Found that the engine isn’t getting any fuel. I went ahead and replaced my fuel filter, spark plugs, spark plug lines (old ones were dry rotted), determined each new plug is sparking. After that i’ve Read on this forum that the Fuel Pump could be an issue and thanks to this forum was able to successfully install a new fuel pump/ strainer(so easy on this car I love it) but then determined that the fuel pump is not turning on. The car wants to fire up but still isn’t getting any fuel because of this. My last guess is maybe the wiring is no good/some electrical problem is occurring where the pump isn’t getting any power. Never really done any electrical work on a car so I’m not sure where to start. I’ve read on here it could be the fuel pump relay. But I have no idea how to rewire the car (I can definitely learn). Also having a hard time finding that part. Don’t know what wires to use either. If that’s not the case then I don’t know where to go next. I appreciate it if someone could help a new C4 owner out.
Schematic is for 1984 but should be similar.
With ignition off you can put 12V on pin ALDL connector G to test wires from realy to fuel pump.
If pump starts then it is probably a bad fuel pump relay.
Appreciate the information JoBy not sure if I can get my hands on a power supply tomorrow but I will test this trick and let you know how it works when I get off work. Thank you for the help.
As you see on schematics you can measure if you have voltage at the fuse ( relay working ).
You can also feed power to pump at the fuse to bypass relay completely. ( use wire with inline fuse ).
So update on the car not getting any fuel pressure I used a multimeter to test the connecter from the battery to the fuel pump 10.4v was the read (low battery/also tried it with my buddy jumping the car) Also found it was receiving a max amp to the harness for the fuel pump 0.14 amps. Not sure if these readings mean anything but it seemed low (I’m also not an electrician so maybe it’s normal haha). Found out that the 2 second of the fuel rail doesn’t drop voltage it holds voltage during the pruning of the fuel rail. The only thing I can think of now is replacing the fuel relay that I have coming in the mail. If not that I guess maybe some digging into the ECM.
If you jumper pins C & D at the Oil Pressure Sw it will apply constant power to the FP.
If that fails to run the pump I suggest you remove the FP assy and clean the electrical contacts where the pump wiring meats the lid. Of course then use a new gasket before reinstalling the assy into the tank.
get a fuel pressure gauge on your engine....fitting on passenger side rail.....supply 12v to pin G on aldl.....pump should turn on.....if not, bad relay or pump.....not a big job to remove it and check.....check and clean all connections.....gauges are not that much at a parts store, you'll be needing it lots......
If you jumper pins C & D at the Oil Pressure Sw it will apply constant power to the FP.
If that fails to run the pump I suggest you remove the FP assy and clean the electrical contacts where the pump wiring meats the lid. Of course then use a new gasket before reinstalling the assy into the tank.
If you do remove the pump assembly I suggest that you might as well replace the pump , fuel sock and gasket while you have it out. Not that expensive and I got those items from rock auto. My fuel sock was black and crushed as who ever replaced the pump and sock had the sock in sideways (goes up and down as viewed from the rear) so did not fit into the sump correctly!
If you do remove the pump assembly I suggest that you might as well replace the pump , fuel sock and gasket while you have it out. Not that expensive and I got those items from rock auto. My fuel sock was black and crushed as who ever replaced the pump and sock had the sock in sideways (goes up and down as viewed from the rear) so did not fit into the sump correctly!
I bought a stainless pump/fuel sender unit years ago.....had occasion to take in out after 6 years...still looks great.....the stock one in there before looked a million years old....
If you jumper pins C & D at the Oil Pressure Sw it will apply constant power to the FP.
If that fails to run the pump I suggest you remove the FP assy and clean the electrical contacts where the pump wiring meats the lid. Of course then use a new gasket before reinstalling the assy into the tank.
jumper pins c&d are they labeled or do you have a drawing of some sort?
Not sure on your car, but there was a oil pressure switch that was sort of an emergency shut off. The theory was that if there was a crash and the engine shut down, the lack of oil pressure would trip the switch which would turn off the fuel pump. If that might be the case try looking for that oil pressure switch. I believe it's on the back of the engine, below the dizzy attached to the regualr oil pressure sending unit. If you look on the above schematic it's right next to the fuel pump relay. Might just be a loose wire.
So i think I narrowed down the problem I hard wired a switch from the battery directly to the sending unit wire harness which it worked because I tested it on the old fuel pump out of the car and ran the pump with my very..sketchy switch and it ran fine for 30 seconds so then I connected my switch to the wiring harness out of the sending unit and it did not run the pump in the car (new pump in car). So I think the wiring in the unit is in lack of better terms. Fucked.
check for power at the relay...by the battery.....change it with the fan relay (same) that's right there, see if that works.....also, the connection at the tank where the 3 wires run through is suspect a lot of times.....I wouldn't bother too much with the oil switch....can be the problem but doesn't sound like it.....supply a ground and power to the wires going into the tank......the purple one is the sending unit and needs no power to test the pump......also, I eventually had to go through every connector(relays, etc) to clean them on my 85.....power should go from ecm to relay to fuse to pump.....you can check at those intervals.....just remember it only comes on for 2 sec.....I think if it doesn't turn on at "G" on the aldl, you may have a broken connection somewhere.....you will learn a lot about how your engine works solving this......good luck.....stay with it....
Not sure on your car, but there was a oil pressure switch that was sort of an emergency shut off. The theory was that if there was a crash and the engine shut down, the lack of oil pressure would trip the switch which would turn off the fuel pump. If that might be the case try looking for that oil pressure switch. I believe it's on the back of the engine, below the dizzy attached to the regualr oil pressure sending unit. If you look on the above schematic it's right next to the fuel pump relay. Might just be a loose wire.
It's actually backwards. The oil pressure switch acts as a backup for the fuel pump relay in case the relay fails. This way once you've cranked the engine over enough to get oil pressure, it'll kick the fuel pump on. The only way to make it a "safety" would be to remove the fuel pump relay entirely so that only the oil pressure switch has control of the fuel pump (this would make for some hard starts, however).
Under normal operation, the fuel pump relay will keep the fuel pump energized even if the oil pressure switch indicates 0 pressure.
Last edited by Nomake Wan; May 12, 2020 at 02:47 AM.
pdate.
The new sending unit and fuel pump relays were replaced and the fuel rails have good pressure now and now ran into yet a different problem with the result being the car won’t start. Now the car only bangs off about 4 cylinders. I looked in the manual and made sure the plugs and wires were all in the correct places( also new plugs and wires). I installed a new starter because the old one needed replacing and that didn’t do the trick (does catch better) even tested the resistance on all the fuel injectors (16-16.3 were the readings on all) I’m running out of ideas and options I’m kind of lost at this point. The only thing my dumbass can think of is instead of trying to jump the shitty battery maybe just get a new one but that doesn’t explain the car not being able to fire off properly.
No fuel pressure.
