Fuel pump circuit issues
07-27-2018, 04:04 AM
#1
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Fuel pump circuit issues
Ok, this is a weird one. I think I've got an intermittent open fuel pump circuit. Question is, where? Tried to drive my car a few weeks ago, I didn't hear the fuel pump prime, no fuel pressure when I checked with a gauge. Fuel pump relay clicks as does the MAF relay. Power all the way to the sending unit connector. Diagnosed as bad fuel pump. Put in a new Bosch pump and was up and running again. Sending unit and pump were previously replaced in 2016. Not sure what brand sender. Most likely aftermarket. Walbro pump. VATS was programmed out last year. Also, when I applied 12v directly to the Walbro pump I removed a few weeks ago, it worked. I should have known something was up and my diagnosis was incorrect. 
A week later, I drive about 30 miles to stay with some friends. Car drove great. Next morning, no fuel pressure. Had to be towed home. Car sat for two weeks before I had time to diagnose. Yesterday, she started right up.
Of course the car doesn't have the common courtesy of staying broken.
Relay and oil pressure sender tested good. Ground behind LH cylinder head looked tested good. Clean and tight. When the fuel pump wouldn't prime, I bypassed the relay and that didn't make the pump run. I also ran 12V to the red wire at the ALDL. That didn't make the pump run either. I've spent way too much time looking at the diagram. Since the relays click on, the intermittent open has to be after the splice for the tan/white wire for the oil pressure sender and pump relay and anywhere up to the pump.
Could a bad sender be the problem? High tank pressure loosening something up? Anyone have a similar issue? Thinking of finding a GM sender or swapping the float to my original sender I still have in the shed. There was more humidity than usual, FWIW.
At this point, the best idea I can come up with to isolate the ghost is to run a fused wire (with a toggle switch) from the fuse box to the wire for the fuel pump at the sender, essentially bypassing the whole circuit. If there's another no fuel condition and that gets the pump going, then the open is before the sender. If it still leaves me stranded, then the sender is the culprit or possibly a dead spot on the new pump (doubtful). In that case, I'd likely replace both pump and sender anyway. I've gotten pretty good at dropping the tank, anyway. It's really not that bad of a job.
Any tips on chasing a ghost? Anyone else have an aftermarket sender cause the fuel pump not to run? Thanks!
A week later, I drive about 30 miles to stay with some friends. Car drove great. Next morning, no fuel pressure. Had to be towed home. Car sat for two weeks before I had time to diagnose. Yesterday, she started right up.
Of course the car doesn't have the common courtesy of staying broken.
Relay and oil pressure sender tested good. Ground behind LH cylinder head looked tested good. Clean and tight. When the fuel pump wouldn't prime, I bypassed the relay and that didn't make the pump run. I also ran 12V to the red wire at the ALDL. That didn't make the pump run either. I've spent way too much time looking at the diagram. Since the relays click on, the intermittent open has to be after the splice for the tan/white wire for the oil pressure sender and pump relay and anywhere up to the pump.
Could a bad sender be the problem? High tank pressure loosening something up? Anyone have a similar issue? Thinking of finding a GM sender or swapping the float to my original sender I still have in the shed. There was more humidity than usual, FWIW.
At this point, the best idea I can come up with to isolate the ghost is to run a fused wire (with a toggle switch) from the fuse box to the wire for the fuel pump at the sender, essentially bypassing the whole circuit. If there's another no fuel condition and that gets the pump going, then the open is before the sender. If it still leaves me stranded, then the sender is the culprit or possibly a dead spot on the new pump (doubtful). In that case, I'd likely replace both pump and sender anyway. I've gotten pretty good at dropping the tank, anyway. It's really not that bad of a job.
Any tips on chasing a ghost? Anyone else have an aftermarket sender cause the fuel pump not to run? Thanks!
Last edited by backtothe80s; 07-27-2018 at 04:11 AM.
07-27-2018, 06:49 AM
#2
Re: Fuel pump circuit issues
Has connector C313 been inspected? That is under/behind the rear seat riser, and includes circuits for the fuel tank wiring. It would also be good to verify the ground connection for the pump.
07-27-2018, 06:32 PM
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Re: Fuel pump circuit issues
The ground for the relay is good. I haven't looked at the ground for the pump lately (G304, I beleive). I last checked it a few years ago. I doubt it has issues, but I was going to run backup power to the pump anyway, so that's a good time to check. Who knows, maybe I'll get lucky and find the build sheet. 🙄
07-27-2018, 09:28 PM
#4
Re: Fuel pump circuit issues
Seen more than one sender that had a wire fail right where it entered the yellow fitting on the top of the sender. The one would work for awhile, hit a bump, then the circuit would die, then if you wiggled the wire it'd start working again.
The pump ground should be a black wire sticking out of the bundle on the drivers side, under the seat or the kick panel, IIRC.
The pump ground should be a black wire sticking out of the bundle on the drivers side, under the seat or the kick panel, IIRC.
07-27-2018, 09:52 PM
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Re: Fuel pump circuit issues
HMMM...that makes sense! I'll wiggle the wires while it's running and see if that changes anything. That's exactly the kind of lead I was looking for. Sounds like it's time for a new sender! I'll check the ground at the kick panel, too.
07-28-2018, 10:15 AM
#6
Re: Fuel pump circuit issues
Seen more than one sender that had a wire fail right where it entered the yellow fitting on the top of the sender. The one would work for awhile, hit a bump, then the circuit would die, then if you wiggled the wire it'd start working again.
The pump ground should be a black wire sticking out of the bundle on the drivers side, under the seat or the kick panel, IIRC.
The pump ground should be a black wire sticking out of the bundle on the drivers side, under the seat or the kick panel, IIRC.
07-29-2018, 09:17 AM
#8
Re: Fuel pump circuit issues
Not using any wiring diagram. In the fall I pulled three interior harness' from 90-92 Camaros and all had the fuel pump grounding underneath the center console. I've never been fortunate enough to have diagrams/schematics that show exact locations of connectors and grounds.
07-29-2018, 11:47 AM
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Re: Fuel pump circuit issues
On the '89, ground is G304 as indicated in the diagram. Power window ground is under the console. No idea on '90+ Haven't had a chance to check it, but I will report back results when I do.
08-12-2018, 12:35 AM
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Re: Fuel pump circuit issues
Ok, update. Finally had a chance to take a look at the car. Checked the ground wire and connection. Clean and good continuity. Car started and ran fine. Wiggled various wires for the fuel pump, banged on the tank, and jounced the car up and down all while running to see if I could make it stall. No dice.
I went ahead and added auxiliary power to the fuel pump tapping into the power and ground wires on the sender AFTER the connector in front of the rear differential. The ground and power wire is routed with the stock wiring. Power comes from the extra battery terminals on the fuse box. Power is switched and fused. If I disconnect the C313 3-pin fuel pump connector while the auxiliary switch is on, the pump keeps running.
If I have another no fuel situation and the backup power doesn't save me from yet another tow, that tells me the sender and/or the pump is the issue. I really wish I could come up with a better way to chase this ghost, but at least this will isolate "the ghost".
Also, I cleaned both sides of the C313 connector on the body and used small needle nose pliers to tighten up the female pins. They were spread out a tiny bit.
Strange observation: I disconnected the fuel pump ground (G304, under the carpet near the driver's seat) and this did not prevent the fuel pump from running. If that's the fuel pump's ground, where is the fuel pump getting its ground from?
I went ahead and added auxiliary power to the fuel pump tapping into the power and ground wires on the sender AFTER the connector in front of the rear differential. The ground and power wire is routed with the stock wiring. Power comes from the extra battery terminals on the fuse box. Power is switched and fused. If I disconnect the C313 3-pin fuel pump connector while the auxiliary switch is on, the pump keeps running.
If I have another no fuel situation and the backup power doesn't save me from yet another tow, that tells me the sender and/or the pump is the issue. I really wish I could come up with a better way to chase this ghost, but at least this will isolate "the ghost".
Also, I cleaned both sides of the C313 connector on the body and used small needle nose pliers to tighten up the female pins. They were spread out a tiny bit.
Strange observation: I disconnected the fuel pump ground (G304, under the carpet near the driver's seat) and this did not prevent the fuel pump from running. If that's the fuel pump's ground, where is the fuel pump getting its ground from?
Last edited by backtothe80s; 08-12-2018 at 12:42 AM.
08-18-2018, 08:44 PM
#12
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Engine: 350-TPI
Transmission: 700-R4
Axle/Gears: 3.27 Posi
Re: Fuel pump circuit issues
Another update. Been driving the car for a few days and once again, it left me stranded. At least it was close to home for a change. My backup power past the C313 connector did not save me, so that jives with Drew's experience. Looks like I'm dropping the tank. Again. Oh well, I'm getting pretty good at it.
I still have my old sender and I can see several places where there could be electrical issues causing problems like the one I'm experiencing. I should have changed the sender when I changed the pump last month or at least closely inspected it. You know what they say about hindsight...
I still have my old sender and I can see several places where there could be electrical issues causing problems like the one I'm experiencing. I should have changed the sender when I changed the pump last month or at least closely inspected it. You know what they say about hindsight...
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