Fuel Delivery Problem

[RGoessl]

Hey All,

I have a 2004 Chevy Aveo, engine won't start because it has no fuel. Checked the fuel rail bleeder and there's no pressure. I checked the fuse and the relay in the fuse box by the battery - both fine. Manually bridging the relay will turn the fuel pump on and I was able to start the car like this. For whatever reason, it seems like the relay is not getting a signal to open up.

Any thoughts on where to go from here? I wasn't able to find any wiring diagram for this so I don't know what is triggering the relay. Can I drive the car with the relay manually bridged for now?

Thanks.

[avguy]

You can diagnose at the FP replay as follows. Pin #85 should have constant ground. Pin #30 should have constant B+. Pin #86 should get voltage from the ECM with the key at ON or RUN. You could run with a suitable gauge jumper, which is properly fused.

[RGoessl]

Here's what I found:

30 always has 12V
87 is grounded
86 gets 9V in ON, 12V when running
85 is ~0.2V

Seems fine

Jumping 30 to 87 (bypassing relay) car runs perfect.

Putting the relay in, car is able to start with residual gas but immediately sputters and dies. Everything here points to the relay being the issue but I've tested the individual relay - sounds like it's working when I put 12V across 85-86. I've tried swapping it with the headlight relay (headlights work fine), same issue. Same results with other relays. I've tried flipping the relay around, doesn't seem to matter.

I'm completely lost here. Every test says the car should be working fine but when I put it all together, it doesn't...

[RGoessl]

86-85 gives ~8V
86 to battery -ve gives 12v

Maybe a ground issue. Odd that only this relay seems to be affected though.

[avguy]

Your first reply said 87 is grounded and that's not what it should have. 85 is the control ground, and when you put the probes of your multimeter from 85 to the positive battery terminal, your meter should read 12V (or whatever your B+ currently is). If you don't get that result, then yes that ground has a problem - probably at the body grounding point.

[RGoessl]

Thanks, I will test that.
Took me a while to find the schematic, here it is for future reference:

[RGoessl]

Thanks avguy.

85 was only giving 0.5V to the battery +ve. Definitely a bad ground there. Grounds are fine in the other relay sockets so I'll have to open up the fuse box and see what's wrong.

Here's a pic with the pins labelled for anyone doing this:

[WyrTwister]

All the relays I have had to mess with on a car , have been $ 10 - $ 20 . Buy a new one . If that does not fix it , you can save one for a spare .

Make sure fuse EF 10 is good and plugged in properly . I think you should have 12 VDC between pins 85 & 86 .when you turn the key on .

If the fuse block is bad , might find one at a salvage yard .

If a fuse block is not available , you may have to trace down the 4 wires going to the relay and splice in an external relay .

Wyr
God bless

[RGoessl]

To fix this, I ended up running a new ground directly from the negative terminal of the battery, into the fuse box and spliced into the wire coming from pin 85 of the relay. Worked perfectly ever since.

[avguy]

Good work! I've done similar repairs on other vehicles, which lasted until they rusted their way into the bone yard. I'm sure your fix will keep working right up to the day that it's no longer on the road.