Apex no fuel pump- no ground from ECU

[madhatter275]

Help! I'm at the end of the rope, ready to take it to a shop but want to pick your brains first.

No fuel pump
Can jump relay to get fuel pump to engage and sled fires up. 12v at the relay, no ground from ECU.
Traced blue/red wire to ecu, shows continuity, sometimes has 12v.
Jumped from ECU to relay, still nothing.
Checked starter relay power block, seems to be powered
All ground blocks in harness test good

Bad ECU? I have another apex I can steal one from but would rather not take it all apart.

 

[pdiddy]

All ground blocks in harness test good

If there are multiple wires going into a ground harness you need to check continuity to ground on each wire. You'll find that bugger!

 

[Srxspec]

Run a ground wire from the pump to the chassis & see if it fixes it.

 

[RobX-1]

All ground blocks in harness test good

Just throwing this out there in case you might have overlooked some ground blocks. On my 08 Apex, I found a total of 6 square grounding blocks and two flat grounding blocks. Of those square blocks, two are the ones above the primary clutch but there are three more further down the wire harness that goes into the nose and near the ECU. There was also one on the passenger side near the fuse box. There was also a flat ground block with the two blocks above the primary and another one with the three further down in the nose.

 

[Mooseman]

Check the main ground wire from the battery. It has a spade connector that can corrode.

 

[madhatter275]

Run a ground wire from the pump to the chassis & see if it fixes it.

I can jump it at the relay and the pump fires up. I can jump the switch side and the relay click and it fires up. So my problem is somewhere upstream, either a bad ground somewhere or the ecu itself I think. Thanks though.

I've announced a bounty system now. Anyone who nails what's wrong or comes up with the right fix, I'll send $40.

 

[madhatter275]

Just throwing this out there in case you might have overlooked some ground blocks. On my 08 Apex, I found a total of 6 square grounding blocks and two flat grounding blocks. Of those square blocks, two are the ones above the primary clutch but there are three more further down the wire harness that goes into the nose and near the ECU. There was also one on the passenger side near the fuse box. There was also a flat ground block with the two blocks above the primary and another one with the three further down in the nose.

Lol, I've found 3 of them. Damnit.

 

[earthling]

I can jump it at the relay and the pump fires up. I can jump the switch side and the relay click and it fires up. So my problem is somewhere upstream, either a bad ground somewhere or the ecu itself I think. Thanks though.

I've announced a bounty system now. Anyone who nails what's wrong or comes up with the right fix, I'll send $40.

Have you swapped the fuel injector relay out?

 

[74Nitro]

Isn't there any codes showing on the dash?

 

[madhatter275]

13-15-22 and 43 was on there previously but it's probably too packed with fun to show it now.

 

[madhatter275]

13-15-22 and 43 was on there previously but it's probably too packed with fun to show it now.

But these might be from turning on the key with the ecu unplugged. 43 was the one that was on the whole time.

 

[earthling]

43 is "ECU was unable to monitor battery circuit' - open circuit to ECU
Have you tried just grounding (not jumping) the fuel injector relay? The R/W wires that feed the ECU are the same as the ones that feed the powered side of the relay coil so all that is missing is the ground from the ECU (your title) which you can just try there. Probably even with the ECU out.

 

[madhatter275]

43 is "ECU was unable to monitor battery circuit' - open circuit to ECU
Have you tried just grounding (not jumping) the fuel injector relay? The R/W wires that feed the ECU are the same as the ones that feed the powered side of the relay coil so all that is missing is the ground from the ECU (your title) which you can just try there. Probably even with the ECU out.

Yeah, and that fires up the relay and the fuel pump. But jumping the B/R with R/W doesn't get me anything because I have nothing coming from the ECU. There is an aftermarket LED light strips kit on it that I'm going to take off. The previous owner put it on and it works, but at this point I'm running out of ideas. I don't want to put in a test ECU from my other Apex b/c I don't want it get fried to?

I've never gotten a ground coming on the B/R wire from the ECU and that is supposed to be a switched ground? Right? Sometimes I get a voltage on it. Or I have no idea what I'm doing. That's a possibility.

 

[earthling]

The ECU wire to the relay (to provide ground) should be blue/red (Y/R)

The ECU is complaining that it has no reference voltage. I would suspect that is the core of your problem. Not sure where it comes from as the ECU sees R/W as the voltage source on two pins (they are tied together). The ECU also has a common ground which goes to one of the ground blocks. I think you have a bad ground block. With no good ground there is no good reference voltage. Look for Black on the ECU wiring and test that to the various grounding points.

 

[madhatter275]

The ECU wire to the relay (to provide ground) should be blue/red (Y/R)

The ECU is complaining that it has no reference voltage. I would suspect that is the core of your problem. Not sure where it comes from as the ECU sees R/W as the voltage source on two pins (they are tied together). The ECU also has a common ground which goes to one of the ground blocks. I think you have a bad ground block. With no good ground there is no good reference voltage. Look for Black on the ECU wiring and test that to the various grounding points.

I checked the black and brown, but apparently there is another ground block under the coolant res. I've probed every black and brown I've seen and confirmed ground. I'll keep looking.