Alright so here's my delima I've done countless hours of research and can't find a definitive answer. I've got a Ls swap with a 4th gen fuel tank and I'm trying to wire up the fuel pump but there's no response when I turn the key switch i disconnected the relay and tried testing the voltage from the PCM wire on pin R9 and I'm not getting any voltage from it and I'm also not getting any voltage from the fuel pump wire on the c100 connector either can anyone help me out? I have no idea what's wrong here

 

 

I dont know if this will help you out any. https://www.thirdgen.org/forums/ltx-...formation.html . But maybe the diagram for the fuel pump wiring at the bottom of the 1st post can help you out some.

 

I modified the harness using pockets guide and also the car is a 1992 Z28

 

that's exactly how everythiing is wired on there which led me to troubleshoot that there's no voltage coming out of pin R9

 

Are you using the factory relays, or the smaller aftermarket ones? Maybe a bad relay, or worst case scenario the pump driver in the ecm is bad?

 

smaller aftermarket square ones I have 4 of them off hand and I couldn't get anything flowing on either one

 

Im not familiar with using the ls1 tank, so i dont know if any wiring from modifying that could cause an issue. Are you able to verify if vats is disabled in the ecm via hptuners or efi live?

 

as far as the ECM goes I had it sent to wait4me performance to get the vats removed and mail order tune

 

Check to make sure you have proper constant 12V and switched 12V to the ECM. I have a feeling the ECM isn't even live yet.

 

where would I check for that? I may have missed a step then

 

Well that's the whole mystery now isn't it? You're just going to have to backtrack all your power distribution to find potential problem

 

alright so I have em power connected to the c207 and it's getting power it might be a faulty PCM at this point so I'm taking it all off and sending it to wait4me and have him rebuild it for me because I don't wanna mess with this harness anymore I'll just finish everything else up on the swap thanks for the help guys

 

Edit, I remembered incorrectly

 

I question whether you were thorough enough with your wiring investigation. Here are the LS1 ECM pinouts.

https://www.ls2.com/boggs/torques/00pinpcm.htm

I don't have a stock ECM but I would guess that if the the constant and switched 12V connections aren't made then the ECM isn't going to work.

Constant 12V are,
Blue 20
Blue 57

Switched 12V are,
Blue 19

Grounds are,
Blue 1
Blue 40
Red 1
Red 40

 

For what its worth,

Eight years ago I had a 411 PCM that would not give 12v on R9. Pocket and I went over everything we could think and couldn't find an answer, chocked it up as the tune having an issue and had no way to check that. I ended up moving my R9 (fuel pump) wiring to a constant on a toggle switch and the whole car ran and drove no problems for years.

Here is where it baffles me. Last year I went in to add some wiring for Vintage Air and for giggles (and after one to many jump starts from leaving the toggle switch on) I probed R9 and low and behold 12v. Got rid of the toggle and hasn't given me any trouble since.

For testing remove the R9 and feed the pump side 12v and see if it fires, if not problems elsewhere.

 

The ECM probably has an internal diagnostic where the driver shuts off if it thinks the circuit is shorted to ground. It can be fooled in to thinking there is a short if your wiring isn't set up correctly, or your relay has an in-rush current that exceeds the ECM driver max current rating. You might have changed the circuit enough with round #2 such that the diagnostic went away and the driver stayed on. I'm not talking about OBD II diagnostics that you see with your tuning software, I'm talking about the ECM diagnosing it's own circuits and protecting itself from damage.