No voltage to fuel pump
 

Finally got the truck running. Drove it to get the exhaust on it yesterday and back home. Started it up this morning and got half way up the driveway and it dies. Tried to restart and it just turns over. I noticed that the fuel pump wasn't coming on when the keys was first turned on. I checked the fuse and it's good, I have 12V going to the relay, but only about 0.1-0.2V going to the pump while cranking. I swapped the relay with the A/C relay since it was the same and get the same results. Could the computer have crapped out on me? Is there anything else I can check to see if the ecm is bad?

Re: No voltage to fuel pump
 

I've yet to see a bad GM PCM. I know there out there but that's the last place I'd look.

Just check with a meter that the PCM is commanding the fuel pump on for prime at the initial "key on" for engine start. As long as the computer is putting out that 12v signal to the relay, the problem then lies somewhere in the other wiring you have for the fuel pump.

I typically use large wires for the fuel pump too, 10 guage. Fuel pumps hate low voltage. The relay is supplied the power in my truck and LS swapped Camaro directly from the battery. Make sure you relay has a nice connection and good wiring.

Good luck and let us know what you find.

Oh yeah, make sure the fuel pump is grounded well too!

Re: No voltage to fuel pump
 

Are you able to "jump" past the relay with 12VDC to see if the pump will run?

Re: No voltage to fuel pump
 

The fuel pump will run if I jump it to the battery. I only have the 12V main going to the relay. On the priming cycle and while cranking, I'm only getting 0.1-0.2V. This is on a new BP Automotive harness and fuse/relay box.

Re: No voltage to fuel pump
 

.1-.2v where? At the relay out going to the pump or the +12v signal from the computer?

If you know the pcm signal is good and the pump runs when jumped to the battery, your issue is somewhere in between, which means old fashioned electrical troubleshooting.

Re: No voltage to fuel pump
 

Put an external ground on the ECM as well just in case. Usually an ECM dies in one of two ways; COMPLETELY and drastically, or slowly and miserably. There are very few conditions in which an ECM can be damaged but still function normally otherwise. Grounding the case fixes the most common non-critical failure which is the internal ground dying. The next is the injector driver internally dying.

The less safety concious among us have just run the fuel pump trigger wire and relay off of the ignition switch instead of the ECM. Its best to have a rollover valve if you do that, but it does work.

Re: No voltage to fuel pump
 

12V to one leg, and 0.1-0.2V to the other three while cranking and prime cycle.

I'll Try the ground to the PCM and see if anything changes.

Re: No voltage to fuel pump
 

Grounding the PCM changed nothing.

I pulled a plug wire and tried my spark tester and no spark. Tried another and same thing, no spark.

Re: No voltage to fuel pump
 

Check ALL your harness grounds and make sure they are clean and tight. Bad grounds are a typical problem on some swaps.

Re: No voltage to fuel pump
 

Ok , I am just thinking out loud . No spark may say that your pcm is not getting power . The no fuel pump may just be a symptom of that . Your motor will still turn over but will not crank ( you should still have spark if fuel pump problems ) . If you are a drive by wire is the throttle body doing its test ( quick close and open ) .

At this point I would check your pcm main power supply and fuses to see if the pcm is for sure getting power .

Just a note , I believe the pcm provides ground signal to the fuel pump relay , not 12v .

I agree with Heavymet . Chances of the pcm being bad is slim .

Re: No voltage to fuel pump
 

I'll go over the grounds again when I get back from the local car show later today. I was trying to get it ready to make this show.

Re: No voltage to fuel pump
 

Yes, the TB is doing its thing. And I believe your correct on the ground signal after watching a video on YouTube.

Re: No voltage to fuel pump
 

PCM supplies 12v to the fuel pump relay.

Re: No voltage to fuel pump
 

Well, it ends up the ECM was toast. After a couple of days of going through everything and everything checking out good, We got another ECM and hooked it up and it fired right up, till the VATS killed it. Got everything reprogrammed so it will start and run again, just need to go back and have a full tune done.

Re: No voltage to fuel pump
 

Thats maybe only the 3rd ECM I've seen be the root cause, so you really got luck of the draw. 99% of the time when people think the ECM is dead, another problem is to blame...but it seems like you actually hit the 1% :lol: