ECU turn on issue

[NateCrisman]

Ok guys, I have a "customer" car at my garage that I'm trying to diagnose. It stopped running on him, he's only had the car for a couple weeks and it was 100% stock and unmolested until he got it.

He trailered it to me, I cannot seem to get the ecu to turn on. It was running/driving and quit unexpectedly. The datalogger will not connect and the MPI relay does not click. Obviously then we have no spark and no fuel pump activity. The MPI fuse under the hood and the ecu fuse under the dash are both good. Iv swapped ecu with my car with no change. Same with the MPI relay. The car has no AFC and the ecu harness has not been touched around the ecu, all the wires look clean. Under the hood the wiring is all clean and untouched.

Any advise on the next thing to check. Anything in the ignition switch that could cause the issue?

 

[prove_it]

Check the grounds, could be loose or damaged. Other than that there is an ignition switch 12+ power supply to the ecm, check to be sure there is 12+. Without that signal the ecm wont turn on.

 

[toybreaker]

Nate, you can do some quick checks at the mpi relay to narrow things down.

Using a voltmeter, check the black/red wire for power, it should be hot 24/7.

Turn the key to the on position, and there should be power on the black/white wire at terminal 3 of the relay.

[Edit] You can also look at the ignition switch harness to be sure there isn't a "t harness" other bodgification there from an alarm/turbo timer/gauge system.

 

[Hertz]

I hope it didn't cook your ECU if there is a short at the ISC.

 

[NateCrisman]

God, I hope not. Last thing I need is #139 going down in the process of trying to help another guy out.

 

[NateCrisman]

Im going over to the garage today, Ill check all the pins for battery 12V, ground, and switched power and see what I come up with (mpi relay as well as ecu small plug)

 

[NateCrisman]

Quoting toybreaker:
Nate, you can do some quick checks at the mpi relay to narrow things down.

Using a voltmeter, check the black/red wire for power, it should be hot 24/7.

Turn the key to the on position, and there should be power on the black/white wire at terminal 3 of the relay.

[Edit] You can also look at the ignition switch harness to be sure there isn't a "t harness" other bodgification there from an alarm/turbo timer/gauge system.

At the relay plug: nothing has battery power with key off, that's the problem.

Black/white wire on top/middle. Pin 3 has switched power. Two relay wires have constant ground. Both black pins 2 and 6

the black/red is pin 10 that is missing 12v battery power. What's that go to?

 

[NateCrisman]

Got the car to run. The black/red wire at mpi relay goes to the plug on pass frame rail under maf position along side fuse box. Had no power there. Had power under mpi fuse but none on other side. Ends up there was bad connvtiion under fuse

 

[gtluke]

Probably the result of installing a GM MAF /ubbthreads/images/graemlins/smile.gif

 

[NateCrisman]

the car has a 2g maf with a "plug in" harness adapter. But he did put the battery in the trunk and maybe the wire going into the fuse box was pulled?

 

[Hertz]

f- it. part it out. /ubbthreads/images/graemlins/devil.gif