Blowing ECM Fuse??

[benmorgan82]

Ok so I parked my truck that has 87 GN engine in it and 2 weeks later go to start it. I hear the fuel pump run crank it and it starts for 2 seconds then dies. Crank Crank Crank no start. I look at FP guage and down to 10 psi and I just installed a walbro pump so I figure its good.

So I start checking fuses and find ECM fuse blow. I change it turn on key hear fuel pump run, crank it and then the same thing happens again.

Any ideas on where I should start? Common problems?

Thanks

 

[mikestertwo]

That fuse also powers the ESC module, the CCCI module (ignition module), and the MAF. Does the fuse blow by turning the key on without starting the motor?

 

[benmorgan82]

no its after i crank it and it starts very momentarely

 

[mikestertwo]

Possible problem with the ignition module?

 

[GNVenom]

Similar to this problem:

http://www.installationinstructions.com/FYI/ccci-failure.pdf

In this case, it's the CCCI fuse that blows shortly after starting, but similar to what you are seeing.

Try disconnecting the MAF sensor and start the car. It will run terrible, but keep your foot on the gas.

Then try disconnecting the ESC module. SES light will come on, and car won't accelerate normally, but you are trying to isolate the problem.

 

[GNX026]

check the injector harness at the EGR valve they are prone to rub through and shorting. sounds like this may be the issue.

Fred

 

[GNVenom]

check the injector harness at the EGR valve they are prone to rub through and shorting. sounds like this may be the issue.

Fred

Actually that's a different fuse - FP/INJ fuse. When that goes, it prevents the injectors and the fuel pump relay from getting power. As a sidenote, the oil pressure switch connector, which most of us have eliminated and gone with a different sender, tends to hit the header and melt - resulting in that FP/INJ fuse blowing. But I digress...

The ECM/IGN fuse only powers the ECM, ESC, CCCI Module (terminal P), and the Mass Airflow feed.

You can isolate the ESC module and the MAF, and still enable startup, so that will get you halfway there.

 

[benmorgan82]

Ok when the fuse pops the SES light no longer works and the fuel pump no longer works. tried disconnecting MAF no change runs for 2 seconds then dies.

 

[benmorgan82]

well went and did some testing and found out when I unplug oil pressure switch the fuse quits popping. so i guess it has a shorted switch.

 

[Quick6'n'-K.C.]

Wow, guess you found the problem.

Might find a book on it, but i thought the oil pressure was tied into the idiot light and nothing to do with the ecm?

BW

 

[Quick6'n'-K.C.]

the factory oil pressure switch completes the circuit to the fuel pump when the oil pressure rises above 4# as a back up in case the factory fuel pressure relay fails. Normally, the ecm signals the relay to start the pump and run it for about two seconds when the key is switched to "Run", then it cuts off if the engine is not started. If the relay fails, there would be no fuel delivery from the pump unless there was a back up circuit. This is the second function of the oil pressure switch. Even if the relay fails and one cranks the engine, the fuel pump will be turned on when the oil pressure reaches 4 psi during cranking. One of the signs of a factory relay failure is delayed engine start when the engine is cranked as it gets no fuel until oil pressure is above 4 psi.


You need to check and see if your hotwire for your fuel pump is not grounding out and causing issues with your factory fuel pump relay

BW

 

[GNVenom]

The oil pressure switch has a pink/black wire, but has nothing to do with the IGN/ECM fuse. It's wired to the FP/INJ fuse.

That is, unless someone did some re-wiring.

 

[benmorgan82]

yeah when i got my wiring diagram out it got me to thinking.... like i said in the original this is my truck with a gn engine in it.... when i saw on the fuse panel that the blown fuse was ECM i thought it had to be in that circuit... i forgot that it was the original s10 panel adapted for the gn engine and harness... turns out that fuse is the FP/INJ fuse... sorry for the confusion... I think I will make me a new panel cover telling which fuse is which for the GN engine

 

[Slokat]

If unplugging the maf allows the car to start with out blowing the fuse but having it plugged in does not. is the culprit that I need a new maf sensor?