well I was trying to wire a switch into my fan so I can turn it on at will and knew I needed to ground the green wire with a white stripe at the fan control relay. Problem is I was an idiot and grounded the green with white stripe wire on the FUEL PUMP relay instead. According to my Haynes this wire goes straight to the ECM. I took the ground off, but now I am getting a SES code 54. what I am looking for are what voltaages should I be getting from the Green with white strope wire at that relay? Cause Im not gettig anything now. I replaced the oil pressure switch and that solved my die at idle issue, but I still have no voltage on this wire and still get SES 54.

any ideas? A new ECM is 89 bucks at the local AutoZone, so I might have to do that, but I was hoping maybe you guys could shed some light and maybe help me save 90 bucks.

 

Teh fuel pup relay is driven by one of the quad drivers. They are TTL level switches which don't respond well to direct grounding.

You may be lucky, and the sensing circuitry which monitors the outputs shut down the driver transistor before it fried. Try disconnecting power from the ECM for about ten minutes, then reconnecting power and try it again. If the same code repeats, you may be looking at a new ECM.

 

yea, thats the first thing I tried. Un plugged the battery for about 30 mins but no such luck. Still got 54.

 

Unfortunately, shorting that line to ground fries the output transister. The oil pressure backup switch will allow the engine to run. Longer crank time, but it works.

If you have a soldering iron and can get a 2N2907 transistor, it is Q6. The stock one is the tall TO92 plastic style cases. The 2N2907 being a metal case. It too will fry if shorted, it is just a drop in replacement.

RBob.

{edit: I'm adding this in as the P4 ECMs such as used in the '90-'92 port injected setups (TPI & MPFI) and the '86-89 MAF use a different relay driver. It is supposed to be protected against short circuits. Haven't tested that feature (yet), so don't know if it truely works or not.

It is the C3 ECMs such as the TBI and '85 - '89 MPFI (and '85 MAF??) setups that use the simple output transistor.}

 

I wouldn't advise "testing" that feature, either. All the C3 ECMs and CCC units I've had open ('156, '869, etc.) have the discrete transistors for outputs. I usually find the MOVs that have been "stressed", too.