Question:

I have a 1982 Corvette with what appears to be an ECM problem… but I’m not sure at this point.  I was diagnosing a “short circuit” problem and put everything back together (correctly, I think) and started the car to check everthing and it started fine.  After putting everthing “back” and restarting the car, it woudln’t.

Original problem seemed to be a short circuit in the parking light circuit of the Viper Alarm System (after market installation).  I removed the fuse from that circuit.  After that there was a 30 milliamp draw on the batter from the CLOCK/COURTESY circuit (this is OK).

Symptoms:  No fuel to throttle bodies (cross-fire injection) NO CHECK ENGINE light (at key on or any other time)
Cranks fine
Disconnecting ECM offers no change (which makes me think
it’s the ECM)
Check Engine Light bulb is GOOD
ECM Fuse is GOOD   (for the computer)
CRANK Fuse is GOOD (for the fuel pump)
INJ-1 Fuse is GOOD (for the throttle bodies)
INJ-2 Fuse is GOOD
Gauges Fuse is GOOD (fuse for Check Engine Light)

I’m stuck.  I have the Alldata CD, Haynes Manual, Chilton Manual, Owner’s manual, and a little know-how (a bad thing at times). Everything I see points to the ECM, but I’m just guessing. Since it wasn’t bad when I started….

Yeah, I could just get another computer, swap the PROM and see if that works, but that’s $100+ I don’t feel like spending on an unknown.

Any suggestions, solutions, or similar situations would be appreciated.  I’ll continue working on this problem until it’s solved (or winter arrives — at which point I won’t drive the darned thing anyway).

Thanks in advance (I never liked TIA, anyway)

Answer:

First, you’ll need a wiring diagram of your engine control harness… Check for +12 volts at the ECM terminals, and for ground. Depending on the particular ECM, you should have power on all of the +12 lines and probably on the battery backup line going to the ECM. Most of that generation of ECM used the battery backup line to the ECM as main power: the actual switched ignition line only provided a gate to turn on the internal voltage regulator inside the ECM. This often comes from a fusible link in the engine compartment. The wire colour for this is usually orange, and the switched one usually is a pink wire with a black stripe.

If you are getting power to the ECM and it’s grounded, you will get a two second or so prime of the fuel pump. The fuel pump prime is run by a hardware backup circuit, so it should happen no matter whether the ECM is running or not. But you do need all of the power to the ECM to get this to work.

Also, while you are working on those circuits, ensure you do not short +12 volts or ground to any of the terminals, or you’ll blow something up.

Related posts:

  1. Wiring Problem, 1969 Z28, help?
  2. No Power, No Juice (Ford F150) Help!
  3. Do you mind answering the dumbest automotive concepts of all time?
  4. 67 Mustang Wiring Problem
  5. Timing off?
  6. 65 temperature gage maxs out when ign on, what can I do about this?
  7. Need help with ECM trouble code