Help! No Start: '88 GM 2.8L MPI V-6

[steve ravet]

Ferrill, Jess B wrote:
> Connecting an LED indicator across the injectors showed no flashes while
> attempting start. Injectors were getting 12 volts power from ignition
> key switch, but the ECM was not providing the pulses to ground through
> its' internal injector driver.  "Oh this will be easy" says the
> confident father!  "Looks like a bad injector driver in the ECM!"
> (Impress daughter with the technical talk, right?)  (P4 ECM #1227727
> upgraded with speed density, has ASWH MEM-CAL).  Plunked down $80 to
> replace ECM with remanufactured unit.  Checked all solenoids for
> resistance (All above 20 ohms).  MEM-CAL transferred from old ECM.  All
> ECM and MEM-CAL connector contacts cleaned; no corrosion or
> discoloration.  MEM-CAL chips seated ok.
> 
> But all symptoms were exactly the same with the "new"  ECM:  Injectors
> not being pulsed, only "12" trouble code. Not the ECM?  Plugged and
> unplugged all the sensors.  Checked most sensors from the ECM
> connectors, everything looks ok.  All fuses have been pulled, checked
> and cleaned. Most but not all connectors have been unplugged, examined
> for corrosion and replugged.  Both banks (1,3,5 & 2,4,6) have the same
> problem.  The injectors are 12 ohms, and I see the expected 4 ohms
> across each bank of three in parallel.

Sounds like a ground problem.  The first thing to do is get the factory
service manual.  It will show exactly what should be grounded, and
where, including splices in the wire harness.

Did you check to see if battery voltage is present at the ECM?

The circuit should be something like:

battery-----fuse----injector-----ECM(injector driver)-----ground
                             (1)                      (2)

If you have a break between the injector and the ECM (1) you would see
the described behavior.  So check at the ECM where the injector driver
wire is, and see if you have battery voltage (actually pulsed battery
voltage).  A bad wire between the ECM and ground (2) might be similar,
but lots more things would be missing a ground, and I wouldn't think you
would even be able to get the check engine light to come on.  but check
it anyway.

> I can disconnect most sensors and the gray and black mini-harness
> connectors and it still shows only "12" trouble codes.  Is this normal
> if the engine can't be run?

I don't think trouble codes are stored until the engine starts.  I had a
MAP sensor come disconnected and it would crank and crank but not fire
up.  No codes were stored until I actually got it to start.  Then the
check engine light came on and I got the MAF code.

--steve