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

[swagaero]

Ferrill, Jess B wrote:
> 
> I hope I am not misusing the DIY_ EFI with a mundane service problem on
> a totally stock car, but it's got me stumped :<(.  Thanks for your
> patience and help.
> 
> My daughter's 1988 Oldsmobile Cutlass Supreme 2 dr.(same as Chev Lumina,
> Buick Regal, Pontiac Gran Prix) with 2.8 L V-6 Multi-Port Injection
> (Auto Trans & FrtWD) would not start after sitting several days.
> Battery was low ("click, click" she said describing solenoid sound).
> Engine would still not fire after attempting jump start and re-charging
> battery.  Fuel pump, filter and system was priming and ok; see 40 psi at
> the fuel rail, pressure regulator works ok dropping 5 - 10 psi when
> vacuum is applied.  Spark is good and healthy, jumps 0.100" gap easily
> and regularly. Car ran well before no start problem, except for
> occasional stall when first started from cold, has 109K miles.
> 
> Car will run for a second if the ignition is turned on to run fuel pump
> and pressurize fuel rail, then pulse injectors with 12 volts, then
> attempt start. Grounding "A" to "B" on ALDL to check for ECM trouble
> codes yielded only the usual "12" s. (Indicating ECM is in Diagnostic
> mode), but no other codes.
> 
> 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.
> 
> Grounds look ok, except possibly sensor (EGR, MAT, MAP, Coolant Temp,
> TPS) grounds (looking at C5 & C10 in harness) are not grounded to engine
> (which one Chilton Diagnostic Chart for EGR, Code 32, says should be
> grounded to engine, but Haynes and the rest of the Chilton charts do not
> show grounded).  Looking from EGR terminal "C" back towards ECM
> connector harness I see a solid ground to engine (the questionable
> ground?) but open to C5/C10 harness terminals (all the charts say this
> should show continuity).  The rest of the sensors (MAP, MAT, etc.) have
> correct continuity back to C5/C10.  This thing is a bear to work on for
> access so it is difficult to trace and open the harness covers to check
> for opens/damage or confirm the C5/C10 ground.
> 
> 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?
> 
> Summary:  After sitting with low battery and jump start/recharge,
> injectors are not getting pulsed, 12 volts is present to injectors, ECM
> has been replaced.  Car will run briefly if injectors are operated with
> separate 12 volts.  There may be a problem with sensor grounds.
> 
> My questions for the group:
> 
> 1)  Any ideas?
> 
> 2)  When a GM P4 ECM car will not run, can the ECM set any trouble
> codes?  (I tried turning on ignition for 15 seconds and cranking for 15
> seconds more which was supposed to set codes on some early GM ECMs, but
> still get only "12"s).
> 
> 3)   What are the minimum sensor inputs required to the ECM to make it
> provide the ground pulses for the injectors?
> 
> 4)  Can the MEM-CAL (which was not replaced, only transferred from the
> old ECM) cause this problem and still have the ECM show "12" codes?
> 
> 5)   The question as to whether C5/C10 should be grounded to the engine
> is still unanswered  and is where I am concentrating my efforts.  If the
> analog type EGR doesn't get a ground for its pintle position sensor will
> this prevent the injectors from being fired?  If the C5/C10 sensor
> ground is not grounded to the engine will this prevent the injectors
> from firing?  (I don't want to just ground C5/C10 and try it until I am
> sure that this is not supposed to be a floating or instrument ground).
> I don't want to spend too much time in this area if it can't cause
> problem.
> 
> Thanks everyone for your help,  I will post the solution when I find it.
> 
> Britt Ferrill
> bferrill at amp.com
> 910+727-5387


check the crank ref signal from ignition back to ecm no signal no
injector pulse.

Steve Parkman
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