[Diy_efi] More 4.3L TBI Timing Issues.

[David Allen]

>>  Running the engine with the diagnostic terminal grounded does not change
the timing, either.>

> Does the CEL light flash when the engine runs with this terminal grounded?

> Yes, it does.  It's not a steady flash, but I didn't pay close attention
to
> it.  Somehting like a long flash, long pause, two long flashes, long
pause,
> long flash, etc.  I can check again to make sure if it will help.

It's indicating when the o2 sensor is rich or lean.  On when above 450mV,
off below 450mV.  It should cycle slowly when you're in Closed Loop. It will
flash fast until the o2 sensor heats up.

> Thank you very much for this information.  This helps my understanding of
> this system greatly.  I knew it was somehow controlled by the ECM, but was
> not sure exactly how it worked.  I'm printing this out to look over while
> troubleshooting this monster.

Hope it helps you. Everyone else feel free to correct or add because I'm not
the most experienced here.

>
> >   The history you give is interesting.  Something strange is
> > going on in the
> > wiring. With the original ECM showing a code 12 that indicates it isn't
> > regestering that the engine is running.
> >   There are 2 orange wires in the harness at the ECM, one is memory
power,
> > the other is diagnostic data. I mixed those two up once. I don't
remember
> > the exact symptoms but it caused problems.
>
> I thought I had those mixed up when I fist made those final connections in
> the dash harness.  I double checked them once I saw the initial problems
> with the first ECM.  I'll check them again just to be sure.
>
> >   When you swapped transmissions, was there any wiring on the
> > orignal trans
> > that came from the Monte Carlo? What about any grounds on the old trans?
>
> There was only the 3rd gear indicator wire (ECM wiring shows 4th gear
> indicator, but the car was only a 3 speed auto), TCC lock-up wire, and
> possibly a ground wire, going to the tranny.  That plug is just tied above
> the tranny now, unused.  Speaking of transmissions and switches, what role
> does the Park/Neutral switch play in the operation of the ECM?  Since I
have
> a manual tranny now, the switch stays in "Park".  Should I move it so the
> ECM thinks it's in "Drive", or does it even matter?

Both my cars have no neutral/ drive switch connected to the ECM. Scan tool
shows it is always in "drive." Not sure about yours, but some ECM's
definately do alter the operation of the engine significantly in Neutral.  I
know a 3800 V6 will not operate the EGR in Neutral. But if the ECM thinks it
is in gear, you can hear the EGR valve buzzing (it is a 3-coil PWM setup)
whenever you rev the engine. (voice of experience - with a bad
transmission - in gear but not moving standing by engine with hood up)

>
> >   Have you connected a scan-tool to the ECM to see what the real-time
data
> > from the ALDL is showing?
>
> I have a copy of WinALDL, but the PC I have it on is experiencing
technical
> difficulties of its own.  Kinda hard to drive with a PC sitting on a
> portable workbench anyway.

That's what those 100 ft RS232 cables are for at Radio Shack!

> I ordered a lap top 'puter, which should be in
> soon.  It's first mission will be to run WinALDL and help me troubleshoot
> this car.  Unless of course I find the trouble before it gets here.

That laptop will be a valuable tool for sure. Don't forget about ROM
emulators and real-time tuning!

> Frustrating is a very light term for it...

Ok. How about "so massively infuriating they make a Preacher cuss on Easter
Sunday!"

> Just for grins, I plugged in the 2.8L ECM last night, too.  Exact same
> timing problems, in addition to the funny idle.
> BTW, when I was looking for the initial problem at the beginning of this
> swap, I looked at the pin-outs of the S-10 ECM and the Monte Carlo ECM.
The
> only difference that I can remember (besides things like the cannister
purge
> solenoid) was the ground circuits for the MAP and TPS.  They're switched.
> The S-10 grounds the  MAP on pin A-11 and the TPS on pin D-2 while the
Monte
> Carlo is just the opposite.  Both ground circuits are good...I checked
them
> at least twice.  That got me thinking...I wonder if the problem could be
in
> a circuit that the Monte has, but the S-10 does not use.  The wiring is
> still there, and could be shorting out into a circuit that the S-10 does
> use...  Something else to think about...

  Could be.  On my Century, I went from a metered-air ECM to a speed-density
setup.  Of course the MAF meter and MAP sensor would have to connect
differently.  After making that change the engine ran fine with the new
setup, BUT the A/C didn't work and the cooling fan didn't work.  Went to the
dealer and he printed out an ALLDATA wiring diagram for both ECM's.  The A/C
wire was swapped and moving that fixed the A/C, but the fan wire was in the
same place.  And it still doesn't work.
  Also, the idle speed was very high.  It was idling at the speed listed
under the lowest battery voltage in the table "idle speed vs. battery
voltage"  Scan data showed the correct voltage. I had to put the "correct"
idle speed in all positions in this table.  Really don't know what is going
on here.

> Thanks again for your help.  I'll post back with any results I get
tomorrow
> night.

Still I tend to think it is something simple to fix but easy to overlook!
Have any of your friends looked at it with you?  Sometimes another set of
eyes looking at the problem can notice something you'd overlook 10 times.
It's happened to me many a time!
David