[Diy_efi] More 4.3L TBI Timing Issues.

[David Allen]

> First, a quick run-down on the vehicle...
> '81 Malibu running a '85 Monte Carlo TBI 4.3 V-6, T-5 5-speed, and an '88
> S-10 4.3L ECM.
>
> I replaced the ignition module, which took care of the
stuttering/sputtering
> problem.  I'm still having some timing issues, though.  The car has lots
of
> spark-knock, even under light acceleration, and the ignition advance still
> seems to be "all or nothing".  The engine revs smoothly, which is
> surprising.

Okay. Interesting

> When I disconnect the connector to set the base timing, the engine RPM and
> timing do not change, and the CEL does not come on.  Unplugging that
should
> set a code 42, right?

It should set a code;  UNLESS this has been disabled in the .bin
calibration.

> Unplugging the ESC module sets a code 43 after about
> 5 seconds.  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?

> Could the ESC module be causing this
> problem?  If it could be, how can I test it before I drop $70 on a
> replacement?  I would also assume that I would get an ESC module to match
> the ECM, right?

  ESC could cause retarded timing, but I think there is an underlying issue
in the ignition system and ECM wiring.  The ignition system has 2 modes of
operation, one is controlled by the ECM and the other is not.
  When the engine is first started, the ignition module fires all by its
self, with no timing information from the ECM. It is just firing when the
trigger wheel teeth pass by each other; or at a fixed advance under high
revs.
  The second mode is when the ignition module tells the ECM when the trigger
wheel teeth pass each other, then waits for a signal to be returned from the
ECM to fire.
  The 2 modes are selected by the "bypass" wire between the ignition module
and ECM. If this wire is disconnected or grounded out the ignition system
will be stuck in the startup mode with no ECM control.  What is strange is,
the ECM looks to make sure this circuit is connected and sets a code if it
is not.
  If there is a broken wire that is also shorted out to another wire it
could give the ECM a signal making it beleive the ignition bypass is working
when in fact it is not reaching the module.
  The ignition control signals are 5 volt and the distributor module has a
ground reference wire (ref low) between the ECM and dist. Any bad grounds or
stray signals could wreak havoc on it.
  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.
  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?
  How is the car's body ground?
  Wiring problems can be hard to diagnose.  I had a problem with the TPS on
my Century.  It would run HORRIBLY rich and set codes, intermittently.  Got
worse and worse.  Finally figure it out when I could rock the engine by hand
(in park) and make it die. The harness had a bad area from bending/ rubbing.
The tape I had wrapped it in hadharneded and then cracked. This one cracked
area bent easily and the wires fatigued. It had run great for 2 years before
this showed up.
  Have you tested the 4 ignition module wires between the ECM and module for
shorts, opens, and resistance?  Something should certainly change when the
set timing connector is unplugged. Unplug the ECM and 4-wire connector at
the module.  Measure resistance between all of the 4 wires; each of the 4
wires and ground; and each of the 4 wires and the other wires in the ECM
harness at the ECM plug. There sould be no continuity.
  Now ohm out each wire from the module connector to its corresponding pin
at the ECM connector. Each should have a good solid connection.
  Have you connected a scan-tool to the ECM to see what the real-time data
from the ALDL is showing?
  Good luck! I know these problems can be frustrating!
David