[Diy_efi] More 4.3L TBI Timing Issues.

[David Daniel]

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.

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?  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.  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?

This TBI swap has been nothing but a series of problems, even though I had
good running, complete donor car.  ECM problems from day 1, which is why I'm
running a S-10 ECM now.

SWAP PROJECT HISTORY:
I started with a great running, but wrecked, '85 Monte Carlo with the TBI
4.3 engine.  I DROVE it into the garage, stripped what was left of the front
clip off, removed the ECM, pushed the wiring harness through the firewall
and coiled it on top of the engine.  Carefully remove the rest of the ECM
harness from the dash harness, marking all of the circuit numbers and
positions in the plugs.  I remove the engine & tranny from the Monte and set
it aside until I finish stripping the Monte.  I DROVE the Malibu into the
garage and remove the ECM, pushing the wiring through the firewall and
coiling on top of the engine.  I remove the engine/tranny from the Malibu
and set it aside.  I install the T-5 onto the 4.3 and set it in place in the
Malibu.  I push the ECM wiring back through the firewall, plug in the Monte
ECM and make the few connections left over for the rest of the ECM harness
that used to be in the Monte's dash harness.  I modified the Malibu's fuel
system using the factory Monte carlo fuel lines, fuel pump, etc.  So far, so
good.  I turn on the ignition and hear the fuel pump whine as it should, so
I cranked it over.  It fired up right away, but the CEL is on steady now,
and I noticed that I had no "pump shot" when I blipped the throttle, which
causes a bog.  I try to pull the codes, but only get a code 12.  Something
is wrong...I check all of my grounds and connections, nothing wrong there.
At least nothing I can find. I try another TPS, hoping that that is the
problem.  No dice.  Just for giggles I plug in a ECM from an '87 S-10 with a
2.8L.  CEL light goes out once the engine fires, and I get a "pump shot"
when I blip the throttle. The engine runs, but the fuel/ignition maps are
way off, making the engine run lean and idle funny.  Now I'm thinking that I
fried the Monte's ECM somehow.  I order a reman ECM and swap over my PROM
and CALPAK.  Same problem...constant CEL, no pump shot, and cannot pull any
codes.  What are the odds that I bought an ECM with the same problem as
mine?  Slim, but I get it replaced under warranty anyway, and I also order
brand new AC Delco PROM and CALPAK chips.  Still no dice.  No "pump shot",
constant CEL, but cannot pull any codes.  Since the 2.8L ECM worked, except
the for fuel/ignition mapping, I borrowed an ECM from an '88 S-10 with a
4.3.  The car ran like a champ with this ECM.  I bought that ECM and
actually started driving the car about 2 months ago (I took about a year to
complete the engine swap, body work and paint, working on it only a couple
of hours on the weekends).  The current problems started about 2 weeks ago.
I started getting a little hesitation and stutter under light load and
steady throttle, and a little spark knock on acceleration. Things got worse
quickly until I had a dead cylinder.  I went ahead and replaced the cap,
rotor, wires and plugs.  The stutter almost went away, but It was at least
firing on all 6 now.  The stutter/hesitation under load got worse quickly,
so I checked the timing, which is where I was at the last post I made.  The
new ignition module makes the car run great, with no stutter or hesitation
at all, but I'm still getting lots of spark knock.  I can't seem to make it
go to base timing, so I can't check or set it.  This thing is driving me
nuts...I'm almost ready to pull the TBI and install my Q-jet intake, Q-jet,
and HEI to get rid of all of my computer controls.

Any help would be greatly appreciated.

Dave
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