1989 2.8 code 42

[cleanz]

OK guys and gals, here we go.
Wifes 89z24 2.8 has poped up code 42 (est circuit). This car is about to drive me nuts with all the probs.
I have rebuilt the engine and trans, replaced all the sensors and control module and swaped out the ecu all within the last six moths or so.
I have used a snap-on scan tool to read the parameters and all looks good.(though I'm still learning)
I'm not one to ask for help, but this one has me stumped. I'm so pissed of with this thing that I can't even get my brain to diagnose it anymore.
We'd sell the car, but we have to much invested in it to try and recover.
Someone out there has had to have had this prob. at one time or another.
I have two mem cal's, but am unable to find my paper work to id them.
1) arda4848
I will have to dig the other out of the car in alittle while and post it.
I'm starting to think the ecu and mem cal are bad because the code is not set any more and car smells to be burning slightly rich, but shows good 14.7-1 air/fuel.
Any help is greatly appriciated.
Thanks in advance.

[SHOoff]

CODE 42

Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.

During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.

An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.

The conditions for setting this code are:

System in BYPASS mode but the ignition module is still controlling timing
- or -
Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.


Typical causes for this code include:

1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM


I bolded a few of those. I was guessing #6 personally. On the Gen II motor the ICM is located under one of the exhaust manifolds. Which is a really BAD location for it to be. Other than that, the age of the car may have ate up some of the wiring.