85 t-type, Code 42

[Bogdansnotch]

I have a 85 t-type, im getting a code 42 on my scantool and would like to know more about what this could be? the car is misfiring pretty bad under full throttle. I am in the process of replacing the ignition control module and coil pack to the 86-87 style so I figure I need the conversion harness? any help would be greatly appreciated

 

[highboost]

give this a whirl.......
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
taken from here
http://www.gnttype.org/maint/malf.html#42

 

[novaderrik]

isn't code 42 the one that every pre OBD2 GM vehicle throws out when you check the codes? or is the TR setup different than every other GM product of the era in that regard?
it means that the ecm isn't seeing an rpm signal because the engine isn't running...

 

[Mike Horak]

I had a 42 when I first fired my 84. After re-inspection of wiring under the hood I discover the cam sensor wiring was shorting to ground. The short may not have been the cause but the noise I heard on the radio speakers (even with the radio turned off) indicated that it caused EMI noise. Fixed the mouse-chewed wiring and cleaned the grounding point on the engine and the problem seems to be fixed.

Now researching the 51 that I have. This is fun stuff.

 

[jckcolarusso]

try a new chip

 

[Bogdansnotch]

im converting the icm to 86-87 with the caspers adapter. im also going with a 86-87 ecm. I got the mat wiring and a new 86-87 gn maf. do I reuse my stock chip since the new ecm doesn't come with one and then go get a custom one done from caspers since I live 30mins away?

 

[highboost]

im converting the icm to 86-87 with the caspers adapter. im also going with a 86-87 ecm. I got the mat wiring and a new 86-87 gn maf. do I reuse my stock chip since the new ecm doesn't come with one and then go get a custom one done from caspers since I live 30mins away?

you will need a new chip for a 84/85 with 86/87 pcm.......

 

[Bogdansnotch]

So i replaced the ignition coil and ignition control module. Installed a new icm pigtail. Ran new lines to the ecm to d5 and b4. I am still getting this code 42. I tried a new chip, different ecm and factory icm and coils that where known to work perfect from caspers. I even ran ground wires to the icm hoping it would be that....Anyone have any other ideas i can try? My timing is way off because of this.

 

[Bogdansnotch]

another thing I want to mention is when the engine is running I am getting 12+volts from the D5 bypass wire. its suppose to be 4.56?

 

[Bogdansnotch]

anyone?

 

[Bogdansnotch]

anyone?

 

[Shawn N]

I would call or visit John at Caspers and go from there.

 

[Bogdansnotch]

I would call or visit John at Caspers and go from there.

I did, hes clueless. he swapped my ecm and icm with a known working one. still the same. checked my grounds last night also... replaced the cam sensor from a working gn also. even replaced the battery with an optima redtop

 

[Shawn N]

What kind of shape is the main engine harness in?

 

[Bogdansnotch]

looks like its fine...

 

[QWKRTNU]

Did u figure it out