1987 350 TBI code 42

[Fleetwood]

I have owned my 87 chevy for over 2 years and I have had a code 42 for most of that time. From what I know this means that the ecm is not talking to the spark module on the distributor? I have just run my truck with this code forever because it has always run fine. Now I am having issues and I want to rule this out. What should I do

 

[Vbb199]

Code 42 is a hard one to diagnose. Being someone who messed with tbi stuff a bit, im willing to bet a lil money its your module in the dizzy, or the coil is fading.

 

[gmbellew]

hard to imagine its running well with code 42 set. this should help diagnose. if it isn't the ignition control module and the EST wire is plugged in, I'd expect to have to carefully evaluate the ICM and coil connectors and wires to look for the issue.

a quick check on the EST wire would be to unplug it with the truck running like you would to set base timing. the idle should noticeably change as the spark advance will be knocked down to base timing. if idle doesn't change, there are problems somewhere. turn the truck off before you plug it back in.

 

[Fleetwood]

Snooped around and found out that my EST wire was cut and poorly reconnected at some point. Soldered it back together and no more code.

 

[gmbellew]

Snooped around and found out that my EST wire was cut and poorly reconnected at some point. Soldered it back together and no more code.

I love an easy fix!

 

[Fleetwood]

hard to imagine its running well with code 42 set. this should help diagnose. if it isn't the ignition control module and the EST wire is plugged in, I'd expect to have to carefully evaluate the ICM and coil connectors and wires to look for the issue.

a quick check on the EST wire would be to unplug it with the truck running like you would to set base timing. the idle should noticeably change as the spark advance will be knocked down to base timing. if idle doesn't change, there are problems somewhere. turn the truck off before you plug it back in.

Where did you get this manual that you sent me a screenshot of?

 

[gmbellew]

Where did you get this manual that you sent me a screenshot of?

in the reference library of this site. it was the drivability and emissions manual, or really the TBI user manual. there are also repair and service manuals and also owners manuals and wiring manuals by year. they are .pdf and word searchable. an invaluable reference for free!