Code 42

[SoCalSlaughter]

Ive been fighting this with my truck since 2008. The truck just recently passed CA smog. Its a 1990 Chevy Suburban V2500 5.7 - TH400. While driving, the engine will have a whistle sound like it has a turbo, when I let my foot off the gas, the whistle will get louder. If I sit at a stop light for to long, the truck will either surge and kick the rpms up, or it will bog and throw code 42 (Spark controller). Shut the truck off, and back on and the light is off. Also, randomly while im dirving the check engine light will come on and go off. I checked the code and its code 13 (O2 sensor). Ive replaced it many times, followed the single wire all the way back to the ecm. I cannot figure out whats going on here. The truck at times, at a light will surge and then die. But always start back up. Ive replaced dizy cab, rotor, distributor, 3 IAC motors, 4 ICM, EGR, ECM, 4 O2 sensors, water temp sensor, fuel pump, fuel filter, spark plugs, wires. Ive added more grounds to the body and engine from the battery and still doesnt help. Sometimes the truck will drive fine for an hour, sometimes I worry if it will make it home. Help me!!! haha

[panhandler62]

Check the knock sensor and crank sensor. Either can cause that sort of symptom and might be setting the wrong code.

[gmachinz]

Have you checked the electronic spark control module? You may need to replace it if the knock sensor doesn't have an effect. Also, check the wiring inside the distributor housing for the control module...I've seen where a pinched wire can cause either a stall or no start condition in a 4.3...I suppose it could be going on with yours as well.

[SoCalSlaughter]

Well the truck doesnt have a crank angle sensor. The knock sensor I havent really messed with. Someone told me it could be the wiring from the control module to the ecu, but Ive checked it and checked it. The main concern is the IAC making that whistle and the engine rpm kicking up or dropping down. And sometimes it will just snap out of it and drive normal. Ill have to check the wiring of the knock sensor, last time I had the transmission off, everything looked to be ok.