I beyond myself with this stupid "Service Engine Soon" light. I've replaced the plugs, wires, Temperature sensor, Ignition control modual , coil Distributor cap and rotor, the distributor itself. but today after 5 miles it came on again. I'm out of ideas now ?

 

and you checked the wires from the ignition module to the ECM as best you can? I have seen them pinched in the bell housing. You have replaced everything that code 42 would set other than a short in the wire or a loose connection. Start it up a start wiggling wires a little and see if you can get the service engine light to come on.

 

also make sure your engine ground is working. I just use a test light hooked to the positive and start touching bare steel on the engine and see if the test light will light.

 

Yes the wires to the ECM are OK, but I'll see if there is a good ground. Thank you !

 

The problem was a secondary product. I got some advice to open the cap and remove the rotor, Look at the ignition Module, 1. If the ignition module is white or red as in a hi performance cheap item, Take it out and throw it away. 2. Go to a supplier who carries GM PARTS. Get a GM and only GM ignition Ignition module. 3. Wipe off the base plate clean with some Acetone and wipe off any and all dirt, old thermal paste, and clean the hold down screws real good. 4. Apply a THIN coating of the white thermal paste to the new ignition module under side, and keep it to the size of a large postage stamp. Reinstall the module, plug in the three connections and put the screws on and tighten ONLY to finger tight, then go 1/8 more. The layer of paste only needs to be about the thickness of a loose leaf paper.

I disconnected the ground cable to wipe out any stored codes. Button it up and fire it off and see if the light for a code 42 or "Service Engine Soon" ever comes on. But 70% of all Code 42's are the ignition Module. Came from a GM senior tech at a Chevrolet outside Detroit. Once I did as told the "Service Engine Soon" never came on again.

 

Awesome. Thanks for posting this. ����

 

Wow, the mysteries are endless. So happy for places like "Blazer Forum". God only knows how many blazers would be stuck on the side of the road permanently.

 

The one other thing I did was replace the cheap yellow Accell silicon wires with a 8mm GM Professional set of wires, and my 350 plug is a RC43TS gap @ 0.35 with a AC Delco #1 Platinum Rapid-fire Plugs gap 0.45 and you would not believe the difference. I hunted around for any data about using these late model plugs, but I couldn't find any. But I did install a MSD High output coil. the stock one was rated @ 33.000 volts and the new one is rated @44.000 volts.