Questions and Answers

Adjusting GMC Yukon Ignition Timing Q. Hi Vince, I set the timing on a 1992 GMC Yukon 4x4, 5.7 liter. I thought I set it at TDC but after all the pinging on the test drive I checked it again and re-set it correctly. The Service Engine Soon light came on sometime during the first attempt to set the timing, now it stays on for the most part. Sometime it goes out for a few seconds, maybe three or five, but comes on again and stays on.

Did the incorrect timing trigger the light? Can I, and if so how do I, download the codes stored in the system?

Thanks,
Joh

A. You will need to jump A-B on the ALDL connector under the drivers side of the dash to get "flash codes" Did you follow the label under the hood to set the timing? Put it in "by-pass" mode by unplugging the single wire connector? If not, timing is still too far advanced. A bad EGR valve will make it ping as well. We'll need to see what codes are set first.