So, I unplugged the ecm and set the timing to zero. When the unit is plugged back in, what should the timing light read off the timing marks? PROM is a stageII jetchip. Or, for the sake of argument, what if the chip were the stock chip? What timing advance should I see? If that's not what I'm seeing, what's the likely reason? Been reading the other postings on this topic, but seeing different answers on what the timing light should see. Don't think anyone's asked what it means when you don't see what you ought to.

92rs 305, no mods to engine, cat back exhaust.

Thanks for your comments

 

"So, I unplugged the ecm and set the timing to zero."


When you say you unplugged the ECM, do you mean you unplugged the EST bypass connector, or did you really unplug the ECM?


"When the unit is plugged back in, what should the timing light read off the timing marks?"

If you did the procedure right, as soon as you reconnect the EST bypass connector, the timing marks should advance WAY past the timing tab - up to about 30 degrees or more in many cases.

 

Merliin,
Yeah, the EST bypass connector is what I disconnected. When Reconnected, the timing doesn't move more than a couple degrees. Quarter-mile times are comparible to what I'm seeing posted here, upper 16's low to mid 80's trap speed. However gas mileage seems like it ought to be better for a small displacement V-8 and overdrive tranny. I average 20-21 no matter where I drive.
So, what causes the advance not to advance?

Mike