Have a 91 with 3.9 - well it just failed emissions the other day so I was going to retard the timing a few degrees. I unplug the coolent sensor, warm up engine and plug my light into #1 (drivers side front) and the mark is not even close to the scale. It is sitting about 9oclock if you were sitting in the truck. I checked the location of the wires on both ends and everything seems to be ok. The truck runs good other than the No and Hc were alittle high. Can anyone explain the timing problem?

 

What did it fail on specifically?

I don't know all about the TBI system but it should all be electronically controlled. So once the distributer is in the correct spot then the computer does all the work.

 

No and Hc were alittle high. The 91 was the last year on this engine that the timing was adjustable.