Timing Advanced....Vacuum Leak

[Reega]

89 GMC K1500 350 700R4

So a couple of years ago I replaced my timing chain and gears, stabbed the dizzy, and tried to set timing @ 0 degrees. EST unplugged. It would fire and die. Slow advancing of the dizzy got it to start, run, and idle “okay”. Somewhere around 20 degrees. Kept searching for the issue but could not find the cause. Since I didn’t know the history of the truck, but could tell the block was wrong, 85 block, and some parts orher “mods” I assumed it was based off some unknown factor. Heads where right, TB, no air pump or cats, stuff like that. Anyways, I think I found the vacuum leak causing the problem, finally. The line going to the charcoal canister.
Is my logic right?? Would that vacuum leak require that much advance? What damage could I have done?? Other things?? Thanks for your ideas.

 

[Schurkey]

Fix the vacuum leak, re-set the timing and see what happens.

Hopefully, the computer enrichened the fuel mixture; with the leak fixed, it'll have to re-learn proper fueling. As always, connect a scan tool, look at the data stream. See what the short- and long-term fuel trim numbers are.

My first thought when reading your post is that the cam isn't timed properly. It would be worth your while to do a cranking compression test; if the readings are even but higher or lower than expected, the cam timing is suspect.

Wouldn't hurt to verify the knock sensor is working properly. Adding 20 degrees of timing would really screw-up the higher-rpm advance. Assure that the timing advances properly when the timing connector is plugged back together.

Most of all, verify that the torsional damper hasn't slipped. If the outer ring spins on the hub, all sorts of "timing" problems are created.

 

[Reega]

Thanks Schurkey.
What’s really crazy is when the the EST is reconnected, you can watch the timing continually advance and retard, but it’s off the scale on the timing cover.