I have a 89 TBI 350. I have been playing with the timing and I noticed that when I put the light on it (with the ESC disconnected) the timing will occasioncally jump like 20 degrees and the fall back to the base timing. Everything from the timing chain to the distributor to the plugs is new within the last few months. What could be causing this?

Aaron

 

How fast is the engine running while checking timing?

The module has a built in advance curve that activates, when in ESC bypass, based on engine speed (can't remember the RPM).

 

I'd say around a 1000 rpm.

The timing jump only lasts for a second or so, just one or two flashes of the timing light, then it goes back to base timing. A few seconds later it will jump again.

AW

 

I'm betting you are activating the module advance curve then.

If I'm correct then raising the RPMs to 1100-1200 should result in the timing advancing to that higher level and staying there.

It should be idling around 500rpms when checking timing.

 

Ill try lowering the idle

 

I adjusted the idle and it had no affect.

Aaron

 

No affect on what? The timing or idle speed?

Does the timing advance when you speed the engine up? Try as much as 2000 rpms.

 

Idle dropped, but the timing problem continued.

 

Intermitten spark jump from other cylinder triggering your inductive timing light?

Maybe even a bad timing light?


Charlo

 

I thought about that too, but you can hear the engine miss when the spark jumps.

 

Rig up a vacuum gauge and check manifold vacuum...I almost guarantee you'll see a drop in vacuum when the timing flucuates. As to the cause? Some kinda misfire/incomplete burn I suppose, is most likely.

 

But what would cause the misfire?