Ignition timing jump when checking timing with light.

[Wags391]

So I finally got to do all the tests today. Vacuum is around 19 at idle and at 2000 RPM. Compression is between 180-185 dry on all cylinders. Spark is good. Bought a tester and the spark has a nice pop, blue in color, and jumps up to and beyond half an inch. I tested the spark with the engine warm also. Same. So where do I go from here? What else can be causing the timing to jump around while checking it with a timing light?

Also, I has said I can't feel anything while driving, like a miss or anything. I do however, notice the voltage dip down randomly. So it is happening while driving.

[MT-2500]

Originally Posted by Wags391

So I finally got to do all the tests today. Vacuum is around 19 at idle and at 2000 RPM. Compression is between 180-185 dry on all cylinders. Spark is good. Bought a tester and the spark has a nice pop, blue in color, and jumps up to and beyond half an inch. I tested the spark with the engine warm also. Same. So where do I go from here? What else can be causing the timing to jump around while checking it with a timing light?

Also, I has said I can't feel anything while driving, like a miss or anything. I do however, notice the voltage dip down randomly. So it is happening while driving.

Did you try another timing light?

[Wags391]

I did not use another timing light. I don't have one available. I can hear and feel the jump even when not using the timing light, so I doubt the light is any problem.

[MT-2500]

Originally Posted by Wags391

I did not use another timing light. I don't have one available. I can hear and feel the jump even when not using the timing light, so I doubt the light is any problem.

Dist and dist module and computer should control timing.
Check dist gear and shaft and dist module.

[Scrapper]

Originally Posted by Wags391

The timing jumps in both modes. The ECM is up behind the glove box and the wire I disconnected is the brown (tan) and black one just below the dash (gives me a code when unplugging it). I know it's the correct wire. I do not have another timing light to use, unfortunately.

did you try getting it up on number 1 plug and take cap off and see if rotor is pointing to number 1 in cap?

[Wags391]

I guess I'll have to test out the dist. Too bad it's brand new a couple months ago. How much play is allowable with the gear and shaft? How can I test the module?


Scrapper, pretty sure the distributor is in correctly. It would be running much worse if it weren't.

[Rick Norwood]

O.K. here is my two cents worth. I saw that the Distributor was replaced, but with what?
An AC-Delco or an Aftermarket Distributor?

If you take the Distributor cap off can you see or feel any play in the shaft when pushing on it with hand pressure (will it wiggle)? You should not have more than a few thousandths movement.

Do you have an AC-Delco Cap and Rotor?

Have you checked your Timing Chain for slop? Excessive timing chain slop will cause your distributor to jump all over the map. It is very easy to check. Here's how:

1. Remove the Distributor Cap.

2. Rotate the Crank Shaft Pulley with a socket wrench in the same direction as it runs normally and watch the needle on the Distibutor Rotor move. I like to line up the rotor with a mark or something.

3. Then, click the Socket wrench the other way and rotate the engine in the opposite direction. Mark the crank shaft pulley before you start and see how much movement there is on the pulley before the Distributor Rotor starts to move.

4. I can't say how much is too much or about right, but if the pulley is moving more than 3/4 to 1 inch or more before the rotor moves, you probably have a sloppy Timing Chain.

[Wags391]

So I checked and tested the distributor in every which way I could find. The dist is a reman from NAPA. I also tested the ignition coil. Couldn't find a problem. Everything tested to spec. The cap and rotor were installed with the engine. Couldn't say if they are ACDelco or not. The engine was installed a couple months ago by a shop in SC.

[MT-2500]

Originally Posted by Wags391

So I checked and tested the distributor in every which way I could find. The dist is a reman from NAPA. I also tested the ignition coil. Couldn't find a problem. Everything tested to spec. The cap and rotor were installed with the engine. Couldn't say if they are ACDelco or not. The engine was installed a couple months ago by a shop in SC.

I would go for another dist from a different brand or batch and use a AC delco cap and rotor.

If no problem found with another dist go for a PCM swap.

[Wags391]

Well, maybe I'll get to a point where I can try that out. I'll post again later if I do.

Thanks.