What do you make of this timing?

[wczimmerman]

Here's a link to a short video showing what I am seeing when checking the timing. I am not sure why it doesn't hold steady.

The advance connector was disconnected
The truck was at operating temperature

https://www.dropbox.com/s/64hylrwwos7fssu/20170408_123212.mp4?dl=0

Any thoughts would be appreciated.

 

[HotRodPC]

I don't have data to watch the video. So what is happening? Is the timing mark moving erratically? What type of timing light are you using? Inductive pick up?

 

[87ChevyR10]

I don't have data to watch the video. So what is happening? Is the timing mark moving erratically? What type of timing light are you using? Inductive pick up?

Yeah, mark is dancing all over the place. OP has a Bosch Fix 7529 digital inductive timing light. The display on the light showed 860 to 870 RPM.

 

[HotRodPC]

Must be the week for bad timing issues. He's not the only one stuggling with timing and dizzy issues.

Since the vac advance is plugged off as it should be, then I can only think of 1 or 2 things. #1 and this can certainly happen, more common than you'd imagine, the induction pick up on the timing light is not working properly, or could even be a bad plug wire causing a bad reading, or #2 the vac advance plate in the dizzy is bouncing or vibrating throwing the timing eratically.

 

[87ChevyR10]

Must be the week for bad timing issues. He's not the only one stuggling with timing and dizzy issues.

Since the vac advance is plugged off as it should be, then I can only think of 1 or 2 things. #1 and this can certainly happen, more common than you'd imagine, the induction pick up on the timing light is not working properly, or could even be a bad plug wire causing a bad reading, or #2 the vac advance plate in the dizzy is bouncing or vibrating throwing the timing eratically.

Wouldn't #2 cause poor running for the engine? Engine sounded fine in the video.

 

[HotRodPC]

Wouldn't #2 cause poor running for the engine? Engine sounded fine in the video.

If it's variables are that far off yes, should be some kind of variable in the idle too. So that would be down to a bad plug wire or bad inductive pick up connection somehow. I would think a Bosch timing light is good quality so I'd hate to suggest a defective induction pick up.

 

[87ChevyR10]

If it's variables are that far off yes, should be some kind of variable in the idle too. So that would be down to a bad plug wire or bad inductive pick up connection somehow. I would think a Bosch timing light is good quality so I'd hate to suggest a defective induction pick up.

Considering the RPM's weren't bouncing around like the timing mark was (only 10 RPM variable), I'd agree with the bad plug wire or bad light.

 

[SkinnyG]

Your profile says an '87 - that would mean EFI, and that the timing is electronically controlled. Try again with the set-timing-dis-connector disconnected and see if it's better.

An EFI engine may not keep the timing exactly stable; it's constantly adjusting.

Seems also to be a pretty fast idle for checking/setting timing.

 

[HotRodPC]

Your profile says an '87 - that would mean EFI, and that the timing is electronically controlled. Try again with the set-timing-dis-connector disconnected and see if it's better.

An EFI engine may not keep the timing exactly stable; it's constantly adjusting.

Seems also to be a pretty fast idle for checking/setting timing.

Good Catch !!! This is true. The ECM is going to set the timing according to what's programmed on the PROM chip. There is a way to set the initial timing though. It's been awhile so I don't exactly recall. It seems one of the plugs on the dizzy must be disconnected too so the ECM isn't interfering with the initial timing adjustment. Though it doesn't matter alot cuz the computer is just going to do it's own thing once you plug it back in. So we need to run down the procedure for setting initial timing on TBI ESC.

 

[wczimmerman]

Thanks to everyone for their replies!

This is most embarrassing: My "advanced timing light" was apparently too advanced for me...I was using it wrong which resulted in the strange behavior shown in the video. I was in the RPM mode and pressing the light (and holding the button) thinking that activated it. What it actually did was a very fast strobe rather than flashing on the #1 cylinder. You have to push the button to put it in advanced mode and THEN you get the strobe correctly.

The result? The timing was initially about 1-2* and rock steady with the computer advance plug disconnected. Based on recommendations, I moved it to 8* BTDC but the truck was pinging badly. With that sound, it confirmed that I was getting slight pinging intermittently at the original setting, so I thought I would test retarding it just a bit. I set the timing to the first "point" below the 0* mark and took it for a test drive. The truck drove great! No pinging and it seemed to accelerate just fine. I am wondering at this point if the timing marks are just off? I do have an Edelbrock intake on the motor (which is a new block from GM) so maybe that changes the airflow which would require a different timing? I don't know. For now, I'm going to leave it and see how the MPG and daily driving do in this mode.

 

[1987 GMC Jimmy]

So you're running it at 2* ATDC according to the timing marks? And you say it's running well? Hmm, my Caprice lost advance when it got cold, and before I retimed it, that's where it was, too. It was a quite a little doggy. It didn't run bad, but there was absolutely no pep. I set it to 10* BTDC initial, and I haven't looked back. I would think something's off there. A couple degrees BTDC shouldn't cause detonation either.

 

[74 Shortbed]

Total advance is what you go by not initial, there could be an issue with the advance mechanism or not setup right to begin with and you wouldn't know it, always set the total first then check the initial, then if the initial isn't right you can change that, once it's all been set up right then you can go by initial because you'll know how many degrees is in the distributor to get the right total...