Lost an ignition module. Why?

[mtnmankev]

Okay, so I've got a new ACDelco ignition module on the way. Until then, I thought I'd check the timing.

I disconnected vacuum advance, set it to 12 degrees. Good baseline, and she seemed to like it.

Here's my concern: When I reconnect port vacuum, I'm seeing an increase of 18 degrees at 800 RPM, for a total of 30 degrees....

That can't be right, can it?

Yes, that is quite correct.
It's not uncommon to have a total advance of 40-42 degrees (mechanical and vacuum combined).
Keep in mind this part of engine theory, it takes time to burn the fuel mixture, so as RPM increases, the spark has to occur sooner to achieve the proper burn time.

 

[AuroraGirl]

Thanks, but I have a back up ACDelco unit that I have laying around.

Also, regarding the weights, they looked in perfect condition. No rust, good springs, etc...

Thanks!

how were the bushings they pivot on? mine just.. dont have any but they work better when they pivot and not shift around

 

[Old60Driver]

how were the bushings they pivot on? mine just.. dont have any but they work better when they pivot and not shift around

The bushings looked good as well. Like I said, mechanically, it looks brand new in there. I'm just weirded out by how much vac advance I'm getting.:/

So, I got some numbers.

With vacuum advance disconnected and plugged, I get the following:

800 RPM - 12°
2500 RPM - 31°

With vacuum advanced connected to port vacuum, I get the following:

800 RPM - 29°
2500 RPM - 47°

Usually, I just set my initial and forget the rest, but, well, I'm curious, so I want to get my head wrapped around this. I wouldn't think I'd be plol

Thanks again!

 

[Old60Driver]

Well, still driving on the back up ignition module, but all seems well. Bout to head out for the backup to the backup ignition module, but a pretty healthy test drive shows she's happy, so I'll not worry too much about it.

Probably going to check my AFR with vac gauge here in a bit. I put long tubes on, and just want to double check that I'm not leaning her out. Performance wise, she's acting better than she ever has.

Still need a few more bits to REALLY wake her up though. lol

 

[AuroraGirl]

Well, still driving on the back up ignition module, but all seems well. Bout to head out for the backup to the backup ignition module, but a pretty healthy test drive shows she's happy, so I'll not worry too much about it.

Probably going to check my AFR with vac gauge here in a bit. I put long tubes on, and just want to double check that I'm not leaning her out. Performance wise, she's acting better than she ever has.

Still need a few more bits to REALLY wake her up though. lol

whats the model number of your distributor? is it possible the vac line is supposed to go to a switch or a device before it goes to the vac advance, and the unit was calibrated to be used in such fashion with emissions equipment? you have an 83, so just a thought.

 

[Old60Driver]

whats the model number of your distributor? is it possible the vac line is supposed to go to a switch or a device before it goes to the vac advance, and the unit was calibrated to be used in such fashion with emissions equipment? you have an 83, so just a thought.

Actually, it's an aftermarket Amazon special. I know, I know...

But it was red, and that adds like 8.57 horsepower, right?

 

[AuroraGirl]

Actually, it's an aftermarket Amazon special. I know, I know...

But it was red, and that adds like 8.57 horsepower, right?

i think i found your wacky situation then.

put a different vac advance on it like an old one or just a nice quality kind