Ignition timing

[kenh]

I want to make sure I understand this correctly. I don't know the exact numbers so are just throwing some out for arguments sake.

The ICM/computer has a total of 30 degrees of total timing advance. If you set the timing at the factory zero the engine will only see the 30 degrees. Now if you set the base timing at +4 then the engine will see a total of 34 degrees timing.

Am I correct?

The reason I'm asking is after installing a new dizzy the engine seemed to much happier with about 3 degrees advanced timing. I know some have talked about setting the base timing advanced a bit. Maybe my harmonic balancer has slipped???

Thanks!!

Ken

 

[PlayingWithTBI]

Now if you set the base timing at +4 then the engine will see a total of 34 degrees timing.

Exactly! The ECM doesn't know what your base timing is unless you tell it. Some have a file where you tell it what your base is, then it'll compensate for that. It'd be a good idea if you watched your KCs and SA retard if you get too close to detination but, IMHO 3 or 4 degrees won't bother it. YMMV

This is another reason for data logging and "tuning", even with a stock engine. GM left a sh!tload of performance on the table even with stock engines.

 

[kenh]

Thanks. Back in the old days we did that exact thing. EXCEPT we had to listen for the detonation. haha

Watching my spark advance it stays pretty much at the base until it reves a bit. Don't have a tach but it then just jumps to a much higher value. Can't read my scale as it kind of crusty, then it seems to stay there. Is this normal? I thought it should be a fairly steady rise to follow the RPM.

Ken

 

[Schurkey]

Watching my spark advance it stays pretty much at the base until it reves a bit.

Define "base". Do you mean the initial timing with the timing wire disconnected? Timing stays at 0--3 degrees until you rev it, then it advances?

Don't have a tach but it then just jumps to a much higher value. Can't read my scale as it kind of crusty, then it seems to stay there. Is this normal? I thought it should be a fairly steady rise to follow the RPM.

Ken

The computer is providing the equivalent of centrifugal and vacuum advance. Wouldn't surprise me to see a big jump right away, but I've never explored the timing curve of my '88. I keep promising myself that I'm going to, but never do.

 

[Schurkey]

Maybe my harmonic balancer has slipped???

Worth looking into. Find "TRUE" TDC for #1, compare the timing pointer to the damper groove position.

 

[kenh]

Yes the initial timing is what I mean. With the timing wire connected, at idle, the timing is the same as with the wire disconnected. Wire connected, Rev the engine a bit and it takes an instantaneous jump maybe 15 degrees????? Stays there as you rev the engine some more. Didn't play with it a lot as I need to stop and take care of some other business. Without a tach, and a clear view of the timing marks, I'm kind of pissing in the wind as I can't provide any hard data.

Ken

 

[Schurkey]

I suspect problems. When I connect the wire on my '88, timing instantly jumps from "0" to perhaps 12 degrees. I've never paid attention to how much it jumps, just that it does. As far as I know, the timing should increase if the engine RPM is greater than 400. (i.e., ignition module controls timing below 400 rpm, computer controls timing above 400 rpm.)

You need to investigate further.

 

[Sam Cooper]

My 89 C3500 with 7.4 L big block has an interesting issue. Lately it has started throwing a code 44 lean condition SES. The idle was also staying elevated at about 1400 rpm.
I looked for a vacuum leak and found none. Then I put my timing light on it without disconnecting the timing diagnostic plug and idle timing was at 30+ degrees. Yikes! When I disconnected the diag plug the timing dropped to 5 degrees. The idle also dropped to 950. If the timing is always staying advanced, that could account for the lean condition. What can I do about the timing always being advanced? I can't smog this truck with this condition. Thanx

 

[Road Trip]

My 89 C3500 with 7.4 L big block has an interesting issue. Lately it has started throwing a code 44 lean condition SES. The idle was also staying elevated at about 1400 rpm.
I looked for a vacuum leak and found none. Then I put my timing light on it without disconnecting the timing diagnostic plug and idle timing was at 30+ degrees. Yikes! When I disconnected the diag plug the timing dropped to 5 degrees. The idle also dropped to 950. If the timing is always staying advanced, that could account for the lean condition. What can I do about the timing always being advanced? I can't smog this truck with this condition. Thanx

Hey Sam,

Your question is a good one, but by appending it to a 2021 thread named "Ignition Timing",
once it falls off the "Latest Posts" display you run the risk of it falling out of view/becoming
unfindable later on?

Go ahead and start a new thread titled something along the lines of
"Help troubleshooting an '89 C3500 7.4 TBI throwing a Code 44".

Guaranteed you will get more eyes/more help by doing this.

Good luck --