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As I dig into an idle quaility issue with my 89 Camaro, I am studying the ignition advance controls & have figured out the ignition module
adds about 6-8 degrees of timing at a specific RPM without any help from the ECM. I was not aware of this until looking at how 2 of my cars behave when the ecm spark control is bypassed. I'm guessing all of the TPI cars, or at least the later years do this?
Having gained that knowledge yesterday, I am now wondering two things related to that.
#1 At what RPM do the Modules advance kick in? Is it supposed to be 1400 rpms +/- ?
#2 is this advance supposed to work only with the esc connector is bypassed, or is the module independent & advances at that set RPM regardless of the bypass status?
Yes, this has an older, aftermarket module & it bumps the timing at 900-1000rpms. Regardless of whether the ECU is in control or if its bypassed. I just borrowed the GM original from another car & it completely changed things. Now, I went through the minimum air procedure again & this is without a doubt its the best the car has run. Game changer.
Now I just need to see if my colds starts are good, But I have very high expectations based on what I am seeing right now.
When the engine was cold, it the idle would be rather high, then come down & jump right back up again. It would do this very consistently while it was warming up. It was this timing shift that was causing it & I have been scratching my head for several days over it.
I'm going to see if there is a better replacement or maybe there are still some GM units out there. Car is completely stock with lower miles, so I would rather not modify other things to compensate for this funky module
As I dig into an idle quaility issue with my 89 Camaro, I am studying the ignition advance controls & have figured out the ignition module adds about 6-8 degrees of timing at a specific RPM without any help from the ECM. I was not aware of this until looking at how 2 of my cars behave when the ecm spark control is bypassed. I'm guessing all of the TPI cars, or at least the later years do this?
Having gained that knowledge yesterday, I am now wondering two things related to that.
#1 At what RPM do the Modules advance kick in? Is it supposed to be 1400 rpms +/- ?
#2 is this advance supposed to work only with the esc connector is bypassed, or is the module independent & advances at that set RPM regardless of the bypass status?
Yes, in BYPASS mode the small cap ICM (maybe others???) will add SA within an RPM area/range. Usually in the 1400 - 1600 RPM range. The main use for this is so that when the ECM is in limp mode, or when code 42 is active, there is still some additional SA. This helps with power along with keeping the engine cooler.
I do know that this SA varies by amount, and what RPM range it kicks in at. I've never done a definitive study on it. Well, just because. It is a feature that is built into the module. A lot of GM DIS systems will do the same thing. Except the lowly '89 TTA DIS, no additional SA with that unit.
Very Interesting, I have owned so many of these TPI engine'd F bodies over the decades & I never knew this detail until this weekend.
I guess I never needed to know until now
1400rpm is where the GM module in the 89 GTA advances. Thats the one I am loaning to the 89 Camaro.
I'll add something interesting to this. With the GM module, I watched the timing advance in "normal" mode.
I did Not see a sudden 6+ degree jump while raising the RPM above 1400 rpms. relatively smooth over all, but no big jumps.
On this aftermarket unit, It still jumps 6+ degrees around 1000 rpms while increasing the RPM, along side the regular advancing so I am inclined to think that the GM module does not advance with exception to limp mode, or timing bypass mode.
I wish I would have used my adjustable timing light to compare total timing between the two modules. I guess it doesn't matter that much I was just curious.
Just thought I would follow up & mention that I installed an AC Delco Module. Was surprised it said "GM" on it & made in the USA according to the box.
This module also jumps the timing at 1000 RPMs when in limp mode, Not 1400 like the originals, but does not appear to be adding any extra timing when the ECM is in control of the advancement, so problem solved on the module side of things.
08-13-2023, 06:54 AM
