97 CMP Offset - Distributor Installation

WICruiser-97 · Sep 22, 2023

I now have the ability to read CMP Offset and find my original distributor setting was giving me -26 degrees - a fair amount off of the require +/- 2 degrees. See my thread re BFX OBDII reader.

I tried to adjust the distributor but best I could get was about -15 degrees before the distributor ran into someething - coil mounting bracket I think.

Pulled the distributor enough to move 1 tooth and dropped back in. Started at +15 degrees but the best I could get was +7 degrees before the number 1 spark plug wire on the cap runs into the intake manifold.

Anyone else had this problem?

I am thinking that I need to move the distributor back one tooth and modify the coil mounting bracket (assuming that is what is preventing the proper setting) to get the setting into the +/- 2 degree required setting.

Erik the Awful · Sep 22, 2023

WICruiser-97 said:
I am thinking that I need to move the distributor back one tooth and modify the coil mounting bracket (assuming that is what is preventing the proper setting) to get the setting into the +/- 2 degree required setting.

Yup. Sounds like a good plan. Except that you shouldn't have to modify the coil mounting bracket. Maybe move two teeth?

WICruiser-97 · Sep 22, 2023

Unless I mistakenly moved 2 teeth the first time it seems that the range of adjustment controlled by the ability to rotate the distributor is too small. My reading went from negative to positive so I must have crossed over the majic setting location when I moved what I believe was 1 tooth on the gear. I cannot modify the intake manifold or the #1 cap wire location so I bliese I am stuck with going back one tooth and modifying whatever is required to get the distrbutor to the required orientation for the +/- 2 degree setting.

Spareparts · Sep 22, 2023

New distributor or maybe the previous owner replaced it?
The cam gear could be 180 degrees out or it sounds like you need to move it one tooth.

Supercharged111 · Sep 22, 2023

When I moved mine 1 tooth I went from 30 off to 90 off. The fix for me was a new distributor gear.

Road Trip · Sep 22, 2023

WICruiser-97 said:
I tried to adjust the distributor but best I could get was about -15 degrees before the distributor ran into someething - coil mounting bracket I think.

Pulled the distributor enough to move 1 tooth and dropped back in. Started at +15 degrees but the best I could get was +7 degrees before the number 1 spark plug wire on the cap runs into the intake manifold.

Anyone else had this problem?

****

Unless I mistakenly moved 2 teeth the first time it seems that the range of adjustment controlled by the ability to rotate the distributor is too small. My reading went from negative to positive so I must have crossed over the majic setting location when I moved what I believe was 1 tooth on the gear. I cannot modify the intake manifold or the #1 cap wire location so I bliese I am stuck with going back one tooth and modifying whatever is required to get the distrbutor to the required orientation for the +/- 2 degree setting.

WICruiser-97,

This specific issue has cropped up before, and the good news is that others have discovered a solution.

Assuming that the rest of the distributor is healthy (no excess wear in the upper bushing, etc) the
root cause is that somehow the distributor gear was 180° out when it was pinned to the distributor shaft.

The reason why there is a right phasing and a wrong phasing for the distributor gear to be pinned to the
distributor shaft is because there are an odd number of teeth -- 13 to be exact.

I was going to share all the math, but the bottom line is that when 1 setting gives you a too-positive range,
and then moving the distributor 1 tooth only gives you a too-negative range, then pulling the distributor >
depinning > spinning the 13-tooth gear 180° > repinning > reinstalling > getting the +2/-2 setting is the solution.

****

For someone who went through the same thing & got the fix, the first 10 posts in this thread
are what you are looking for: (Can't set distributor correctly)

****

As for why you are faced with this problem? The most common answer is that the aftermarket
distributors are being assembled incorrectly. If you aren't here because of an aftermarket dizzy
then the answer becomes a bit more esoteric.

Best of luck --

WICruiser-97 · Sep 22, 2023

Thanks for the history and fix. I had not considered the gear orientation.

I have no way of knowing if the distributor has ever been replaced or the gear removed as I purchased the truck, not running after sitting for several years with an intake manifold coolant leak. I did a complete rebuild but did not do anything more than remove/install the distributor.

I will try repinning the gear and see if that fixes the problem as it has for others and report back.

Supercharged111 · Sep 22, 2023

If it's the original distributor plan on buying a new gear and then be prepared to flip it if you get it wrong on the first go. ANY visible wear is enough to screw you over.

Caman96 · Sep 22, 2023

Having 3 different threads on this doesn’t help.

97 CMP Offset PID

I have read other threads on this subject but newly registered to allow me to actually post here. I have a '97 C1500 w/ the 5.0 Vortec that I recenlty rebuilt. Installed the distributor with the rotor pointed to the "8" and the enigne runs but thows a code for cam offset. I have the Torque Pro...

www.gmt400.com

Using BFX OBDII reader for CMP offset

I purchased the BFX OBDII reader (Android WiFi version) and downloaded the Torque Pro app. I was able to connect the two and see general engine operation information but not able to see CMP Offset on my 1997 C1500. I read somewhere that the DashCommand app would allow me to read CMP Offset so...

www.gmt400.com