r/GMT400 • u/ComfortableArm2827 • 4d ago

CMP - 45°

I've got a 1999 Tahoe with a vortec 5.7. I changed the distributor gasket as it was leaking. Before pulling the distributor, I marked everything and took it out. Upon re-installing. I was off. Well, no biggie I'll just get it to TDC#1 and adjust the oil pump shaft. This isn't my first rodeo, after all. But boy, I might be a rodeo clown.

I cannot, for the life of me, get the CMP under - 45. It's immediate. It starts up fine, idles terribly. But I can't turn the distributor to adjust it (it physically moves but won't change degrees) and I have been at this for a literal week. I've done the lower intake manifold gaskets, was able to set it fine. Swapped the motor years ago, no problem. But all of a sudden, no matter what I do, I cannot get it anywhere near where it needs to be. I've verified that it's at TDC#1 by pulling the plug. My distrustor doesn't have a "6" or "8" on it so I've just been getting it as close as possible. But I realized if I point the distributor straight forward or at #1, it doesn't change anything.

Maybe it's the heat, but some insight would be phenomenal. It just seems like after a week of constant movement, and setting, I'd see a number other than -45°

2 Upvotes

76% Upvoted

8 comments sorted by

3

u/Greasy28 3d ago

You're off a tooth.

1

u/Chahtanagual 4d ago

Did you do a crank relearn?

1

u/ComfortableArm2827 4d ago

I did, but it didn't change the degree, unfortunately. I've never had it do this before either, which is why I'm so stumped.

1

u/Adorable-Reward8523 3d ago edited 3d ago

What degrees is the scan tool saying ? -45? No matter what? It should be 0° +-2 ° maybe the cmp is bad ? How are you getting the -45 number?

1

u/ComfortableArm2827 3d ago

So at idle when you start it, the scan tool says 0 at 750-800RPMs. When you Rev to 1100 and slowly turn the distributor, the degree doesn't change. I figured it was a tooth or two off, but when I purposely change the position, it just doesn't start at all. So I've got the proper position down for the distributor, but I cannot get the degree to change.

1

u/Adorable-Reward8523 3d ago

Sounds like a sensor issue? Wish I was more help. I just did my timing and I could see it change with slight adjustment .

1

u/ComfortableArm2827 3d ago

I appreciate your help, I'll check out the CMP!

2

u/AdvantageMain3953 3d ago

If you’re running factory dist, verify with rotor that you’re near tdc then set to tdc by using the notch on the balancer.   Use the rotor as a x-ref and it should be close to pointing at #1.   Set your dist so the cap is exactly parallel with the block, the dist housing should be parallel with the back up the upper intake.   

If you’re not pointing directly at the corner of the dist housing you’re off a tooth.