Barely Running Believe its a CMP issue.

[1952Chevy]

I'm 9 hrs away from home(Las Vegas). About to start a camping trip tomorrow. I took the truck out to get groceries and started misfiring.

No fault codes
No misfire count.
Has fuel(pump and filter are not new).

What I noticed though was my CMP offset is bouncing anywhere from -40 to 40. When it's -1.2(where I set it). The truck seems to drive fine. When it starts bouncing I have issues.

What's the likely culprit?

99 k2500 Suburban, 7.4l, 4l80

 

[Caman96]

Maybe a worn distributor gear?

 

[1952Chevy]

Distributor was brand new, has about 2k miles on it.

I checked fuel pressure, changed the fuel filter(brought pressure up about 5psi).

Replaced crank position sensor. Still getting massive fluctuations in my cmp offset.

 

[Road Trip]

I'm 9 hrs away from home(Las Vegas). About to start a camping trip tomorrow. I took the truck out to get groceries and started misfiring.

No fault codes
No misfire count.
Has fuel(pump and filter are not new).

What I noticed though was my CMP offset is bouncing anywhere from -40 to 40. When it's -1.2(where I set it). The truck seems to drive fine. When it starts bouncing I have issues.

What's the likely culprit?

99 k2500 Suburban, 7.4l, 4l80

+/-40° seems to be a *lot* of bounce for mechanical play, especially if the engine is still noise free.
Obviously it could be at either end of the comparison circuit. (CKP at the front of the crank, or the
CMP sensor inside of the dizzy. I'd check the security of the connectors on both sensors...
(your reply #3 just came in) ...I'm assuming that if you don't see anything obvious in the engine bay
wiring harness, then the CMP sensor inside the distributor is the next most probable cause of the
bouncing miscompare?

 

[Road Trip]

No fault codes

That's confusing. According to the P1345 DTC anything exceeding a +/- 15° error
should trip this code when it occurs?

At any rate, I've attached a couple of pages out of the '99 FSM that discuss this
area, including some diagnostic tips on the 2nd page.

EDIT: Is your distributor locked down? Or can you rotate the distributor housing
by hand? Stranger things have happened.

Best of luck with this. I wouldn't stray too far from civilization until you get a
handle on the issue...

 

[Road Trip]

Distributor was brand new, has about 2k miles on it.

What brand dizzy was this? There have been a few threads in the forum about
premature Vortec dizzy failures...

 

[1952Chevy]

That's confusing. According to the P1345 DTC anything exceeding a +/- 15° error
should trip this code when it occurs?

At any rate, I've attached a couple of pages out of the '99 FSM that discuss this
area, including some diagnostic tips on the 2nd page.

EDIT: Is your distributor locked down? Or can you rotate the distributor housing
by hand? Stranger things have happened.

Best of luck with this. I wouldn't stray too far from civilization until you get a
handle on this...

Exactly. I remember when I installed the dizzy that even at about 6degrees I was getting a code. Now I'm fluctuating over 80 degrees total. The distributor is locked down. One of the first things I checked.

 

[1952Chevy]

What brand dizzy was this? There have been a few threads in the forum about
premature Vortec dizzy failures...

It was from O'Reilly, I'd have to look through receipts

 

[1952Chevy]

Well I think the game plan tomorrow is to remove the cap and rotor, if everything looks good there, I will try a cam position sensor. I really don't want to replace the whole distributor again. We will see what happens though.

 

[Caman96]

Well I think the game plan tomorrow is to remove the cap and rotor, if everything looks good there, I will try a cam position sensor. I really don't want to replace the whole distributor again. We will see what happens though.

If it was a house brand distributor at Oreilly’s, if possible, doubtful if your on a Road Trip(), use original or buy GM Genuine cam position sensor.