5.7 Vortec missfire issues

[CKVortec]

I skimmed over this, so I apologize if this has been asked or done already. Have you tried the distributor itself? On both of my 400s, they both developed a wonky misfire. Changed plugs, wires, cap, egr, etc. Didn't do anything. Had it hooked up to a really high end scanner and it showed the misfire was coming from all cylinders at different times. Changed the distributor and ran like a Rolex watch after that.

Was there a reason that you changed the whole distributor rather than just the cam sensor? that's all there is to the distributor other than bearings and somewhere to attach the cap and rotor.
I plan to swap out the sensor next since I have an old one on the shelf (I have a bunch of spare parts)

 

[Aarong23]

Was there a reason that you changed the whole distributor rather than just the cam sensor? that's all there is to the distributor other than bearings and somewhere to attach the cap and rotor.
I plan to swap out the sensor next since I have an old one on the shelf (I have a bunch of spare parts)

Whenever we scanned it(with some scanner that cost several grand) it was showing crazy misfires all over and the guy said he thought it was jumping the arc maybe? I cant remember. It was like 12 or 13 years ago. He and my dad both deduced it had to be the distributor, so that was what we swapped out and it fixed it. Im not sure what it in it was bad though. We got lucky because my dad had a spare distributor in his shop, so it was free to replace it.

 

[SUBURBAN5]

This used to belong to the Alaska Railroad, so it was a base model with no frills except some funky 19.5 inch wheels and tires and HUGE running boards. It also used to be School Bus Yellow, couldn't stand it!
It has come a long way from the $2500 eyesore that I bought years ago.

Looks great.. we had mine for 23yrs hood and roof were starting to fade. I bed lined the roof with cheap liner lol. Couldn't stand it.. hood got replaced due to uncontrolled events.. saving up for a paint job or paint correction... want to eventually restore it... just money money money...

 

[geeeee89]

Please read the original post before jumping to conclusions, the CMP is set dead on zero degrees. and, yes, the snap-on scanner works to set this. Also, this is the 3rd engine replacement I have performed on the exact same drivetrain and none of the others had any issue.

Is the CMP offset the same as “setting cam sensor timing” because if it is I Didn’t know that and suggested CMP offset because you didn’t list it. I didn’t jump to any conclusions, I suggested what fixed mine after an identical issue. If you don’t like the suggestion don’t use it. Next time I won’t waste my time

 

[CKVortec]

Is the CMP offset the same as “setting cam sensor timing” because if it is I Didn’t know that and suggested CMP offset because you didn’t list it. I didn’t jump to any conclusions, I suggested what fixed mine after an identical issue. If you don’t like the suggestion don’t use it. Next time I won’t waste my time

Yes, CMP is your cam sensor and CKP is your crank sensor. the "offset" is setting the "cam sensor timing" by rotating the distributor and using a scan tool to get as close to zero as possible. any more than 2 degrees plus or minus will pop a code and the check engine light will come on.
Don't get offended, I'm not. Just frustrated.

 

[CKVortec]

well, still no winning on this issue. compression is good, as I assumed since the idle is so smooth.
I swapped the cam sensor and no change.

I'll have to put this on the back burner for a while, but my next move will be to compare some readings on the scan tool between my Suburban and the pickup and see if anything jumps out at me then swap parts from one to the other and see what happens. Like the distributor, coil and ignition module assembly, plug wires.

If anyone has any bright ideas let me know, I am assuming there is no vacuum leak since it idles so well and the MAP sensor readings look good to me.

 

[SUBURBAN5]

I'm just asking. The parts on (the shelve) are they new or have they been there a while.. asking because you said mpfi and there's wires so no chance of premature aging ect.. I know you said you switched it back to cfi again jw.. I'm just trying to think

 

[HotWheelsBurban]

Was there a reason that you changed the whole distributor rather than just the cam sensor? that's all there is to the distributor other than bearings and somewhere to attach the cap and rotor.
I plan to swap out the sensor next since I have an old one on the shelf (I have a bunch of spare parts)

I seriously love the quote on your signature. That needs to be on a T shirt!

 

[CKVortec]

I'm just asking. The parts on (the shelve) are they new or have they been there a while.. asking because you said mpfi and there's wires so no chance of premature aging ect.. I know you said you switched it back to cfi again jw.. I'm just trying to think

The parts from the shelf are use stuff, I'm not even sure if they are good or not, but when swapping parts I got no change in performance, still random misfires. the injector set I changed out was also an MPFI unit, just unknown condition. Since it made no difference I will be swapping back to the new set when I figure out the root cause of my issues.

 

[SUBURBAN5]

Now here's my second question... if you plug in the scanne . Read live data and drive around. Nothing pops up with like cylinder 1/3/2/4. Either like spark jumping or fuel pressure dropping or anything that's stands out... I understand you have great pressure and I also know you've been reading the motor with the scanner. I'm just curious what all live data can show while your driving and see what it shows.. may be small but could be a factor.. btw i dont own a fancy scanner that's why I'm asking. Kind of like this. Say it's a spark or volt tiny difference. At least in norrow to electrical. Say its fuel pressure same thing. I just dont know if a scanner can read fuel pressure on each cylinder. Like I said never had a fancy scanner.. I just feel like something dropping for a few minutes hints the misfire. But going up to speed or idling no misfire detected because of the demand... maybe I'm wrong or you covered it already just trying to think as if it was my truck....