Need help!!!! Multi cylinder miss fire

[Cheer0s666]

Hey guys I recently got my 2012 5.7 rebuilt from a rebuilder. Started it up and it drove good the first day but then I went to drive it the next day and it has a miss on 4 6 7 swapped coil packs around checked spark plugs and still the same thing anyone experienced this before?

 

[Cheer0s666]

Also smells like it’s running rich all injectors were tested and all looked good

 

[EdGs]

I'd be going right back to the rebuilder.

If you just got it done, I wouldn't have touched anything on it right away.

Cylinders 4, 6, and 7 are three of the MDS cyinders, along with cylinder 1.

Let us know what they say.

 

[Burla]

Codes must say something, only 3 misfires?

 

[Cheer0s666]

Only throwing p0300

 

[Cheer0s666]

Took a temp gun to it and the cats are clogged

 

[Burla]

Are you messing with us?

 

[Cheer0s666]

No? Temps are dropped a lot less after the cats could that cause the misfire? Also noticed injectors are just not firing at certain times

 

[Burla]

What fuel pressure on/back of the rail?

 

[Cheer0s666]

Not sure blows blue smoke though think the clogged cats could cause the miss?

 

[Flip-er]

I'd be going right back to the rebuilder.

If you just got it done, I wouldn't have touched anything on it right away.

Cylinders 4, 6, and 7 are three of the MDS cylinders, along with cylinder 1.

Let us know what they say.

WEll just learned something new
Did not know those cylinders were MDS
BUT then again I am not very tech minded, BUT always good to learn new things, so thank you

 

[EdGs]

Not sure blows blue smoke though think the clogged cats could cause the miss?

Think you have bigger problems, blue smoke usually means burning oil.

I'd be getting hold of the rebuilder.

 

[Cheer0s666]

Thought blue smoke means rich you can smell it’s dumping more fuel then needed

 

[Wild one]

Thought blue smoke means rich you can smell it’s dumping more fuel then needed

If it thinks the cats are over heating the computor will command the injectors to add more fuel to cool the cats

 

[Burla]

I thought it diverted blinker fluid to coat them?

 

[Cheer0s666]

Update got a majority of it fixed replaced cats now it runs good when starts up all injectors fire but then it just randomly shuts off 4 and 6 and starts to miss on those cylinders any help would be appreciated

 

[jws123]

Check the compression.

 

[Cheer0s666]

Compression was good

 

[Sherman Bird]

Only throwing p0300

"Doctor! I have a splitting headache!".... Is it a brain tumor? Eye strain? stiff neck muscles?
This scenario is THE EXACT correlation of what a P0300 is!
This is, along with the lean/ rich codes, THE MOST misunderstood code in the OBD2 system.
I had a P0300 on a 1998 Chevy Tahoe with the 5.7L "R" engine once that drove other shops AND ME crazy!!!!
The ultimate problem??? There was a passenger side (bank 2) catalytic converter whose heatshield had cracked a weld and rattled like silverware when the engine was revved. Everyone ignored that as insignificant, including me.

Eventually, the noise annoyed me to the point of extreme frustration, So, I raised the truck up on the lift and rewelded the cracked heatshield weld.... The P0300 went away never to return.... to this day. Heck of a lesson, eh?

 

[Rufi]

Missfires wiil dump fuel in your new cats and destroy them very rapidly if you keep on driving. Clogged cats are a result, not the cause.