Running rough

[carrmann]

I just want to start this with I may have just gotten some bad gas. I filled up and started noticing it 'missing' while driving. It may have already been doing it before and I just now noticed. But anyways, it continued so I pulled codes. I DO have a Tech 2. No noticeable misfire under full WOT.

Codes were:
P0300 Engine misfire detected
P0106 MAP sensor performance
P0102 MAF low frequency
P0011 Camshaft position system performance
P0455 Large EVAP leak
P0430 Cat low efficiency bank 2
P0420 Cat low efficiency bank 1

P0420, P0430, P0455 has been on for a long time so nothing new there.

I changed the MAP and MAF sensors, reset codes. Drove it, drove awful. Dead spots, popping, etc. Finally got a codeP0175, P0172. Basically bank 1 and 2 rich. P0101 MAF sensor performance. I took out the new maf and put in the old maf, runs MUCH better now but I still am seeing multiple cylinder misfire. However its primarily in cyl 7&8. I did the misfire detection graph on the tech 2, and 7 was the worst by a magnitude. Primarily at very low to no throttle (was fine at higher throttle amounts). It will run fine for a minute then miss a couple times then run fine. Most misfires detected right off idle with a rev etc (7&8).

I'm still thinking water in the tank (this is all the same tank). I just put some heat/octane booster in it to see if it improves at all. I checked the oil, trans fluid, and radiator fluid. Everything looks good and smells good (no mixing).

Any other tables I could check in the tech2 to monitor it?

Thank you

 

[Joseph Garcia]

Pour 2 containers of Techron Gasoline additive into your tank and see if things settle down. No need to fire the parts cannon yet, if you suspect bad gas.

 

[Charlie207]

Check your grounds.

 

[opfor2]

Are you using E85 fuel?

 

[carrmann]

Are you using E85 fuel?

no, never

 

[carrmann]

it seems to have cleared itself up. New fuel, cleaner etc. I did check plugs #5 and #7 (easy to check). Both had gaps in the .07 range (.04 to .06 seems norm and I can't remember what I gapped them to). Neither looked particularly dirty or damaged.

I still feel an occasional shudder. The misfire detector special function though shows it 'misfiring' mostly on #7 at lower rpms when cruising. I can't seem to feel it when its doing that most of the time. Where does it get the 'misfire' data from? Whats detecting it?

 

[Cut Wagon]

Maybe swap coils from one that isn’t showing misfires to #7. See if the misfire follows it to whichever one you use. At least you can eliminate the coil being the problem.

 

[rdezs]

I was just having a conversation with someone else regarding a misfire on number seven.... He sprayed brake cleaner around the intake runners while idling, discovered he has a vacuum leak either at the intake manifold runner or possibly the o-ring for the injector on that cylinder. Literally takes 15 seconds to test.

 

[carrmann]

I will try both of those ideas, thank you