Ok, working a new to me 03, 13xk miles. DTC 0308 and the occasional 0300

1. Swapped plug with #6 cylinder - no change.
2. Swapped coils left to right, swapped used injector in position number 6, #6 injector in #8 position, new plug wire on #8 coil. Still DTC 0308

Other symptoms

-02 sensors switch properly
-Only other code is the occasional 0300 (multiple misfire)
- runs fine at speed, although will occasionally idle really rough, then just stop
- will not set the dtc if the code is cleared while driving, until truck is idled again.

At this point, I seem to have ruled out plugs, wires, coils, and injectors. So what else is left?
1. Bad valve?
2. Blown head gasket on #8 (truck runs fine, 180 degree inline stat with 185 temps, drinks no water)
3. Bad injector wiring?
4.

What else am I missing? And why does it randomly start idling rough, then just go away? It's very strange.

 

Have you ever sea foamed it? Personally I would run a can in the fuel and a can in induction vacuum hose and then see if it cleaned or unstuck anything. $6.99 a can at Walmart. It's an inexpensive thing to do.

 

Had a consistant misfire a few months back. Ended up being a short from my O2 sensors to my ECU. Put in a used ECU, problem was fixed.

 

I had an ECU that was bad a few months back, had to swap in a new one, but on that truck/ECU the bad side 02 was completely dead. Did your 02's cycle normally?

 

Don't vacuum leaks usually cause problems at idle but go away under load? Plenty of hoses and crap clamps to go bad.

 

That's a great thought, and I have checked most of those. Usually the vacuum leaks caused problems at idle with carburetors because of low manifold pressure and lean mixtures. Fortunately with todays MAP sensors and motorized idle air controls the computer usually compensates for those sorts of things.

Now a bad MAP sensor or idle air control motor could be a definite possibility for a P0300 (random misfire - not making the proper adjustments - especially at cold start or during idle)- but not sure it explains only cylinder #8, unless the vacuum leak is only on that cylinder. This train of thought has definite possibilities - anyone ever run in to that?

 

I am having similar issue with #6 and #8, however, when I pulled wires and plugs and grounded to manifold, I got no spark from plug. Changed plug and wire still no spark. now I ordered new coil packs, but if there is something else I could check, I would prefer to not have to replace the packs.

Codes are:
P1300
P0306
P0308

 

6 and 8 are on different coil packs, and 6 is tied to 7 (they fire at the same time) and 8 is tied to 3, I am guessing it is unlikely you have two bad coil packs. Flip the coil packs and see if follows the bad cylinders (8 will become 7, 6 will become 3).

BTW, you might want to start a separate thread...

 

I did and it fell to the bottom. My problem is similar is why I posted here.

 

More data from driving today:

When highway driving, after clearing codes - codes will not reappear.
Short stops, and restarts - codes don't reappear.
Significant idle periods, or stops for than a few minutes - codes come back. Always 0308 and sometimes 0300.