rough idle and p0300 random

[mkcom1]

Hi

So this is a 05 1500hd 6.0, 128k. I have replaced cats (they were starting to go) all four o2's, wires,plugs and (as part of another issue the throttle body and wires to the ecm from same along with connector and i did a reflash of the ecm ) also fuel pump and sender. All parts are gm. I am having a p0300 only at highway speeds with no loss in power or driveabilty issues other than a rough idle standing still. The DTC will reset after a few on/off cycles but then reappear when I go on the highway again. I looked at all my specs with my code reader and found that both banks short and long term fuel trims are running negative. Not high negative, i.e. double digits but generally negative. In my thinking a negative fuel trim indicates the ecm is leaning the engine in response to a rich condition. My thought is that if this is true perhaps I have one or more injectors that are leaking at idle, not bad, but enough to lean the motor out causing a rough idle. Not sure why I would get a missfire code at highway speed if this is true though? Looking at the maf data it appears to be fluctuating smoothly as I open the throttle with no spikes etc. I am thinking of either pulling all the injectors and having them flow tested and cleaned and or just replacing all of them. With 128k and using 10% ethanol it only seems logical that they might not be performing at peak. So with all of this being said does anyone have any thoughts, tips,advice. Also I have looked online and found a few places that do hydrosonic cleaning flow testing etc on injectors injector rx and marren. Does anyone have any opinions of these companys. Also in looking for new injectors I found a company called Motor man fuel injectors. Anyone use them or have opinions or another rec on a place to get these other than gm parts direct. Trying not to go broke. Any help is much appreciated. I can provide a datalog file if needed, but tried to attach an xps file of same and can't

 

Thanks ken

[jcallipare]

Did you get any resolution on your issue?

[mkcom1]

no not yet