P0300 Misfire Help Needed

[fataugie]

Good Morning all,

 

I've got a problem with P0300 misfire on my 2003 2500 HD 6.0L 4x4 with 57K miles.

 

During a recent 350 mile trip, the MIL flashed at me multiple times during the trip. Just prior to the trip, I filled up and added Techtron treatment to the tank. I figured it was the treatment working it's way through the crap. When it kept doing it (over a dozen times during the trip), I got concerned and had Autozone pull the codes. P0300. OK, since then, I've run 2 tankfuls through and still getting the misfires.

 

 

Still getting the misfire on the same cylinders 2, 5, 6, 8. Out of the four, 2 and 6 are the worst. I cleared the codes and history back on Saturday. The only codes were P0300 and the cylinders 2 and 6 showed 58K of misfires. The other two were much less.

 

Took it to the dealer on Tuesday who replaced the fuel filter and did a fuel system cleaning. I then replaced plugs and wires (AC Delco for both). $450 and nothing changed.

 

Anyway, so since this past Saturday, I've accumulated 2500 or so on #2 and #6 and about 800 on #5 and #8.

There is a pending code and here are the details:

 

DTC: P0300

 

Accell pedal position 0-

Accell pedal position indicated angle: 0%

Barometric Pressure: 13 PSI

Desired Idle Speed: 575 RPM

Engine Coolant: 192 F

Engine Load: 25%

Engine Speed: 2555 RPM

Fuel Tank Pressure - Volts: .02V

Injection PWM avg. bank 2: 8.6 mS

Long Term Fuel Trim Bank 1: 3%

Long Term Fuel Trim Bank 2: 1%

MAF: 69.21 gm/s

Manifold Air Pressure: 58 KPA

Short Term Fuel Trim Bank 1: -3%

Short Term Fuel Trim Bank 2: -2%

Start Up ECT: 37 F

Throttle position desired angle: 21%

Throttle position indicated angle: 21%

 

--------------------------

 

I'd really would like to avoid just throwing parts at the d**n thing. The wiring looks good from what I can see, nothing is obviously damaged around the coils or injectors, but I don't really know that much about fuel injection. The tech who worked on it said the misfires became worse when he sprayed the engine down to work on it. I have no idea exactly what he meant, if he used water on the engine or carb cleaner around the ports, who knows.

 

If I take it back, the first thing I'm going to demand is a new tech, I think this one was guessing at best.

Any and all suggestions would be appreciated.

 

Thanks

 

Tony

[michigansilver03]

p0300 is a random misfire, have you notice a strange smell. It maybe the Cat Converters going bad

I'd have the exhaust back pressure tested.

[fataugie]

Actually, it's random / multiple misfires which I realize. No smell. I know the smell of a plugged cat (rotten egg) and there isn't any smell present. If the cat was going bad, shouldn't all the cylinders misfire at some time or another? They aren't. Just the four I listed. They WILL go bad if I don't get this solved soon, dumping raw fuel into them is not good.

 

Thanks though, I appreciate it.

 

Tony

 

 

p0300 is a random misfire, have you notice a strange smell. It maybe the Cat Converters going bad

I'd have the exhaust back pressure tested.

[michigansilver03]

Actually, it's random / multiple misfires which I realize. No smell. I know the smell of a plugged cat (rotten egg) and there isn't any smell present. If the cat was going bad, shouldn't all the cylinders misfire at some time or another? They aren't. Just the four I listed. They WILL go bad if I don't get this solved soon, dumping raw fuel into them is not good.

 

Thanks though, I appreciate it.

 

Tony

 

 

p0300 is a random misfire, have you notice a strange smell. It maybe the Cat Converters going bad

I'd have the exhaust back pressure tested.

 

 

Just it is strange this all happen with your mileage, I don't want it say coils, but it maybe cheaper to have the back pressure tested, Try swapping the coil and see if it follows the coils.

 

Good luck

[nmw75]

Hello,

 

Has there been an outcome to this problem? I have the exact same problem with my 2004 Sierra with the 5.3l and only 30k on it.

[bobcat5544]

Hello,

 

Has there been an outcome to this problem? I have the exact same problem with my 2004 Sierra with the 5.3l and only 30k on it.

 

This is an old post. If you are haveing trobble please post the problems you are having including your vehicle info here since you can't make a new post until you make 5 post on other topics or click on my name and send me a personal message.