Misfire

[mulletman]

i have a 2007 nbs sierra 1500 5.3 280,000 km

 

i keep getting a p0303 code when i am idling hook my dads otc scanner up to it and it miss on #3 steady and when i rev it up it goes away when i rev it up to 2000 rpm and let it come down it will misfire on random #'s but only once and then lots on #3 when i am driving it around with the scanner on it runs great when driving i pull a 27 foot trailer around up hills no problem lots of power but when i am sitting at an idle it will miss i have smoked tested the intake no leaks took the fuel rail off and swaped the injector with #8 swaped the coil with #6 still ran the same changed the o2 sensor on that bank before the cat nothing did a compresion test between 120 and 130 on all my scanner says the fuel pres is 58 key on and 43 when running just last night i up plugged the map sensor while the truck was running and the rpm went up about 100 and no more miss so i took my brothers map sensor off his 08 same part number and tryed it in my truck still misfired since it runs better in open loop i am thinking that it is a sensor problem and not internal i am taking it to gm on sat so they and put there scanner on it and tell me whats going on i am also going to get them to relearn the crank sensor too. i know what some of you are going to say its the fuel pump but it runs good at higher rpm and pulls the big hills no problem with my 6000lbs trailer the biggest problem with the misfire is when i am sitting idling somewhere and it sets a code the p0303 code as soon as i pull away when it goes into 2nd gear it will hammer it kinda like when i had my map sensor unpluged it will hammer 2nd and thats it no other gears i know that the map sensor tell that computer how hard the motor is working for shifting hope the dealer can tell me something any ideas any one???

[mulletman]

i have a small tranny leak front pump seal wondering if my crank sensor could be dirty?

 

 

can i pull it out and look at it with out getting it relearning it?

[Wires]

Do you have a CAI on it? I had an issue where the pipe going onto the throttle body popped off, and when driving, vacuum pulled it on and it was fine. Idling it started tossing codes (I don't remember if it was a misfire or lean bank code???)

[mulletman]

whats a CAI?

[rodram]

... that would be Cold Air Intake ..

[mulletman]

nope truck is stock

[mdauwald]

I know you said you swapped the injector and coil but did you also swap the ignition wire?

[441G]

check cylinders that fire before and after 3 - also afm lifter and valve spring