phoenix5

I have a mainly stock 2007 silverado 2500hd 6.0l gas

I have been getting a p0300 code for random/multiple cylinder misfire intermittently when accelerating up to between 70 and 80mph, most usually the mil blinks a few times around 75mph but sometimes the light will stay on, and the code is for p0300.

I have replaced spark plugs (properly gapped), new Taylor spark plug wires, and have been using 91 octane (highest available) and still this code comes back but only when I get to around 75mph and of course its not consistent, and being that it isnt specific I dont know what I need to do to fix it.

Please help.

2xLS1

iTrader: (25)

Use a scanner to look at misfire history by cylinder.

phoenix5

Okay, I have a bullydog and I also have a bluetooth obdlink mx but I do not know how to access history or the other advanced functions for vehicle diagnostics, I can see the pid sensor data and freeze frame, but I usually just clear the code. There is a vehicle report function in the obdlink but I haven't used it on my truck. I am actually at work and wont have access to my truck until late in the evening.

I thought that even if there were more than one cylinder misfiring that it would give a code for each cylinder like p0301 cylinder one misfire etc

2xLS1

iTrader: (25)

When you clear the code you are also clearing the history. A scanner like HP Tuners will let you look at the misfire history by cylinder by selecting those PIDs in the table display..

phoenix5

Thanks for the information, so I will need to wait for the code to come back in order to get history information that will tell me more specific details?

At least on my obdlink the pids are live sensor data, is this correct or should it have more to it?

terravast4

iTrader: (25)

might do a pressure check of exhaust for a bad catalytic converter

jaawood

How many miles on your coil packs?

dustiebutt

I am having the same sort of issue in an L76 transplanted into a '93 pu......HPT misfire history showing tons of misfires for #5 & #8.........swapped coils, plugs, injectors and plug wires around with NO change........60 lbs of constant fuel pressure.........these are not big misfires, I can feel them just slightly........I am going to check the wiring, redo some grounds but if thats not the problem, the cause may be rooted in the ecm........chasing tail again !!!

2xLS1

iTrader: (25)

You could try a crank sensor relearn to make sure they are not false.