P0300 random missfire, can't diagnose

[ChevroletTough]

Hey guys, new here but I've been reading alot. I'm a member over @ GMFULLSIZE as well. I've had a p0300 random missfire code for awhile now on my 04 5.3L 1/2ton. I can't seem to figure out the issue.

 

Only does it if the RPMS hold over 2500. I can even get it to do it when in park or neutral holding the RPMs in that range. CEL flashes.

 

Fuel pressure checked 58lbs (I do not have the fuel pressure regulator)

Injector pulse was all checked

sensors all checked fine

Accelerator is calibrated correctly

new NGK iridium pulgs and Napa Belden premium wires (was doing it before this as well)

Coil packs were all checked

intake was sprayed and checked for leaks

 

 

The only thing I've been reading on is a crank relearn from a GM tech 2.

 

The local GM dealership suggest I unplug the MAF sensor and see what happens (the CEL light will come on and stay on of course, but if it doesn't flash while the MAF is unplugged... maybe that's the problem?

 

 

I have noticed my fuel pump is a little louder now, it is the factory fuel pump. I've got around 122,xxx miles on the truck

 

Only engine/drivetrain mods: K&N 77 series intake, corvette servo.

 

Would seriously love to resolve this damn issue. I know there are others with it too.

 

Thanks in advance!

[ChevroletTough]

missfires are on cylinder 1,5,6,8 both banks... very strange.

[DaveH71]

Few things to check.

 

1st pull the crank sensor and check for excessive rust around where the sensor pushes into the block. Have seen this code caused by rust forming around the sensor and it would keep the sensor from seating correctly in the block.

 

2nd check valve lash on effected cylinders. Had and 07 classic recently that had a p0300. Checked everything, last thing to check was valve lash, ended up being a bad cam at 170,000 miles.

[silveradosid]

plugged cats will also cause random miss fire codes, my 01 did this with 130k on it

[ChevroletTough]

Few things to check.

 

1st pull the crank sensor and check for excessive rust around where the sensor pushes into the block. Have seen this code caused by rust forming around the sensor and it would keep the sensor from seating correctly in the block.

 

2nd check valve lash on effected cylinders. Had and 07 classic recently that had a p0300. Checked everything, last thing to check was valve lash, ended up being a bad cam at 170,000 miles.

 

 

Oye Vay. Never had to remove the crank sensor. Living in WI, salt has caused a few issues. I found a video on how to remove it.... looks like removing the starter first? I had to replace the starter this winter due to a failed solenoid.

 

 

 

If I replace the sensor, do I need a crank tech II relearn?

plugged cats will also cause random miss fire codes, my 01 did this with 130k on it

Exhaust seems to flow well. But thanks.

[ChevroletTough]

Is this the right part #?

213-354

 

Amazon has it for a good price, and it's prime shipping.

 

https://www.amazon.com/ACDelco-213-354-Original-Equipment-Crankshaft/dp/B000C9JXZ2/ref=cm_cd_al_qh_dp_t

 

***EDIT*** I looked the part on ACDELCO.com and that is the right part number. Ordering now.

[DaveH71]

Yes the starter needs to be at least unbolted and pushed out of the way. The crank sensor is right behind it.

 

No tech 2 needed, it will relearn itself. Just do a few drive cycles.

[ChevroletTough]

Thanks. I'm getting mixed results with the whole GM tech II needs. I'll just call the dealer to confirm (not that I don't believe you, I just want clarification.)

 

GMFULLSIZE forums say I do need one.

[ChevroletTough]

Dealership said I really do need a relearn. So, after replacing I'll run it down and get that done. $30.

[txab]

You need a re-learn

[ChevroletTough]

Thanks. I've got the part, now just need to replace it. Assuming I can drive it about 5 miles to the dealership afterwards to get it relearned?

[ChevroletTough]

left (passenger) rear manifold bolt is broke, but I don't hear an exhaust leak?

[ChevroletTough]

Taking it to a local dealer as they said they want to look at it. They don't think i should replace the crank sensor yet. We'll see..... I may still replace it and have the relearn done.

[ChevroletTough]

SUCCESS!!!!!!!!!!!!!!!

 

They checked the crank shaft sensor, it was reading weird. Tried a relearn (just for Ss and Gs). no luck. Replaced it with the sensor i bought (they had it up in the air anyway and just said we'll replace it). I advised them to call me as I wanted to replace it first and then have them do the relearn, but they didn't charge me any extra to replace it since it's so easy. All good to go now with a new sensor and relearn.

 

I've been fighting this for almost a year. Thank you guys so very much!