P0300 Code 6.0L 1500HD

Vortech91 · July 10, 2019

I just bought a 2001 silverado 1500hd with 140k miles. Truck runs really good, idles nice, tons of power, never stalls. The problem is it flashes the "check engine light" once warmed up, around 2000 rpm or so light load. It will continue to do this while driving and I believe preventing the torque converter from going into lockup. Scanner shows most misfires are from cyl 5 and cyl 8 (10-20k counts) and cyl 1/6 (maybe 100-200 counts). I paid a shop to do a crank relearn, which they said they did, but I cant verify that. no fix from the relearn. I changed plugs, and wires. swapped coils around, and replaced injectors on cylinder 5 and 8. problem still with cylinder 5 and 8. Fuel pressure is 55 engine off and 49 or so engine idling. I checked the ground tsb on back of head. (added a ground wire from braid at firewall to engine alt bracket). Fuel filter is good. What is my next step? Do I drop 300 on a gm tech 2 clone to do the crank relearn again? do I do intake gaskets (idles fine) I already cleaned MAF. I was thinking of just getting the code calibrated out, but Im not 100 sure that it isnt missing. I cant feel any hesitation at all, it doesnt throw code under hard acceleration, just very light highway driving. Do I keep throwing money (EGR block off, fuel pump, crank position sensor). Does anyone have a suggestion on a good dealer or shop to fix this kind of problem in southeast MI?

I can provide freeze frame data, if needed.
LT trim bank 1 7.8%
LT trim bank 2 5.5%
ST trim bank 1 -3.9%
ST trim bank 2 -.8%

I have access to additional data if more will help

On another forum someone suggested fuel pressure being suspect, but wouldn't short term fuel trim numbers be positive to compensate for lack of pressure causing the miss? I would also think that WOT runs would show more misses if fuel pressure were too low. WOT acceleration is excellent with zero "check engine light" flashes.

Things I am going to do

I ordered the Ilink400 so that I can hopefully do the crank re learn myself. (I really hope that fixes it)

I ordered intake gasket set.

I am going to do a compression check on all cylinders, and a running compression on cyl 5 and cyl 8 and one other cylinder as reference. I guess if some cam lobes were wiped out, this could explain the problem.

Jglew82 · July 10, 2019

Fuel pressure does look slightly low - should be around 60 plus or minus about 5 ps when runningi, which might explain why your LTFT's are trending lean on both banks. I don't think doing a crank learn will do anything to be honest. Check your pump, pressure regulator (block your return line and re-test pressure) and filter to make sure there are no restrictions.

Edited July 10, 2019 by Jglew82

riverbanks · July 10, 2019

Yup,and was the pressure test done cold or warm?and Wondering if egr is misbehaving

Vortech91 · July 10, 2019

Fuel pressure goes to 60 if I pull the vacuum line off the pressure regulator. fuel pressure was checked on a somewhat cold engine. not full operating temp.

Formulabruce · July 10, 2019

I would remove the air box ( one large hose clamp) and then Clean the throttle and plate ( both sides) very thoroughly, with Throttle body cleaner ( not carb cleaner). Even a slight air restriction or dirt on the plate can cause some problems. This area needs to be "surgical clean" to work well.

Vortech91 · July 18, 2019

I received my Ilink400 scan tool and followed the procedure for crank relearn. It has been one week and no codes have been set. If you have a 6.0l with P0300, but do not feel any misfires, try a crank re learn. The shop that claimed they did this will not get my business again. To my knowledge the cheaper scan tools that will preform this task are GM tech 2 clone, or Ilink400. Snap on, and higher prices options will also do this.

Edited July 18, 2019 by Vortech91