Misfire/speed triggers check engine

[SJ75]

I have a 2500HD,  2003, 202000 miles 6 liter gas.   So I have been battling the dreaded throttle body code.  It comes with 0300, 0600 codes.  Replaced the throttlebody, fuel pump, plugs, plug wires, coils, and computer. 

Here is what it is doing right now.    At idle it has noticeable misfires.  Under power it doesnt misfire.   If I run over 60, the check engine flashes for 3-5 seconds. then goes out.  It will only do it if I run for at least a minute or more over 60.  No sounds, or vibrations, gauge indications, that indicate any issue. if I keep going.  It can take a while for it to cycle like that again.   Below 60, I can go and nothing shows.  No check engine light.  Also cold days if I dont let it warm up it can trigger the reduced power mode if I move it above 50.  But once warm it is fine.    It does restart with no issue.    Oil level does not change over the life of the oil,  no visible exterior fluid leaks.

The mechanics around here just like to check the codes and and say it is the throttlebody when that has been replaced 3 times.  (I kept the last one).  They dont seam to want to do anything past that.

Also, It doesnt like staying in over drive.  it shifts out sometimes.  Sometimes it stays.  Dont think it is the clutch.  it shifts smooth and quiet in all gears.  Most of the time I only know it shifts by watching the RPM's   I am thinking solenoid is going bad.  Thoughts?  

This engine and transmission have never been opened.  there has never been a need to get inside either.  only the valve covers removed to inspect for a possible issue that might  be cause a misfire.

[riverbanks]

Injector balance test needed?or put some techron in the tank

[Benh]

I have essentially the same problem, with misfire code.  My truck stays in OD above 60, but the torque converter will lock below 60, but will unlock above 60 regardless of the load.  What is an injector balance, and what is techron?  My truck is 2001 2500HD, 6.0.

 

Thanks

[riverbanks]

Techron,a very good injector cleaner,the balance test,requires a good scanner and afuel pressure gauge,sees if all are behaving the same,a last item to do,have you cleaned the MAF?

[Benh]

I have not cleaned the MAF.  The scanner I have is not fantastic.  What is being read by the scanner.  Is the guage to monitor the fuel rail pressure?

My truck has about 270000 kms on it.  Is it possible that the injectors need to be replaced?

 

Thanks

[riverbanks]

High mileage, anything is possible, check spark plugs, hopefully all even in color, fuel pressure is not measured by scanner, what codes?

[Benh]

I just changed the plugs and wires.  The code I am getting is P0300.  The old plugs were almost exactly the same color.

 

Thanks

Edited February 15, 2020 by Benh
Additional information

[riverbanks]

Good to hear on plugs, does motor misbehave or just tranny kicking out of high gear,if no skipping,odd behavior, you could try a crankshaft relearn procedure,needed by a good scanner

[Benh]

It seems to idle and run extremely smoothly. There's no odd behavior other than the torque converter and throwing up the code.  It doesn't seem to have a lack of power.  

 

Thanks

[SILVER SLED]

Try a crankshaft position sensor relearn.  

[SJ75]

I dont think they did a balance check at any point.

 

I wil start with running some techron through it first

[kdog55]

Ill second the crankshaft position sensor relearn. I dealt with the blinking CEL for years {05 2500 HD/ 6L} and finally had my friend do a relearn and haven't had it since. It literally takes about 30 seconds to do, but you will need a professional quality scan tool. 

 

[SJ75]

Since the thread seams to be hijacked,   Should I be doing the same thing and run a relearn?   Or something different