Misfire/speed triggers flasing check engine update info

[SJ75]

The update info ;    Now that this project has me doing almost all highway  except the last mile two new clues have emerged.    two points on the high will most likely trigger the Flashing CEL.   going over 60 on shallow long down grades where light power has to be applied to keep speed up. steeper down grades backing off throttle completely doesnt do it.  up hill under power nothing.  flat runs only if the run is long and it gets over 60.     The other clue since it sat for a while because of work stoppage,  Iet it sit for two weeks or more and just turning the electrical system on will trip the reduced power.  Start it up and it still responds to throttle inputs in  park,  let it warm up, shut it down and restart and the reduced engine power disappears.  the cel stays on for a while.  it too clears on the next start.

 

possible suspects?  MAF? IAT? Gasket? Crankshaft sensor?

 

Original:

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]

The,shut it off and restart makes reduced power disappear,makes me think power or ground problem,try gmupfitter.com for wiring schematic,check all grounds

[Formulabruce]

Do BCM ( under the truck, DS, on the cab mount extension facing rear) and engine ground back of engine pass side to firewall.

 Also, in 2004 GM updated the valve-body etc.on the 4L80E transmission to address some issues in 2003 and back models.

 Depending on tire size and load on engine, the trans will go into lock up between 55 and 60. IF that solenoid  wears ( which they do, all the upshift solenoids do) it may cause the trans control to send  signals to the ECU as a failure. With the miles on that trans, I would get it it rebuilt and updated with a new or updated rebuilt valvebody, a new Sonax Boost valve in the pump and new clutches and steels and seals.

 I also would put in a bigger aftermarket trans cooler which will fit in the stock location with minimal work.

 Good luck !

[SJ75]

On 6/2/2020 at 9:59 PM, Formulabruce said:

Do BCM ( under the truck, DS, on the cab mount extension facing rear) and engine ground back of engine pass side to firewall.

 Also, in 2004 GM updated the valve-body etc.on the 4L80E transmission to address some issues in 2003 and back models.

 Depending on tire size and load on engine, the trans will go into lock up between 55 and 60. IF that solenoid  wears ( which they do, all the upshift solenoids do) it may cause the trans control to send  signals to the ECU as a failure. With the miles on that trans, I would get it it rebuilt and updated with a new or updated rebuilt valvebody, a new Sonax Boost valve in the pump and new clutches and steels and seals.

 I also would put in a bigger aftermarket trans cooler which will fit in the stock location with minimal work.

 Good luck !

 

 

Tires I dont think play a roll here.  News ones put on in decemeber with the problem going back a couple years.

 

I never got any letter from GM about an upgrade to solve problems in the 4L80E.  Then again  the dealers around here dont want to do anything. So finding a reputable place around here is a shot in the dark. Since I am not hearing or feeling anything, I will start with the solenoid. And look at the rest when I have the money.

 

I will do the ground check as well.  When All this throttle body  code started that cold 10 degree january morning 4 years ago, it went to a place where I think they did more damage then good.  That place is gone and nobody knows where the guy went.

[davester]

GM makes regular changes to their transmissions over time to improve them and fix problems/issues with them (as well as engines and other parts of vehicles).  They never send out letters to prior customers letting them know they've made these changes (nor do other manufacturers).

[Formulabruce]

Your transmission HAS lived a longer life than GM planned on. The solenoid plungers go in and out of a bore in the valve body at super fast speeds. This can, and does wear the Valvebody, and make pressure changes that cause issues in driveability. IF you go the solenoid route,

1. KEEP the transmission pan "gasket" and re use it. Its metal covered by rubber that WORKS. Replacements are paper.

2. Buy all the upshift solenoids and replace them with the lock up solenoid.

3. Buy the lock up solenoid Harness as these get hard and brittle.

  I went this route on a '03 HD, and was less than a year I was buying a rebuilt updated TB and all the rebuild parts and boost valve.

 Highly recommend the bigger trans cooler out front. 

 

[SJ75]

On 6/8/2020 at 2:22 PM, Formulabruce said:

Your transmission HAS lived a longer life than GM planned on. The solenoid plungers go in and out of a bore in the valve body at super fast speeds. This can, and does wear the Valvebody, and make pressure changes that cause issues in driveability. IF you go the solenoid route,

1. KEEP the transmission pan "gasket" and re use it. Its metal covered by rubber that WORKS. Replacements are paper.

2. Buy all the upshift solenoids and replace them with the lock up solenoid.

3. Buy the lock up solenoid Harness as these get hard and brittle.

  I went this route on a '03 HD, and was less than a year I was buying a rebuilt updated TB and all the rebuild parts and boost valve.

 Highly recommend the bigger trans cooler out front. 

 

@Formulabruce.  So where is a good place to get these parts from.?  Along with a good instruction manual on how to do it.      Unless by some miracle I find a shop that listens and wants to help,  I am looking at doing this on my own.  I am mechanically  inclined.     

[Formulabruce]

 Buy the upshift , and lock up solenoids off ebay, as well as the harness. Thats really all you can do without taking the valvebody down.

 There are plenty of places that sell updated valvebody and new sonax boostvalve for the pump.

 For now, the solenoids and the harness and a B&M supercooler out front ( easy install to original mounts and 2 hose clamps. )

 There are a few videos on you tube to help you through the solenoid swaps. There are also location maps on the net to show you where they are.

 The one end of the pan is tricky getting down, but it will come. RE USE the original pan gasket.

 Good luck !