03 1500HD crew 75,000 highway miles. Engine warning light comes on at 65mph and above goes off below 65.The code says misfire on #1 and #6.The truck has new plugs/wires the dealer checked the coils,injectors and sensors. The dealer suspects carbon build up on valves and the only way to confirm this is with a $600.00 tear down and then a $2000.00 plus valve job to fix the problem. I know there is an induction cleaner but the dealer doubts that it will work. What if I don't fix it? I burn quality fuel ( BP and Mobil) use full synthetic oil there is no reason I should be doing major engine work at 75,000 miles. Any other options? Thanks in advance.

 

Is this a diesel?

 

Sorry 6.0 liter gas.

 

is there just a miss fire when cold or hot the 5.3 &6.0 have intake leak problems leaking vacuum causing
miss fire codes

 

Are you using crappy gas, IE arco, discount gas? because those cause lots of carbon to build up.

 

Only quality fuel (BP or Mobil). Light only flashes at 65 and above engine is hot. I don't know the codes but I'll find out.

 

so how do you know if you have a intake leak i have a 2004 2500hd with a 6.0liter in it and I am have a lean code po171 and p0300 random misfire code the frist thing i thougth was vac. leaks but did not find any. does any one have any ideas?

 

MCOLLINS72022,

Start a new post for more feedback.

 

Had same problem at about 70mph code read misfire change injectors on cylinder with the misfire no more problem. Since I know how to do it that's why I did mine's you may want to try a injector flush first.


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