My truck now has about 115,000 miles on it. A couple of years ago this truck began setting injector related trouble codes - like P0302 and sometimes P0089/93. This code setting process was getting worse as time passed - over about a 2-year time period. It looked like the engine had a bad #2 injector. The engine also ran a little rough and we frequently smelled the acrid gases of incomplete combustion in the cab. I began preparing for an injector replacement.

For most of the truck's life I had used some sort of fuel treatment - mostly Stanadyne and/or Power Service. I also used some ATF. Once the code setting began I stopped adding anything to the fuel. Then... the problem went away all on its own.

It's been more than 6 months since the codes went away and the engine returned to running smoothly and normally.

Some could argue that the ATF might have fouled the injectors. Maybe. I also think the problem could be attributed to an easy life in a cool environment. I know that the 6.2L/6.5L diesels I've owned all ran smoother after a towing trip where the engine was worked hard or a period of time and number of miles. I know that hotter combustion temperatures and higher fuel flow rates help clean the injectors, though I haven't towed with this '01 GMC for quite a while.

We'll see what develops....