Black Tailpipe

bsc · July 19, 2003

When I tow my 5th wheel the tailpipe gets very black carbon buildup. After I disconnect and drive for another hour or so the tailpipe is perfectly clean. This carbon builds up after driving for 8-10 hours at 70 miles per hour. The truck is a “02” 2500HD 8.1 Ally. The truck doesn’t labor and seem to run great. I asked the dealer if there was any type of fuel or air mixture that could be adjusted, they said “No”, this is normal.

Is this “normal” or am I running to rich under a load ?

Thanks

BSC

R Dogg 56 · July 19, 2003

You're probably running a little rich. Are you noticing a drop in fuel milage?

MarkD · July 19, 2003

Knowing how GM likes to muck with things, you may have a detonation issue under load. To fix this, the PCM will add fuel to cool the combustion chamber. I would try a couple of things.

1. tow with at least one tank of the best/highest octane gas you can find.

2. Hook up w/ someone with a diagnostic tuner and note your Knock retard and O2 levels.

3. Run in tow mode if you are not already to raise rpm and keep motor from lugging.

This should provide you with enough info to make an informed decision about what the dealer told you.

WEFs99 · July 19, 2003

It sounds normal to me. It senses the load so the computer compensates with more fuel.

bsc · July 19, 2003

Thanks for the quick responses.

I do run in “Tow Mode”, so I am stretching the time between shifts. In my run from CT. to MN. In April, I didn’t notice any issues with power, the truck was always responsive.

I do feel the mileage while towing is a bit low. Without towing I get between 13 & 13.5 highway. When I first started towing my mileage was around 8. For the trip in April it was around 6.

I understand that I am pushing in allot more fuel, I just figured if I had extreme carbon buildup in the tailpipe, I was not burning all the fuel, so maybe I didn’t need to push as much in the engine.

I don’t have access to any type of analyzer so I can’t check that, but I will certainly use the highest octane gas on my next trip to see if there is any difference.

Thanks Again,

Brian