My buddy, who is rarely around a computer, has a 2006 Cummins with a 6 speed, Airdog 150, S&B dry filter cold air intake, and 4 inch straight pipe to dual 6 inch stacks. I only know enough about the common rail systems to know how they work. Lately when he gets on his truck, sometimes it will smoke like a freight train, and other times it won't smoke at all. His truck is completely stock other than what I listed, and I know a stock truck shouldn't be smoking like it has bigger injectors and a programmer. On top of that, no matter how much he babies it, the best he can get for mileage is about 16 mpg. We were wondering if that sounds like some bad injectors or what? He's going to hook up a scanner and see if anything comes up. What do you guys think?

 

Well you didn't list that he had a programmer just a lift pump and from what I hear that wouldn't make it smoke by any means it's usually the programmer and bigger injectors that makes it smoke. The only other possibility is a bad injector or a possible leak in your intercooling system. Causing it not to get enough air which could be means to bad mpg just throwing some ideas out there.

 

I forgot to add that he has the factory match Autometer gauges in his truck too. He has fuel pressure, pyrometer, and boost. The truck will hit about 35 psi wide open, so I can't see there being a leak in the intake system when it's making that much. No it does not have a programmer or any fueling modifications other than the S&B, 6 inch stacks, and Airdog 150

 

Thing thats throwing me off here is how you say its intermittent...

 

Does it miss or knock when it does it? If not, then I wouldn't think it is injectors?

It almost sounds like the rail is being pressurized all the time (as in at the max psi), and when he gets on it it has all that pressure to dump fuel. I would have someone hook up and find out the rail pressure. If it turns out to be a rail pressure issue, it could be a number of things.

 

CP3 maxed out would rattle so bad he would shut it off! Try and unplug the Cp3 say wow and plug it back in. How long did it take to recover? 16mpg is fair but black smoke
can only be a few things. Plugged air filter, boost leak, Map sensor. Did he buy the truck like that? Maybe it has a program already in it? Get the ECM reflashed. Check the turbo for damage too.

 

Nope he bought the truck bone stock with 50,000 miles on it. He did the air intake, airdog, gauges and exhaust. It doesn't knock or miss when it blows black smoke. All of the modifications have been on the truck for probably a year or two. This only started happening about 4 or 5 months ago. He doesn't drive the truck daily, so he barely puts on about 6,000 miles a year. Since it is intermittent, I was thinking the same thing about rail pressure. If it was a bad injector it would be all the time and there would be other signs too right?


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