Black Puffs of smoke!

[Skipper 05MA]

We recently acquired an 08 Esses with the ISM 500 Cummins. Upon down shifting we notice a puff of Black Smoke from the exhaust. We have had the engine services..oil, filters, etc. but still see it. Any thoughts? Thanks

[Steve Ownby]

Are you under heavy throttle pulling a grade or some other condition? Black smoke usually results from lots of fuel in the combustion chamber & most likely is not a problem. Cummins' web site has a contact email function that I have found to be helpful. If it is just a brief puff & doesn't last I would not be concerned If your check engine light is not coming on. If it continues & you are worried it would be worth a trip to a Cummins shop for piece of mind. The ISM is a great engine with good power & reasonable mileage. It has a rep among diesel mechanics for being relatively trouble free.

Steve O
'03 Sig

[RustyJC]

Black smoke is a symptom of more fuel than air available to burn it. The black smoke is partially oxidized fuel. I have to watch the shifts on my truck because, with bigger fuel injectors and a modified fueling schedule, it's easy to overfuel it and generate black smoke that clears up when the turbo catches up and makes enough boost to burn the fuel. I have to roll into the accelerator more gradually after a shift, watching the boost gauge so that I don't fuel faster than the boost is coming up. In your case with an automatic transmission, if your foot is on the floor when the transmission shifts, you're probably going to overfuel for just an instant until the turbo adjusts to the new engine speed/load after the shift - thus, the puff of black smoke.

To minimize smoke, be sure that your air filter is clean, the charge air cooler is clean and that none of the hose connections on the pressurized side of the combustion air system are leaking.

Rusty

[EngineerMike]

Skip- check w/Cummins on the status of your ECM flash, you will need engine number which on mine is on upper rear engine flange on PS (rear = rear of coach). I just checked mine (ISL built March07) and it has version 13 software in the computer. For my rig they are up to version 32 so I'm 19 versions behind. I think the versions came fast & furious for the early Diesel Particulate Filter engines which started in 07. Your 08 probably has an early DPF engine so a check is in order.
Like the others say- no big deal, probably a fuel/air table issue or an injection timing thing that will get ironed out w/updated ECM software. You may also want to ask if your engine is due for any recalls or campaigns (mine has 3 stacked up).

[Steve Ownby]

Skip is a lucky guy. Cummins got a waiver on the ISM so he has an 08 with no dpf.

Steve O

[Skipper 05MA]

Thanks, I really appreciate all the great info. The smoke is a very brief puff which (I think) is when the trans downshifts. It doesn't necessarily need to be under heavy load. I've changed all the fuel filters and the air filter is still with normal limits. We need to make a run to Spartan for some tire wear issues on the right side of the coach so I'll have that checked then. Does Spartan do this or will they refer us directly to Cummins? I do have a Coach Care facility north of KC and was impressed with their maintenance on my 05 Mountain Aire.

Thanks, Again!

[Gary RVRoamer]

Why not call Cummins Tech Support and ask them if this is normal. I've never heard of it in a properly running modern turbo diesel. The electronic controls are supposed to prevent that sort of thing.

I don't think Spartan will work on the Cummins, but everything that feeds it fuel and air is theirs and they can check all that out.

[BZam]

Quote:

Originally Posted by Skipper 05MA Thanks, I really appreciate all the great info. The smoke is a very brief puff which (I think) is when the trans downshifts. It doesn't necessarily need to be under heavy load. I've changed all the fuel filters and the air filter is still with normal limits. We need to make a run to Spartan for some tire wear issues on the right side of the coach so I'll have that checked then. Does Spartan do this or will they refer us directly to Cummins? I do have a Coach Care facility north of KC and was impressed with their maintenance on my 05 Mountain Aire. Thanks, Again!

Had you been using your compression braking? When I got my 99 DP I went down the Grapevine into the Bakersfield and at bottom I accelerated and notice this black smoke in puffs. Stopped and went back. Got under and it was hot back there but engine was running OK. Wife started looking up Freightliner places in Bakersfield and thought I would limp in. We went on and no more signs of smoke so went to first rest area, checked things, and all was normal. We went on to a big RV club and was telling some of the 'experienced' this story. They said that is normal after using the compression brake on big letdown.

At an FMCA I was told to turn it on when starting down and leave it on. But I just use it as needed coming down and don't leave anymore than necessary based on going back that day and seeing how hot that underside of was!!!!!!