More Black Smoke than "Normal"

[johnbrowder]

Janene and I are on a 6 week western US trip that is scheduled to end up in Austin at POG. We have logged about 3500 miles and things are going well. I have noticed recently that on acceleration (or even kicking on high idle) I see a brief puff black smoke from the exhaust. There has always been a little, I would guess it is twice as much now. I never recall seeing ANY when turning on high idle. It still only last a second or so.

We have been in cooler temps, less humidity, and higher elevations than routine. No engine fault codes, and no change in mileage.

Should I be concerned?

[grantracy]

I had the same problem and went to a DD service facility, turns out defective injectors were the culprit. Also discovered hardware for Jake brake was broken...don't know if the two were related...anyway that was my experience.

[Jon Wehrenberg]

John,

When you get back to lower elevations see if it has gone away before considering remediation. I know DDEC is supposed to compensate for loss of boost due to altitude, but that might be normal.

[Larry W]

John
We live at 6000 ft above sea level. Our bus puts out more black smoke when starting from a stop or when I really ask for power with my heavy right foot. At lower elevations the smoke is a lot less. There is just not as much air at higher elevations. At 10,00 feet is is not possible to see 30 pounds of turbo boost. We are currently on the return leg of a trip of about 6000 miles. Here at 1200 feet there is very little smoke and it is easy to see 30 pounds of turbo boost. As Jon advised check all when you are at lower elevation.

[johnbrowder]

OK, if Jon W says it, I buy it! Plus, that's what I really wanted to hear. By the time we get to TX we will be back at "normal" elevations, and I should have a pretty good idea if smoke is back to baseline. I will try to post a followup.

[AmeriStar]

You might consider changing your air filter. Most people neglect this simple but important change.

[Mark3101]

Has it happened on more than one tank of fuel? I have seen similar smoke when I got a suspected bad tank of fuel, and it went away after the next fill. My mileage suffered as well until the next fill up.

I would tend to think it is elevation related, but the above could also be the culprit.

[Lawrence M.]

John,


FWIW department, I had the same situation at high altitudes during my trip back to CA from Sturgis. It subsided as I came closer to sea level.

[Jon Wehrenberg]

While maintaining a clean air filter is important, if my memory is correct I think DDEC adjusts fuel flow based on the mount of air available for combustion. If I could remember where I read this I would post it. A dirty air filter on later model DDEC coaches results in less horsepower because of fuel flow restricted to compensate for reduced air flow, but does not produce the clouds of black smoke associated with a dirty filter on older engines.

DDECI had the ability to roll out clouds of black smoke upon rapid throttle application because the injectors were responding to the throttle position with no compensation for the amount of air or boost that was available. As a result a driver could punish surly toll booth employees with air rich with black smoke, but the downside was that in Colorado Springs pulling away from a traffic light was a slow painful smoke filled process until the turbo boost kicked in. Later DDEC versions corrected that issue.

[AmeriStar]

Yes it is important to have clean filters. 'Black' smoke from a series 60 during operation is NOT NORMAL at any altitude.
This is one of the negative's associated with increasing the 12.7's horsepower to 500+.
The DDEC does make adjustments for air density and temperature, but only as a reaction.
The initial first burst of fuel after each idle period, signals the ECM and adjustments are made from there to the air fuel ratios.
It is our experiance from out fleet operation, that simple things like air filters, are the best place to start a diagnosis for black smoke.