Cause of excess soot from exhaust?

[ICPete]

Over the past 1,000 to 2,000 miles I've noticed a lot of soot coming out of the exhaust:

 

 

Close-up of tip:

 

 

Close-up at top of muffler:

 

 

The truck pretty much sat unused for 4 months over the summer and was driven about 2,000 miles between late September and last week. I noticed at our last stop how much soot was getting deposited onto my motorcycle that is carried on the bed behind the cab. The deposited soot looked almost like snowflakes except black instead of white. The soot stained the paint and could not be simply blown off; I had to use a wash/wax product to clean the motorcycle to get rid of the soot stains. Before this summer I had never seen any soot deposits on the bike or on the truck bed. The heavy soot stains running down the exhaust pipe remind me of a wood stove chimney when it is burned too cold and generates a lot of creosote!

 

Also my mileage seems to be dropping to more like 7 MPG, whereas it used to be around 8 MPG. This change has occurred since 2,000 miles ago.

 

Would this be highly suggestive of a bad injector?

 

I had an overhead run at a Detroit Diesel shop in Elko NV about a year ago (11,000 miles ago). The current odometer reading is 926K. During the work in Elko they also did a blow-by test of some sort (though not on a dyno) and stated it was within the normal range. The truck ran great after that service and I was getting around 8 MPG as I said.

 

Is there any kind of definitive test for a bad injector? It looks like reman injectors can be had for around $150-250 each (with core return). I'm sure the labor would add quite a bit to that. Is there a certain logic that suggests if one injector is failing, the others can't be far behind, implying once you've paid for the labor to access the injectors, perhaps all six should be replaced at once?

 

I'm also wondering whether injectors degrade gradually, so that one might expect some performance or mileage improvement via their replacement. Or are they more like spark plugs, in that they pretty much either work or don't work?

 

BTW, I've searched the forum for "soot" and for "injector" and didn't come up with anything relevant. I've also looked through the Heavy Hauler guide. There was some info about white smoke, but my engine doesn't appear to make white smoke at startup or when cold, so this is something different.

[ICPete]

I should also point out that the exhaust pipe was totally clean and polished 400 miles ago. So that heavy soot running down has accumulated in just 400 miles (that is, a one-day trip across South Dakota)!!

When I cleaned it 400 miles ago, it was not quite this dirty, and that would have been built up over more than 3,000 miles at that time.

So it definitely seems to be getting worse fast.

[hdonlybob]

Not a master mechanic, but it appears to me to be unburned fuel...

Would suspect something in that area.

Good luck.

[Pat & Pete]

Maybe yer burnin' pine instead of oak ?

[MrSeas]

How's were your boost and EGT's looking when you noticed a decrease in MPG?

Any rain water get into the stack?

Any unusual coolant or oil usage lately?

[Darryl&Rita]

Black smoke or soot is always the same, whether it's from your neighbors' kids' brodozer, or your RV puller. It's either excess fuel, or lack of air. Check all the boots, from the turbo to the intake manifold. Make sure the CAC (charge air cooler) isn't leaking boost pressure. That is all free. Then it's time to start testing injectors. You can pull them yourself, and deliver to an injector shop for testing.

By the looks of the "slobber", you're in the excess fuel camp, so it's time to start pulling injectors. Check your oil level too, excess fuel can end up in the crankcase, diluting the oil, and ruining bearings.

[Steve from SoCal]

I agree with Darryl,

 

First thing to check is the oil level, BEFORE you start the truck again. With that much accumulation in the short time you may have a burned piston.

 

Steve

[ICPete]

MrSeas: I don't have an EGT or Boost gauge on the truck. We did have heavy rains a few days before the recent 400 mile trek. I think coolant level is unchanged; I'll check the oil Thursday.

 

Darryl, good suggestion; I'll check the turbocharger output air connections and hoses for potential leak sites, especially at the CAC. Recently the oil level was near the bottom line on the dipstick, so I added 5 or 6 quarts to get it near the top line. So I don't think it's getting diluted with fuel, but I'll check it again and smell it for diesel.

 

Steve, how does excess fuel tend to burn a piston? I don't understand...or do you mean a burned piston causes accumulation of unburned fuel, since it's not generating compression in that cylinder? I guess a burned piston sounds like the more expensive repair, compared to replacing injectors!

[Steve from SoCal]

Steve, how does excess fuel tend to burn a piston? I don't understand...or do you mean a burned piston causes accumulation of unburned fuel, since it's not generating compression in that cylinder? I guess a burned piston sounds like the more expensive repair, compared to replacing injectors!

 

Diesel engines unlike petrol engines burn hotter with more fuel, an injector that is leaking into a cylinder will over time burn the piston. If you are sure there is no oil dilution then it is not that likely. You still want to borescope the cylinder with the bad injector.

 

Steve

[rickeieio]

We did have heavy rains a few days before the recent 400 mile trek.

 

Clean up the pipe and drive it. Rain water in the exhaust, accumulated recently and over the 4 months of inactivity, just made a mess.

 

But, keep an eye on things in case I'm wrong. If the pipe stays clean, yer good to go.

[Star Dreamer]

We agree with Rick. Prior to changing to our weed burner exhaust we used to get that soot all time due to rain water getting in the exhaust. Check that out before tearing apart the motor.

 

Dave

[Darryl&Rita]

Good catch on Rickeieo's part. Missed the rain. Clean it, drive it. Keep an eye on the oil.

[Bob A]

Sure looks like rain to me

[skp51443]

Do you have a low-point drain hole on your exhaust, something like a small hole to let rain water drip out?

[RandyA]

There has to be a lot of moisture in the exhaust. Just soot should be dry. If your "moisture" is from diesel fuel also getting in the exhaust stream you should be able to identify it simply by wiping your finger across the inside of the exhaust stack and smelling the stuff - it will be thick, greasy and stink of diesel. On the other hand, if the moisture is water, the heat from the exhaust will turn the water in the lower part of the pipe into steam, the steam will "clean" accumulated carbon (soot) in the muffler and then condense back to a mixture of water and carbon soot as it gets to the cooler (upper part) of the exhaust stack making the mess in your picture - just like your analogy of creosote from a cold stove pipe - especially if you burn green pine . I'm not a diesel mechanic but do know enough chemistry to believe you have a water collection issue. Many automotive exhaust systems have a weep hole or drain, usually in the bottom end of the muffler, so that moisture from exhaust gas condensation (your intake air is often moisture laden from high humidity) can drain out. So, Stan's comment of having a low point drain hole in your exhaust will help solve a water collection problem. I put one in mine years ago. Again, IMHO, a 3/16" hole drilled just before the ell that feeds the stack allows water to drain without creating an exhaust leak issue - just a nasty mess below the hole . An empty gallon can placed on the top of the stack during storage can help as well. I agree with Dave and Rickeieo and believe they hit the nail on the head.

 

Despite my simple observation and comments, it would be wise to follow the previous advice of checking for turbo leaks, diesel in your engine oil, excess fuel or a restricted air intake.

[NoDirectionHome]

Just a thought but, if your injector cups are leaking... I'm thinking you might see a similar exhaust situation. Here's to hoping it was just a bunch of rain.

[skp51443]

Chatting with an old Army buddy and he reminded me of a slobber problem we had. Sitting in Korea near the DMZ in February with an M35 (2.5 ton truck) and our towable generator died. Ended up letting the M35 idle in far below freezing temps for almost 2 weeks to have radio power. My buddy, a youngster at the time heard a funny noise as he was topping off the fuel tank from a Jerry can. Being young and foolish (20 something) he decided to look into the issue himself without adult (that would be my) guidance. He figured out it was something in the exhaust making the noise. Of course the solution to something making noise in the exhaust is to climb in and mash the gas to try and blow it out. He blew a huge glob of diesel slobber out of the stack and all across the platoon area. Trucks, tents, camo nets, anything not under cover, to include a couple people all developed big nasty black spots.

 

While young, but not being stupid he realized what he had done and in the finest traditions of the US Army Intelligence Corps he discretely hopped down, closed the door and walked out into the woods. Many hours were spent cleaning gear and we gave up and just painted one jeep. It was many months later as he was processing to leave country that he told a couple of us "whodunnit" thus solving the mystery.

[Broncohauler]

We did have heavy rains a few days before the recent 400 mile trek.

 

Clean up the pipe and drive it. Rain water in the exhaust, accumulated recently and over the 4 months of inactivity, just made a mess.

 

But, keep an eye on things in case I'm wrong. If the pipe stays clean, yer good to go.

X2

If I don't put a bucket over my pipe when not in use, it will blow the black gunk all over.

Try cleaning it up and cover you pipe. If that doesn't work then start looking at the motor.

[RandyA]

Just a thought but, if your injector cups are leaking... I'm thinking you might see a similar exhaust situation. Here's to hoping it was just a bunch of rain.

Hummmm.......... could be but when the injector cups on my Volvo were leaking I was getting diesel in the coolant and the exhaust would look like a steam locomotive when it would (finally) start. The smoke was white, not black. Don't know how a Pete engine would react to bad injector cups - might be different. I had Volvo do a complete overhead on mine and had to replace the coolant hoses and radiator expansion tank - $2,500 later it purred like a new truck. IMHO, unless you have some symptoms or signs on your truck we are not aware of I doubt that injector cups are your problem - at least not the problem causing the black gunk. Again, I am not a diesel mechanic. After six years of HDT ownership I am still a freshman and always learning.

 

Stan - I enjoyed your story. If I did that I would go hide in the woods as well . But, inquiring minds want to know, why was there so much un-burned diesel in the M35 exhaust? Was it a combination of the cold weather and long idle plus some engine blow-by?

[Alie&Jim's Carrilite]

Stan - I enjoyed your story. If I did that I would go hide in the woods as well . But, inquiring minds want to know, why was there so much un-burned diesel in the M35 exhaust? Was it a combination of the cold weather and long idle plus some engine blow-by?

 

In the old Korea days, they would mix kerosene in the fuel so it wouldn't gel. Engine tolerances were so loose that diesel in the exhaust wasn't uncommon as well.

[skp51443]

Yep, well below freezing temps, and the idling engine that barely kept warm even with the radiator blocked with a couple ration boxes let the exhaust cool to the point the water in the exhaust was condensing in the stack and draining back to the low point in the exhaust system, under the frame.

 

Gotta love the M35, I was the only one in the company that was older than a couple of the A models we had.

[glowplugrelay]

Your pix look exactly like the ones I took some years ago. The truck was a Western Star and the mechanic recognized it right away as the turbo failing. Turbo was replaced and problem solved. Took some elbow grease to clean those 2 stacks plus the streaks going back.

 

My recollection was the oil was leaking past the bearing on the exhaust side and getting pushed up the stacks.

 

 

/dc.

[snowboat]

Pull the exhaust off of the turbo after it has cooled down after a drive, It should be dry and sooty. If its oily, is the turbo seal. Let it idle for an hour and cool down. Pull the exhaust off of the turbo and if it is fuel and runny, then an injector is over fueling. You can also start the engine and put a temp gun on each exhaust port going into the manifold and look for a significantly colder hole as it comes up to temp a close to no load full RPM. The cold hole(s) is over fueling.