Smoking

[Rattlenbang]

While driving my 6.9 E350 motorhome through the mountains, I noticed that flooring it on steep hills creates a continuous belching of black smoke as long as the pedal is fully depressed. If it was a turbo model I'd suspect a fault in the turbo creating not enough air pressure but since this is N/A there's not much on the intake side of things. Air filter isn't new but you can easily see daylight through it.
Is this typical under high load conditions for this engine or is it a problem? The IP is newly rebuilt.

 

[Cubey]

Get a pyrometer ASAP and keep an eye on it. Let off the throttle just enough to stop the heavy smoking or you might melt the pistons.

These things are 100% mechanical so air/fuel doesn't adjust automatically for higher altitudes. What altitude were you at when it happened?

My F250 is a 6.9 NA and did the same in Colorado. Beware that when I was at about 10,000 feet, if I turned it off, it wouldn't hardly restart again. Even with an electric fuel pump on it. Once I dropped to 9,000 or less it was fine again and has been ever since. Luckily I didn't melt my pistons when I was blowing smoke since I don't have a pyrometer on the F250.

My RV came to me with an old high quality pyrometer, thankfully.

 

[Rattlenbang]

I was only a couple thousand feet so I doubt that was it.
I've installed pyrometers on turbodiesels because you can overheat those heads leading to cracking because they're usually aluminum heads, but I've never heard of N/A diesels having overheat problems unless cooling system issues.

 

[Scotty4]

Just drove cross country in my 85 6.9 NA and with the pyrometer I could watch it climb probably 100F/second or so it felt lik on some inclines and would need to keep my foot out or down shift snd grandpa up the hill.

Fresh coolant, cleaned radiator, bypass filter, thermostat, engine temp just hung at 185-190 the whole way. I maintained less than 1000f egt to be safe but a few passes could have easily had me well over 1200 had I kept on it.

 

[Cubey]

I was only a couple thousand feet so I doubt that was it.
I've installed pyrometers on turbodiesels because you can overheat those heads leading to cracking because they're usually aluminum heads, but I've never heard of N/A diesels having overheat problems unless cooling system issues.

Hm, well somone on here a few years ago warned me about getting a pyrometer and I've seen mentions that NAs need it more than turbos? But without having the posts handy, it's just hearsay.

 

[IDIBRONCO]

Hm, well somone on here a few years ago warned me about getting a pyrometer and I've seen mentions that NAs need it more than turbos? But without having the posts handy, it's just hearsay.

Nope. You're right. The turbo will push more air into an engine so it will burn more fuel. When our engines smoke black out of the exhaust, it's from being "overfueled" under those conditions. Basically, the black smoke is unburned fuel, which raises your EGTs. Since a N/A engine, is limited on the amount of air that comes into it, that engine is also limited on the amount of fuel that it will burn in any given situation. It will still have the same amount of fuel going through the cylinders at a given throttle position, no matter how much air is or isn't coming into the engine (assuming that the pump and injectors are the same and in the same condition between the two being compared). Same fuel+less air=black smoke.

 

[Rattlenbang]

And my understanding is that with turbos you essentially get more fuel/air due to boost, more power, more combustion, more work, and the excessive temps generated is what blows heads. You read about it all the time with turbodiesels; you work them hard eventually you have to replace heads. I've probably replaced a dozen heads on Mitsubishi Delicas, because you push a very heavy 4x4 with a small 2.5 litre turbodiesel, and eventually the heads crack. They were never designed for the North American market where people drive much faster than in Japan. Im going to have to dig into this further.
The other thing I don't understand is why should full throttle result in not enough air? The fuel is metered so essentially black smoke means the air flow is less. Why should there be less air flow because you're hill climbing? Because the machine squirts fuel according to throttle position but engine working hard is running at a lower rpm than it should for that throttle position?

 

[hacked89]

You're trucks timing and fuel is likely tuned to just be on the edge of not smoking on sea level. There's not a barametric pressure sensor feeding a computer controlling the fuel and timing for atmospheric pressure changes. Just going up a few thousand feet brings you to around 13.2 from 14.7. So your truck sucks in X dense air at sea level without smoking but now you go up in altitude the air is less dense, but have the same amount of fuel - > black smoke

Also fuel curves aren't flat so what is your rpm when no smoke mountains hill versus WOT

Sent from my SM-G955U using Tapatalk

 

[Cubey]

Why should there be less air flow because you're hill climbing?

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It's not just less "air" (air pressure, to be more accurate) but also less "oxygen" which is needed for proper combustion. If there's too much fuel but enough oxygen, it won't combust properly, hence black smoke. NAs need the air pressure since they don't have a turbine to suck in the air. The higher up you go altitude wise, the less oxygen there is. As I understand it, turbo'd IDIs have less of a problem with it due to the forced air intake, instead of relying on natural air pressure.

If you go from sea level to 8k feet in the mountains in one day, it can make you sick because your body needs time to adjust to the chnge in oxygen level. Same reason they have to pressurize jets at high altitudes and provide oxygen masks if there's decompression, lack of oxygen.

IDIs can't adjust at all, so if they are tuned for, let's say 3,000-7,000 feet and you start going above that, the worse it'll get. Maybe it'll be fine at 8k and 9k but once you hit 10k, it might really suffer, like my F250 did. Below roughly 9k ft and it's perfectly fine, no excessive smoke, no noticeable loss of power, gets normal MPG, etc.

What I did on my F250 to help it was remove the foam liner on the (then new) air filter, and also remove the air intake tube. That did seem to help it a small amount power wise. It was still smoky but it seemed to be starving for "air" a bit less.

 

[IDIBRONCO]

The other thing I don't understand is why should full throttle result in not enough air?

This is because a our diesel engines don't have very much intake vacuum compared to a gas engine. A N/A engine doesn't get enough air to burn all of the fuel that goes into the engine at full throttle if the fuel is set to perform properly at lower throttle settings.
All I know about a Mitsubishi Delica is what you've just said. Just remember that the 2.0L (I think) diesels that were put in smaller Fords in the early 80's also had head cracking problems. These engines are much sturdier built than the small engines, in my opinion, and work better in a bigger, heavier vehicle. I think trying to compare a 2.5L engine in a heavy vehicle to a 6.9L engine in a heavy vehicle is apples to oranges. One is already overworked just going up and down the road empty.