StakeMan

My peak boost drops as the truck gains altitude.

Mexstan

Does this happen as soon as you start climbing or only after you reach a certain altitude? If it happens only after you reach a certain altitude, approximately what altitude do you start to see the drop?

Push Rod

[quote author=Mexstan link=board=20;threadid=12216;start=15#117524 date=1048004935]
Vapor lock in the common rail??

As for excess fuel I don't see how this could happen with injectors. If there was vapor lock would there not be the opposite and the injectors inject a very small amount of diesel?
[/quote]

The more I think about this, the more it sort of makes sense (although, as CP pointed out, vapor lock wasn't the right term). The common rail system, upon engine shutoff, releases pressure on the rail. Whether it releases it to 0 or not, I don't know. But have you noticed that D-Max and CR Cummins engines require a few cranks to get started? Thats because the CP3 is gear driven and needs to spin over a few times to get rail pressure up. The ECM, during starting, won't crack the injectors open, until it sees that rail pressure is up.

Soooooo, what we have is the leftover fuel vaporizing in the rail after shutdown. Since vaporized fuel is much more compressible than liquid fuel, when starting the truck the next time, the CP3 requires more turns to bring rail pressure up (due to compression factor of the vapor).

As for my excess fuel theory, its either:
1) dead wrong, and all the extra smoke is just from inefficient combustion (as the system wasn't designed to inject already vaporized fuel) due to changes in timing.

2) right, as the rail would require more fuel than usual to bring pressure up (due to the compressibility of the vapor). Once the vapor shot through the injectors, the overload of fuel would follow.

Rod

Mexstan

Rod, you are making sense to me, but I still have a problem with excess fuel being delivered into the combustion chamber. The reason I say that is because the injector is designed to inject a metered amount of fuel on each combustion stroke. Or am I wrong? So, if only a metered amount of fuel is injected, how can there be an excess? If the injector somehow opens up with a mixture of vapor and diesel then that would mean a lean mixture and could not cause black smoke. As I said in an earlier post, I do not see a lean mixture that fails to ignite accumulating due to the purging action of the exhaust stroke.<br>Or did I misunderstand some obvious point?

Scotty

When pulling my 34.5 ft 5th wheel from Calgary to the west coast, down thru CA and across to NV, AZ, and over to TX I noticed a few things. Power in higher elevations was down a bit. I am referring to overall power. Not on the grades.<br>Boost at elevations over 2000 ft was down 2 psi at WOT.<br>Fuel mileage on the mtns was at 11 mpg<br>on the flats 13 mpg. Smoke was more apparent at higher elevations [unburnt fuel?]. At sea level at the Gulf of Mexico I had more power, 0-60 empty was definately faster then at 3800 ft in Calgary [a full one second].<br>At sea level...there was no smoke. nuttin nada unless I hit the throttle at a low rpm in the wrong gear. I did that on purpose to see if it would smoke...it did.<br><br>Spool up was slower at elevation too. Not a huge difference but enough to notice if one has owned their truck for awhile and knows the sounds and what is usual.<br><br>As for back pressure...I did not know that the exhaust I have would create back pressure off the turbo other then the small opening right at the turbo.<br>When I had the factory exhaust and was at or above 340 HP I would get a shudder under hard throttle...I was at the limits of the efficient clearing of the exhaust. I put the 4&quot; system on and the egt dropped 50F and no more shuddering.<br>Of course I exceeded the limits of the drive pressure on the turbo next...changed that...then changed it again.<br><br>I think its safe to say that the stock truck comes fairly well matched. I still stand firm that the air intake is the initial limitation.<br><br>I only write about what I have experienced first hand rather then what I have read...I have found that there are some things that may apply in theory but not in the real world.<br>Family and friends did not like that with me...I always had to test and try. ;D

Push Rod

[quote author=Mexstan link=board=20;threadid=12216;start=30#117938 date=1048085970]<br>chamber. The reason I say that is because the injector is designed to inject a metered amount of fuel on each combustion stroke. Or am I wrong?<br>[/quote]<br><br>You're close, but the fuel amount is not metered, but timed. The ECM knows if it holds the injector open for x milliseconds (or nanoseconds) at y PSI rail pressure, it will inject z amount of fuel. You throw some different densities in there, I'd guess it would throw the timing off.<br><br>But this is pure conjecture based on my understanding of how the injection system works. It may be martians who don't like your truck <br><br>Rod

Mexstan

On reflection about the timing/metering I bow to your superior knowledge and admit that for once in my life that I am wrong. You are correct, the fuel is timed and not metered.<br><br>BTW. When I worked in the good ol' USA I was classified as an alien. So, I am found out again. Actually I am not from Mars but I am not allowed to identify which 8)planet I actually come from. Could be all those high intensity vibes from me are affecting my truck. ;D

Scotty

[quote author=Mexstan link=board=20;threadid=12216;start=30#118090 date=1048109375]<br>On reflection about the timing/metering I bow to your superior knowledge and admit that for once in my life that I am wrong. You are correct, the fuel is timed and not metered.<br><br>BTW. When I worked in the good ol' USA I was classified as an alien. So, I am found out again. Actually I am not from Mars but I am not allowed to identify which 8)planet I actually come from. Could be all those high intensity vibes from me are affecting my truck. ;D<br>[/quote]<br><br>I knew your posts here where 'code' for your motherland.<br>

Mexstan

Scotty, fooled another one. Those posts are only for my time on earth. Sorry, can't reveal my real motherland. ;D

StakeMan

Here in Denver we start out a mile high and climb to 10,000ft going over mountain passes. It not a sudden change in boost. I just notice it when I reach the top and put the foot to the floor to finish off 1 last PSD.

Mexstan

Have just checked my manual but can't find the info I need to answer your question. I am guessing that anywhere after about 7,000 feet that the wastgate will be completely closed (before WOT) and that from there on up in atlitude that the boost will start decreasing and that a noticable dropping off of engine performance will be noticable.<br>Maybe someone with more knowledge than I can answer this more accurately.

cp

[quote author=Mexstan link=board=20;threadid=12216;start=30#118153 date=1048121029]<br>Have just checked my manual but can't find the info I need to answer your question. I am guessing that anywhere after about 7,000 feet that the wastgate will be completely closed (before WOT) and that from there on up in atlitude that the boost will start decreasing and that a noticable dropping off of engine performance will be noticable.<br>Maybe someone with more knowledge than I can answer this more accurately.<br>[/quote]<br><br>You got it right...at the altitude the waste gate is fully closed, aka the 'critical' altitude, is the highest altitude at which the engine can make the same boost as it could at sea level. From that point on, boost pressure drops at the same rate as atmospheric pressure, about 1&quot; Hg per 1000 ft. I would be surprised if the critical altitude for the turbo in the CTD is as low as 7000 feet, as most aircraft turbos' critical altitude is up in the teens or low twenties.<br><br>Up to the critical altitude, for a constant manifold pressure, horsepower increases. See this link about the Mosquito fighter which discusses this effect. http://www.home.gil.com.au/~bfillery/mossie06.htm

Mexstan

Thanks CD. I forgot the term &quot;critical altitude&quot; as it has been a few years that I have dealt with this. You are quite correct that the critical altitude for piston aircraft turbos are around the mid teens to low twenties. From my experience most general aviation aircraft run out of breath around 14,000 to 18,000 feet. I guessed (maybe incorrectly) that the turbo's in cars and trucks would have the wastegate set to a lower altitude and just pulled 7,000 out of my hat. One reason I arbitrarily lowered the critical altitude for the trucks was that I guessed again and that the truck manufacturers would want to keep the boosts as low as possible for as short a time as possible to prolong the life of the componants.<br>Anybody want to set me straight on this?

Sarge1124

Power wise you will see a great improvement over a gasser, but as you get up there in elevation, like Vail pass which is roughly 10500 ft. those EGT's will really climb fast if you stay on it. I pull a 20ft Arctic Fox travel trailer 8000lbs with no problem and plenty of power to spare. Mike

parshal

[quote author=F11Engineer link=board=20;threadid=12216;start=0#115458 date=1047571752]<br>In about 2 months I'll be new to diesel ownership (ordering my 2500 4X4 tomorrow). ;D ;D ;D<br><br>This summer I'm planning to tow 5000# around the Colorado Rockies. Anyone have any tips for a noobie on differences driving a diesel at higher elevation? What about gotcha's to look out for? <br>I've got plenty of experience towing with gas engines, but the last few months reading this forum leads me to believe a diesel is a different beast and there may be a few things I ought to be aware of in advance instead of learning about them on the road! <br><br>Thanks.<br>[/quote]<br><br>You should not have any problems with a stock truck and 5k lbs. A jake brake could be helpful but isn't an neccesity for that size of a load. Use engine braking when possible and save your brakes. You'll be fine.