I have a 2007 American Tradition with about 65,000 miles, a 400 Cummins and an Allison MH3000 transmission. Here's the problem: When I take off from a dead stop, the coach is very slow to accelerate in 1st gear, and shifts into 2nd at about 1800 ( in other words, before the turbo has a chance to kick in ) then shift into 3rd again at about 1800 ( before turbo ) but finally stays in 3rd long enough for the turbo to kick in, and then accelerates like it should in the rest of the gears. The Mode light is NOT on, and I have the accelerator pedal all the way to the floor like I always do on takeoff. Any ideas?
extremely slow takeoff
- Thread starter roamer50
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Could be lots of things according to this page. I would take it to a dealer specializing in diesels and let them diagnose it for a hundred bucks or so rather than swapping parts.
https://www.cumminsforum.com/forum/07-5-09-3rd-gen-6-7l-powertrain/954162-truck-starts-off-slow-turbo-kicks-45-mph.html
https://www.cumminsforum.com/forum/07-5-09-3rd-gen-6-7l-powertrain/954162-truck-starts-off-slow-turbo-kicks-45-mph.html
Utclmjmpr
Well-known member
The 2007 is computer controlled,, you need to visit a Cummins dealer and get it checked out. My American Trad is NOT computer controlled so I was able to get into the "P" pump and reset it for much faster & sensitive reaction to the turbo,, a big difference. (130000 on mine) >>>Dan
Gary RV_Wizard
Site Team
You have a misconception re the turbo - it "kicks in" under any acceleration and is driven by the volume of air flow through the engine, not rpms.
Your problem is almost surely one of these things:
Dirty fuel filter(s) (there are two of them)
Dirty air filter
Air leak in the charge air intake path (loss of vacuum)
Turbo not working at all or only partially
I'd start with fuel & air filter changes, which are always the first thing to make sure of when doing any diesel engine diagnosis.
S
sightseers
Guest
I'll bet Gary is right.
and turbo's wear out rather quickly.
and turbo's wear out rather quickly.
Utclmjmpr
Well-known member
The only way a turbo will "wear out quickly" is dirty air or dirty oil.>>>D
SargeW
Site Team
My guess was going to be a loss of boost pressure. A loose fitting or a cracked hose. Usually not too hard to diagnose or fix.
S
sightseers
Guest
Utclmjmpr said:
you shut them down hot all the time, and they will die young.
SargeW
Site Team
sightseers said:
Yep, idling before shut down is definitely a good idea. I try to be at a coolant temp of 180 or below before shutting down.
catblaster
Well-known member
I found a stuck wastegate and an exhaust brake that would not release. While working on those I found the exhaust manifold cracked under the turbo and leaks at the flange. After fixing those she had so much more boost it blew off one of the hoses to the intercooler. It had those symptoms also. Like Gary said it could be many things.
Gary RV_Wizard
Site Team
"Hot" in this case means after an extended run at highway speeds. The turbo cools down to normal operating temperatures quickly when you slow down and should usually be ok by the time you reach a parking spot that is well off a major highway. What you want to avoid is driving at 65 for hours and then pulling directly into a highway rest area and shutting down without a couple minutes for cool-down..
It's one of those things that probably won't hurt noticeably if done once in awhile, but if repeated regularly over the years it will definitely take its toll in wear & tar.
It's one of those things that probably won't hurt noticeably if done once in awhile, but if repeated regularly over the years it will definitely take its toll in wear & tar.
catblaster
Well-known member
On my old Deuce and a Half you can tell when the turbo has spooled up when you first start it. The engine tone changes distinctly and on shut down the turbo can be heard for 30 seconds or more spooling down.
These old motors start dry and the engine change corresponds to the oil pressure rise. On shut down there is a very small amount of oil bleed down and that is where the problem comes in. The hot turbo body will transfer heat to the shaft and burn the residual oil, "coking it".
Its not just old Deuce motors but almost all turbo motors will have a problem. Maybe there is some new technology that has come with the newer engines, if so I would like to know it.
These old motors start dry and the engine change corresponds to the oil pressure rise. On shut down there is a very small amount of oil bleed down and that is where the problem comes in. The hot turbo body will transfer heat to the shaft and burn the residual oil, "coking it".
Its not just old Deuce motors but almost all turbo motors will have a problem. Maybe there is some new technology that has come with the newer engines, if so I would like to know it.
S
sightseers
Guest
On the company owned commercial trucks we used (or abused) we would wear out a turbo every 100k or so.
I once had one blow on the freeway and the truck went into turbo run-away, it wouldn't shut off from full throttle.
It was a fun standing on the brakes and bringing that smoke bellowing beast to a stop.
I once had one blow on the freeway and the truck went into turbo run-away, it wouldn't shut off from full throttle.
It was a fun standing on the brakes and bringing that smoke bellowing beast to a stop.
catblaster
Well-known member
sightseers said:
That seems to be a problem with some of the old army trucks also, so bad that now someone is making a spring loaded gate that shuts off the intake air to kill the motor on a runaway. If the seal blows to the the intake scroll you get a runaway engine, if it blows to the exhaust scroll you get a mosquito fogger.
We had a mosquito fogger happen when leaving Seoul Korea on a M35 and another on a M88 tank retriever during a parade for the Secretary of Defense. The smoke covered the entire review stand and press corps. It was perfect, she blew just at the start of the stands and of course was still bellowing smoke until they hooked up the recovery vehicle. Acres and acres of oil smoke.
Gary RV_Wizard
Site Team
I don't think it is new turbo technology as much as refinement of it. Better alloys, finer machining tolerances, and improved oiling all contribute to longer turbo life and higher reliability. But a turbo spins at very high rpms and is driven by extremely hot exhaust gases, so it's always at risk.
