05 monaco 400 cummins ISL power loss

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dave lawyer

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Aug 28, 2013
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I have a 400 Cummins ISL diesel that is way down on power since I first purchased it. The miles is 50K. It odes not burn oil or exhaust black smoke, but does whistle loudly and the boost gauge is buried at over 50 lbs. It seems to buck at an even run rpm of say 1500 with little load or even backing off the gas. When I first purchased the coach it would easily maintain 60 to 65 mph on hills, now it's lucky to hit 40 or 45mph. I have heard that there are some turbo issues with this engine. Anybody help with this?
 
50 pounds of boost on that motor is highly unusual. Have there been any mods to the motor?  The turbo waste gate should be opening to avoid that kind of boost.  That's a fast way to destroy a turbo from the inside.
 
Yeah, something is seriously wrong to produce that much boost. My ISL is governed to 24 lbs or boost.

The whistle suggest an air leak in the intake. Air may be bypassing the charge air cooler, which can give major performance problems. I would start by tracking down the source of that whistle.

Some ISL engines had a recall for piston road wrist pin problems, but I don't recall any turbo issues on pre-2007 ISL engines.
 
That's the kind of boost I would expect with an after market kit like Banks or some such tuner being used.  If that was the case, then the lack of power could be directly related to the after market parts. 
 
This does not address the turbo issue but the power loss and bucking description is exactly what ours did last year with a plugged fuel filter.
 
I think the loud whistle maybe the key. This is most likely an air leak in the turbo system. Try this, is the whistle louder at high rpm than low rpm? The bucking could be a fuel filter as Jeff suggested or a fuel pump issue ( I had this on a 2000 ISC).

ken
 
Had the same problem. Was a bad (leaking) turbo controller. The vacuum line running to it and then to the turbo leaked internal to the controller. The controller sits on top of the engine valve cover. It is a square box of about 6x6x2 inches with two vacuum lines and a signal cable running to it
 
I had a similar problem a few years ago, but with my Dodge Cummings pickup. The whistle is the key. I had a cracked intercooler, and was actually leaking air out. Check all your rubber hose connections and look at the intercooler.
 
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