Cummins 8.3 ISC Low power problem - easy to fix once you find the problem

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azyxzer

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I have a 2008 Fleetwood Providence 39R with a Cummins 8.3 ISC. Lost a ton of power on a trip to the Heber, AZ area over Labor Day. I saw it was due to low boost (only 16-18 psi instead of normal max ~35 psi). It didn't give a check engine light or set any codes. I crawled underneath it while we were camping and couldn't find anything obvious with the intake plumbing, so had to come home the same way (25 mph up the steepest hills, great way to make friends).

Once I got home I started checking into it more, and ended up pulling the bed apart to get to the top of the engine. I had my buddy sitting in the back near the engine with a scanner to see if anything showed up in the data (diagnostic connector is on the back of the coach), and once we got on the road he yelled at me to stop because he heard a big boost leak. The problem ended being the rubber elbow that connects a steel pipe to the intake manifold and to the air brake compressor on the other end. It was split on the inside of the "ell" facing the block and couldn't be seen when installed (and in truth I didn't think to check for that anyhow). I changed the elbow and also the straight hose on the compressor end of the pipe and that fixed it. Total price for both from Cummins was about $65.

I only mention it here because I could have saved myself a ton of work (tearing the coach apart and troubleshooting) if I had known to look at this first.

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that looks like a TON of work to get to.

i fought a boost leak on my cummins pickup, and after looking hi and low, found the intake gasket was bad, but it sure sounded like it was out under the driver tire and only would show up when towing a trailer, any other time, it was quiet. 

 
Yes it was a royal pain, and I could have skipped most of it if I knew what needed to be changed (you can do it from underneath without removing anything). Since the parts are cheap and easy enough to change, I would recommend pre-emptively replacing them for anyone with an engine like mine to avoid a long drive with low power like I had. I guess 14 years of heat and pressure cycling were enough, even with only about 40K miles on it.

I agree, boost leaks sure are hard to find without a dyno, and even worse when they are 30 feet away and under the floor/bed ;)

 
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