I have a 2006 40' Beaver Monterey equipped with the Cat C9-400 engine...we currently have 40,270 miles on this unit. Last fall as we were returning from the Monaco rally in Tucson we had a similar power loss problem to what has been described in the previous posts. Since our C9 has the pre-2007 EPA emission configuration, our experience with this engine may not be precisely relavent to problems with 2008 and 2009 model year units but here goes.
Our coach had been running fine from Tucson to just south of Monticello, Utah on a late-Saturday afternoon. With no warning, the check engine light illuminated. As most men would do in this situation, I immediately checked the oil pressure and coolant temps as I said absolutely nothing to my wife...I was "hoping" that whatever the problem was would somehow miraculously go away!!! It went out a few seconds later but them re-illuminated. Concurrently, I lost all power and dropped from 65 mph to barely moving along the side of the road at 3-4 mph. On a heavily travelled two lane road pulling a 22' car trailer, finding a spot to get off the road and out of the way was challenging.
I shut the engine off, checked the oil/coolant levels and looked for obvious signs of any problems in the engine compartment, Finding none, I started the engine and it idled fine. It ran up to high-idle with no trouble and the check engine light was no longer illuminated. So I put it in gear and we were back up to 65 mph in no time.
A few miles later, the check engine light came on again followed immediately by another complete loss of power. I saw a turnout ahead and pulled in believing that I had a fuel filter problem. I got out my tools and replaced both fuel filters. Once primed, the engine fired up OK with no check engine light and we were back on the road. A few miles later we lost power again...fresh fuel filters didn't solve our problem. We turned around and limped back to Monticello rather than take the chance of getting stuck on the narrow parts of the highway between Monticello and Moab in the dark.
The ECM fault codes showed low turbo boost, low engine oil pressure and low fuel pressure. The engine would idle fine but no longer would run up to the high-idle point. Calling Cat 800 number only confirmed the nature of the three fault codes which I had already retrieved from the ECM. Since my Geico insurance was going to cover towing/transport of the mh to the nearest repair facility and Cat warranty was not going to cover a field service call to diagnose and hopefully make this repair in the field, we stayed overnight in Monticello and the next morning put the motorhome on a lowboy headed to Wagner Equipment (the nearest Cat dealer) in Grand Junction, Colorado. We unhooked the trailer before loading the mh on the lowboy...the engine could barely generate enough power to jump onto the trailer and then jump onto the step deck portion of the lowboy.
After 2-3 days of trouble-shooting, the techs at Wagner discovered that the root cause of this problem was a broken o-ring on the check valve piston in the fuel system that allows excess fuel to return to tank...it was stuck between the piston and check valve housing. The o-ring kept the check valve stuck in an open position causing the fuel pressure to drop below 22 psi...enough fuel pressure for the engine to idle but not enough to run at high-idle under any load. The Cat spec for fuel pressure on this generation of C9 is 55 at idle-75 psi at full load. This low fuel pressure was one of the causes for the check engine light to illuminate and for the engine derations/loss of power. This low fuel pressure also triggered the low turbo boost fault code to be logged .
The faulty check valve is not a serviceable item so it needed to be replaced...the new Cat part number installed was a 294-8620 Regulator Assembly. All of Wagner's work was covered by Cat warranty...the 294-8620 assembly was only $41.12 but the warranty labor was almost $600.00. Geico paid the $1,400.00 transport charge to get the mh from Monitcello to Grand Junction.
The problems I discussed above may be unique to my Cat C9 engine arrangement but some of the symptoms described by others sound strangely familiar to my experience. Hope this helps somebody else from chasing a disabling engine problem out on the road.
Though my out-of-pocket cost for this experience was $0, the inconvenience and the explanation of this problem to my wife were both priceless!!!
PS Checking the date/engine hour details of the low engine oil pressure fault code confirmed that this fault occurred following the last oil change over a month prior...it had nothing to do with the root cause of the o-ring failure.
Jim