General Boards > Technical Support
C-9 Flames out at low speeds
Eric Maclean Co-Admin:
Bob
If you have removed the fuel filters you need to purge the air out of the system before it will start again .
Your coach should have an electric priming pump with controls in the service bay .
If you have the older Raycor system there should be a Schrader valve next to the water separator on the housing unscrew the Schrader valve cap depress the valve core with a suitable tool and run the pump till you get clear fuel ( no bubbles)
Next loosen the secondary fuel filter a turn or two and run the pump until clean fuel spills down the sides of the filter and while still running the pump retighten the filter .
Next with everything tightened back up run the pump ( it will sound slower ) for approximately 45 seconds this is to move clean fuel up and through the fuel rail in the engine and out to the fuel pressure regulator.
Once all of that is done the engine should start ( run it at 1000 to 1200 RPM for 20 to 30 seconds to be sure you have moved any left over or traped air out of the fuel rail.
Your problem sounds like the system is sucking air somewhere ,on these engines everything from the engine drive mechanical pump back to the fuel tank are on the suction side of that pump so if there is any spot where the system can suck air it will .
If your coach has the Raycor fuel separator pay close attention to the plastic site glass it has two O rings on each end of it and they are a common area where air can be sucked in .( Many here have upgraded to a cat pump setup as described in coach assist ) No sure if yours has been done or not.
Another area where an air leak can occur is anywhere in the fuel line between the separator and the fuel tank.
Some of the earlier coaches had a plastic fitting where the fuel line connected to the tank that would crack and create a problem.
I also believe Dave Atherton spoke of the mechanical gear pumps in those engines getting weak and that running the Cat priming pump ( which is rated as a lift pump ) continuously would cure the problem.
These HUEI engines need a constant supply of clean no air fuel to the mechanical pump in order for the mechanical pump to keep 60 or 70 psi on the fuel rail
Any air will make this near impossible and the engine will not run well have low power out put stall and over time will destroy fuel injectors as they rely on the fuel to cool them .
Hope this helps
Eric
Bob Dunlap:
Thanks Eric,
Your answer is very in-depth but to technical for me to follow exactly. I don't know what a Raycor system is or what a Schrader valve might look like. I'll consult a couple of Cat folks in our park to see if they can follow your instructions.
Eric Maclean Co-Admin:
Bob
The Raycor fuel separator is the fuel filter water separator if you go to the coach assist section of the forum under common problems you can see pictures
Of the system.and how to identify whether or not you have air in the system.
And a Schrader valve looks like a regular tire valve.
Eric
Bob Dunlap:
Thanks Eric. That helps a lot.
Here's where we stand today. When I got up this morning, I was poised to contact a Cat mobile repair facility to see if they could help. I thought I'd give it one more shot at starting. It started right up. Just had one little "burble" when I started to move forward and then the engine quit. I started it again and it's been just fine. Having said that, the anomaly has been just like that for the last year and a half, so I'm not sure changing fuel filters did the trick. I'll follow up with your suggestions in your previous post checking other sensors.
Richard Davis:
Bob! I also have an '06 Monterey with the C9. I suffered with the same kind of issues you are having (mine did not get anywhere that severe). The fuel pump on the C9 is a relatively small mechanical gear fuel pump. CAT specs stipulate that the C9 should not be installed more than 10 feet from the fuel tank without adding an auxiliary fuel pump. Motorhome manufacturers ignored that warning. To compound the issue, builders also used plastic fuel line connectors that tended to suck air as they aged. The fittings did not ever leak out since they were sucking fuel into the engine fuel pump. Diesel engines do not like air in their fuel as Eric pointed out. After doing much research on the issue, I followed Dave Atherton's advise to replace the original water separator with the CAT primer pump (FYI, the '06 Monterey does not use the fancy water separator system Eric was referring to). (There is a description of the process on the BAC forum along with a parts list for the project.) I also replaced the plastic fuel line connectors with brass compression fittings so there would be no more air leeks. If you have not already done so, replace the fuel pressure regulator that is attached to the return fuel line on the rear of the engine (front of our engines since they are in backwards). There was an upgrade on the fuel pressure regulator for the C9. Dave gave me the new part #. A failing pressure regulator can cause the kinds of problems you are having. I suspect most of your problems are coming from a loss of adequate fuel pressure at low RPMs. The CAT primer pump solved these issues for me.
Good luck. Richard
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