C12 stumbling under load

[Brian Buchanan]

We have just set off on a winter trip to Arizona, and have a lingering stumble causing us to struggle to reach speed and maintain it, have recently changed the fuel filter. Is there a transfer pump in the fuel tank? Just looking some ideas that I could check on the road. I originally suspected a fuel contamination, but after flushing the fuel tank I found no evidence of any contamination.

Update:     Thank you again for being the wealth of knowledge that really is priceless. Again you have diagnosed an issue from miles away, we were able to source some parts in Indianapolis yesterday to repair the issue and by noon today we have crossed the mighty Mississippi and are making up some lost time. I remember questioning the value of joining BAC four years ago, but now you just can't put a real price on knowledge ... Thanks

[Frank Bergamo]

Brian,

Does your coach have the Raycor primary fuel filter setup? If it does, then here is a link that may help you. They are problematic with sucking air and causing the problems you are describing. There are four o-rings, that once replaced, will get your C-12 running great again. Hope this helps. http://beaveramb.org/forum/index.php/topic,5598.0.html

[Fred Brooks]

    Brian,
I am pretty sure your coach has a Racor primary fuel filter/water separator. Not sure where the location is on a 98. There have been numerous failures with the fuel line between the tank and primary fuel filter. Another issue is the 4 O-rings that must be replaced when you remove the plastic bowl and filter screen to clean it. The hose between the Racor and the fuel pump located at the right lower corner (looking at the engine from behind the coach) has also developed leakage.  http://beaveramb.org/forum/index.php/topic,10708.msg72858.html#msg72858
hope this helps, Fred

[Mike Shumack]

One test to check for for air in the fuel system is to remove the "return" fuel line and put a section of clear hose in there so you can watch the fuel flow and see is any air bubbles are in the return fuel.

There is an in-line "test fitting" available that has a clear section so you can see the fuel, but probably not worth the cost if your just going to do this test once. Like this https://tool-xpress.com/store/product/apex-sight-glass-8-m50042/  but a piece of clear tubing is cheaper and does the same job

[Dave Atherton]

Gentlemen, I would suggest on let’s go a little deeper on the subject C-12 air within the system.
First of all the C-12 fuel system is different being it has a fuel manifold that retains pressure after
the secondary fuel filter. Within the secondary fuel filter base that fuel filter screws on to ( has what
is called two valves that are not called a check valve the way there made. To answer the question
at hand reason the engine is surging because return fuel to fuel tank the valve in secondary fuel
filter base is sticking with fuel fines and not holding pressure within the fuel manifold on engine.
At some point the engine will be very hard starting or no start. Change out valve will correct problem.
Looking real close at the secondary fuel filter base you will see a hex head on bottom corner
that is the valve in question ( remove and replace with new upgrade valve and problem corrected.)
Dave Atherton Retired Cat Mechanic.      Last Later to day I can post the Caterpillar part number

[Mike Shumack]

Dave, should a fuel pressure gauge on the secondary filter housing (on the Compucheck fitting) continue to show fuel pressure after engine shut down? If yes, how much pressure should there be, and how much time is allowed (if any) for that pressure to bleed down?
Thanks

[Scott Shearer]

Adding to Mike's question, does this apply to the C13?

 -Scott

[Dave Atherton]

Gentlemen. This valve caterpillar part number 238-0296,  O-ring seal 6V-4589. The following
Engines that have a fuel manifold, 3176, C-10,  C-11,  C-12,  C-13,  3406E,  C-15,  C-16,  C-18.

The fuel manifold maintain 90 psi fuel pressure running or shut off. Note: extreme care must be
Used working on fuel manifold and or changing the 238-0296 valve.
Dave Atherton Retired Cat Mechanic

[Bill Borden]

Hi Dave,

My C-12 is running great thanks to you and since I like to keep it running that way I pay attention to your advice.  With your assistance years ago I changed out the Racor with a Cat primary fuel/water separator with great success. 

So I looked up the Check valve for future reference at the Cat parts store.  I was considering updating the Valve at the next Secondary Fuel filter change.

So to help out, here are the updated part numbers.

The check valve, 238-0296 is now replaced with 281-2725: VALVE GP.  https://parts.cat.com/en/holtca/281-2725

The Oring's, the valve has 2 are 6V-6923 & 033-6033, as called for on the part drawing & spec.

The Oring, 6V-4589 has also been updated to 136-7227.  This one was not mentioned as used on the new Check valve.

Just confirming, we should be using the 2 Orings as called for in the drawing?  Correct?

Thanks for all your help Dave in keeping us on the road with knowledge and advice.

Happy Thanksgiving to All!

[Mike Shumack]

Thanks for providing the link.
Interesting, even funny, that the parts links show that under the category "carburetor". Who would have thought?