Engine surge

[jeffprupis]

At a stop my engine keeps surging from approx 700 - 800rpm and bac. When driving, no surge. Any ideas? TIA

[Dave Atherton]

Jeff, engine surge at idle is caused from air Leak on the he suction side of your engine from fuel
Tank to fuel transfer pump. Reason it will surge at idle because the fuel transfer pump cannot overcome air, when you speed up to road speed th fuel transfer pump is maintaining fuel pressure.
This has been been going problem because location of fuel tank located in front of motorhome and
Engine is located in the rear of motorhome. Location of air can come from the water/ fuel filter and
fuel connectors. We have had many motorhome owners change over the the upgrade from Caterpillar,
and many have installed a electric fuel pump that will provide the correct fuel pressure and volume
You can read more on this subject by going to ask Dave located in the technical part of the forum.
Dave Atherton Retired Cat Mechanic

[jeffprupis]

Thanks Dave. Will look at files. ITMT, am I doing any harm to the engine if I do nothing? TIA

[Doug Allman]

Jeff,  As a guy whom followed Daves advice and changed my C-12 to a CAT fuel water seperator here is the change we saw.
Far less noise from diesel at idle. No surging of tach while idling. Smoother performance when accelerating. Mileage, I never look at it as I just fill it to get where we are next headed.
The diesel engine is lubricated with the diesel fuel flow. Air flow does not lubricate so dependent on volume of air flow over time it could have its effect.
The injectors are lubricated with fuel, not air. These are critical tolerance and very expensive to replace.
I am sure Dave can better respond to allowing this to continue.

[Dave Atherton]

Jeff, anytime air enters the fuel system problem will follow. Remember your injectors are cooled by diesel fuel. At present you are in the early stage of things and will not get better. There is a few easy steps
I can provide technical support for you as how you can check your fuel system. Will have to get back to you this evening to do this. We have several problems since I have been with the Beaver group
and the main problem has been the fuel system on many motorhomes. That being said I do not want
to say run out and go to a service shop for large outlay of money. This is something we have with
our group that can provide support and information for you to do a in-house repair at little cost.
Dave Atherton Retired Cat Mechanic

[jeffprupis]

Thanks Dave, I'd appreciate that. Bear-in-mind however, I am NOT a mechanic.

[Doug Allman]

Jeff, Dave can get you a list of the CAT parts to get and someone whom is a either a home garage mechanic or a licensed mechanic at a business can do this wrench work very easily.  I believe I remember the CAT parts costing less than $150.00 when we completed it.

[Dave Atherton]

Jeff, I sent you the information on your problem. The pictures  will show step by step
guide,  you do not need to buy any parts just follow directions should take a about 30
minutes to complete. Dave Atherton Retired Cat Mechanic

[jeffprupis]

Thanks Dave, how or where did you send the information?

[Dave Atherton]

Jeff, sorry had another Jeff having same problem and sent information to that person thinking
I was sending to you.  If you can have someone to assist, you can determine if your fuel system is
getting air into system by the use of a plastic line at hardware store 1/2 inch about 2 feet. The
next step under your bed on back of engine head right in the center you will see a hex fitting
Connect to a elbow on engine head. This hex fitting turns downward at a slight angle to to left
Looking to rear of motorhome. On this hex fitting there is a hose attached to the other end. Note:
This hex fitting is called your return fuel pressure regulator. Remove the hose on the downward
end on hex fitting and connect the plastic hose and put open end into a gallon container. Start
engine and watch the clear plastic hose real close. What you are looking for is presents of any
air bubbles in your fuel system while engine is running. This will confirm air within your fuel
system and engine surge. Where to look for air , connection fittings, water fuel filter connections.
This you will find where problem is located. Reconnect hose on rear on engine at hex fitting.
This the easy way to check your fuel system at this location and work back from here. This
information you can show someone that can help you. Dave Atherton Retired Cat Mechanic.