Fuel System (low Fuel Pressure Will Cause Problems)

[Edward Buker]

Dick,

From my experience the many small bubbles are signs of a leak. Air is being drawn in through a small leak source producing many repeated bubbles. Usually there will be some seepage while sitting but not always. If you are trying to sort out if yours has a leak and are on the fence then compare it to several others at the same RPM like idle when you get the chance.

Later Ed

[Dave Atherton]

Gentleman, indication of large bubbles is air leakage into fuel system. A string of small
Air bubbles in most cases is acceptable in troubleshooting Cat fuel systems with use of
install of clear site glass or clear line in fuel system. To besure in troubleshooting ( air
within fuel system. ) attach site glass or clear line to engine return to fuel tank. Connection
will tell what is coming out of engine fuel rail and will go back to air in fuel system after
injectors. Again a little stream of trailing bubbles is ok. In most cases air in fuel system
start at pickup tube exit from fuel tank than primary fuel water filter suction line to the
fuel transfer pump, after the fuel transfer pump, pressure is going to the secondary filter
than into fuel rail on engine. Dave Atherton Retired Cat Mechanic.

[Edward Buker]

With all due respect to Dave, he has a lot of experience with these fuel systems. In the case of this Racor unit, when mine had a minute plastic crack at the bottom, the fuel suction that was being pulled from the bottom of this plastic tube pulled air in through the crack that produced many small bubbles in a stream that rose in the fuel and mixed in the turbulence of this unique design much like in Fred's posted photo. This is a comment on detecting a leaking plastic tube or Oring and not on what is or is not acceptable from a bubble size/quantity in the fuel stream as Dave aptly pointed out.

Later Ed

[Dave Atherton]

Gentleman, air within the fuel system can be located from start of fuel tank and ending when fuel exit the engine.
ED pointed out the Racor primary water/fuel filter problem over time will need attention and what to look for. This
water/fuel filter is one area that will allow entry of air into fuel system. Have pointed this out. In troubleshooting for
air, connection of site glass or clear line on discharge of water/ fuel filter, if air is present than connect clear line on
both suction and discharge of water/ fuel filter ( bypassing water/ fuel filter and see if air is present, in most cases
there is no air present, than repair or replace water/fuel filter. Note: I'm not downgrading how Beaver built there
motorhome or what kind of parts were installed. When certain problems keep popping up many times, there is a
reason as to why and with my background of many years to point out problems. cannot sugar coat the problem
because I did not create the problem. Pointing out problem and correcting problem, this is where I'm coming from.
Going deeper, entry of air or low power, injector failure all work hand in hand. This is one of the areas that over time
is starting to stand out. Dave Atherton Retired Cat Mechanic