Low Power in some Cat Engines models

[Dave Atherton]

inquiry's about motorhome having low power. Maybe I can shed some thought as why this is
happening with certain series Cat Engines. Caterpillar Engines starting with the 3126 A series
models up to the Caterpillar C-9 engines, have a singe stage fuel transfer pump that pulls fuel
from the fuel tank in front to engine in the rear of motorhome. Diesel fuel is pulled by suction
and passes through a primary water / fuel filter than on to the fuel transfer pump, at this point
The fuel transfer pump discharge ( pressure ) pushes fuel through the secondary fuel filter under
Pressure. ( secondary fuel filter is 2 micron and creates a 5# resistance) entering engine. This
Is how the fuel system works on engine listed above. low power starts in the fuel system and
depending on how bad problem is or how long problem been ongoing, will start breaking down
systems. Main cause for low power ( Air Within Fuel System ), the single stage fuel transfer pump
new was very limited on how far it could pull fuel by suction with fuel tank 38 feet. When the
engine built at that point fuel transfer pump would preform pulling fuel up to 6 feet. With time
and miles things are starting to stand out ( air entry into fuel system ) for many reasons. This
has been known for some time on engine performance and Caterpillar made a Electric Fuel pump
with water/fuel filter to correct the problem of engines equipped with heui injection pumps that
will provide a constant fuel flow to the engine. Why many do not understand low power untill
time stands out is because Cat electronic engines the engine ECM adjust the air/fuel going to
engine and reduces power to fuel conditions going into engine. This is basic what is causing low
power and without getting into filters or fittings or aftermarket add on to engine. Last thing
Dave has not mentioned the Caterpillar engines above the C-9, meaning C-10 up to C-18  because
fuel Transfer pump and fuel system is built different and can maintain constant fuel flow
providing there is not entry into the fuel system. Dave Atherton Retired Cat Mechanic

[Mark Bryant]

Thanks Dave for your advice! My engine proformance has improved greatly!

With Respect

Mark Bryant

[Jim Edwards]

Hi I am not quite understanding this post and reply. Dave are you saying that there is a retrofit electric fuel pump for the C9 ? If so where might these be obtained? Would you have part number?

Also Mark, what did you do to improve performance? Did you find an air leak? Fuel pump pressure issues?

Please advise.

Thanks   

[Doug Allman]

Hello Jim,  The best explanation is if you go to the heading when you open the BAC website, not the Forum heading, you will see about 3/4 the way across the top TECHNICAL INFORMATION. In this area you scroll down to the ASK DAVE area and Dave has put up a very good informational comment about this.
Basically if you have a C-9 you need to do as Dave indicates then you will get the performance that the CAT C-9 is capable of all the time in all conditions. That is what Mark Bryant found when he updated his C-9 to meet CAT specifications.
It all boils down to if you are starving your CAT of fuel it will not purr like a CAT should. If you do not have CAT filters then that is another area that needs updating so you do not get air in the fuel.
I know of many that have completed both the updates and they are all smiling.

[Dave Atherton]

Jim, maybe Dave can help this a little better to understand. The engines that I posted have a
single stage fuel transfer pump ( and can be called a single stage piston pump ) because
this little piston runs off the end of heui pump. The distance fuel is pulled from and than adding
the 5 psi resistance pushing through fuel through the secondary filter the single stage fuel
transfer pump cannot maintain a constant fuel flow to engine above 1200 rpm. What Caterpillar
has made avaible for all Caterpillar engines on road and off road equipment is a electric
Fuel pump along with combo water/fuel filter. This pump is added into the suction side of fuel
system and will maintain a constant fuel flow to engine to meet Cat spec for correct fuel
flow and pressure. This has been avaible for long time ( electric fuel pump ) and nobody has
Picked up on problem with motorhome low power. Dave will go into the difference with bigger
Caterpillar Engines C-10 up to C-18 later because fuel wsystem is different than the Cat C-9 and
down. Dave Atherton Retired Cat Mechanic