MBE 4000 SERVICE MANUAL
17.1 FACTORS THAT AFFECT WHEEL HORSEPOWER
The factors affecting wheel horsepower are listed in Table 17-1.
To begin low horsepower diagnosis, refer to section 17.2
Factors
Considerations
Power Rating
Is the correct power rating programmed into the PLD? Is the driver aware of
the effects that cruise power, or the lack of cruise power has on perceived
power?
Road Speed Setting
Is the road speed setting causing a perceived lack of power?
Crank Case Overfilled
If the crank case level is too high, there will be a loss of power due to
churning losses created by the crank shaft throws contacting the oil.
Fuel Blend (specific gravity)
Check the specific gravity of the fuel/vehicle system. A good number 2
diesel fuel has a specific gravity of 0.840 or higher @ 60°F. It should be
noted that No. 1 diesel fuel can reduce horsepower to 7% less than No.
2 fuel. Blends of No. 1 and No. 2 (common in winter) will produce less
horsepower, depending on the percent of the blend. This is a common
concern when dealing with low power complaints in cold climate locations.
Fuel Filter Restriction
Check for fuel flow restrictions which can be caused by fuel heaters, water
separators, fuel flow meters, undersize or improperly routed/damaged fuel
lines, faulty check valves, contaminated fuel filters or high fuel pressure
resulting from a plugged restricted fitting or regulator valve. Replacing the
fuel filter is often the best recommendation in lieu of testing for the filter
condition. Make sure the recommended fuel filter is being used. Refer to
Technical Service Letter (05-TS-12REV – MBE 4000 Fuel Filter Update).
Fuel System Leak
Fuel system leaks which result in aerated fuel are normally caused by a
leak at the connections and /or filters between the suction side of the fuel
pump to the supply tank and not between the pressure side of the pump
and engine.
Fuel Tank Vent Restriction
A plugged fuel tank vent will create a vacuum in the tank and result in a
loss in fuel pressure at the injectors. This will reduce fuel delivery rate.
Air in Fuel
Aerated fuel, caused by a fuel system leak, will result in reduced fuel
delivery and late injection timing.
Plugged or Cracked Fuel Tank Stand
Pipe
If the fuel tank stand pipe is plugged by a shop rag, fuel delivery will be
restricted. A cracked stand pipe will allow air to enter the fuel system and
reduce fuel flow and cause late injection timing.
Faulty Injector/Unit Pump
A faulty injector/unit pump will limit fuel delivery and alter the combustion
process such that power is compromised. Using Idle Smooth Balance
(ISB) in DDDL can help identify a faulty injector nozzle.
Valve Lash
Incorrect valve lash will alter the combustion process such that power is
compromised.
Air Flow Restriction
Air flow must not be inhibited by a plugged filter, or inadequate inlet air
duct shrouding.
Faulty Turbocharger
A turbocharger that has wheel rubbing, oil leaks, bent blades, etc. will not
provide adequate air supply.
All information subject to change without notice.
(Rev. 2007)
6SE412 0702
Copyright © 2007 DETROIT DIESEL CORPORATION
From Bulletin 1–MBE 4000–07
17-3
