TESTING AND ADJUSTING
7. ENGINE MISFIRING OR RUNNING ROUGH
Fuel Pressure is Low
Make sure there is fuel in the fuel tank. Look for leaks or bad
bends in the fuel line between fuel tank and fuel transfer pump.
Look for air in the fuel system, sticking, binding or defective fuel
bypass valve. Check fuel pressure. The outlet pressure of the
fuel transfer pump must be a minimum of 415 kPa (60 psi) at full
load speed. The pressure in both fuel manifolds must be 415 to
450 kPa (60 to 65 psi). If fuel pressure is lower than the above
pressure, install new filters. If fuel pressure is still low, check the
fuel transfer pump and fuel pressure regulator valve in the fuel
Air in Fuel System
Find the air leak in the fuel system and correct it. If air is in the
fuel system it will generally get in on the suction side of the fuel
Leak or Break in Fuel Line Between Fuel Manifold
Install a new fuel line.
and Cylinder Head Defect in Fuel Injector(s)
Temperature of an exhaust manifold port, when the engine runs
at low idle speed, can be an indication of the condition of a fuel
injector. Low temperature at an exhaust manifold port is an
indication of no fuel to the cylinder. This can possibly be an
indication of an injector with a defect. Extra high temperature at
an exhaust manifold port can be an indication of too much fuel to
the cylinder, also caused by an injector with a defect.
Wrong Valve Clearance
Make adjustment according to Subject, VALVE CLEARANCE.
Wrong Fuel Injection Timing
Make adjustment to timing.
Bent or Broken Push Rod
Replacement of push rod is necessary.
Fuel Has "Cloud Point" Higher Than Atmospheric
Drain the fuel tank, lines and fuel manifolds. Change
Temperature ("Cloud Point" = Temperature
the fuel filter. Fill the tank with fuel which has the
Which Makes Wax Form In Fuel).
correct "cloud point" and remove the air from the system with the
In some installations it can be necessary to use fuel heaters to
insure proper fuel flow and to prevent filter blockage from fuel
wax. The fuel temperature at which flow is reduced and filter
blockage occurs is usually dependent upon the amount of wax in
the fuel or its cloud point.