Diesel Custom Tuner
Join Date: Aug 2005
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Misfire, Lack Of Power, Buck/jerk, Excessive Smoke, Crank/no Start - 6.0l Engine - Di
FORD: 2003-2005 Excursion, F-Super Duty
2004-2005 E-Series, F-650, F-750
Some 6.0L vehicles may exhibit a misfire, lack of power, buck/jerk, excessive smoke or crank/no start. There are several potential causes for these symptoms, including injector concerns.
If normal diagnostics lead to an injector concern, use the following diagnostics to confirm the cause of injector failure and/or to rule out other conditions which may cause the same symptoms as a failed injector.
NOTE: IF DIAGNOSING A LACK OF POWER CONDITION, BE AWARE 2005 MODEL YEAR VEHICLES HAVE A "FORCED LIMITED POWER" STRATEGY WHICH LIMITS ICP PRESSURE WHEN THE FUEL LEVEL IN THE TANK GETS VERY LOW (WELL AFTER THE LOW FUEL LIGHT COMES ON). WHEN THIS OCCURS, DTC P115A WILL BE STORED IN THE PCM.
LOW OR NEGATIVE FUEL PRESSURE
Internal injector damage can be caused by lack of fuel system supply pressure. Restricted fuel filters and/or fuel line(s), or an inoperative fuel pump can create a low or negative fuel supply pressure. Low or negative pressures may hinder the return stroke of the injector intensifier plunger to its rest position, leading to internal injector damage. To diagnose for low or negative fuel pressure and to confirm if any injectors have been damaged:
Perform standard diagnostic procedures including verification of supply fuel pressure while the symptom is evident.
Repair causes for low pressure on the supply side of the fuel system.
Diagnose for failed injector(s) only after rectifying fuel supply pressure.
COMBUSTION GAS ENTERING THE FUEL SYSTEM
Inert combustion gas in an injector can cause a random misfire in one or many cylinders. Combustion gas may leak past the injector's needle and seat, or the copper combustion seal. Once the combustion gas enters the fuel rail in the cylinder head, it then distributes to other injectors, typically on the same bank. To diagnose for combustion gas entering the fuel system:
Remove outlet fuel lines from the fuel filter housing on top of engine.
Install a balloon over each fuel line with a zip tie.
Disable the fuel pump and FICM relays.
Crank engine and watch for compression pulses in the balloon.
For each line where compression pulses are evident, remove all but one of the glow plugs from the affected cylinder head(s).
Crank engine and watch again for compression pulses.
Remove the glow plug and transfer it to the next cylinder in the head and repeat Step 6.
For each cylinder where compression pulses are evident remove injector(s) and inspect copper gasket and lower O-ring, replace if necessary. If gasket(s) and O-ring(s) are OK replace injector(s). Retest to confirm repair.
ERRATIC HIGH PRESSURE OIL SUPPLY
Erratic supply of high pressure oil to injectors may cause a rough running engine. High pressure oil flow can be disrupted by faulty check valve(s) or a faulty IPR valve.
To diagnose, first perform a slow neutral run up in park/neutral. If the engine runs rough between 1200 and 1900 RPM proceed to Check Valve Diagnosis; if the engine runs rough between 3000 and 4000 RPM replace the IPR valve.
Check Valve Diagnosis
To isolate the bank with the faulty check valve, disconnect all of the injector electrical connectors on one bank.
Perform a Power Balance test. Engine misfires should be constant on the four disconnected cylinders and the operational cylinders should be contributing evenly.
Repeat steps 1 and 2 on the opposite bank.
If the operating contribution is erratic on one bank, replace the check valve on that bank.
Notice that if the fuel pressure goes low you can kill an injector. The PCM also limits the ICP pressure if you are running on empty.