2002 Ford F-150



April, 11, 2008 AT 12:43 PM

Engine Mechanical problem
2002 Ford F150 6 cyl Two Wheel Drive Automatic 102000 miles

I have a couple of trouble codes that come up on my OBDII Scanner that I was hoping to get an answer on. I receive a P0306 Cylinder 6 misfire, P0171 System too lean Bank 1. I also get a misfire detected at 1000 rpms which I can't think of the code off hand. I have random excessive cranking on startup no matter hot or cold. I orginally had a couple of additional messages that called for the H02S12 to be replaced and for the MAF to be replaced. I replaced and these messages are gone however I now I have the above codes. Someone suggested I replace the cylinder 6 fuel injector which I heard is a big job to do. Is there anything else I can look at before I go this route? Any other diagnosis I can perform before I sink money aand it doesn't fix my problem?

4 Answers



April, 11, 2008 AT 1:12 PM

P0306 misfire at no.6 cylinder-could check the spark plug/compression/injector.

P0171 A lean fuel condition can be caused by: * Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

On many Fords, a P0171 Lean Code may sometimes appear because of a bad Differential Pressure Sensor (DPFE). This sensor monitors EGR flow, and is located on the engine near the EGR valve. There are two hoses that connect the sensor to the tube that runs from the exhaust manifold to the EGR valve. The sensor misreads EGR flow and the computer increases EGR which has a leaning effect on the fuel mixture. The fix is to replace the DPFE sensor.



April, 11, 2008 AT 1:15 PM

You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
The other thing it could be is the Idle air control valve Ford had problems on a few models with this part.



April, 11, 2008 AT 1:22 PM

Rasmataz, Thanks for the quick reply. What is the proper way to clean fuel injectors? As far as the MAF this has been replaced less than 1000 miles ago should I still clean it? I will check for the vacuum leaks and EGR operation. I would rather check this before getting involved with tearing out the intake manifold and all that goes with it.



April, 12, 2008 AT 4:53 AM


Should you clean the injectors in place or remove them and use some type of injector cleaning machine? It depends.

The easiest route is to clean the injectors in place because you do not have to remove the injectors (which can be a real chore on some import engines). Running cleaner through the injectors while the engine is running also removes many of the deposits on the valves and inside the combustion chambers. This eliminates the need for an extra cleaning step if the engine is full of carbon deposits. The job takes only 10 to 15 minutes, and you can usually tell right away if the treatment addressed the problem (engine runs smoother, idle misfire gone, etc.).

When doing the cleaning procedure itself, you must use pressurized equipment to feed the solvent directly into the fuel rail while the engine is running. This means you either have to disable the fuel pump and plug the fuel return line, or install a U-tube so the fuel will recirculate right back to the tank. Disabling the fuel pump can set a fault code on some cars, requiring you to clear the code after the job is done.

Easy as it is, there are some limitations with on-car injector cleaning. One is that badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned. Some baked-on deposits can be very difficult to remove, requiring you to prolong or repeat the cleaning process. And if on-car cleaning does not work? You will have to remove the injectors and have them cleaned on an injector cleaning machine - or replace them.

Another limitation with on-car injector cleaning is that you may have to do some additional tests to confirm that the injectors responded well enough to your cleaning efforts. A test drive may be needed to see if the driveability symptoms have been eliminated, or you may have to check emissions to make sure HC and CO levels are back to normal. A power balance test is another way to confirm engine performance and check for weak cylinders (there should be less than a 10% power variation between cylinders). An injector pressure drop test will tell you if the injectors are flowing evenly or not.

There may be some risk to the vehicle's fuel system when using concentrated solvent to clean the injectors in place. Most equipment suppliers say to disconnect and plug the fuel return line so that solvent does not circulate back to the fuel tank. Strong solvents may attack rubber and plastic components in the fuel pump, regulator and fuel lines, creating additional problems that you don't need.

On-car injector cleaning also involves some risk to the person who's performing the service. You have to disconnect pressurized fuel lines, make sure there are no fuel leaks, and feed high-pressure solvent (which is just as flammable as gasoline) into the engine while the engine is running. Safety precautions should always include eye protection, making sure there are no open sources of ignition (sparks) nearby, and avoiding direct exposure with the cleaning solvent.

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