How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Ron Your Own Question
Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 23821
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
Type Your Ford Question Here...
Ron is online now
A new question is answered every 9 seconds

Ford F-150: 2002 F-150 4.6L - Started missing badly. Threw

Customer Question

2002 F-150 4.6L - Started missing badly. Threw codes PO303 (missire #3)and PO316 (crank position sensor). Replaced #3 COP, fuel injector, spark plug, and replaced Crank Position Sensor. Installed new fuel filter. No vacuum leaks detected. Started it up and it still missed at idle and a little just off idle under acceleration. It then accelerates smoothly and does not miss under load or cruising speed, or WOT. Still misses badly at idle. "Service Engine Soon" light finally came on after about a week. Checked the codes again and it throws the same PO303 and P)316 codes. Help!
Submitted: 2 years ago.
Category: Ford
Expert:  A. Penland replied 2 years ago.
Since you have already replaced the coil, spark plug and fuel injector for #3, you should inspect the basic mechanical parts of the engine. The best thing to do first is to do a manual compression test of #3 and all the cylinders on that side of the engine. They should be ar70 psi on ach cylinder.We have seen valve springs break and valves sticking in the valve guides that can cause miss fires. Also, check the electrical connectors for the coil and the injector for #3 to make sure they are making good contact. Poor contact can cause a miss fire to.
Customer: replied 2 years ago.
The truck has 136,000 miles on it. Never missed an oil change at each 5,000 miles or less. Pretty sure there are no mechanical problems - doesn't sound or act like a stuck valve or broken valve spring, no signs in the exhaust of a broken or weak piston ring. Cranking shows equal compression on all 8 cylinders. All electrical contacts are sound to #3 C-O-P, spark plug, injector and to the Crank Position Sensor. All check out with an ohm meter. Could it be the PCM?
Customer: replied 2 years ago.
Do you know about the "Mode $06" scan from the OBD II? Auto Zone suggested looking into that.
Expert:  A. Penland replied 2 years ago.
Yes. MODE 6 DATA is a table of parameters that the PCM is monitoring, like miss fires per cylinder, 02 sensor voltages, long fuel trims, short fuel trims, EGR percentages, etc....It is basically what the PCM is monitoring while the engine is operating and the minimum and maximum voltages and percentages any sensor should be operating at. You will need the proper computer scan tool to access MODE 6 DATA.I also doubt your problem is caused by the PCM. Also, a properly maintained engine can still have valve train issues. We have seen this ethanol fuel cause all kinds of issues.