My 2002 5.4L v-8 F-150 has recently been experiencing misfire problems. Started with #4 cylinder (PO304, P0171 code), so I replaced the #4 coil pack and it was fine for about 2 weeks, then misfire issues again. Replaced #4 injector, no change. still reading (P0304, P0171 codes)

Today, plugged in the reader and now getting P0301 in addition to P0304 and P0171 codes, so suddenly #1 cylinder is apparently misfiring as well. Been using Dorman replacement coil packs for quite awhile and never had any problems before. Getting ready to pull #1 and #4 coil packs to check resistance. Any other possible suggestions? Plugs just changed less than 1 year ago, 207,000 on the odometer.

 

Waste of time, resistance will never tell you anything useful unless the coil is fully blown open.

Swap the COPS to another set of easy-to-reach cylinders and see if the faults move.

 

How many miles on the spark plugs and what brand are they?

 

Thanks...resistance check was the only test my Chilton manual offered. Would I be better off biting the bullet and using Motorcraft coil packs? As mentioned, never had any issues with the Dormans from Autozone, but maybe I've just been lucky so far.

 

Motorcraft Platinum... AGSF-22W. Probably less than 16,000 miles in service.

 

Misfire with lean code suggest lack of fuel. If it was the plugs or coil pack, the exhaust should be rich. What is the fuel pressure?

 

Haven't checked the fuel pressure. How do I do that?

 

With a fuel pressure gauge attached to the Schrader valve on the fuel rail. 28 to 40 PSI. You can borrow/rent a gauge from the parts store.

Lean codes are frequently caused by a vacuum leak, biggest suspect is the PCV elbow behind the intake, it rots and splits.

Best coils are Motorcraft, Delphi, or Denso. Dorman anything is suspect. The only cheap coils I'd take a chance on are Araparts.

 

Thanks for the helpful info!

 

A note about "lean" codes. They do not mean the engine is running lean, usually it's the opposite. Those codes are set when the PCM has reached the limit of ENRICHMENT but the O2 sensors are still showing that the mixture is lean, usually due to un-metered air entering the system (intake leaks). That means that the fueling system is dumping excess fuel into the system which usually ends up damaging the cats.

A marginal ignition system will misfire when the mixture is too far off and the misfires will add to the load of raw fuel entering the converters as well as the measure oxygen level in the exhaust stream.

Over 90% of the time, "lean" codes are caused by intake vacuum leaks with the PCV system being the most common culprits. A weak fuel pump or restricted fuel delivery system that cannot deliver fuel in volume at pressure is the other but less common problem.

Did you pull the freeze frame data? That will tell you the conditions when the fault code was set. Vacuum leaks usually are the worst at or near idle speeds when manifold vacuum is at its highest. Fuel delivery issues usually pop up when the engine load is high and more fuel is demanded but the demand cannot be met.

Chiltons, bless their hearts, made some of the finest aftermarket manuals for several generations of vehicles. Unfortunately, they're pretty close to worthless for diving into the advanced electronics used for the last 20 years, IMHO.

 

My truck is having the same issues. 02 screw w/ 243k miles. engine light on Monday started flashing at me. from what I found online that means a misfire. Taking it to Autozone because they will scan it for free. Im hoping this isn't too expensive of a fix because like so many, im strapped for cash at the moment. this is my daily to work and back. (30mile round trip) and I am that one guy that was not given the gift of being mechanically inclined. I doubt I could even get the spark plugs out myself. and when I read things like Schrader valve and PCV valve it makes my head spin.

 

Thanks! I need to upgrade to a diagnostic tool that captures live data, since my little Innova 3030F only reads static codes

 

The shrader valve is similar to the valves in the valve stems on your wheels through which the tires are inflated.

The PCV (positive crankcase ventilation) valve is a check valve that is inserted into the passenger side valve cover with a hose attached to it that connects to the intake manifold. The purpose is to ventilate the base of the engine to the intake. The PCV valve should be changed periodically with a Motorcraft unit.

 

thanks for the info.