I thought I had the problem fixed with a cylinder 4 misfire and a bank 2 lean but it still occurs. I have a new coil, wires, plugs, EGR valve and have removed the intake plenum to clean out the EGR ports to each cylinder. The only other thing I can think of is I have a bad fuel injector. After visiting auto websites, I see Motorcraft injectors for my 1998 F150 4.2l listed as CM4785 F65e-A4a or FS65EA4A. While looking for a cheaper price on Ebay, I see one CM4785 listed with the numbers F65Z 9F593-A. What is the difference? The spray pattern, material they are made of, what? I have been getting codes PO174 and PO304 and you can really feel the loss of power when this cylinder acts up. The truck has 235K on it. I am the original owner and have been changing the oil every 3K. Thanks.

 

Check compression on all cylinders so you can see the high and low pressures to see if all are within the specified limits for high to low value.
There may be a valve seat sealing issue, valve hanging up, broken valve spring etc.
Good luck.

 

Replaced all six injectors and the truck seems to run with more power than it did when I bought it new from the dealership. Was leery of the injectors I bought since the O-rings which plug into the fuel rail looked to be only half the thickness of the stock ones I pulled out with a lot of force. Took one out after coating it with motor oil and it swelled. Hope this problem is solved! Thanks to all whom contributed. Not bad for an engine with 235K on it!

 

Which part number dis you end up going with? New or remanufactured?

 

I replaced all six which I bought from uscarburetors. They are refurbished and are part number F65-A4A-9F593. The truck runs great, the #4 misfire is gone, but when I hooked my scanner up I got codes 171 and 174 (both banks lean) with O2S, HTR, and EVA monitors flashing on my Innova scanner. Thinking I may have a vacuum leak somewhere I sprayed all around the intake plenum, injectors, and hoses with electrical contact cleaner and didn't notice any change in RPM. Trying to figure out where to go from here.

 

If the spray cleaner is not flammable it won't offer a change.
Very often you won't see a change in engine idle even with flammable spray.
The proper way to see the difference is looking at the short term trim table reactions on your Scanner set to view them...
This is the most sensitive way because the Ox sensors react immediately and change the short term trim readouts in real time..
Good luck.

 

This CRC contact cleaner is extremely flammable. I used it a couple of months ago to find a hole in one of the two elbows on the lines coming off the PCV valve behind the bank two valve cover. I replaced every single piece of that configuration while I had the intake plenum off. I'm going to have to get a scanner which gives live data display. On my particular engine ('98 4.2l) the fuel trims are controlled by vacuum alone, aren't they? I thought I saw a video of someone working on a linkage rod back there which fell out from a worn out grommet. Maybe that was on a Windstar engine, I can't remember.

 

/Both long and short fuel trims are tables in software program.
They have inputs from the OX sensors and Mass Air mainly, but have inputs from other sources.
Any vacuum leak indirectly affects these tables by being sensed at the OX sensors as excess oxygen in the exhaust.
The short term tables are instant reacting.
The long term tables store the average of all the inputs and vary slowly over time by additions and subtractions..
The short term tables will react instantly to a detection of flammable substance sucked through the leak area.
This is why looking for an idle change is not the best way to find a leak.
If the leak is very small, you may not hear an idle change because the computer will / can still make adjustment via the IAC opening corrections and not be detectable by hearing the change.
Good luck.