Good evening all,
Looking for some help on what direction to go. I used to work on automobiles in the days when electronic ignitions were just coming out. Gave that up to work on aircraft. After a few recent bad experiences with the local garages I have decided I will fully maintain my own.
My 2002 Ford Ranger recently kicked a P0304 code along with a noticeable miss from idle and during moderate acceleration. I used a simple reader to get the code. After some internet investigation I decided to change the 3 left hand side plugs and also swapped plug wires. I then used a spark tester that only gives a visual that the cylinder was firing. I compared it to another cylinder. Checked compression which was around 175, (comparable to adjacent cylinder.) Followed this up with replacing the 6 intake seals, cleaned and tested injectors, swapped injector 4 with another injector, cleaned all the carbon out of the intake which was a result of the dreaded pvc elbow that had cracked previously. I had taped up the elbow to get me by and forgot about which ended up collapsing. In the process of cleaning the intake out I decided to pull the valve cover and found the pvc check valve somewhat plugged and cleaned that as well. Through all this I had what I felt was quite a bit of oil present in the intake. i also cleaned the EGR up as well. After the second drive the code kicked again. So I went and bought an advanced code reader. Here is the FF info given:
P0304
RPM 1697
Load 58.0%
coolant 185
STFTRM1 .8
LTFTRM1 -2.3
STFTRM2 2.3
LTFTRM2 -7.0
MPH 45
Fuel Sys Closed
So then I decided to take some readings at idle:
ABSLT TPS 19.6
RPM 1054
Load 51%
MAF 1.12
Coolant 81
IAT 25
IGN Adv 15.5
STFTRM1 9.4
LTFTRM1 0
STFTRM2 4.7
LTFTRM2 3.9
02S11V .070
STFTRM11 1.6
02S12V .5
02S21V .75
STFTRM21 0
OBDII STAT CA

As the engine warmed up several of these variables changed such as 02 information. I can also graph certain items though am still trying to wrap my hands around exactly what I am doing. I am guessing my bank trims are out of whack on the one side. I am in the process of studying and trying to get a better understanding. Any help or further diagnosis requests is appreciated.

Cheers!

I'd replace all plugs and wires to start. The lopsided fuel trims may be due to the PCM attempting to compensate for the misfire.

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2003 Edge 4x4 Sonic Blue 4.0 SOHC, Auto, 4.10 LSD, 4-door Supercab

The 4.0L is a SOHC not DOHC. What condition are the plugs & wires in?

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2010 Ranger XL 2.3L 5 Spd 3.73:1 Bone Stock
2013 Scion FR-S 2.0L/H-4, 6spd, 4.11:1 Fast Enough Stock

I thought it was SOHC though if so why does each head have a cam shaft that directly moves the valves? I may be thinking old school put this to me would indicate dual overhead cams.

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I replaced the left side plugs and then swapped one of the wires with #4 cylinder to eliminate that possibility. The wires look in good condition but from past experience that doesn't mean they are. I am thinking what I did would have move the misifire unless this is somewhat of a false reading and the problem is coming from another cylinder. I don't like to just throw parts at it.

sohc means one cam opens and closes both the intake and exhaust valves. dohc means two cams per head one for the intake valves one for the exhaust valves set up in a hemi configuration .

Thanks for the information cowboykilroy. I found this out by asking someone at work. Dummy me. Well tonight I ran diagnostic views of the 02 sensors. The forward bank 1 and 2 indicated proper voltage cycling using the graphing function. I also unplugged the #4 injector and the engine definitely ran rougher. I have read a lot about cracked heads between the valves. I am going to stick a video scope in the cylinder and take a look. I wish there was an easy way to test the coil. The problem with the newer rangers is one pack for all. I would imagine this is expensive.

Connect a test lead to the coil output and hold the other end near a ground (like say, part of the body) run the engine and look for the arc.

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2003 Edge 4x4 Sonic Blue 4.0 SOHC, Auto, 4.10 LSD, 4-door Supercab

Thanks for the input. Used a spark tester that does the same thing. Only problem is it doesn't measure voltage.

Found the problem. Broken exhaust valve spring. Runs like a top. I unfortunately wasted money on wires and plugs. Should have known better that the way I troubleshot was correct and should have kept going. I had myself convinced it was electrical though the code reader was giving good information that had I listened would have sent me there sooner than it did.