I have a 99 ford ranger 4.0l 4x4 I got rear ended and then my truck started running rough so I put a obd device on it and it said cylinder 4 misfire so then I replaced all spark plugs and wires what else could it be that's causing the misfire and how do I check I don't know a lot about working on my but I want to learn

 

Welcome to the forum

You need 3 things make a cylinder fire
1. Fuel, in the right mix with air
2. Spark, at the right time
3. Compression, above 120psi

Ford numbers V6 engine cylinders this way
3 6
2 5
1 4
Front

4.0l engines eat spark plugs, so misfire is often spark plug failure, they crack, Motorcraft or Autolite seems to last the longest.
But only use regular copper or Double Platinum for any brand, skip single platinum, they don't last any longer than regular copper in Ford's Waste Spark system

Spark plug tips can tell you the condition inside the cylinder, too much fuel, too little fuel, oil coming in or coolant coming in.
Google: spark plug condition

Loads of pictures on what the tips tell you
If you still have the old spark plugs see what they compare to

The spark plug wiring is "odd" on the 3.0l/4.0l coil packs
3 4
2 6
1 5
Front

The 1, 2, 3 side is easy
The 5, 6, 4 side often gets mixed up
So first thing to check is the spark plug wiring, and then check it again, lol.

Fuel injector test
Cold engine
You know where the coil pack is
Unplug the 4 wire connector on the coil pack, you want No Spark
Crank engine a few times
Pull out #4 spark plug and #5 spark plug
Both should be wet with fuel, compare #4 and #5

If #4 is dry then you found the problem, check fuel injector connector, then repeat test.
You can rent a Noid Light, it plugs in between fuel injector and it's wire connector.
Noid light will flash on and off as you crank the engine IF computer is opening the fuel injector.
Test light won't work for this, the injectors are only opened(powered) for a few milliseconds, so too fast for regular test light to show power.
If Noid light flashes then computer is working, if #4 plug is dry then injector is clogged or bad, thats assuming #5 plug was wet, if #5 is dry then fuel pressure was lost.
You can test a fuel injector with OHM meter, Ranger injectors should show 11-18ohms, but that just tells you the wire inside is good, it can still be clogged.


Unlike fuel or spark, Compression is black and white, it can't be intermittent.
For this reason people often test compression first, so it can be "taken off the table" as the reason for the misfire, or found as the reason for it.
But %-wise compression problem is a long shot when you have a single cylinder misfire, but not a No Shot :)


When you are in an accident there is an "inertia switch" in the passenger footwell of the cab that can be damaged, it passes power to the fuel pump, it is there to cut fuel pump power in the event of a collision or roll over, you don't want gasoline continuing to pump out of a broken fuel line, that would be a bad thing, lol.
It has a reset button on the top, but that is only to get you going if everything else checks out after the accident, it needs to be replaced.
This wouldn't cause just a single cylinder misfire, No Start is more likely result, so just a heads up that it should be replaced

 

I read my obd test again now I have 4 pending problems as cylinder 2 and 4 misfire and system to lean on bank 1 and 2

 

misfires will set Lean codes, so follow up on why you are getting misfires

 

My 2007 Ranger FX4 has been misfiring for 3 yrs(P02 & P05). Ford and 2 local garages have independently replaced spark plugs and wires, coil, coil packs and injectors. One shop added fuel injector cleaner. Recently checked compression, cat converter, ox sensor and head casket. all OK. It passed emissions 2 yrs ago but misfire returned shortly after and emissions was due again 7/2/2019. Brought it to a local garage that also does emissions testing and after spending nearly $700.00 on replacing all this stuff AGAIN, misfire returned before I could get it to emissions. I added a fuel stabilizer ( not injector cleaner). Two days later the engine warning light turned off and codes were cleared. I took it in for emissions and passed. Misfire has not returned. I think Rangers don't like ethanol

 

2005 ranger 4.0, did plugs and wires, same thing but cylinder 2. I thought it was cross threading, but I recently heard that the factory plugs were not always fully tight, causing the threads to get dirty not allowing for the plug to fully install. I'm about to carefully clean the female threads and see if that does it. I figured I'd share this here in case future people have this problem. I'll try to remember to update this post if it works.

 

I cant believe it! It wasn't cross threading, I just kept putting blaster on the plug threads and just worked it in and out. It took about 15min. I changed the oil directly after to mitigate any contamination. Cleared the codes and bam! It sounds practically brand new with 270K. Today was a good day :)