2002 Explorer 4.6L misfire cylinder 4 (solved) | Ford Explorer Forums - Serious Explorations

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2002 Explorer 4.6L misfire cylinder 4 (solved)


December 3, 2016
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Year, Model & Trim Level
2002 Explorer Eddie Bauer
2002 Eddie Bauer Explorer, 4.6L v8, 131k miles.

On the way home from work, my check engine light came on. I could feel the engine stumbling, so I figured I had a misfire. I got it home and pulled the codes : P0304 Cylinder 4 misfire.

I pulled cylinder 4 plug (last cylinder in the back on passenger side). The boot and plug were oily. The firing end of the plug was a little dark. I changed the plug and boot thinking that a little oil had gotten into the plug well and was causing the misfire. That did not fix the problem.

I then swapped the coil on cylinder 4 to a different cylinder. Still getting misfire code for cylinder 4.

I then checked the spark on cylinder 4 using a HEI ignition tester. the spark looked fine (blue) to me.

I checked the resistance of the #4 fuel injector. Honestly, i don't remember exactly what it was ... but i checked online and it was in the good range (11-18ohm). I compared it with the resistance of injectors on 2 other cylinders and it was basically the same (less than 1 ohm difference).

I didn't have the tools to do any more tests, so i took it to my local shop. He did a compression check on the right side and it passed (220). Fuel pressure was good, and the injector was firing. He pulled the coil and tested it and it passed. He even tried a new coil, but that didn't fix it.

He concluded that it was probably the PCM. He suggested taking it to the dealership and getting the PCM reprogrammed or getting a new one. I imagine either of those 2 options isn't cheap.

So, I have a few questions:
1) Is the problem likely the PCM at this point? Is there anything else that could/should be checked? I would guess PCM failure is rare (no basis for this, just guessing)
2) does reprogramming the PCM ever fix something like this? what would cause the programming in the PCM to get corrupted?
3) I *think* the PCM programming has some vehicle specific stuff in there. So I can't just swap in a new one. The new one has to be programmed, right? Any other options for getting a PCM than through the dealership?

thanks in advance,

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lots of views, but no replies. was my post too wordy?

anyone? anyone? bueller? (sad attempt at humor, i know)

seriously, any responses would be greatly appreciated.

I'm not saying this is your problem but it is highly possible. The reason I'd like you to check the following is because you observed "oil" around spark plug but there is no likely source for oil.

Take a very good look on top of and around the intake manifold to see if you detect any coolant or some sort of wetness. Apparently, these engines are notorious for the intake manifold gaskets to start leaking and the most obvious sign of a leak is a coolant leak not necessarily an air intake leak.

Take a look at THIS THREAD where I was also wondering why I had engine oil inside a spark plug well. In my case it is the #8 cylinder which is located on the opposite side of #4.

If coolant gets in the right place it can short out the COP for that cylinder causing a misfire and if it continues the COP will get fried and you'll need to replace it.

I'm actually in the process of replacing my intake manifold, something that many folks before me have had to do. You mileage is apparently right in line with when this problem can start to happen. Let us know what you find.

BTW, the reason why there is coolant around the intake manifold is because there are coolant crossovers (aluminum on the front side) that are a part of the intake manifold on the front next to #1 and #5 and on the rear next to #4 and #8.


See the pics of the underside of the Dorman replacement intake manifold:

I agree with SyberTiger and I am same boat thinking my spark plug well was oily just due the appearance but it is coolant that has mixed with surface grime and other contaminants to look like an oily substance. I bet if you try Syber's burn test technique with some of the fluid soaked on a qtip it won't readily ignite like it might with true oil

Was the #4 plug loose? I had a misfire and cleared it about a week before it threw the plug 200 miles from home.

Was the #4 plug loose? I had a misfire and cleared it about a week before it threw the plug 200 miles from home.

Wow, how was it that the plug was loose and not torqued?

hey, thanks for the suggestions. sorry it took so long to post back ... real life intercedes some times.

i checked and didn't detect any wetness around the intake. my mechanic cleaned up around there when he was checking things out, and he didn't see anything either. i pulled the coil again, and the boot is dry as a bone. no signs of any oil or coolant. therefore, i can't test it with the "burn test" to see what it was. there is obviously a leak somewhere because it was wet with something (oil or coolant) when i pulled it the first time. it must be a slow leak since it is dry now.

However, the cylinder is still misfiring. Since it is dry, i don't think moisture in the plug well is the main cause of the misfire. i could be wrong, since i am an amateur mechanic at best.

I moved coils around before to see if the misfire moved, and it did not. Also, my mechanic tested the current coil on #4 and tried a new coil, but that didn't fix the problem. so i don't think the moisture in the plug well caused the coil to go bad.

any other suggestions?

Can the computer cause a single cylinder misfire? If so, can reprogramming it fix it? If i have to replace it, is that something i can do, or does the dealership have to program it before it gets installed?

Was the #4 plug loose? I had a misfire and cleared it about a week before it threw the plug 200 miles from home.

no, the plug wasn't loose. i replaced them about 40k ago and torqued them myself. it was still snug.

Was anything done to verify the COP electrical connector is good and on all the way....the plastic tab isn't broken?

BTW, why would the PCM program get screwed up. Unless it self modifying firmware I don't see how this would be the problem.

After that, next guess would be the cam shaft or crank shaft position sensor. They are located bolted on the outside of the timing chain cover. Make sure they are both plugged in properly and no damage to wires. You can unplug them and use electrical connector cleaner to make sure they are clean...for all I know you've got oil on/in the connectors.

yes, i checked and the COP connector is on all the way and the plastic tab is not broken.

i have no idea how the PCM program could get screwed up. My mechanic suggested getting the PCM reprogrammed or replaced. Screwed up programming sounds like an extremely rare (if not impossible) failure mode to me. that's why i was asking if anyone had seen reprogramming fix something like this. I was also wondering if a PCM issue would likely cause a single cylinder misfire.

i checked the spark with an HEI spark tester, like this one: https://www.amazon.com/OTC-6589-Electronic-Ignition-Tester/dp/B0050SFVO2 (but not the same brand). spark looked good to me. i tried moving the wire and COP around while the spark tester was connected and it didn't make a difference to the spark. so i deduced the wire and connector were making good connection to the COP.

i will check the cam position sensor connection. though i would guess that if the position sensor was bad, no cylinders would fire. if the sensor was making contact sometimes but not others (bad connection), i would expect the misfire to move around to different cylinders. neither of those are true. all cylinders are sparking, and only #4 is misfiring.

Sorry I haven't given an update. I tried all these suggestions. I even made another attempt and moving all the coils around to different cylinders. Nothing worked, still misfiring on cylinder #4. On my last attempt to fix it, I reset the computer and started it up. It was still misfiring, so I turned it off and parked it in the driveway in frustration.

The holidays came and went, and I didn't have time to work on it, so it just sat in the driveway, and I drove the Ranger.

A little over 3 weeks ago, I decided to bite the bullet and take it to the dealership to have them fix it. I made an appointment for the following Monday. Over the weekend, I remembered that I had reset the DTC codes the last time I was working on it, and had not run it enough for it to throw the misfire code. So, I went out Saturday to drive it around so the code would be set when I took it in. The damn thing ran great, no misfire. So I parked it. Drove it again that night, no misfire. Drove it twice on Sunday, no misfire.

So I called the dealership first thing Monday to cancel the appointment. I knew it wasn't fixed, but I thought it would be a waste of time/money to take it in without a code set.

Drove it Monday evening, and it started missing again, and threw a misfire code on #8. This was the first time it had moved to a cylinder other than #4. So I said, maybe it is the coils, and they are all weak. So I ordered a cheap set of coils from Amazon. I figured it was worth $35 to try.

That fixed it. no more misfire. I have been driving it now for 3 weeks with no issues (knock on wood). I guess the moral of the story is, moving coils around isn't a surefire way to verify the problem isn't the coils.

thanks everyone for the help.


Glad you got it going. Please provide update again after a couple oil changes on the set of coil over plugs. Amazon reviews sounded positive on those parts. I know I was tempted to buy a set and ended up needing 4 all on driver's side bank immediately so spent 4x that much at retail auto parts store counter for half as many. I think others on the site will be interested to hear how yours hold up long term and could be great options for engines getting up in mileage.

This is my last update. I sold the explorer. i had probably 3k miles on it since I did the coil swap. It was still running great at that time. Sorry I can't give a review of the "cheap" coils with more miles on them. Glad I didn't take it to the dealer since I ended up selling it. I know they would have swapped coils to start with, and it would have cost a fortune. So at least for me, the $35 was well spent :)

fwiw, a link to the coils I bought (from "U.S. Based Seller")