Mysterious Misfires

[alohamonte]

I replaced the plugs and wires in August 2017 because I was getting misfires and a lean code/ CEL. Misfires stopp and CEL was reset and has not come back.

The misfire came back in December 2017, no CEL.

Since it had been over 100,000 miles since it was last done, I replaced the upper intake gaskets and while out, inspected the injectors. They all looked clean, no visible sign of build up. Gave them a quick soak, replaced the orings, and put everything back together. I also replaced the spark plugs again after seeing that #4 showed a bit dark, rest were normal.

After all of that, I could still feel the miss. So I connected the explorer to my phone via the Torq app to monitor it in real time. After driving for 60 miles, cylinders 1,2,3 showed 0 misfires. 4 and 6 each showed less than 10 misfires, and 5 recorded about 140 misfires.

The ignition coil still under warranty, so I am going to replace that just to rule it out. Aside from that, what could cause only the cylinders on the driver side to have misfires?

 

[alohamonte]

Could it be camshaft position sensor? I've never replaced it, and not sure where its located on the motor...so it would be an original part.

 

[koda2000]

I'm thinking a bad plug wire. Did you check to see if any (especially on #5) looked like they might have gotten burned on the exhaust header? What brand of plug wires did you install 100K ago? I doubt it's your coil as they work with pairs of cylinders and you have 2 cylinders misfiring and not just one. I believe #5 and #1 or on the same coil.

Try this: Take a spray bottle with tap water in it and mist the plug wires at night in the dark and see if you see any arcing. If you want to cheap out, Autozone used to keep single plug wires in stock behind the counter, so you could just replace the #5 wire. Don't think the cam position sensor has anything to do with it. On the OHV 4.0L (if that's what you have) changing it is a major PITA.

 

[fast_dave]

I've read that you replaced your wires in AUGUST, and are having the problem re-occur in DECEMBER.

ALSO - koda2000 offers some good advice!

Additionally:

• The 4.0 OHV has a twice fire ignition system utilizing a high-power coil, and thus it's pretty hard on wires (and spark plugs), especially on the twice-fire side of the engine. The twice fire side of your engine is easily established by looking at the condition of the Driver's and Passenger side plugs after 15,000 miles - the plugs with more wear/larger gap are on the twice fire side.
• With the ABOVE in mind, it's wise that you choose to spend a few extra bucks and use MOTORCARFT high-quality wires. The connectors on both side of the wires are VERY high quality, as well as assure that the wires lock-down on the coil due to the plastic locks on the end of the wire.
• ADDITIONALLY, you should be using Di-Electric Grease on both connection ends of the spark plug wires - Coil Side and Spark Plug Side - to prevent arcing due to the high voltage put out by the coil. This grease will will prevent any arching that can occur due to the high voltage, as well operation in wet/humid climates.

Hope that helps!

 

[koda2000]

OP, sorry, I misread the original post and didn't realize you replaced your wires in Aug '17, but same advise applies.

 

[Dono]

Are you seeing a coolant level drop at all?

 

[Turdle]

Could be the type of spark plug. This waste spark system fires from ground to electrode on the driver side, so the proper autolite plug should be used.

 

[fast_dave]

Could be the type of spark plug. This waste spark system fires from ground to electrode on the driver side, so the proper autolite plug should be used.

Turdle - Just throwing this out there for general thread info; My 4.0 OHV "waste spark/twice fire" is on the Driver's Side Cylinders

 

[alohamonte]

No notable coolant loss. The original radiator and water pump were replaced this past summer due to a hairline crack in the plastic side of the radiator.

Misfire results from this morning's commute are:

#1-0
#2-0
#3-1
#4-6
#5-70
#6-5

The 1 miss on #3 was unexpected. I will test compression this weekend.

 

[1998Exp]

Turdle - Just throwing this out there for general thread info; My 4.0 OHV "waste spark/twice fire" is on the Driver's Side Cylinders

The waste spark system ALWAYS has two plugs in series with the coil, on opposite sides of the block; one cylinder is on compression stroke; the other on exhaust. Because exhaust gas is conductive, the plug in the cylinder on exhaust stroke is practically shorted out, and does not really "fire," so there is no "double wear" due to this arrangement. However, as Turdle pointed out spark polarity is opposite on opposite sides of the block; one side fires from the center electrode to ground; the other goes the opposite way, so double-platinum plugs are highly recommended.

 

[fast_dave]

The waste spark system ALWAYS has two plugs in series with the coil, on opposite sides of the block; one cylinder is on compression stroke; the other on exhaust. Because exhaust gas is conductive, the plug in the cylinder on exhaust stroke is practically shorted out, and does not really "fire," so there is no "double wear" due to this arrangement. However, as Turdle pointed out spark polarity is opposite on opposite sides of the block; one side fires from the center electrode to ground; the other goes the opposite way, so double-platinum plugs are highly recommended.

Thanks for the explanation! Check it out - when I change my plugs at 15,000 - 17,000 miles, the (3) plugs on the drivers side are always appear a little more worn as well as having a slightly larger gap than the (3) plugs from the Passenger Side. Overall, the plugs are always in very good condition, and probably could be left in longer, but I love my Ex ;-) That and what are we talking about - $15 - $20 for (6) plugs when they're on sale or have a rebate?!;-)

I concur with purchasing high quality, double platinum plugs for this engine - as well as high-quality Motorcraft wires.

 

[96eb96]

No notable coolant loss. The original radiator and water pump were replaced this past summer due to a hairline crack in the plastic side of the radiator.

Misfire results from this morning's commute are:

#1-0
#2-0
#3-1
#4-6
#5-70
#6-5

The 1 miss on #3 was unexpected. I will test compression this weekend.

Doubt it is the ignition coil, like others mentioned it is waste spark and they are pretty reliable. My old one I replaced was all cracked and rusty and worked fine, but for 30$ I replaced it with a Ford one.

I had this same issue in 4, eventually it rose to 1000s of misfires. You can take off a bit of coolant and observe if the level starts to rise when it runs. Also you can blow compressed air at TDC and check for coolant rise or bubbles. (Or a compression test).

Likely a cracked head, a big OHV issue. Considering the age of the vehicle and the rust, I used K-seal and I have 1000s of miles of mountain driving with no issues. Just drove in the heavy snow yesterday and it was revving like crazy sometimes. I change coolant every 3 years, so it is very clean. If you have dirty coolant, you should probably flush things out before using that. I can say that the heat was so hot I had to turn it off on max, and we have like single digit temps here. It don't affect anything and my temp gauge says constant, something it never did. Also fixed a tiny leak for a scratch in a freeze plug I replaced. I could drain the product and it should still work, but it is good peace of mind and don't affect anything. The K-seal has silicates(liquid glass) and tiny copper bits that wick into the crack and form a glass from the combustion temps. When used as directed it should be fine. Such products are used on the assembly line, and coolant has silicates that can plug very tiny leaks. Sometimes the engine has to be run with the plug out so the chemical gets in. Also, you may have to replace the plug to complete the repair, it may be cracked.

I've seen a pair loaded heads on ebay for $400 with great reviews, so add gaskets, bolts, etc, you are probably under $600 to do the job. If was an AZ vehicle with no rust I may have taken that route. I know I probably took a few months off its life driving it in the salt yesterday :lol:. I saw other reviews for this engine and it seems to work well. In the worst case you flush it out and do the repair. It says not to let it come in direct contact with the radiator metal, so I drained a bit of coolant added it to the coolant sensor hole. Maybe that is overkill.