03-13-2018, 02:32 PM
Join Date: Apr 2016
Since it's quick and easy, I'd pull that cylinder's plug wire off the coil, stick a bolt (or wire, whatever) in it to see if it's sparking while cranking the engine, but if it's still using the waste spark ignition system (3 coils for 6 cylinders) then that's unlikely as it would tend to make two corresponding cylinders misfire instead of only one.
Next I'd do a compression test on that cylinder. In this case I would have done that when replacing the plugs because you already have the plugs out at the time.
I'd also check the oil and coolant for signs that they're mixing, and look for air bubbles in the coolant reservoir, wondering if there is a head gasket leak or warped head, and look around the block for signs there's an external leak.
Next I'd hook up a scan tool to look at live data running, or maybe do that first since it can save some time. is the check engine light on, any OBDII codes set?
If nothing shows bad up to this point then I'd put a multimeter on that cylinder's fuel injector plug to see if it's getting power, trace back the circuit if it isn't, or if it is then get a set of fuel injector o-rings, pull the fuel rail, and either replace the injector or swap it with a different cylinder's injector to see if the problem follows the injector.
Some people might try cleaning individual injectors or if it's flowing at all, put some fuel injector cleaner in the tank (maybe twice the strength that the cleaner states on the bottle) and run it a little while but not too long as unburnt fuel can wreck the catalytic converter, BUT IIRC injectors for that engine are inexpensive so it could make as much sense to just replace it while the fuel rail is off, not have to disassemble it again if it turns out to be the problem.
When you pulled the plug out in the prior step you could look at it to see if it looks like it's getting wet from unburnt fuel, though it could be harder to tell with new plugs. Did the old plug from that cylinder look different than the rest and how if it did?
Don't know what to say about buying a lemon, I mean did it not do this when you bought it? Did the prior owner make any statement about the problem?
If you got it cheap enough, even pulling the head for truing, replacement, or just new gaskets could be cost effective esp if you DIY, but of course when that is done it will need new intake manifold gaskets, injector o-rings, and probably a good idea to do other things while they're easily accessible like PCV valve.
A new intake manifold gasket is a good idea anyway as they tend to go out every 100K mi. or so, but in this case I'm doubting it's the problem right now if you only have one cylinder consistently misfiring. Live data from a scan tool could better show what's going on.
Please post your vehicle year/model/engine/(n)WD in help topics.
'98 Explorer XLT 4L SOHC 4WD
'14 Explorer XLT 3.5L NA AWD