Cylinder #4 is causing me grief again

[ERUSH97XLT]

Hello,

Cylinder #4 is misfiring again, so my nifty OBD-2 Laptop hookup says. No codes, active or pending. The subsequent rough idle is slightly annoying, but not nearly as bad a last time. Check out my previous thread for more info on my issues with cylinder #4:

http://www.explorerforum.com/forums/showthread.php?t=225969

Here's my process:

If this was a gross air/fuel/ignition issue, all cylinders would be misfiring or running a bit rough. Since my scanner tells me the misfires only occur on cylinder #4, this narrows down a lot (Vacuum leak, MAF, IAC, EGR, DPFE, etc.), right? Unless there is a slight vacuum leak right at #4's intake. . . what do you think?

1. Ignition:

I just replaced the sparkplug again with little results. I'm reluctant to replace the sparkplug wires again because they are so fresh (and a bit more expensive than a sparkplug). The resistance is right (about 5 k-ohm per foot; the #4 wire is about two feet long, so the measured resistance of about 12 k-ohm should be acceptable). Perhaps there is a ground-fault somewhere in the wire that occured so soon? I also checked the primary and secondary resistance at the coil. All is well; the primary resistance measured less than one ohm on all terminals and the the secondary resistance measured equally at about 13.5 k-ohms across coil pairs. Any more ignition thoughts?

2. Fuel

I'm going to run some injector cleaner in with the next fill up. Maybe it's a dirty injector? If this doesn't work, I'll remove this injector and more thoroughly clean or replace it (if necessary). I can't think of any more fuel issues which would affect just one cylinder. Maybe a dirty valve? I seafoamed the intake a few months back, so I doubt much carbon has built up in this short amount of time. Should I seafoam again?

3. Compression

I'm nervous about this. If all else fails, I'm going to do a compression check. I don't want to replace rings or a head gasket.

Any thoughts?

ERUSH

 

[ERUSH97XLT]

Hello again,

I recently filled up with some injector cleaner additive with noticeable results. I figured this had to be the root of the problem, so I pulled all the injectors and soaked them in seafoam for about a day. Everything runs smoothly now! I have to admit, I haven't used injector cleaner for some time now. I guess the build up got the best of me. Thanks to those who have viewed this thread!

ERUSH

 

[Runnin'OnEmpty]

Hi ERUSH, I hope your misfire is fixed, but I doubt that
it is. The reason I think that is a cyl 4 misfire and rough
idle upon startup are common symptoms of a failed
lower intake manifold gasket.

When the gasket starts leaking, coolant is drawn into
cyl #4 after cooldown, and the residue gradually fouls
the plug. A new plug will remedy it for a while, but the misfire
will come back; and the only reliable cure is a new lower
manifold gasket.

Let us know how it goes......

 

[ERUSH97XLT]

Hi there,

Thanks for the input!

Couple comments:

The changed plug wasn't fouled at all (I've only had this one in for about eight months; would a leaking gasket foul the plug in this short of time?).

I went for another test drive with my computer hooked up, and the misfire counter didn't notice any misfires, nor could I feel them.

Also, the rough idle occured all the time, not just at start up.

Perhaps it was a combination of the two. A defective sparkplug and a dirty injector in my eyes will cause issues. What do you think?

ERUSH

 

[Runnin'OnEmpty]

Hi there,

Thanks for the input!

Couple comments:

The changed plug wasn't fouled at all (I've only had this one in for about eight months; would a leaking gasket foul the plug in this short of time?).

I went for another test drive with my computer hooked up, and the misfire counter didn't notice any misfires, nor could I feel them.

Also, the rough idle occured all the time, not just at start up.

Perhaps it was a combination of the two. A defective sparkplug and a dirty injector in my eyes will cause issues. What do you think?

ERUSH

It might have been a dirty injector and bad plug, hope so.
I've read so many threads on the #4 misfire, and my own experience
with it makes me wonder. Only time will tell.

When the plug fouls from coolant, it dosen't look like an oil-fouled
plug. In fact the plug will look almost normal, or possibly a little
damp. Apparently the burned coolant builds up on the insulator
and shorts the electrode to ground, and it's almost invisible.

One giveaway though, will be a plug with rusty threads that's
harder than the rest to remove. The moisture in the cylinder
(after shutdown) tends to rust the threads, at least in my
experience.

Maybe your miss being in #4 is just a coincidence....?
How did the threads look on the plug you removed?

 

[ERUSH97XLT]

Thanks for the input!

Nothing about the spark plug seemed abnormal (no rust, fouling, breaks, corrosion, etc.) I did test it with my multimeter, though. There seemed to be a break in the conductor within the electrode because my meter registed this portion as an open circuit.

Everything seems normal now with the clean injectors and new plug. I guess we'll see in a few months. I'm banking on this being a funky coincidence.

Thanks again,

ERUSH

 

[Runnin'OnEmpty]

Thanks for the input!

Nothing about the spark plug seemed abnormal (no rust, fouling, breaks, corrosion, etc.) I did test it with my multimeter, though. There seemed to be a break in the conductor within the electrode because my meter registed this portion as an open circuit.

Everything seems normal now with the clean injectors and new plug. I guess we'll see in a few months. I'm banking on this being a funky coincidence.

Thanks again,

ERUSH

Sounds like you may have gotten lucky, ERUSH. Explorer plugs
that I've checked have had about 5-10K ohms internal resistance.
Obviously a bad plug.
Good luck....