99 ford ranger 4.0 v6

So my check engine light has came on for a misfire in cylinder 4. Originally it happened and when I changed plugs the plug was cracked. Once I replaced it the problem was fixed at least for awhile. So when if came back I replaced the plugs again and non were cracked but the ones out of 3 and 4 were fouled with a kinda white substance. So once replaced the problem was solved for just a few days then the check engine light came back on. After about a week though the light went back off.

So I have new plugs and wires and I have spark at the coil. I do know that typically if the coil starts to go bad the problem would present it's self in two cylinders ie:3 and 4. So the next obvious step would be to replace the coil but as I said the coil shows spark and I have spark at the plugs,

So my question is has anyone experienced the coil working on and off which would maybe explain the check engine light going on and off. I have noticed my gas mileage has gone down some but not a bunch.

My mechanic has told me that the valves do go bad commonly so I may need a valve job. But it's strange that cylinders 3 and 4 spark plugs are showing fouling and I know they are paired together on the coil.

Any help would be appreciated.

 

Your conclusion about the coil pack is good.

3 and 4 are wired in series from 1 coil in the 3 coil pack.
Since they are in series a failed wire or plug on 1 can cause both cylinders to misfire.

Google: How to Check an Ignition Coil Pack the easy way

Good video on how to test ford coil packs

Yes, coil packs can fail intermittently so testing is not conclusive for a Good coil, but will tell you if a coil in the pack is bad.
It would be nice if all test equipment we used were calibrated the same, lol, but it isn't that way, so what you would look for is one coil in the pack being different from the other 2 coils, the actual numbers are important but only in how they compare to each other.

4.0l OHV engine never had valve problems, odd thing for a mechanic to say
3.0l vulcan engine had valve issue in the early 2000's

As a heads up, the 4.0l OHV is known to ruin spark plugs other than the Motorcraft brand.
Other brands will work, just won't last as long.

 

So like I said I tested for spark at the coil pack, engine light was off at the time and came back on about a day later, and I had spark.

So what your saying is I need to test to see what kinda of spark I'm getting in terms of ohms and compare that number to the other heads/connections in the coil pack?

 

Watch the video.

You test the coil pack, on or off the car.

Checking for spark doesn't really tell you much, outside of no spark at all "having spark" doesn't mean it will fire a spark plug or ignite fuel mix.

After using the OHM meter to test your coil take OHM meter to auto parts store and test a new one or wrecking yard and test another used one.

 

The white residue on 3 & 4 plugs tells me there could be something else going on. I have heard that the 4.0 OHV engine is prone to developing a vacuum leak in the intake gasket in that area. This could cause a misfire but should not leave a residue. I don't know much about the OHV intake but if it has coolant going through it, a very small coolant leak into the cylinders could leave a whitish residue.

It is pretty easy to check for a vacuum leak but I am not sure how you would check for a very small coolant leak into the intake.

 

I seem to be replacing a plug every 3 or 4 months or so. #5 twice and #3 another time. The enamel has cracked around the electrode in two cases and the electrode itself kind of disintegrated on another . I was told early on that I needed a valve job for $1500. Went for a second opinion. Diagnostics showed it to be #5 plug. Cost $105. 3 or 4 months later and two times after that same issue. 2000 ranger starts bucking again. Has 13000 mile on her. Driving me crazy. Good truck other wise.
Tom

 

You should have started your own thread for this.

First, you can only use Motorcraft or Autolite spark plugs in a 4.0l OHV engine, it will "eat" all other brands.
2000 Ranger has the 4.0l OHV engine, 2001 got the 4.0l SOHC.

Ceramic is pretty sturdy stuff so doesn't crack easily, but what can crack it is heat and/or shock waves.
If a cylinder is running Lean it will heat up, this can also lead to pinging/knocking.
Pinging is a shock wave, it will damage pistons, valves and spark plugs.

Lean on one cylinder often won't show up on O2 sensor.
You could just have a couple of dirty injectors, run a can of Seafoam in the gas tank, see if things get better; I put in a can every year, seems to cut down on the odd ball misfires at idle.

Make sure EGR system is working, EGR cools cylinders when engine is under load, accelerating.

Check those spark plugs every few weeks or more often, take pictures of the tips each time, see if you can pin point when they start to fail.


Valve job is done when valve seats are leaking "air/exhaust" so you get low compression, it would have nothing to do with spark plug issue you are seeing.
If you are burning a little oil that is valve guide seals, under the valve covers, they can be changed without removing heads.

 

This thread is pretty old now, but Ill reply in hopes someone may actually search for similar issues. Everything that the fine gentleman above are guiding you through are spot on. Always start with the easy cheap things to diagnose first.

This is my experience with OHV 4.0. Check for loss of coolant, if any missing, check obvious places first ie. hoses/under engine. The truck I have had the same issues you were describing, but the cylinder heads were cracked, in the small bridge between the exhaust valve and intake valve for both cylinder #s 3 and 4. Your mechanic is sort of right in saying they have common valve problems, but specifically its a cylinder head issue. They do crack, and its always Cyl #3 and 4.

I work at a dealer, and before my time (when these were prevalent) this wasn't an uncommon thing to do heads.

 

'99 B3000.
I've replaced #5 spark plug 3 times in 6 years. Guy at O'Reilly's Auto Parts said "common problem for #5 plug exclusively & to use Motorcraft plugs only.. not AutoLite."
I just got another misfiring & "check engine light" flashing; scanned it & once again "#5 misfire". Checked #5 plug & white porcelain insulator was cracked for the 3rd time on a Motorcraft plug. Popped a spare in & all is good now.... 'til the next time.