Hey, been having this as an on-going issue. Right now it seems to only Misfire when the outside temps about 65 and humid. Cold and dry its fine.

It has 211K on it. Well maintained. So far I have replaced the Fuel pump (it died on its own), Crankshaft position sensor, the Coil, Plugs and wires, cleaned MAF, tested TPS, Cleaned EGR, replaced PVC, cleaned K&N filter with K&N cleaning Kit, cussed at it, replaced fuel filter.
Edit: forgot about the 02 senors. both up stream have been replaced as well.


usually the misfire happens in the first 10-15mins of operation, and under load or acceleration. on days it don't mf, it runs like new.

What next?
Only codes thrown are MF random cylinder or like 3 & 6 or 4 etc. Usually I don't even get a code or pending code.

 

At 211k it should have newer O2 sensors, upstream

Try a can of Seafoam in the gas tank, could have dirty injector tips that are dripping fuel instead of spraying fuel.

If its an "oiled" air cleaner then that could be the problem.
Stock Ranger air box and air filter had better flow than add-ons, but add-ons do "look" better, lol.

Humid air, of course, has more water vapor and water doesn't burn, it steams which means you need very good air/fuel mix and strong spark at that time.

Make sure you don't have any vacuum leaks:
After engine is fully warmed up, let it idle
Unplug the 2 wires on the IAC Valve, it will close all the way
RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leaks.
If idle stays high then you need to find the leak

 

[QUOTE=RonD;2135289]At 211k it should have newer O2 sensors, upstream

Both upstreams have been replaced. forgot to add that to the post.

Try a can of Seafoam in the gas tank, could have dirty injector tips that are dripping fuel instead of spraying fuel.

Did seafoam and marvel myster oil. both in oil and gas.

If its an "oiled" air cleaner then that could be the problem.
Stock Ranger air box and air filter had better flow than add-ons, but add-ons do "look" better, lol.
.
The K&N / air box came standard. ....

 

Today, I cleaned the battery terminals. so basically reset the comp.
Thing idled fine but missed/hiccuped like made for first few trips, still missing, but not as bad.

 

I guess next step would be to get a Bluetooth OBDII reader, under $40, with extension cable
It works with free APP on any smartphone or tablet

You can then view live data while driving.
Could be Air Temp sensor or MAF is giving PCM(computer) wring info.

OBDII readers work on ANY vehicle made in, or imported into, the US or Canada since 1996, so not a Ford thing, good tool to have in the drawer

If you have an OBDII reader now then have a look at air temp and MAF data while driving, also Throttle position sensor see if it is stable or "jumpy"

 

I have a scan tool but not real sure what the parameters should be.
I see the IAT with is close to the outside air temp, might be 10-15 warmer after engine is warmed up. I see the MAF GR/SE number goes low at idle around 4 or 5.0 and rises with increasing throttle, seems to change fast if I change throttle.

I used an ohm meter on the TPS it looks nice and smooth.

 

IAT(air Temp) sensor is located in the MAF assembly so it is at the air filter box.
It should read outside temp at startup, but it should go DOWN as engine sucks in air, air flow cools the sensor.
After you shut off warm engine then IAT temp would climb

If IAT is reporting higher air temp than it is, then computer would be running engine too Lean

I would be tempted to get a 6 wire MAF from a wrecking yard to try, 1995 and up had the 6 wire MAF setup

MAF should read "engine displacement" at idle, 600-800RPM, in grams per second(GR/SE) so with a 4.0l engine 3.8-4.3 would be correct after warm up and lower idle

 

This one has a separate temp senor. I can check the accuracy with that and a lab thermometer at warmer temps. I didn't think much about this, but with it being its own sensor I can test it. I will post results later today..

Thanks.

 

That would be an ACT(Air Charge Temperature) sensor, did see that on the wiring Diagrams for the 4.0l

But should still being going down with faster air flow

If MAF has 6 wires then it has an IAT sensor inside

ECT(engine coolant temp) sensor goes up as engine warms up.

 

I checked it out.. Took a pan of hot water, placed the ACT sensor in it, showed 111'F and thats same as the lab thermometer. So that is dead on.

 

Took off the MAF. really cleaned it well. No real change. Idle seems better. Misfired bad first 10 mins of driving. Even heard back fire through the intake
Code was thrown for misfire cylinder 4. After 10 mins or so of driving its fine.

 

Good code, so did you swap spark plugs around like 5 to 4 to see if code changed.

And have a look at #4's tip, that may tell you something.

Back fire is from the misfire, air/fuel mix was unburned in #4 so was dumped into exhaust manifold, it hot gases from #5 or #6 hit it just right then "back fire" explosion in the exhaust manifold.
Which is actually a good sign, it means #4 is getting fuel, but may be too much or not enough so not definitive that it is a spark or compression issue

Backfire from intake could mean lean mix in #4, but only after engine warmed up, lean fuel mix with high vapor(hot gasoline) can self ignite as it goes into a hot cylinder while intake valve is still open, so backfire from the intake, but this would usually blow off vacuum lines

 

Back to the original problem. I changed the spark plug in #4. And as if by magic, no more misfire. The plug only had 800 miles on it, looked good, clean, basically looked new. Gap was good.

 

I have had new spark plugs fail more often in the last 10 years than the 30 years prior in my DIY mechanical life.

Maybe I am just old and like all old people say "they don't make um like they used to", lol, or...........
Maybe they really don't make them like the used to

Glad you got it fixed, hopefully for good

 

Yes that does some to be more frequent that ever. Its been an on going problem. I figured it might be something else, but I changed, or checked pretty much everything. but if I change the plugs when I am lucky enough to get a misfire code. only thing to note, its usually 4, 5 or 6. only once did it happen on the other side on #3

 

Ford uses Waste Spark so each spark plug fires once every 1 RPM
So it fires on compression stroke and exhaust stroke(the wasted spark)

Because they use Waste spark they only needs 3 coils for a 6 cylinder engine because 2 of the cylinders will be at TDC at the same time
So the two spark plugs sharing a coil are wired in series
One will spark "normal", center to tip, the other will spark "reverse", tip to center

Coil wiring reflects the shared spark
3 4
2 6
1 5
Front

1 and 5 spark at the same time, as do 2 and 6, and 3 and 4

In the above 1, 2, and 3 would spark "normal" and 5, 6, 4 would be "reverse"

With waste spark you should only use regular copper plugs or Double Platinum, because single platinum would wear out on one bank the same as regular copper, just FYI

It could be the "reverse" side spark plugs tend to fail more often, but just guessing

With regular copper, what I use, lol, I swap the wires around once a year, so
4 3
6 2
5 1
front

That's to get even wear
As long as the matched cylinders share the same coil in the same order it doesn't matter which side it is plugged into

 

I never thought about the cylinders firing at same time. The wires going to 4,5,6 are slightly longer. New plug fixes this for a short time. Could wires be the issue? I changed all that and the coil. I always use the best. I think the wires are bosch, and the coil is motorcraft.

 

No, if it were the wires then changing spark plugs wouldn't have fixed it

And I don't think it would have caused it, but can't say for sure

 

Changing the plug seems to have fixed it. Just seems the plugs on that side of the motor always go bad.

 

If you are using single platinum, or single anything, then yes one side will always wear out faster than the other.
Use regular copper or DOUBLE platinum only if vehicle uses a Coil Pack, Waste Spark system

 

I have double plats in it before. The iridium or whatever they were seem to fail faster, so I went back to double platinums. will see what happens. Might try copper if they will fail again. I will know in about 200 miles...

 

Its back......!
In june of 2018 I replaced the plugs and wires... not just any but the high dollar jobs from Rockauto. I got the NASCAR approved wires and the iridium plugs. Misfire issue has been gone.

Now 2 days ago, same MO. after 10 mins of driving, when under load, misfires started up again. I probably have less than 2,000 miles on these plugs/wires... I give up. everything else is changed.
coil, plugs, wires, fuel pump, fuel filter, cleaned MAF, We determined its not a injector since it back fires in the intake. Only thing that corrects this issue is changing the spark plug. I did not get a misfire code, (not even a pending code)

 

Whats the gap now?
Check a few spark plugs

You may want to start with .050 instead of .054

 

I didn't get a code yet, but usually its always on the drivers side, so I gaped those plugs down to .045 runs great again

 

Couple days ago I started it, and the idle was rough, usually it smooths out... then it will misfire as I drive

This time the idle was rough, then smooth for a second or 2, then rough a few seconds, then smooth for a couple of seconds,.. alternated a back and forth before smoothing out...
I think that's tied into the whole issue... what would cause that???