I know mine is an Explorer, but Explorer forums don't seem to have anybody that can help. Hoping Rangers do.
Just hit 190K, Two months ago, light occasional misfire. Changed plugs (been a while), great for a day or two, came back.
Belden wires showing halos, got new ones via warranty. Ran great for a day or two, came back.
How hard can this be? Changed coil pack. Ran great for a day or two, came back.
This is silly. Checked fuel pressure at rail, 60PSI, never wavered while driving (fuel filter early in the year plus annual injector cleaner).
Cleaned MAF with proper stuff.......Ran great for a day or two, came back.
Getting worse. Between 25 and 35 on a light grade it can shake so bad you think the mounts are gonna fail.
Checked spark voltage at both ends of all wires, about 10KV.
Pulled plugs...all clean, nice light tan on electrodes.
Took it to a shop for diagnosis. First, #4 injector wires mouse eaten and no other place visually on entire harness. Shop pulled plenum, new injector plug, soldered and shrink sleeved. Ran great for a day or two, came back.
They find "occasional" #4 misfire...swapped plug with another hole, problem did not move.
Recommended #4 injector...had a local injector shop rebuild same p/n. Ran great for a day or two, came back.
Days of scan tool and road tests....everything looks fairly good. B2 STFT is roughy same as B1. B2 LTFT is slightly higher than B1 (4.7 vs 3.8).
Found the line to the charcoal cannister perished and split...replaced..Ran great for a day or two, came back.
Went to clean Throttle Body and MAF...battery died. Obtained new battery, removed and cleaned parts, new gaskets. Ran great for a day or two, came back.
Noticed while running good B2 LTFT at zero. When it started running bad again, 4.7. Battery out for an hour probably reset values.
Upstream O2's .105-.705 or so. Today, downstream O2 looked locked at .775, but actually moved a bit, .773-.778.
Road test thirty minutes later, downstream at .135.
Transmission had been getting...strange. 4th gear before 28MPH, never used to do that, OD off, can't feel engage or disengage.
After the memory cleared and it ran good, transmission hit 4th at 40 like it used to, and OD worked like it always has.
Sprayed upper engine all around plenum and intake while watching scan fuel trims with carb spray...no changes at all in fuel trim.
Pulled PCV and vent line to snorkel, sprayed carb cleaner into valve cover while running (intake gasket valve guides), no change in RPM's.
Clear Flood, no dead holes. Cylinder Balance shows all cylinders seem to drop about the same amount.
No coolant loss, no steam out exhaust, tried four tanks of pet...gasoline in tank, two different sources, no change.
Tested EGR (in case the internal spring had failed), works normally. Tapped around the edge of the diaphram to set any carbon, left hose unplugged. No change.
Need to do a compression test still, but nothing points to that.
I am out of bright ideas. No matter what, problem is still there, goes away for a day or two and comes back. Seems to be getting more frequent and severe.
No idea how to test crank sensor. Don't have a lab scope.
Wife's can, 16 years we've had it, only automatic on the property..for her.

 

Welcome to the forum

Alot of stuff in that post

No, not a crank sensor issue, they work or they don't and engine will not start when they don't

So basically its misfiring under load, and you should get Flashing CEL(check engine light) when that happens
And it runs OK for a few days then starts to actup, then after a reset of computer???, it runs OK again??

Does it run fine until engine warms up and computer goes in to Closed Loop?
Or can the misfires also come with cold engine?

Unplug the EGR valve vacuum hose and plug the hose, then drive it for a few days, you will get CEL and EGR codes, thats fine, if you don't that would be a bad sign, lol
It could be a computer issue, although rare, the PCMs can fail and its usually very odd issues that can come and go, and be hard to nail down

EGR valve is not used at all when engine is cold, and its then used mostly when accelerating or when engine is under a load, i.e. going up hill
If computer is opening it too much then misfires, and it could come and go like the 2 day thing

After engine is warmed up, and idling, you can unplug the 2 wire connector on IAC Valve, valve will close and RPMs should drop to 500, engine barely running, or engine may even stall, either is GOOD it means no vacuum leaks, just a simpler test than spaying flammable stuff around engine bay

Your issues are puzzling so just guessing at this point

The battery dying thing is interesting, any more on that?
One oddity seen is a failing alternator can send out AC ripples instead of just DC volts/amps
These AC Ripples play heck with computer data and cause odd codes to come up some times but also odd running issues because computers input data is corrupted when it happens
The Crank sensor and Cam sensor both use AC Volts

You can test for this but it can come and go
With engine running test battery volts, 13.5 to 14.8v is expected, NO HIGHER than 15v
Then switch meter over to AC Volts, under 0.4vAC is maximum allowed
REV engine a few times just to see if AC volts change

 

Battery was old, almost 10 years old. I went to start the vehicle after it sat most of the morning, slow crank, warning lights pulsed a bit. Got two more starts and it was toast.
Alternator....a bit over a year old. 14.4 or so when I checked output. Voltmeter on dash in the middle where it's always been.
I'll check AC component.
There are no codes. There is no CEL. (well, when I drove it with EGR unplugged I got a code I had to delete, but no CEL).

I need to check to make sure the store sold me double platinum plugs....reading indicates with the waste spark protocol you MUST have that....I do know Autolites are in there, new as of about 30 days ago.

 

I had that typed up this morning and didn't hit "reply".

Next query.....NAPA sold me Autolite AP-103's for this. That's when we started going downhill, if I recall. Slight misfire, 10-year-old plugs, but these are single platinum plugs.
Someplace I read due to the type of coil you need dual-platinums.
And, how does the return on the plugs work?

Certainly NOT through the metal plate on the base of the coil. Ohmmeter goes nowhere.

One of the wires into the plug in the side of the coil pack?

Where does that ground on the engine block?

Some other place I read they ground through the opposite plug, which makes no sense, but okay.

I think I need to get DP probably Motorcrafts.

 

You should use regular copper or double platinum spark plugs with waste spark

Single platinum work fine but will wear out on one bank of the engine the same as regular copper would, so a waste of money, but nothing wrong with using them


Crank sensor would set a code for sure, as would cam sensor

I would say you are fighting a computer issue at this point, EGR problem was last hope of external issue
Spark and fuel are both controlled by computer in 1999, and sensor inputs are pretty well monitored if any jump out of "range"
Controls are as well, i.e. IAC valve, EGR and other solenoids
Non-monitored things like fuel pressure have been tested

Only other thing I can think of is an exhaust blockage that comes and goes, but extreme longshot

Its a pain to swap out computer when you have a separate PATS module, they are a matched set
Forscan may be able to do that, re-match new PCM to PATS module, it not an expensive software
Article here: https://www.forscan.org/forum/viewtopic.php?t=1500

 

I was leaning towards PCM. Looked one up, $84 for that unit. I can get the keys reprogrammed locally.
I did DeOxit5 on engine gang plug, pulled the PCM, DeOxit5 on connectors opened the unit, inspected for water or corrosion, burned bits, visual as new.
There ain't much left, it's just a feeling I have that the PCM is going to do nothing.
I still have higher LTFT on B2 than B1.
When this happens, it;s like an intense cluster of massive misfires, yet the tach doesn't wobble the needle at all.
And none of the numbers on the scan goes nuts when it happens. TPS, MAF, STFT, LTFT even IAT all stay doing what they were doing.
Trans guy says it isn't the trans, as tach doesn't wobble. He actually got it to do it on the interstate a bit and watched needle.

 

If possible when it happens shift to Neutral and REV engine to get tach to go up and down, that would take trans out of the picture or point to torque converter/transmission/differential as the problem
If engine REVs smoothly then it ain't the problem

 

I've done so much in the last two months...I THINK we've revved it unloaded and felt it. Heck, sometimes you get a definite miss at idle in park, but cannot find it.
Trans shop said not trans at all. He's done enough of these..anything doing that to cause that roughness would cause tach to fluctuate as clutches engaged or disengaged. Or slipped. I did service the trans about 10 days ago. No metal bits.
What I cannot fathom is the lack of tach flutter when something is causing this. Clusters of misfires or whatever should have dumped power or at least cause vehicle to slow, and none of that happened.
No overheating. No clatter of moving bits.

EDIT: Possibly acts like a crossfire situation, where a cracked and carbon tracked distributor cap caused spark to show up on a wrong cylinder at the wrong time. But, new plus, wires and coil pack.....still not sure how to know for certain signal isn't breaking up from crank sensor.

 

A bit more data. I went out just now....cold out...pulled 3&4 plugs (same coil), inspected, checked gap. 4 may have had a bit of shine to the end of the metal ring but now sure.
Started it, checked voltage,. 14.5, so good.
When it started felt like a crossfire or something for a second. Then gone.
Drove it, still cold, gauge not up yet...you could tell it wasn't going to be good right away.

Very low speed...20-25...surged. in and out. Not the hard cluster. Did it for a mile or more. Even at 35. So it does it in what appears to be open loop.

Did an in-the-dark underhood looking for sparks. None.

 

Pondering...I think tomorrow I'll check lash on timing chain. At 190K, probably shot. Retarded cam timing could do some of this. I recall Chrysler V-8's...boy, little stretch and they'd fall on their face.

 

10-12 degrees of TC slack. Fine.
However:
The crank sensor trigger wheel...there are marks on part of it.
Not sure how far around, but two marks on at least half the segments, spaced about 1/8" apart.
Not grooves, just discolored marks (brown, to be precise).
They are exactly lined up with the two pointed tabs on the sensor proper.
No looseness in the trigger wheel.
I'm wondering if the sensor is getting vibration and causing some issue?

Just reporting what I've found.

 

Further question.

I know on earlier Fords we could unplug the MAF and drive it.
I did on this 99 just now, the symptoms are more muted and more intense. Stronger you drawn out and not as sharp.

Also, mile and a half (and tried to die every time I left a stop sign), NO CEL. At. All.

I noticed before with the EGR unplugged for a test it set a code, but no CEL.

Why no CEL?

I checked, it DID set a P0102 and one for IAT, same component. Still, no CEL.
There is a "roughness" at idle. Touch the wheel or top of the dash, you can feel it. Cylinder Balance Test shows same drop on all six, while the roughness is there.

 

You have a 6 wire MAF sensor in a 1999 Ranger???

Oh forgot, this is a 1999 explorer
So yes
P0100 Mass or Volume Air Flow Circuit Malfunction, or P0102 MAF low
P0109 Intake Air Temperature Circuit Malfunction, or P0112 IAT low

Should be set after key on

With MAF sensor unplugged it depends on outside temp and elevation on how engine runs
The computer has the air/fuel mix tables it uses for Open Loop operation, then modifies that using current LTFT(long term fuel trims)
The weight of the air is what MAF is used for, and not sure exactly what Ford uses when MAF is "off-line", maybe air weight at 60deg 1,000ft elevation, that would be a safe mix, not too lean not too rich, if you were in Denver it might not run,lol

 

Engine off, restart, no CEL. THEN I cleared codes.

 

Wife now reports symptoms changing, as I discovered last night. Surging. Usually as a lead-in to bucking and shaking, which seems to be a bit diminished.

Car cooling, tools out, compression test shortly.

 

157-172. No issues. About what I expect with 190K on the clock and a fuel issue.
I am convinced the ignition is fine. Balance test with rough idle shows similar cylinder drops.
Tomorrow or Thursday (depends on availability of vehicle) I'll pull upper plenum, make sure the shop didn't pinch something between upper and lower, use one of my injector test lights (they call it a NOID light now, I think) and see what each output gives me at the plug.

 

Still not sure why CEL does not come on when I purposefully set a code. Code is there, just no light.
Key on, light on, start vehicle, light goes off.

 

PCM failing is most likely the case after all the testing you have done

 

I'm just about there. Cleaned some grounds this afternoon between car use. Wife says it was perfect this morning, out and back.
I really want to check the wiring and plugs on the injectors, and make sure the upper plenum is sealing before I jump on the PCM.

I'll know before Friday.

 

The car is fine. Three days, dry and warm, cool and wet, up hill and don.

I have a couple of scenarios.

One, for some reason I had a really dirty injector and the two cans of injector cleaner I put in 6 weeks ago finally softened the junk up and it flushed out.
Not likely but probable.

Two, when I did the compression test, I had all six plugs out. I have experience with trash in cylinders blowing out when you crank the engine with plugs out. Last one was a V-12 Lincoln.
IF the shop dropped something into the intake like a piece of gasket when they did the injector...could have been migrating to a valve-seat interface.
Since the car went back together after the compression test, hasn't missed a beat.

Still monitoring. Right now, wife is happy.

 

Good stuff

I guess its a mystery until its NOT, lol

 

those '99 explorer 4.0L pushrods were always finnikey

 

Yeah, I can see that especially with waste spark system. However, for over 190K, the cam sensor a number of years ago, upper and lower plenum gaskets a couple of years ago, ball joints and such late last year.

My 1950 Tudor was 20 years old when I bought it.
I just wish it looked and ran like this did when it was 20 years old.

Still good today, keeping an eye on it.

 

Three week or so update.
Vehicle has been just fine.
No hiccups, no shaking, no misfire.

Since the compression test with all plugs out.

 

Thanks for the update