99 pushrod 4.0L 49,825 miles, intermittent miss under load when towing.

Pulled & checked the OEM plug gap & they were WAY out of spec!!!!

I had pulled & set these plugs to the minimum specified gap when new, because it's always opening with time.

It seems I'm averaging about .002" of wear per 10K miles, so there is no way these plugs would maintain the specified gap over their stated 100K life, even if they started servce at the MINIMUM specified gap, to allow for wear!!!!

SO, any of you out there with a miss under load, with 25K miles or more on your platinum plugs, should perhaps place plug gap on your suspect list too!!!!

Any experiences out there with plug gap erosion rate with time, on the pushrod 4.0L OEM platinum plugs????

Or plug gap erosion rate for any of the Ranger engines????

 

i change my plugs every 15-25k anyways. i wouldnt notice

Matt

 

Did you put the
OEM plugs back in the same bank they came out of? The OEM plugs are single platinum, the GND electrode is platinum in the plugs in one bank, while the center electrode is platinum in the plugs in the other bank, due to the spark polarity when they fire in series...If you switched them, they will erode fast.

 

Well Bob, I removed, regaped & reinstalled them one at a time, so if they're messed up, it's because the factory had them that way to begin with & with some of their screw-up's I suppose thats not to be ruled out. lol

I began a log of the first 3 plug numbers & they were all the same, but I didn't remember to check the remainder.

Only #1 was close to the max gap, the remainder were well over.

I'll be towing again tomorrow, same load, over the same road, with the same gas, so we'll see if the re-gap fixed her up for sure or not, I'll post the results on the miss.

I had begun to notice a slight, random, miss, in gear, at idle, which it has never had, then when it misfired twice on two different tow sessions on different days & with the mileage on these plugs, I began to suspect plug gap erosion.

Even if gap isn't the cause of my misfire, seems to me with an average or .002 erosion per 10K, these plugs should be pulled, say every 25K miles for a re-gap, to keep them in tolerance.
No way are they going to go 50 or 100K miles & stay in spec, even if I were to begin at min gap to allow for wear, which I did!!!!!

Just a heads up for everyone, from something I found yesterday!!!!!

 

Pawpaw, I bought my former 94 4.0 new back in 94 with just under three miles. I first changed plugs at about 89,000 (maintenance, not due to problems) and the gap was in the real low 60 thou range. Food 4 thought.

 

Well I had a good tow yesterday.

Tugged the Tracker over & through the Blue Ridge Mountains to the lake & back, with my 99 4.0L 5spd auto.

Tried lugging the engine pretty hard in OD, to see if I could cause it to repeat it's misfire, it didn't!!!!!

Also now idles in gear without the slight random miss.

So I'm gonna pronounce this puppy "well" for the time being!!!!

I'll reiterate, looks to me like the OEM plugs in the 99 4.0L are going to need re-gaping about evey 25K miles, to keep the gap in spec!!!!!

SO, any of you out there, with a misfire, slight random miss at idle, or maybe power or mpg not up to snuff & with 25K miles or more on your plugs, just maybe they need regaping, mine sure did!!!!

I had pulled & set mine to the minimum gap when new & with 49K miles on them, they were WAY out of spec, due to plug gap erosion, so imo there is no reason not to suspect there are others out there wih the same situtation!!!!

Just a heads up!!!!!