A stupid rookie mistake

[Zorba]

Posting this here for the next rookie that comes along. Short version:

Replaced spark plugs with the forum recommended XP-985 Autolites. Fire it up. Runs rough, throws a code. "Cylinder 5 misfire". Yea, no shit - at least I know what cylinder is misfiring. I also hear a rapid tick,tick,tick,tick,tick... Stick my head under the hood, and sure enough, it sounds like its coming from the vicinity of #5. Shut down, and grope under the coil rail, and you guessed it! #5 boot was bent over at an angle, not on the plug at all, and apparently arcing to the block.

Lesson: You can't see them, so grope all 6 boots before calling it good. Last gas motor I worked on had a distributor and you could see things! Engine cooling now, I'll fix it after I have lunch.

 

[CharlesHS]

GROPING....... under the boots.....
With all the political correctness and thin skinned people in this world; someone is bound to take offense......

 

[Head Lice]

GROPING....... under the boots.....

Fondling under the footwear . . . . .
Fetish ?
Thought this was a simple plug change . . . . ?

 

[Zorba]

La, la, la, la, la, la... I'm ignoring you guys...

It *is* amazing how much better the engine runs when it runs on all 6! Dunno what its problem is - my Mercedes runs just fine on 5. Reminds me of the time I was riding shotgun with my dad as he pulled a 29 ft. fifth wheel over the high pass in Lassen park on 7 cylinders. We didn't know it at the time - instead of a 454 V8, it was a 397 V7!

 

[TJ2]

Forum recommended huh?
I use Champions.

 

[CharlesHS]

Never considered my interests in headlights and peaches a fetish.

 

[pagrey]

Forum recommended huh?
I use Champions.

I use the factory NGK ZFR5N, personally I enjoy checking them every few thousand miles when normal plugs wear out and if the plugs lasted forever I'd be too lazy to do it.

 

[CharlesHS]

I use the factory NGK ZFR5N, personally I enjoy checking them every few thousand miles when normal plugs wear out and if the plugs lasted forever I'd be too lazy to do it.

A friend of mine who is a 25+ year jeep technician at the dealership recommends the NGK over the platinum tips. He said that about 15 years ago there were multiple Jeep vehicle problems with misfires due to the platinum tips and they decided the NGK‘s were the spark plugs to use.

 

[cliffish]

La, la, la, la, la, la... I'm ignoring you guys...

It *is* amazing how much better the engine runs when it runs on all 6! Dunno what its problem is - my Mercedes runs just fine on 5. Reminds me of the time I was riding shotgun with my dad as he pulled a 29 ft. fifth wheel over the high pass in Lassen park on 7 cylinders. We didn't know it at the time - instead of a 454 V8, it was a 397 V7!

You have the 5 cylinder diesel benz 300D? Turbo? My first car was a 1977 300D, non turbo. 0 to 60 in 24.8 seconds, I kid you not, but that car pulled a horse trailer with 2 horses without an issue.

 

[AjRagno]

Make sure also that the wiring harness loom that runs from the valve cover and down the side of the block is routed outside of the coil rail (resting on it). If it’s behind the coil rail the edge of the block will wear through the loom and then the wires as the motor mounts flex.

 

[Zorba]

Make sure also that the wiring harness loom that runs from the valve cover and down the side of the block is routed outside of the coil rail (resting on it). If it’s behind the coil rail the edge of the block will wear through the loom and then the wires as the motor mounts flex.

Which was EXACTLY what had happened at #5, said harness had gotten looped over the top of the plug/boot and pulled it down. I put new loom on it while I was there...

 

[Zorba]

You have the 5 cylinder diesel benz 300D? Turbo? My first car was a 1977 300D, non turbo. 0 to 60 in 24.8 seconds, I kid you not, but that car pulled a horse trailer with 2 horses without an issue.

I grew up with, and learned to drive on, a '71 220D with manual. As an adult, I had a '74 240D auto, and now the '85 300SD auto (with turbo) that I've owned for the last 20 years. I've driven the non-turbo 300D, but never owned one. I liked the '74 the best, even with the auto, but it had a VERY bad case of cancer. But when I hear people complaining about this or that car being "underpowered", my response to that is "Pfffft!" Try 68 HP in the "uprated" 240D engine in a 3,400+ lb car - and I never really felt "underpowered", although you *do* need to know how to drive one of those old naturally aspirated MBZ diesels. My 300SD is about 120 HP, which is PLENTY, even with the slushbox.

True story: When Mercedes introduced the 5 cylinder OM617 engine in 1975, it stood the automotive world on its head! The following decades saw lots of 5 cylinder engines from many manufacturers, both gasoline and diesel - Mercedes must be onto something here. "Almost the power of a six, almost the economy of a four." was oft touted. BUT - Mercedes didn't engineer that engine for any of that. They wanted a more powerful diesel engine for the W114/115 chassis, and a six cylinder diesel wouldn't fit, so they figured out how to balance a five by adding an additional cylinder onto the OM616 240D engine!

Then two years later the W114/115 chassis was obsoleted for the W123 (which is what your car was), which did have more room under the hood, but the engine had already been designed. The successor 3 litre diesel was a six, introduced in 1986, although they *did* make another five later, the diesel engine in the 190D 2.5.

 

[Zorba]

I use the factory NGK ZFR5N, personally I enjoy checking them every few thousand miles when normal plugs wear out and if the plugs lasted forever I'd be too lazy to do it.

That's what was in it. I certainly can't say anything bad about them, they had performed WELL past their expiration date. I had noticed a very subtle "stumble" at idle, that is now gone with the new plugs, but I'm sure that was because the NGKs were flat worn out (.063" gap on the one I bothered to measure, others looked similar) rather than a failing in the plug's design.

 

[AMS417]

I "restored" a 1982 300D. It was a cream puff. Sold it to some hippies during the bio fuel crazy for about what I had in it. I loved that car, my wife did not. It was the Baghdad Taxi Cab. So smooth, and fuel economy most people would not believe. Did some minor tuning to it, and it was decent for a diesel. Not fast, but had some get up.

 

[Zorba]

Yea, my wife doesn't particularly like mine either - but after owning it 20 years, I'm sure not interested in anything else!

 

[Jerry Bransford]

A friend of mine who is a 25+ year jeep technician at the dealership recommends the NGK over the platinum tips. He said that about 15 years ago there were multiple Jeep vehicle problems with misfires due to the platinum tips and they decided the NGK‘s were the spark plugs to use.

He should have understood the problem before damning all platinum plugs. The TJ went to a waste spark ignition system in 2000 which fires the plugs in alternating directions on both strokes. Twice as often and in opposite directions. That causes problems for single-tipped platinum plugs where the platinum is on just one side of the electrode. Single-tipped spark plugs like the Autolite AP-985 and Champion 3034.

But when the correct double-tipped platinum plugs are installed, the types with the platinum coating on both sides of the gap like the Autolite APP-985 or Champion 7412, it runs perfectly well.

The CORRECT platinum tipped plugs run beautifully in all of our TJs.

 

[CharlesHS]

Actually he explained the waste spark theory and how it works.
His opinion is NOT to use platinum on the 4.0L and I trust him and his experience of working on Jeeps for more than 35 years.
Interesting that I had the Champions in my ‘01 and received terrible misfires, but as soon as we removed the platinums and installed the NGKs the misfires went away.
If the platinums work for you that’s great, but not for me.