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Check those spark plugs!

3834 Views 7 Replies 6 Participants Last post by  jocrazy0
Ok, this is NOT an advertisement for Bosch plugs though it may look like one.

After my incident with the bad gas and the second tank I experienced in eastern New Mexico, I decided to replace my plugs with a better quality set. For about 1/3 the price of the P.O.S. Champions the dealer installed, I got the Bosch platinum +4 plugs ($36/6 out the door from Autozone).

Last weekend I made a 800+ mile round trip over two days. My fuel mileage JUMPED from 12-13mpg to more than 16mpg, a 3-4mpg increase (for the math disinclined). I am beginning to think that a LOT of my mileage and performance problems were incorrectly gapped or simply defective spark plugs. I think that tank of bad gas may have done me a favor.

Unfortunately I have no long distance trailer tow at high altitude trips coming up so I have no reference back to my problems in New Mexico, but it looks like the plugs may have been most of the issue.

Bottom line: CHECK THOSE PLUGS! (I now have 49,700+ miles @ 23months).
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good idea to check the plugs. did you have a set that were the incorrect plugs? i know there was a recall for some JK's that had the incorrect plugs installed from the factory.

i doubt it was the brand of plugs that made the mpg increase for you - it was the fact that the gaps were all wrong and probably misfiring a lot of the time.

did you ever find out why the plugs ended up that way?
After seeing those plugs in your picture, I'm wondering if *any* properly gapped brand of plug would have given you better gas mileage. You were screwed from the word go with the original plugs.
What did the set of plus that the dealer put in after the first set look like when you pulled them?
The dealer installed the 'correct' plugs, Champion RE14PLP5. The plugs removed were all gapped correctly (calibrated eyeball), or at least all the gaps appeared to be the same. That was after a little over 900 miles driving.

All the original plugs removed were the same brand and model. As you can see from the bad gas thread, the gaps were all over the place. I'm blaming that on the bad gas and high engine loads imposed by towing the trailer in the high hills south of Moab down to Gallup. I've had a couple of engineers tell me that the severe pitting on the electrode of the worse plug could be from the spark firing from the curve in the electrode; the high current from the spark melting and removing metal from the electrode.

What is truly weird, is the first tank of gas (Texaco Premium) that also had the HEET and STP treatments in it and new plugs, I got 15.6mpg in the high mountains east of Gallup up to 7000ft+ just east of Albuquerque (still towing my 4000lbs of trailer). Then I got the second tank of I'll call bad gas east of Albuquerque, at the half empty mark the engine started acting up and I limped into a small town in west Texas on I40 (50-60mph.) The mileage steadily declined back down to 12mpg by the time I got home.

That 12mpg is still more than what I was getting on the way UP to Moab. On that segement I was getting between 9.5 and 11mpg. The difference between the trip TO and after the plug replacement is what makes me suspect that my original plugs were bad.

I could speculate on and on about different things causing what resulted in my expensive repair in Gallup. Bottom line is I'll probably never really know what caused the plug failure. I guess I could try putting the second set of plugs back in for my weekend trip coming up (~600 miles this time) and see if the mileage compares to last weekend's trip. What I'll probably do is punt, leave the plugs in, and get on with life.

BTW. Changing the plugs wasn't that bad. It took me less than two hours including setup and cleanup time. A 5/8 plug socket, universal joint, and long extension will make your efforts easier. Mine was complicated a bit by having to remove/reinstall some supercharger plumbing. The worse plug to remove is #5 which is the right rear most plug. It is covered with the heater hoses on that side and sandwiched between the battery and engine. I'd advise doing the replacement when the engine is stone cold to save the burns.
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JOCRAZY- Bosch 4300 series I assume, but they range from 4301 to 4309...(?) Which part # ?
Also, any idea if going to the Bosch Platinum plugs will void engine warranty?
the supercharger makes plugs and gapping MUCH more critical!
coming from a forced induction background, I can tell you proper plug gap as well as plug heat are extremely important to a FI motor.
adding boost usually means running a tighter gap (to prevent the plug from 'blowing out', or failing to ignite the mix)
also when we went to the higher boost levels, dropping back to a cooler plug helped prevent missfires

I was running a Ford 5.4 V-8 and ~16lbs of boost for about 560 HP at the crank.
quite a bit more than the standard jeep kits make, which amplifies the problems, but the principles remain the same.
JOCRAZY- Bosch 4300 series I assume, but they range from 4301 to 4309...(?) Which part # ?
Also, any idea if going to the Bosch Platinum plugs will void engine warranty?
Well, the model number on the box is 4482. The sub number is "0 242 229 700-0P6". The SKU is "28851 01929". the name is BOSCH PLATINUM +4 which I assume refers to the four discharge electrodes surrounding the central spark electrode.

And venom: I wouldn't have any idea how to gap these plugs. I left them as them came out of the box. I have read that about forced air induction motors about the gap being critical, and the plug I was looking for really was a plug known as a "surface gap" style (no gap to set). Didn't see them so I took these. I still ponder having those four electrodes protruding out abound the central node, but I think I won't have to worry about them for quite awhile. We'll see.

BTW - if anyone can point me at a place that still carries those surface gap plugs, I am still interested. It would be a cheap investment in comparison to have a set to try.
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