1. Spark Plugs and etc for a 4.2L

    Just wondering if you any of you all had any good experiences with the so called preformance spark plugs to give the ole 4.2L a little extra power boost or gas mileage. And, yes I have read the threads on the Motorcraft carb, the Weber card, the iginition upgrade, and to convert over to fuel injection. Just thought I would ask.

    Also, have any of you all seen a difference in preformance with the Octane of gas used?


  2. #2

    Re: Spark Plugs and etc for a 4.2L

    I've been using the Platinum spark plugs on my AMC360. i noticed a significance on performance but not so much on fuel economy due to the size tires Vs. gearing. but yes, it's better than the conventional sparkplugs. Fuel injection is the way to go if your looking for the optimum fuel economy and performance rather than a carburated system. the Octane used on fuel does have an impact on performance. too much octane on the older engines may sometimes cause a spark knock or pinging that will affect your fuel economy and performance..

  3. Re: Spark Plugs and etc for a 4.2L

    I use plain old Champion copper plugs or "truck plugs" and have had the best luck. I've used the autolite platinum plugs before and haven't noticed any difference whatsoever. If you do decide to go with the TFI upgrade, you can widen the gap to .045" or there abouts and you will see a slight improvement in gas mileage and power. I noticed about a 2 point increase in gas mileage and low end grunt has definitely improved. Every bit of improvement is welcomed here in the Mile high!
    '89 YJ, Howell TBI, 35"s, Lock'd & Load'd

    Build it, Wheel it, Break it, Repeat

  4. #4
    Join Date
    Jan 2007
    So Cal lower desert

    Re: Spark Plugs and etc for a 4.2L

    I'm useing the bosch platnums and the TFI upgrade. I seem to be a happy camper but I always use premium so that may not be needed huh?
    1990 Jeep YJ. Nothing special, just the normal "can't drive without stuff", Its all a jeep thing.

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