My goal is to get 25+ mpg from my 99 XJ with 30 x 9.5 R15 ATs - Page 236 - JeepForum.com

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post #3526 of 3596 Old 06-16-2017, 02:33 PM
mschi772
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Originally Posted by StPaul59 View Post
So far one week with the FR5-1 plugs , a hotter and longer plug than I used before, my mileage is actually worse. It seems I've dropped about 1 mpg. Time will tell though..
Keep us updated. 1 week of driving is a spec of sand on a beach in terms of data.


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post #3527 of 3596 Old 06-16-2017, 04:32 PM
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Originally Posted by Newtons3 View Post
I am expecting to hear more like this. Keep us posted. Interesting initial resilts.
I got to admit, I'm pretty shocked by this. Hotter, longer plug and...... Nothing.
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post #3528 of 3596 Old 06-16-2017, 09:19 PM
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Originally Posted by StPaul59 View Post
I got to admit, I'm pretty shocked by this. Hotter, longer plug and...... Nothing.
I'm not familiar with the specifics on everyone's engine. My experience with my OBDII 4.0's is that they could use a colder plug. My engine could use a hotter plug right now, but I am hoping that the timing changes this weekend will change that.
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post #3529 of 3596 Old 06-17-2017, 03:10 AM Thread Starter
Charley3
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Originally Posted by StPaul59 View Post
So far one week with the FR5-1 plugs , a hotter and longer plug than I used before, my mileage is actually worse. It seems I've dropped about 1 mpg. Time will tell though..
What gap are you running them at? What coil and plug wires do you have? You'll need to drive it at least a month to know how it affected your gas mileage.

If I were going to run that plug I would gap it at 0.045 with a stock coil and plug wires, or 0.048 with an upgraded coil and plug wires. I have read that a larger gap helps ignite the combustion more easily and this is particularly helpful with E10 gas. However, you have to have a strong enough coil to for the amount of gap.

My 96 XJ liked the FR5-1 plug gapped at 0.040.

My 99 XJ did not like the FR5-1 plug, but that might have been because my cousin gapped it at 0.035, or might have been because the gas now-a-days has 10% ethanol in it.

I read what Newtons said about that not being it, but I'm not so sure. I've read two other sources that said longer plug projection helps ignite E10 gas. One of those sources was Champion spark plugs. I'm considering the NGK ZFR5N (slightly longer tip projection than FR5-1 according to what NGK tech support told me).

The NGK ZFR5N and Autolite 985 have the longest tip projection that I know of. I think the NGK ZFR5N is the best designed copper plug and the Autolite 985 is the next best copper plug. That's my opinion.

If you visually compare NGK, Autolite, and Champion copper plugs; it looks obvious to me that NGK is the best made followed by Autolite. For one thing, NGK plugs have chrome plated threads which prevents rust, promotes a good ground, and makes removal easy. It also makes it unnecessary to use anti-seize. Also, I'm a fan of NGK V-Power center electrode with V-Groove.

I personally prefer NGK brand, but Autolite and Champion have a lot of fans too. So they must be pretty good too. However they lack chrome plated threads. So they need copper anti seize applied lightly to their threads (only on threads - don't get it on anything else!)

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #3530 of 3596 Old 06-17-2017, 09:15 AM
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Gapped at .040/ .041ish

Stock coil and wires
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post #3531 of 3596 Old 06-17-2017, 02:48 PM Thread Starter
Charley3
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Originally Posted by StPaul59 View Post
Gapped at .040/ .041ish

Stock coil and wires
Try that long enough to be sure how it affected your gas mileage. At least a couple weeks, preferably a month.

If that doesn't work well for you, then try NGK ZFR5N (copper V-Power) at 0.040, or Autolite XP985 (iridium fine wire) at 0.040.

IMO

P.S - if you had an upgraded coil and plug wires then I would suggest 0.044 to 0.045 for any of those plugs.

I'm no longer wanting to try 0.050 or larger for two reasons. It's come to my attention that large gap can cause a rough idle. I've read about that on many forums. And NGK website FAQ says not to increase gap more than 0.008 because the ground electrode might not be perpendicular to the center electrode if the gap is increased more than that. An NGK support technician told me not to increase gap more than 0.010. So I guess 0.008 is a conservative figure while 0.010 is aggressive but probably okay. So based on that I would not go more than 0.008 or 0.009 larger in gap.

That's me personally. Mschi widened the hell out of the gap on his Autolite iridium plugs from 0.035 to to 0.050. That's a huge increase of 0.015. He says it works well, but I'm afraid to be that aggressive with increasing my gap. This is the only time I can remember myself being more conservative than Mschi.

If I could have found a plug that was 0.044 out of the box, then I would have widened the gap to 0.050 (with upgraded coil and plug wires), but I'm not going to stretch a 0.035 plug farther than 0.044 or 0.045.

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #3532 of 3596 Old 06-17-2017, 03:36 PM
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Originally Posted by Charley3 View Post
The only Iridium plug that I know of for Jeep 4L engines is the Autolite Iridium.
Autolite XP985
CHAMPION 9034 {#RC12WEPB5}
BOSCH 9656
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post #3533 of 3596 Old 06-17-2017, 06:01 PM
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Most of my mechanical energy is focused on my Metro right now (head swap, new exhaust, transmission seal replacement), but I have a list of things I want to do with the XJ after that, and I'll try to remember to take some photos of my plugs for you guys for the fun of seeing how they're doing after all this time.

Interesting point about the angle of the ground electrode. I'd imagine that if it gets too far and too angled, spark would start to jump to the side instead. I'll be on the lookout for that with mine. Maybe I'll even see if I can catch a spark on "film" with my girlfriend's fancy camera.

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post #3534 of 3596 Old 06-18-2017, 08:21 AM
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Originally Posted by mschi772 View Post
Interesting point about the angle of the ground electrode. I'd imagine that if it gets too far and too angled, spark would start to jump to the side instead.
This is what I was talking about in an earlier post. It has been documented and proven. That's One of the benefits to side-gapped plugs. Cut or grind that electrode back and this shouldn't be as much of a problem.
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post #3535 of 3596 Old 06-18-2017, 02:40 PM Thread Starter
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I used to think I was having pre-ignition with 87 octane gas. Now I'm not so sure. I wasn't having pinging or anything like that. At least not that I noticed, but the Jeep is a noisy vehicle so it might be hard to hear. What I did notice was a very rough idle on 87 octane when my plugs are gapped at 0.045. I put in some 89 octane and the idle is smooth. It runs dandy on 89 so I just stuck with it.

3 years later I read on several forums for Corvettes, BMW, Jeep, Chevy and Ford, AMC and other vehicles people talking about getting a rough idle after widening their plug gap to around 0.050. These were folks with upgraded ignition systems. They said they could not detect a miss, but for some reason their idle was rough after increasing their plug gap.

I also read someone post that smaller gaps are less efficient for highway cruising, but give a smoother idle, and the smoother idle is why car manufacturers tend to specify small gaps. I don't know if that's correct, but that's what they posted and it sounds plausible to me.

I also read on NGK website the warnings about not making plug gap to wide causing the ground electrode not to be perpendicular, and NGK told me that on the phone too. Newtons also warned me about that. In hindsight, I now realize that Nick at Kolak warned me about this (by telling me not to regap my Autolite plugs larger than 0.045). Nick was really saying don't increase the gap by more than +0.010. He did not explain why, but I'm guessing it's partly due to the ground electrode needing to remain perpendicular, and partly so I can have a smooth enough idle.

So for all these reasons I'm thinking that 0.043 to 0.045 is plenty of gap for me (and I'll keep running 89 octane). I think 0.044 is a nice compromise between the stock 0.035 gap which is less efficient (with upgraded coil) while cruising, vs a larger gap that may idle rough or cause the ground electrode not to be perpendicular.

A 0.035 gap out-of-the box plug can safely (conservatively) be regapped to 0.033 (+0.008) according to NGK FAQ. Regapping it to 0.045 (+0.010) is pushing the limit according to NGK support, but is probably ok. i.e. - probably perpendicular enough.

One nice thing about Autolite that I noticed is they offer serveral platinum and iridium plugs that appear (at casual observation) to be the same plugs as their platinum or iridium plugs for Jeeps, but with an out-of-the-box gap of 0.044. That's attractive to me because if they are the same plugs, but with a longer ground electrode, I could run them as is (0.044) without needing to recap them, or Mschi could regap them to 0.050 and still be within a very conservative regapping amount (+0.006).

NGK does not offer equivalent plugs with 0.044 gap. I think Autolite may (platinum or iridium). I did not check Champion.

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #3536 of 3596 Old 06-19-2017, 05:50 AM
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Filled up with shell instead of BP. Well see if that helps.
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post #3537 of 3596 Old 06-19-2017, 01:42 PM Thread Starter
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Originally Posted by StPaul59 View Post
Filled up with shell instead of BP. Well see if that helps.
Brand could make a difference with regard to the quality of the fuel injector cleaner additives, but I don't see how it could make a difference with regard to gas mileage. However, fresh gas burns better than old stale gas. So I would recommend a gas station that's busy and sells a lot of gas because the gas will be relatively fresh.

I'm having stale gas problems right now myself because I didn't drive my Jeep for three months. It's a little harder to start, idles a little rougher, and doesn't feel like it has quite as much performance. I haven't tested the gas mileage with stale gas, but I assume it's not as good. I'm trying to burn up this tank of gas so I can refill it with a fresh tank and in the future I will add Stabil fuel stabilizer just in case I don't drive much.

Warning: I often edit my posts a few times to get them complete or correct errors.
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post #3538 of 3596 Old 06-19-2017, 02:31 PM
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The gas you use can make a significant difference, on top of that every other tank of reg gas I buy I put in a lucas treatment. it works wonders I also use it for my yard equipment gas. BTW my 94XJ get closer to 25mpg of course it is the four cylinder and manual Trans. but running the lucas gas treatment has made significant difference.
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post #3539 of 3596 Old 06-19-2017, 03:46 PM
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Originally Posted by RDJJeep View Post
running the lucas gas treatment has made significant difference.
No offense, but has it? Do you have good data to back that up? Lots of people will convince themselves of things like this for a variety of reasons when they're not actually true.

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post #3540 of 3596 Old 06-19-2017, 04:14 PM
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Originally Posted by mschi772 View Post
No offense, but has it? Do you have good data to back that up? Lots of people will convince themselves of things like this for a variety of reasons when they're not actually true.
I keep track of my mileage for work. I did the math to determine my average mileage over a few months time last year and yes I get upwards to 25 miles to the gallon.
I do not contribute all of that to the gas treatment but it does help over all.
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