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Unread 09-19-2011, 07:14 PM   #1
Anderson75
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Decrease in mpg's????

Over the last 2 months, I have had a pretty drastic decrease in my mpg's. In July I changed the plugs and was getting similar mileage as before the plug change. Since then, I had the KK at the dealer for an oil change. I had the AC checked for a leak and engine checked for a feeling similar to a 'misfire.' Since I got it from the dealer, the mileage has gone down from 18+ to around 15 for every tank. I ran Lucas Oil fuel treatment through it with my last tank just to see if it would help....nothing. Is there anything the dealer could have done that would have affected my mpg's?
Guess I could pull the plugs and see if any of them are fouled..air filter is fine...I just don't know why it would all of a sudden get worse mileage. Any ideas of what to check next?

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Unread 09-19-2011, 08:09 PM   #2
VMF
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what king of plugs did u install?
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Unread 09-19-2011, 08:16 PM   #3
Poncherello
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Wow, I was thinking of a few things.

#1 Did the dealer actually change the plugs?
#2 Did you change the type of gas, buy it from a different station (oxygentated gas will do that)
#3 The weather can play a factor and/or where your driving city vs hwy amountof traffic. Plays a big role where I am from.
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Unread 09-19-2011, 08:22 PM   #4
tjkj2002
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Quote:
Originally Posted by VMF View Post
what king of plugs did u install?
That's the big ? right there,the wrong plugs will cause many issues.
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Unread 09-19-2011, 10:17 PM   #5
streetglideok
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Wrong plugs, and/or gapped wrong. I take it no engine light on at the moment? How many miles are on this? I cant comment on how good Lucas fuel treatment is, but can say Techron and BG 44K are pretty good cleaners to try. You havent been putting E85 fuel in have you? If you switched brands of fuel, you may of went from a company that runs pure gasoline, to one that is running 10% ethanol. Some states dont require stations to put a notice out about it still. That would give you a drop in mileage. Are you letting the jeep idle any longer in the am to warm up? What weight of engine oil are you running, and how often do you change it?
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Unread 09-20-2011, 07:22 AM   #6
Anderson75
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The plugs were definitely changed, I did it myself and gapped at 43 just as the manual said. I put in the Autolite Iridiums because they were supposed to be better. The decrease didn't start until a good 2000 miles after the change. As for the gas, I had been buying from BJ's when I noticed the decrease and started buying from more reputable stations; Chevron, Sunoco, etc. The oil is changed at least every 5k miles or whenever it starts looking too dark. No change in driving/idling. If anything, I've been more conscious of my driving habits trying to take it easier.
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Unread 09-20-2011, 07:51 AM   #7
thethein11
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I always thought I read and was told you don't gap iridium plugs.


Some back up to my statement

http://www.densoiridium.com/faq.php

Quote:
Originally Posted by densoiridium.com;
Q. How do I gap Iridium plugs
A. Before attempting to gap any DENSO Iridium Power spark plug, please review the specification chart to see the factory-preset gap. In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations. Should you decide to re-gap your Iridium Power plug, use extreme caution as improper gapping may damage or destroy the Iridium center electrode or porcelain center. To increase the gap size: Step 1 Use needle nose pliers or spark plug gapping tool to bend the ground strap up to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. To decrease the gap size: Step 1 Use the same method as above, however bend the ground strap down to the desired height. DO NOT LET THE PLIERS OR GAPPING TOOL TOUCH THE IRIDIUM CENTER ELECTRODE OR PORCELAIN. Step 2 Re-check the gap with a calibrated gapping tool. WARNING: Failure to follow these directions may permanently damage the spark plug. Note: Never use a round gapping tool to check the gap or to increase or decrease the gap setting.
http://www.spark-plugs.co.uk/pages/t..._plugs_faq.htm

Quote:
Originally Posted by spark-plugs.co.uk;
Q14. Should I regap my Iridium spark plugs?
A14. In most circumstances, no. The nature of Iridium spark plugs means that they are able to utilise a larger gap setting while actually requiring less voltage and straining the ignition system less. If you *have* to regap Iridium spark plugs (e.g if misfire occurs due to gap being too large) then do so with extreme care. Do not use a slide type gapping tool or put pressure on the brittle centre electrode in any way as it may become damaged.
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Unread 09-20-2011, 08:34 AM   #8
tjkj2002
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Quote:
Originally Posted by Anderson75 View Post
The plugs were definitely changed, I did it myself and gapped at 43 just as the manual said. I put in the Autolite Iridiums because they were supposed to be better. The decrease didn't start until a good 2000 miles after the change. As for the gas, I had been buying from BJ's when I noticed the decrease and started buying from more reputable stations; Chevron, Sunoco, etc. The oil is changed at least every 5k miles or whenever it starts looking too dark. No change in driving/idling. If anything, I've been more conscious of my driving habits trying to take it easier.
Switch back to copper core plugs,iridium plugs are a no-go for your engine.Before the switch have a fuel induction cleaning done then switch the plugs.
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Unread 09-21-2011, 07:16 AM   #9
Anderson75
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tkjk2002, why only the copper core for the KK? It was running like crap before I changed them and I got the same (18) mileage for the first couple thousand miles.... Everywhere I read about spark plugs, the iridium is always listed as 'premium.' So why the basic copper core? Isn't better better? At only 27k miles, should there be a significant build up requiring a full fuel induction system cleaning?

thethein11, The autolite iridiums came pregapped at 44. Hard to believe a careful adjustment of -1 should have a drastic negative impact. Come to think of it, most of them weren't even adjusted, close enough for government work right out of the box.

So, what are the rest of you using when you change plugs? Anyone tried Pulstar copper core plugs?
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Unread 09-21-2011, 09:58 AM   #10
streetglideok
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If something runs bad, and you substitute what is known to work well 100% of the time, with something not even designed, by heat range, or gap/performance for your engine, its hard to gather conclusive results. Everyone throws the name premium around, like they all claim to be mechanics. Premium is what works best in a given situation, and what is claimed to be premium, may not really be. The iridiums work differently yes, and the gap is different, but the demands for ignition coils are different as well. Those plugs may fit several different vehicle brands, and what a chrysler needs, will not be the same as what toyota needs. Thats why you see GM wants 0.060" for plug gaps on some, chrysler likes .035, or .040 on some, and ford likes .044, .052, .035, etc. If you are having a running issue, if you want to save headaches and money in the long run, put what should be in there first, and get it running right. Then play with the sparkplug of the month, or what have you. You'll spend less time chasing your tail.
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Unread 09-21-2011, 02:12 PM   #11
Skipper6413
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My question is how did you ever get that high of mpg? My brand new 2011 Liberty gets about 15.5 in normal urban driving, with miserly takeoffs and driving.
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Unread 09-21-2011, 04:37 PM   #12
WA_KK
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Quote:
Originally Posted by Skipper6413
My question is how did you ever get that high of mpg? My brand new 2011 Liberty gets about 15.5 in normal urban driving, with miserly takeoffs and driving.
The milage should increase after the engine breaks in. Takes a little while

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Unread 09-21-2011, 05:55 PM   #13
Anderson75
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I got around 20 towing a trailer for 1300 miles, half of it through the mountains. That was right after changing the plugs. The mileage didn't decrease until after I took it to the dealer. Back to my original question, is there anything the dealer could have done to change the mpg's?
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Unread 09-21-2011, 06:49 PM   #14
streetglideok
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Look under the hood for any stickers, indicating an emissions change, I believe chrysler is a black and white sticker, with lines on it to be written on. The only thing I can think of is, they did a pcm reflash under warranty, for a known issue or something. Normally there is a sticker under the hood alerting that it was done, as it affects an emissions component(pcm). May be why the decrease, as sometimes it will make changes, like backing off ignition timing, etc. Thats the only thing I can think of they did, other then doing an oil change and putting 20w50 in it. If none of that applies, install NGK plugs, gapped to the sticker on the vehicle, not a service book, reset fuel trims, and drive for a week, and compare mileage. There has been issues known within the industry, of plugs causing performance issues only after a few thousand miles of driving, but performed fine initially.
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Unread 09-21-2011, 06:52 PM   #15
tjkj2002
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Quote:
Originally Posted by Anderson75 View Post
tkjk2002, why only the copper core for the KK? It was running like crap before I changed them and I got the same (18) mileage for the first couple thousand miles.... Everywhere I read about spark plugs, the iridium is always listed as 'premium.' So why the basic copper core? Isn't better better? At only 27k miles, should there be a significant build up requiring a full fuel induction system cleaning?

thethein11, The autolite iridiums came pregapped at 44. Hard to believe a careful adjustment of -1 should have a drastic negative impact. Come to think of it, most of them weren't even adjusted, close enough for government work right out of the box.

So, what are the rest of you using when you change plugs? Anyone tried Pulstar copper core plugs?
Your engine and ignition system is designed to run best with copper core plugs,your coils are tuned for the resistance of copper core plugs and the less resistance of the other plugs can cause running issues which effect mpg's.Copper core plugs also give a hotter spark then platinum and iridium plugs.Stay far away from pulstar plugs,just another split fire spark plug gimik that costs you money.

Depending on how you drive the carbon buildup in the intake track can be very bad or not so bad at 30k,drive like a grandma and it's going to be bad,drive it like you stole it it will not be as bad.
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