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This is a very confusing issue I got ya'll. I hope I can explain it right. Its a 99 convertible sebring w the 2.5 ltr v6. Has 122K miles. Car is clean and very nice. Has new timing belt, valve cover gaskets, rack n pinion, plugs, wires, and other things have just recently been done to it. But, I have the cmtc trip info computer in the dash. Its a JXi. Lately i have noticed that when the cmtc says theres say, 50 miles left, after I go about 12 miles it says theres 21 miles or so left. The readings are probably correct because i can almost see the gas needle moving when im driving. I know, when its cold you get worse mpg, tire pressure can cause worse mpg, weight in the trunk/car causes worse mpg, when you speed to and from red lights and gas with ethanol gets worse mpg but this isnt those things that cause a couple miles per gallon here and a couple there. Im not driving fast, with anything at all in the car, no cold weather here in June in SC, tire pressure is perfect. In other words ive already tried everything I could think of but this car is getting a third of what its supposed to or should get. If i watch the cmtc it drops 2 and 3 miles at a time each time it drops after a mile or so. When you go a mile it should drop a mile in the range info but after a mile it drops 2 and 3 even at a time. Crazy! Like 20 bucks of gas only gets me 6 gallons of gas down here and those 6 gallons are only getting me like 50 miles or so. Somethings WRONG. And its not leaking gas anywhere either. Anybody have a clue whats going on or what I may need to do or check? THANK YOU FOR ANYTHING you can tell me! Marc C. (its the same car im having the a/c issues with right now) Thanks again!
 

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Maybe the replacement of the timing belt wasn't done properly? If it's off a notch or two, I know it can make a difference. Also, I THINK a funky O2 sensor can effect mileage. I'm not a mechanic, so don't take my word for any of this. I'm just speculating. I've never owned a 2.5 V-6, so don't know anything about them. Have you checked for any engine codes? Run them first and see if anything shows up. If you can't do it, take it to your local Advance, Autozone or O'Reillys and have them run the codes for you. It's a free service.
 

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Ignore the computer completely. It's constantly updating, as you say, so if there are 50 miles left and then you stomp on the gas, it will simply recalculate and decide that you have 30 miles left, for instance.

Is the car running OK? Power OK?

The only good way to monitor gas mileage (short of a precision meter plumbed inline) is to top off the tank, drive it down to about 1/4 of the tank or about 300 miles (in other words, don't refill it too early). Top it off again and divide miles by gallons used. Do this at least 3-4 times over the same route and same conditions. Keep a spreadsheet and calculate monthly averages. Let us know what you get by this method.
 

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The CMTC can be inaccurate right after a reset or battery disconnect as it is in the process of updating and averaging. After time and mileage is accumulated, it will become more accurate at averaging. Don't drive by the CMTC.
A better way to compute mpg is with the trip odometer and gallons used on your fuel fill receipt over a few tanks as Bob mentioned.
Our '98 JX 2.5L gets about 22 mpg around town and 30 highway.
How does it run? Any signs of richness? Any recurring fault codes? Did you ever solve the misfire and suspected catalytic converter issue? Were you able to finally change all 6 plugs?
Bosch may not be the best choice, the Champion RC10PYP4 double-platinum are the recommended direct replacement.
If the oil burning issue is inside the combustion chamber instead of when passing out of the chamber, it could cause plug oil-fouling and misfire. Poor fuel economy could be from any number of things.
 

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Discussion Starter #5
Wow. I have a lot of checking to do and tests to run, calculations to make and . I thought because Bosch were more expensive they had to more better. Theres no codes.It runs better than any Sebring I've owned. I sold that cat issue Sebring. This is one just bought a month ago. All that work done to it was by someone else so... But man, this one rides and drives like a car thats brand new. I thought I got lucky when I found this one. Anyway, you all are right on the money. All I can do is keep accurate records, divide and add and subtract, check couple sensors, get the champions in there, then I'll know more precisely what its getting. I'll post back a good bit of info in couple weeks.
 

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Personally, I've tried Bosch plugs in several different Mopars I've owned over the years and have been greatly disappointed in them. I strictly run OEM plugs in my vehicles nowadays and that's what I'd recommend. I won't even put a Bosch in my lawn mower anymore.
 

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Bosch plugs always gave me a rough idle. Champions run best in MoPars.
 

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Agree with the Bosch comments - most Stratusphere and ASEC members with the 2.5L V6 have stated the same thing regarding those plugs.
 

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Discussion Starter #10
Yea, Im def convinced myself. I guess just because you might pay more for something doesnt mean its always better. And really, this isnt the 1st time that i've heard the bosch plugs arent the best for the 2.5 sebring motor. But now im at the point that theres no way im throwing them back into my sebrings. So Champion is what the engines in the 96-2000's like? And not necessarily platinum? Just the standard plugs? I dont know what the OEM plugs were. The Sebring dealership is where i can find the right plugs? And what about the wires? I used 2 kinds of those. On the black one I gave to my sister I used the 42 or 47 dollar Advance plug wires. On mine I used the 30 dollar Oreilly's auto parts plug wires. Sisters seems to be pretty smooth sounding and running with those 42 or 47 dollar Advance Auto plug wires. But maybe OEM on those as well?
 

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If you still have the store receipt for the Bosch plugs, take them back and get the OEM Champion Double-Platinum RC10PYP4 or RC10PYPB4 plugs.
OEM are Champion platinum. It is specified on the underhood label.
A premium set of brand-name wires should be good.
 

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Champion plugs fixing issues in MoPars goes back to at least the 70s-models LA engines and Slant Sixes.
Reminds me ... the guys I trust with my trucks might've put in something else, last tune up. I need to look....
 

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Discussion Starter #13
I certainly go get the champions then. Even if receipt is lost I think i'll go grab the Champion double platinums. I think if the timing belt was off a tooth or two even, there would be some type of timing issue maybe? Like a backfire or a hard time shutting it off? Some type of timing symptom if belt was off any. The gas mileage is going to be posted sometime soon with the details and as accurate as possible. But im betting its going to be well below average. We'll see. Post it soon, Thanks, Marc C.
 
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