Chrysler Repair: 06 T&C Limited (Re: Gas Mileage issue), fuel mileage, gas mileage

Question
QUESTION: I have gone through a tank of gas now and nothing at all has changed. I am still getting 15-16 mpg. I asked another technician that I know about this and he said to check the Long Term Fuel Trim. He said the readings should be in the -10% to +10% range. I have a scanner that can read live data and here are the results: When accelerating or cruising is 0% to +7%; when idling is +14.8%; and when decelerating is +20%. I would like your opinion concerning the cause and possible correction for the the idle and deceleration readings being out of range please. Thank you for your continued help sir.

ANSWER: Since you own an apperently good scanner I'll assume you have a fair amount of knowledge. Long term and short term fuel adaptives, or in your terms, trim, tolerances are a bit different. Most all scanners will read the short term values, which are for the most part live data that the PCM uses to adjust injector pulse width. Long term adaptive is not live, rather a contantly updating average of the adjustments made by the PCM using the data from the short term adaptive. That number is then used by the PCM to provide a baseline injector pulse width for the operating range in which the currently is operating. What is concidered a normal reading on either is variable. The top readings that can be adjusted to are -33/+33 before the PCM turns on the check engine light on for a  fuel rich or lean condition. You are still well under those numbers before you would have to look for a problem. As far as your fuel mileage, well that will take a lot of digging. There are many, many things that affect fuel mileage, from the fuel you use to the construction of the tires. A good place to start would be, What was it before the recent repairs were made?

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QUESTION: Yes sir, I do have a fair amount of knowledge. I do all of the PM on the vehicle and the repairs if I know what is wrong with it and have the proper tools. I bought the van used about a year ago and it has always averaged what it is getting now. I haven't been very concerned with the mpg until now with gas being so expensive. An average weeks worth of driving consists of a pretty even mixture of city/highway driving. The highway driving is at a steady 60mph also. With the vehicle not even reaching the all city 17mpg mark under these driving conditions there is a problem somewhere.

Answer
These vehicles were not known for getting good fuel mileage. Even when new and under ideal driving conditions they were only rated at an average of 20 MPG. After a quick WEB search I was able to find out that most all drivers found that they couldn't even achieve an average of 18 MPG. In the end it will come down to how much money and time do want to invest to try and get nothing more than a marginal increase in fuel mileage.