171and 174 codes affect gas mileage

Hi all

I have a 99, 3.8 windstar with 124,000 miles on it, I have to change the isolator bolts and seals, but I was wondering if the gas mileage will increase after the repair, right now mileage isn't to good, I already did the plugs, wires and both filters

question 2..... does the spark pack need to be changed when the plugs are changed, or at a certain mileage??

Thanks

0171 and 0174 are caused by the system being too lean. This means the fuel to air ratio is off and there is too much air and not enough fuel.

The codes are triggered when the PCM adjusts the Short term and Long Term Fuel trim values to max out. The max values will depend upon what version software is in your PCM, but roughly it is 25% variable in both lean and rich directions.

Your pcm is dumping in extra fuel to adjust the mixture because of the extra air leaking in your system. Solving the problem should cause the pcm to cut down of the fuel used.

Theoretically this will improve your mileage.

There have been posts here mentioning that fuel economy was poor with the lean code problem....and that it improved after the repair.
Most people mention mileage of 20mpg to 23mpg on the interstate.....that is calculated by odometer mileage divided by the amount of fuel added to the tank, over several tanks of fuel.
I seem to get about 21 or so with my '96 3.8L on the interstate.
Of course, in town will be lower, and in my case as well as many others, the gasoline is 10% ethanol, which will give you slightly lower MPG because it has lower energy ( BTU's ) as compared to the same volume of non-oxygenated fuel.
But it will only be 1, maybe 2 mpg lower.

thanks for the info huskerdooo and wiswind,

I'm finally gonna get rid of them codes sunday, I hope for good,
I have been looking around th site and found alot of good info on my windstar, just lubed up the doors to get the locks to work, and dome light to turn off, now i got one happy wife, few little things to do but the locks were annoying