I don't know if this is even the proper place to post this, but I will try it for now.

I was on a road trip the other week and had the alternator go out on me. I replaced it on the road and went on my way. I noticed the shift pattern to be really different. I do know that after disconnecting the battery for 15 minutes, the computer will reset the shift habits of the driver. After about a hundred miles, I refueled at a costco and noticed that my gas mileage decreased significantly. Prior to my alternator change, I was getting 13mpg in the city and about 15 to 16 on the highway. When I fueled up, I calculated it to be 10mpg. So, I diconnected the battery again, and let it sit while I went into costco and did a little shopping. Also had a polish dog and a drink. Not that that was important, but sometimes makes a Costco trip worth it.

Anyway, I finished my drive home and couldn't even get 13mpg the rest of the trip. Now, the shift pattern on my 2000 F150 seems to be back to normal, but I went on another trip this past weekend of about 400 miles, and was able to only get 12mpg. And that was ONLY freeway miles. I have the 5.4 liter with an automatic. No modifications. I think I have the 3.55 gearing and that's about it. Any help as to why my mileage has decreased so drastically? Any comments or suggestions would be greatly appreciated.

 

The PCM takes a long time and many driving cycles to build and populate it's control tables.
A 400 mile drive is considered only one drive cycle.
Never power down the PCM unless there is a good reason to do so. This clears all the learned driving you do, that builds the tables the engine runs on.
The purchuse of gas from another location brings another unknown into the mix.
I would say that your mileage will tend to return over the next 30 plus days depending on how much driving is done over your usual routes.
The PCM has an incredable amount of programming and routines it does to run and keep track of all the engine function and constant testing.
It even builds and alters the misfire tables as the engine ages and even accounts for a change in power from fuels used. This is why powering down is not a good idea unless it absolutly has to be done..

 

I have noticed the same thing after disconnecting the battery. On the interstate I will be at a comfortable cruising speed, then abruptly the rpms go down about 500rpms and then resumes cruising at a steady rpm. After about 100 miles it rerturns to normal.

Have not noticed a reduction in MPGs. Dont track that, b/c it is too depressing.

 

It's a big@ss truck. You are not gonna get many more than 12 or 13 average anyway. What kind of truck, how many miles, does it need servicing, many different questions you could ask. Just something to think about.

 

on the 2002 F-150 I used to have the owners manual stated that the transmisson go's into a learning mode to adjust shift paterns in relation to your driving habbit's after battery is reconected, maybe try disconecting the batt ( booth - and + ) and reconect after five min, drive easy for the first hundred miles...

 

Hey Bluegrass, thanks for your input. You always seem to be right on with your comments and I, along with many others I'm sure, really appreciate it. I sure hope the mileage does return.

And Mr "T", I have a 2000 Lariat extend a cab, 5.4 Liter, 3.55 axle with a limited slip unit, towing package, 4x4 off road, all pretty much stock. I have 150k on the odometer and I usually get 13 in the city and I have been averaging about 15.5 on the highway. Don't put my foot into it much and stay pretty much at the speed limit. I have gone faster and know that it kills my mpg, so I try to drive slower. I am **** about tracking my maintenance records and I can back up my mileage statements as well as oil changes, filter changes, trans oil changes, tire rotations and any other type of maintenace issues. I pretty much even have all the gas receipts for the f150. The only issues that it has had are the cruise control deactivation switch, the alternator, pax door lock actuator, and an 02 sensor. No other issues.

Thanks for your comments guys, I really do appreciate it and hope this issue would answer questions that others may have had.

 

I find this problem rather odd. Its basically the exact opposite of what it should be. I disconnect my battery everytime I get ready for a long haul trip, because that specifically resets the ECM back to factory default which increases my milage by the ton. I usually go from around 11MPG to 15 MPG on the highway with this simple procedure. And I can get up to 17MPG from my blown Navigator on interstate driving. Its 326 miles from Atlanta GA to Charleston SC and after resetting the battery, I could almost drive from here to there and back. Without resetting the battery, I can just barely get from here to there.

 

98, you need to take into account your engine is modified so what you are saying does not apply to a stock unaltered engine.
Your blower setup is running less then optimun for the PCM to make that much of a change in the oppisite direction.
Remember to compare apples to apple and not some other arrangement.
Then it doesn't become so funny after all.