leeboy

I just swapped my 4.10's for 3.54's.... The Dodge dealer told me he didnt think i had to do any ECM flash or speedo gear change. So, i never.....Any input on that? I thought id gain a few mpg's but my overhead is showing 2mpg's less than normal....In the city it used to average 14 and now its sits at 12...Could i be getting worse milage now? Do i have to do something to the overhead computer....?? I dont wanna put the 4.10's back in...(haha)

dozer12216

He is correct. The tone wheel is on diff case and would be unaffected by pinion ratio in front of it. Is the speedo and odometer showing correct information. Use GPS device to confirm. Reset avg fuel milage screen several times. Perhaps a reset of computers is in order. Disconnect batteries for overnight.

leeboy

I will start with the battery disconect this weekend. I guess i need a highway run to see what it will do.

leeboy

I took a burn down the highway.. and at 60 MPH's I was climbing past 20 MPG before i came to my turnoff.....

Valv

Don't believe the overhead computer, they are not a reliable source of data. The only way to find out it to fill tank completely, reset the trip odometer, and calculate the mpg at next fill (divide total miles by gallons used)

leeboy

Well, this sucks....just did a hand calculation and im getting a whopping 13mpg in the city with my gear change....I wonder if i wasted my $1000 now on the change...

2500Ram

I would believe your numbers, hand calculated with the swap. With the 4:10's in the city it's much easier to get up to speed, now with the 3:55's your engine is lugging a little more and burning more fuel to get to the same speed, do you notice more smoke? Take it out on the hwy and watch your MPG's go up about 2. And don't race between stoplights and you'll be back in the 14's.

Good luck.