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-   -   Sudden MPG loss! (http://www.ramforumz.com/showthread.php?t=146795)

bdodge445 07-05-2013 10:38 AM

Sudden MPG loss!
 
I just regeared my '95 Ram 1500 to 4.56 with 285's and all was well with the world, plenty of power and my mileage jumped up to 18-21 corrected mpg highway at 65-70 mph went on like that for about 500 miles, then the floor fell out, still have the power but my mileage dropped to 11-12 highway for no apparent reason. Any ideas about why the sudden loss in mpg's? And please don't tell me it's the 4.56 gears because as I said the first 500 or so miles I was getting 18-21 MPG corrected.

maust1 07-05-2013 10:45 AM

What do you mean by corrected?
What gears did you start with?
I know you don't want to hear it but those new gears should not improve your mileage. I also wonder if you cats are clogged, or maybe the intake.
Mick

bdodge445 07-05-2013 11:08 AM

Quote:

Originally Posted by maust1 (Post 1142653)
What do you mean by corrected?
What gears did you start with?
I know you don't want to hear it but those new gears should not improve your mileage. I also wonder if you cats are clogged, or maybe the intake.
Mick

By corrected I mean that say with the stock setup I drove 100 miles my odo would show 100 miles, but since now I am much lower geared that same 100 miles would show up as 125 miles on the odo. That is not exact but you get the idea, I did the math to figure out exactly how far I did travel to get a corrected MPG rating. I started with 3.55 gears. I know it's not the gears dropping my mileage because they actually made it go up quite a bit for the first 500 miles, same driving style, same route, nothing changed except the mileage for no apparent reason. Trust me, the cat is not an issue ;) Could be intake though I did fix the plenum gasket, but maybe overnight something got into the airbox, I'll have to check on that. Has new plugs, wires, cap, and rotor as well. Unless the new gears or bearings are for some reason suddenly binding, but there is no excessive heat or noise, I'll have to pull the diff cover and take a peek:thk: Thanks for the quick reply!

bdodge445 07-05-2013 11:29 AM

Also while I'm begging for help:wavey: could someone tell me how many teeth I need on my speedo gear to get things working again, I've tried looking online at all sorts of charts and all sorts of equations and it seems to be about a 50/50 split between 36 tooth gear and a 39 tooth gear I'm running 285-65 R16 with 4.56 gears :4-dontknow: I don't like looking down at 83mph to go 65 :Wow1:

Gen1dak 07-05-2013 12:46 PM

I'd chalk those initial numbers up to math and the transition to gears mid-tank. Just a couple gallons off. Can you guarantee you had the right amount? It's easy to mis-judge. Also, you have to consider what rpm the engine is operatiing at now as opposed to pre-swap. Not discounting some other issue, but considering what was just done, I mean, it is the 800lb gorilla in the room. For comparison, I have a '93 5.9 with 4.11's and the same size tires as yours, snags 15mpg......if my calculations are correct.

bdodge445 07-05-2013 01:08 PM

When I check my mileage I always fill up the tank to the top to avoid guessing how many gallons I've used. I ran two full tanks with the new gears used the same equation getting 18mpg the third tank of gas after the gear change is when I saw the drop in mpg using the same math. I know the gears seem to be the logical answer, but with those gears for the first two tanks of gas, around 500 miles I was getting 18 or better mpg then on the third tank using the same math, same driving conditions, everything the same, the mileage dropped out for the last 300-400 miles. @ 70 GPS MPH I'm turning 2200 rpm which is right about the sweet spot, at least in my truck anyway.


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