Abysmal MPGs and Other Headaches - DodgeTalk : Dodge Car Forums, Dodge Truck Forums and Ram Forums
 
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#1 Old 12-21-2011, 10:18 PM
toyokota34
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Abysmal MPGs and Other Headaches

My MPGs are rapidly declining. Started off around 14MPG when I bought it, and has been slipping slowly the last few fill ups, going from 13 last week and to an 12mpg this week. These figures I calculate based on the tripometer and gallons put in, not the trip computer which is always a gallon or so on the optimistic side. Since I bought this truck, I've done all the standard maintenance. Put in new plugs at proper gap (OEM spec Champions), new air filter (K&N I bought for the long life, not any expectation of performance gain), oil change, checked air pressures, and I use a bottle of fuel system cleaner once a month to wash out crap from the E10 fuel here. Fuel is 87 octane ethanol blended fuel. I don't even drive this thing that hard, to the point I baby it compared to other cars I drive, and it doesn't make a bit of difference. Cruises at about 1500RPM, rarely go much over 2200RPM when accelerating.

I was wondering what is normal for these to get? My driving consists of about two mostly highway trips of 30-40 miles, and 2-3 short trips of about 5-10 miles out in the country a week. Live up in PA, so air temps have been around 38-50 degrees when the truck is driven. Engine makes pretty of power still though and runs buttery smooth like a V8 should when cruising and accelerating.

The only issues I can think of are A: it idles rough occasionally, stumbling a bit, but I chalk this up to the low idle speed in newer cars (650RPM IIRC in this) as I've noticed it in a Suzuki too on occasion, and B: shifting from 1st-2nd, 2nd-3rd is occasionally rough, jerking the body/seat a bit (normal?).

Next, any suggestions to increase MPGs in these if what I'm getting is about normal? I'm getting a tonneau cover for Christmas (never thought I'd say that), and was considering some of these fuel saver tires when I get tires if the cost is about the same (and the ride/handling quality is not affected), but beyond that I'm stumped. I don't think a CAI is worth the money on these, as even though the air flow would be less restricted I don't feel it would be taking in any cooler air based on where the filter sits in most kits I've seen. I noticed a little boost when I did a glass pack and larger pipe in my old Corolla, but I really don't want to put some noisy muffler on this thing. I really don't want to take the plunge on O2 sensor(s) if it isn't throwing a code.

I'm just starting to get frustrated with this truck as for the money I'll have put into it by the time inspection rolls around I could have fixed the few nagging issues on my Corolla (a fluke CEL due to a buggy sensor that affected nothing, and gotten a pro repair on the rear defroster), had an entirely new exhaust system and CAI fitted, and had money left over for cosmetic work (Grille, lights, maybe a tint job). Thus far I'm in it a stereo (knew about it, and to be fair I splurged on that), fan belt (worn out and slipping), bumper jounce (obliterated), air filter (over spent and got a K&N but still needed one), spark plugs (knew), headlights (failing filaments and need aiming), oil drain plug (Cross threaded), and it will need tires (knew) and probably brakes (developed a vibration like a rotor is warped or needs machined due to being eaten into by worn pads) to get through inspection in addition to the crappier than expected fuel mileage (I was expecting between 15-16 at least). Also needs the rear bumper repainted and several rust spots fixed (three on the driver's door, one on the fender, which again I knew about) I got a deal on the truck but now I'm starting to see why...

Truck is a 5 speed auto, LSD, 4.7L V8, with (worn) 265 size all season Michelin tires.

Last edited by toyokota34; 01-16-2012 at 06:48 PM.
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#2 Old 12-21-2011, 10:56 PM
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cant say anything for sure but I would guess its that tranny in our trucks. I get 11-12 or so in the city. now granted I havent gotten around to plugs yet and I am sure it needs them. I know that my mpgs have dropped since I started driving it. I was around where you were city with 19-20 highway. It has gone way down.

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#3 Old 01-16-2012, 06:48 PM
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cant say anything for sure but I would guess its that tranny in our trucks
Yeah, that is what I'm guessing as after two + months of doing it things haven't changed.

Just an update, it seems like I'm getting .2-.3 MPG more with my new tonneau cover but nothing else. It doesn't seem like how I drive it makes a big difference either. I was looking at getting a Superchips Flashpaq tuner. Does anyone use one? Do they make any real difference with an otherwise untuned engine? I know plug in chips are generally a scam, but I understand these actually flash the ECU with new settings after backing up the prior settings. Thanks
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#4 Old 04-09-2012, 02:42 PM
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Just a quick word about O2 sensors. Just because it isn't throwing a code, doesn't mean the O2 sensor isn't going bad. I've read that the sensors can get to a state where they are slow to react but still work. This will cause loss of fuel mileage because the PCM can't make the adjustments to the air/fuel mixture quick enough. If you don't know how old the O2 sensors are, maybe you should replace them.
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#5 Old 04-13-2012, 10:45 PM
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Thanks for the advice. Bad news is though, I sold it about a month ago. Paid a ton of money to get it through inspection, and it was going to need tires this summer and a rear bumper, so I wound up selling it before gas got too high. I never could get it over 13.5mpg, and I loved the truck, but if I had put another dime in it I wouldn't have gotten my money out of it so I had to let it go.
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#6 Old 04-30-2012, 04:24 AM
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One thing I thought of right away, is the K&N oiled filters coat the MAF in oil, and when it gets screwy readings, fuel mileage tends to suffer.

I would get some MAF spray cleaner at any autoparts store, and a dry-element air filter like the Amsoil EAAu filters. AFE also makes some dry element filters. Some MAFs have to be replaced after being coated in filter oil.

After all that, pull your negative battery terminal and let it sit for 10 mins.

After the PCM re-learns and sets your fuel trims according to accurate MAF readings, your MPG should mprove.

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