Horrible MPG part 2! (on a 5.7 with bolt on's)

[Sublimeon24s]

Hey guys,

My car is still getting super horrible gas mileage and im hopelessly making this thread to see if anyone has any other opinions on why......

I filled up and topped off the tank this past Frday with 25,348 miles on the dash......Ive baby'd the throttle since and have not gone WOT a single time.......here it is 5 days later and Im down to a little less then quater of a tank with 25,552 on the dash meaning Ive only traveled "204" miles according to EVIC and ill already be needing to fill up tomorrow.......after being "granny" on the throttle since the fill-up, it says ive gotten 13mpg average in Evic..........this was all City driving for the most part to and from work - Light to Light sorta thing

My car has minor bolt-on's:

Predator 93 CAI tune with MDS disabled, 6k shift points, EGR disabled and blocked off, tire size adjusted for 22s
Airaid CAI
Ported TB
170 T-stat (its FL and super hot, car still gets well above 181)
Resos deleted

On other forums there saying its because I have MDS disabled and EGR shut off, but I recall there being PLENTY of people on here who have done both those things, have Cams, superchargers, etc and still getting way better mileage then me......even in SRTs!

Help!!!!!!!!!!!!!!!!! If I go to the dealer and say "whats wrong with my car", there just going to say the obvious: "Well you have a tune on it, your EGR is taken out, youve lowered your T-stat, etc etc etc" What kinda stuff should be I looking for to determine what it is?

[Hemi31]

On other forums there saying its because I have MDS disabled and EGR shut off, but I recall there being PLENTY of people on here who have done both those things, have Cams, superchargers, etc and still getting way better mileage then me......even in SRTs!

You do realize most cammed cars will get better mileage than a stock car will right?Turn your MDS back on and let it do it's job.

[diablotoona]

I would datalog a few things to make sure you dont have a sensor on the frizt someplace.
Good ones to start with would be your long and short term fuel trims, these will tell you how much fuel the pcm is adding (at part throttle) to get you to stoich.
Could be an exhaust leak which would cause the pcm to think you are running too lean and then in order to prevent that it would dump fuel in to try to correct that. The trims would tell you this as well, they would be waaay positive if this was the case.

[jhs914]

1. Get rid of that 170 degree thermostat. The computer will make the car run too rich because the coolant is not getting up to temp. I also live in Florida and I run a 180 degree thermostat with no problems.

2. Turn MDS back on. That is good for 2-3 mpg.

3. Get rid of those heavy 22" rims. Heavy rims don't just add to the total weight of the car, they add rotational mass. Every time you accelerate the motor has to spin those four heavy wheels up to to speed. Not only does this slow down your acceleration, it also uses more fuel. Don't want to get rid of your wheels? Pay up at the pump.

4. Turn the EGR back on.

One other thing. Coast as long as you can to a stop and use as little brake as possible. The computer turns the fuel injectors off while coasting. Braking turns kinetic energy into heat and that kinetic energy took gasoline to produce, only to waste it as heat when you use the brakes.

My '05 Magnum RT with 20" American TorqThrusts and running a Diablo 93 CAI tune gets 18-19 mpg in suburban driving and around 23 mpg on the interstate cruising at 70.

[marshall9779]

If it's mostly city driving, I don't think there is much you can do or anything wrong. Get on he highway and see what Evic is telling you when cruising. The biggest killer of gas mileage is sitting at a light, therefore mileage is 0.

[monty1269]

Welp.... I dunno how much this helps you.. but I've got:

Spartan Cam
stock heads
stock headers
JBA cats
SLP catback
CMR - MDS DISABLED

22" Foose Nitrous

170* stat

EGR deleted/blocked

I'm still gettin' just over 300 (highway) miles to the tank - and I dont run it till the fuel light comes on. well, maybe sometimes

I do NOT have EVIC, so I just use my handy calculator so, just say 300 / 20galtank = 15mpg. We DO have 18 gallon tanks right?...Dude... forget EVIC for a tank or two...and some math. Maybe your tire size is off or something. .. i dunno.

[daveleck]

I have posted a million times complaining about the fuel economy with my 5.7. There's always some joker on here claiming to get 26mpg around town. It simply isn't true. When I got my supercharger and it's heinous canned tune, my fuel economy went from 14/21 to 11/18. After getting a CMR tune done, I am back up to 14/23 and the car runs like a dream. I do nothing but rush hour driving and am very happy to get 14mpg with more than 420rwhp on tap.

PS - I recently added a DashHawk and now see the MPG claim that EVIC pulls. It is totally wrong. It tells me that I'm getting 21mpg around town. People need to do the actual math at the pump.

[Sublimeon24s]

Well........I turned MDS back on for my ride to work today and it showed 16.4mgp avg when i checked it in EVIC when I parked versus 11-13mpg its been showing lately. But DAM the car doesnt have the get up n go when that it does with MDS off, when its trying to switch from 4 cyl to 8cyl when you juice it from cruising..........that dreaded delay was back where it pauses for a second before it goes which Ive had gone now for the last 7 months

Do you think a good CMR tune with MDS off could get me better mileage? Its almost worth it to me to have it disabled and keep the instant power then this hesitation crap

[turbohips]

Maybe silly question but have you changed the settings in the programmer for your tire size already? Not sure if that has any effect on the EVIC

[Sublimeon24s]

Maybe silly question but have you changed the settings in the programmer for your tire size already? Not sure if that has any effect on the EVIC

Sure have, but thanks for the suggestion

[Bonez]

My case, is that when I added the Predator, my MPG tanked. Before the Predator, I was using the Superchips tuner and getting in the area of 20 MPG. With the Predator, I get about 15 MPG. I'm not complaing, but this is what I saw on my Magnum. The wife is now driving the Magnum and she is getting about 15 MPG also. There is NO WOT with her driving.

[momad]

I think the key is to coast up to stop lights and for God sake get rid of those 22's

BTW- I should be in town this Friday. You/your dad going to Old Town?

Give me a call.

[8yourM5]

wow my car gets 15/24 if I am putting around town/freeway

[done]

Well........I turned MDS back on for my ride to work today and it showed 16.4mgp avg when i checked it in EVIC when I parked versus 11-13mpg its been showing lately. But DAM the car doesnt have the get up n go when that it does with MDS off, when its trying to switch from 4 cyl to 8cyl when you juice it from cruising..........that dreaded delay was back where it pauses for a second before it goes which Ive had gone now for the last 7 months

Do you think a good CMR tune with MDS off could get me better mileage? Its almost worth it to me to have it disabled and keep the instant power then this hesitation crap

Hesitation crap? Four Hundreths of a second?

[Sublimeon24s]

Hesitation crap? Four Hundreths of a second?

More like a full second, sometime almost 2 in my car.......with MDS on if I give it WOT, it doesnt kick down and go.........it speeds up gradually for a second or 2 then kicks down and takes off........with MDS off its kicked down and took off instantly every time for the past few months