NxLS1496

iTrader: (1)

ok, i just put in about 6.36 gallons into my car. 93 octane. All city driving and i only got about 100 miles. This is driving like a complete granny. its an a4 and every time i started off i kept the rpms under 2000. and didnt exceed speeds of 55mph. not one wide open throttle run. that averages out to about 15.7 mpg. i know its an LS1 with even worse an auto, but c'mon i expect at least 17mpg. plus its florida, no hills. i just cleaned my air filter and i always use my a/c. i have dr's out back and run them at about 25psi and i run the fronts at about 35 psi. i doubt that matters though. thinking about trying some injector cleaner. also, sometimes while my car is stopped, it will vibrate a little bit, stop and do it again. it doesnt do it while the car is moving, i think one of 02's might be going bad but no check engine light though. also, my highway mileage sucks too, i keep it at about 75mph and i get a BEST of 21mpg. all mods are in sig, thanks guys.

Ragtop 99

iTrader: (7)

A/C in town kills the mpg.

How old are the plugs and wires?

when you coast, do you hear anything? Warped rotors or bad tires will add rolling resistance.

A4s have a very low idle speed. They will vibrate at a stop sometimes.

jmm98LS1

iTrader: (28)

What rear gear do you have?....how many miles on the car? I have 3.23's and never got better than 22mpg on the highway even when new and bone stock, so I don't think you're too far off. Like Ragtop said, a/c kills in town mileage, and if you spend any time in stop/go traffic that'll hurt too, and your 25psi rear tires aren't helping either.

mpe488

I would kill you for your 15.7, I've never done better than 13 city. I baby it all day, and it's had brand new plugs/wires/oil/oil filter/fuel filter for as long as I've had it. I do 22-23 highway though, that's at 75-80.

I would want to try a tune to see if it's running super rich, that's my theory (see dyno results.) But I don't have $400, and I'm afraid I'll waste $200 if I try a mail-order tune

Sgt. Spuds

iTrader: (1)

Your getting just what I get when I drive like a bitch.

VIP1

Sounds normal to me.
I used to get 18-20mpg with 80+% highway and 20% city. But now with age and the new fuel with 10% ethanol, I get 12.5-14.5mpg with 80% city and 20% highway.

NxLS1496

iTrader: (1)

thanks for the help everyone, i guess its about normal then. rear gears are 3.23's, its all quiet when coasting and thanks for info on the vibration ragtop. im not sure how old the plugs and wires are but ill be changing them out in the next two weeks when i install headers and ill change out my 02's just in case. car has 72k miles on it. and VIP1, thats what i was thinking about the ethanol.

mrhzk35404

iTrader: (7)

Sell it and get a Civic. I get about 200 mile to the tank but my car is a M6.

NxLS1496

iTrader: (1)

actually i was toying with the idea of getting a $500 pos....like a 1986 corolla or something.

'99slobird

iTrader: (7)

That's what I did. The calalier gets 35 mpg and the TA stays under the cover in the garage most of the time. Now I have alot more time to do other stuff since I'm not washing my car 3 times a week.

FlashLCD33

iTrader: (8)

This doesn't seem right at all..

My friend has a heads/cam/stall Trans Am. Runs mid 11s. That has a 9'' in the rear and a th400 transmission (only 3 gears). In town he gets 16 and gets on it quite a bit.

98BanditWS6

Sounds about right to me.

Auto+city driving+ A/C = **** poor fuel economy.

As for highway MPG, what gears do you have, 2.73's or 3.23's?? That makes a big difference. I'd figure aout 20-22MPG with the 3.23's, and about 23-25MPG with the 2.73's.

VIP1

Its well documented that although ethanol has a higher octane rating (an thus raises the octane of gasoline) it contains less energy than gasoline and fuel economy plummets. Compare the E85 (85% ethanol & 15% gasoline) mpg versus the E10 (10% ethanol & 90% gasoline -- the new gasoline formulation since MTBE is no longer allowed) mpg on flex-fuel vehicles. Now compare that to the "old" gasoline which didn't contain any ethanol. You'll see better fuel economy with the "old" gasoline. Get a copy of the July 2006 Car and Driver. You'll see all this and more about this subject in there.

ChevyThunder17

iTrader: (48)

A couple of things:

1. With my A4 SS, I tightened up the timing tables. In other words, set the low table equal to the high table. That brought me from 17 MPG to 22 MPG consistantly.

2. Dump your plugs. Something non-platinum. I pulled my plugs at 70K for reasons passing understanding. I could measure the gap with a tape measure it was so bad.

3. Keep in mind that the fuel is currently oxygenated. That does kill your economy a good bit. I notice it in any of my cars (I have five of them).

4. Keep your pressures up, 35 psi on all four corners.

5. You don't have to be getting a SES light for the o2's to get sloppy. I change them at 50K, regardless. Another instance where oxygenate fuel sucks.

NxLS1496

iTrader: (1)

Thanks for all the input, that really helped. what do you mean about the timing tables?
and will non platinum plugs hurt performance?

98BanditWS6

Resistor/Copper plugs don't last nearly as long, and they don't provide nearly as good or consistant spark like Platinum does. I'd step up to Iridium (AC Delco Iridiums are good), many guys on here have had good luck with them.

ChevyThunder17

iTrader: (48)

Well, with HP Tuners you can simply copy the values from one timing table to the other. GM uses two timing tables, one low and one high. The ECU will select a point between the two depending on feedback it receives from the engine sensors, most notably the knock sensor. If at a given point of RPM and load it detects knock it will pull out timing for that point. Knock sensors can sometimes confuse knock with other noises, such as when you hit a hard bump. You get false knock, you lose timing. Lower timing can lead to lower gas mileage. It's not a guaranteed thing, I'm just saying by changing that one thing *I* noticed a difference in my gas mileage. Your results may vary.

I don't run Iridium since I run nitrous. While I know they aren't platinums, my preference is with copper. Copper plugs definitely don't last as long, but I don't mind pulling them when I do an oil change just to look them over. They only cost a buck or so a piece, so it's not like it'll break the bank if they eed replacing. I was replacing them between 7-10K miles on my VW Jetta 1.8T and that never had an issue. I definitely wouldn't say that the spark isn't as good or consistant, I made almost 300 at the wheels on the 1.8T with 23 psi. And most folks on this board will tell you NGK TR55's if you are stock or TR6's if you are making a good bit of power or running on the bottle. Those are copper plugs and work great.