More Gas Milage Problems/Questions

[GreenTaurusSHO]

Ok... here's the latest.... i've posted before.. and I have received some good information from you all that i've tried.. but still no real luck. So i'll start over... Over some time i've noticed my car getting just "OK" gas mileage. I've been getting around 20 MPG on my MTX SHO.. and i'm not fully satisfied with that. The engine has 147K on it. Here's what I ahve done to try to improve this.
New: Plugs/wires/IAB/02's/ECT/Thermostat/IAC

Fuel Filter was replaced around 2k before the replacement of all that stuff. When I replaced all those parts i mentioned, I went from aroudn 250 per tank to 275... and this has always been on 13.5 gallons of gas... so 20mpg... Someone suggested removing the old K&N I had, cause the oils on the filter can hinder the MAF. I took the MAF apart, and there was oil residue on it, so I cleaned it with QRD Electroinics Cleaner. Nice and clean, and I replaced the factory air box back in with a paper filter. Stil... 275 to the tank.... 20 MPG

I've even been trying to drive slow to see what happens.. but If I cruise at 55-60... it'll get 275 to the tank.. if I do 70-85... which is at least a couple times a week, cause i'm late, i'll get 250... so what's next?

Could it be my tires? an alignment? I don't have factory spec tires on the car.. i forget what came with the car, but i'm runnign 255/65/16 or something like that...regardless they're not the factory size...

So could it be fuel related? I'm willing to try anything to help improve my fuel economy... it burned me up the other week when my friend laughed at me and told me his SS Camaro does better than that...

So anyway.. sorry for such a long post..but i'm upset... it sometimes makes me want to sell my SHO... so any help woudl be great... and please no responses telling me i'm a dumb kid that drives too fast or that I shoudl be happy with 20 mpg.... the da** thing is supposed to get 26.. and i'd be happy with 23 even!....

Thanks!

Adam

 

[Tom Higginbotham]

Adam,

Is that 20 mpg city driving or highway driving?

I used to get around 18 mpg city driving and after the 60K tune-up, it went up to around 20 mpg. However, on the interstate/highway, it averages around 28-30 mpg depending on how much the cruise control was used.

Have you checked your tire pressure lately? What type of gas are you burning (premium, regular unleaded, mid-grade)?


Tom

 

[GreenTaurusSHO]

That would be Premium.. 93.. havent checked pressure lately.. but I doubt it would bet that sicne it isn't a recent problem.. I do mostly highway driving.. about 70/30 percent city driving. What I don't understand is the folks that claim about getting 28-30 mpg when the car is rated at 26..??

 

[750sho]

My girl got 28.5 out of my old SHO... best i ever got was 24.5. Try driving like a woman, only safer, and you'll be good!

 

[GreenTaurusSHO]

I tried the woman thing....for most of the tank.... didn't seem to do much.... i dunno...

 

[NBSHO]

Gentleman,

I just replaced my air conditioning compressor because the clutch was dragging REALLY bad. Prior to this I had done a complete tune up, replaced the TPS, thermostat, and cleaned the K&N pannel filter with no real improvement. I replaced the compressor...no she sipps the gas like a lady sips champagne!

 

[Slo-Sho]

Ok... here's the latest.... i'm runnign 255/65/16

That's like a truck tire! The stock size is 215/60/16. Mentioning this initially probably would have saved you this big headache.

 

[SHOZ123]

Tire pressures are very important to gas mileage. if you want the best mileage pump the fronts up to max rating on the sidewall and the rears at 6 lbs less.

You are filling the car up all the way when you get the numbers for your calculations correct?

 

[sdpatt]

Proper fuel efficiency must be measured over more than 13.5 gallons. You refer to that amount as a tankful, but it is really only until the pessimistic LOW FUEL light illuminates. There is more than 5 gallons remaining in the 18.6 gallon tank at that level. The LOW FUEL light is not a precision indicator of the fuel level.

Reset the trip odometer and record the amount of fuel added over several fill ups. Use these numbers accumulated over a longer span of miles to more accurately determine your fuel economy.

I would be pleased to achieve 20 mpg around town in my SHO. I am quite sure that the engine and control system are in good shape from the continual maintenance I perform, the dyno numbers from a basically stock engine and lack of error codes. I regulary get around 17 mpg in mostly city driving. For a full tank on the highway at 75 mph, I see around 24-26 mpg.

If you are not getting any error codes and your O2 sensors have recently been replaced then you can guarantee that the engine control system is working as it should. Twenty miles per gallon in mixed city and highway driving is not bad. The mileage of any car, especially one with an engine that can breathe like ours, is very dependent upon the pressure applied to the right pedal and the amount of time spent stationary at stop signs and lights.

Your car will most likely achieve 24-26 mpg on a long highway stretch at a steady speed of less than criminal velocities, with properly inflated tires and less than maximum loading in the car. You will not achieve that number in any stop and go driving around town so don't lose sleep or sanity because of it.

An SS Camaro can easily get better than 20 mpg on the highway, but I doubt seriously that he gets that level of efficiency around town. Probably more like 15 mpg. Don't let his casual remark affect your understanding of the fuel efficiency that you car should and can attain.

 

[Fourcats]

Having not run the milage #'s lately, I'm not sure what I get. But I do know EVERY time "I touch the pedal", gas is wasted. I use "cruise control" as much as possible and keep the tires topped up. Try hooking up a VACUUM gauge and monitor it while you drive. It will show you exactly what your foot is doing, among other things.
And lastly...are there kids around? They may be "borrowing " some...

 

[40BelowSummer]

But I do know EVERY time "I touch the pedal", gas is wasted.

I wouldnt really say wasted :evil_gri:

 

[Randall]

My SHO gets an average of 19 mpg city and 24 mpg freeway, but it was getting 21 mpg on the freeway until I found the tires were underinflated by 17 psi each. Check this out, it is well worth it, and I know from having 235's before that those ate about 2 mpg's on the freeway over the stock tires. Good luck, and try to remember that your friend with the Craparo could get up to 50 mpg, but he still would be driving a chevy!

 

[GreenTaurusSHO]

Ok... but it has been said "I get 24-26" at 75 on the highway.. I don't get this... I always get 20.. but i'm not really too worried about it as much anymore... I think i'm becoming a basket case and just started to notice this more. If anything, I do belive it could be the compressor, as it is original having 147K on them... and for the tires, they're 215/55/16... a bit wider I belive....

 

[shobikes]

Ok... but it has been said "I get 24-26" at 75 on the highway.. I don't get this... I always get 20...

You stated you do "70/30" highway to city. Have you ever done a long trip on the highway using one entire tank only on interstates? That's when you'll see true "highway" mileage. I've seen 28.5 from my '89, with no bike rack on the roof, but running the A/C the entire time, and through completely flat terrain. I got over 25 with two bikes on the roof, coming back from the coast.

That said, if you split your highway drives with city plodding, especially in hilly terrain, especially if (like me) you enjoy hearing those secondaries open in 2nd gear, you'll be very lucky to ever get more than 20mpg average. It still ain't bad for a performance vehicle. Check out mileage ratings for the Boxster or the WRX or the M3/M5. We're doing amazingly well to get a real 20mpg out of 3-liter, 200-hp cars with 150,000 miles or so...

 

[jelloslug]

Since I swapped in the digital dash I have an average MPG and in instant MPG gauge that I can look at any time. When I don't try to save gas I get an average of 20-22 MPG on a 70-30 mix of highway to city driving. On the expressway with the cruise set at 65-70 I get an average of 30-33 MPG every time though.

 

[bolsterboy]

e30 m3's get 17 city 26 hwy and thats a 4 banger

i know cause thats my "planned" next car