Poor MPG, Running Rich?
Thread Starter
Staging Lane
Joined: Apr 2005
Posts: 59
Likes: 0
From: Pittsburgh, PA
Poor MPG, Running Rich? car: 1999 Z28 m6 61k miles
I am getting around 13 mpg city not driving hard at all (just commuting to work) I usually hit 4th but rarely 5th. I am planning on pulling the plugs and seeing if they say anything, but could I just be running rich? I notice my borlas pop every once and a while which would be a symptom of running rich.
Any advise would be awesome
thanks
I am getting around 13 mpg city not driving hard at all (just commuting to work) I usually hit 4th but rarely 5th. I am planning on pulling the plugs and seeing if they say anything, but could I just be running rich? I notice my borlas pop every once and a while which would be a symptom of running rich.
Any advise would be awesome
thanks
When I think of commuting, I think of a moderate highway cruise around 70 mph in 5th or 6th gear, with a little residential/city driving on each end. I get right around 20-22 MPG with 4.10s, dead o2 sensors and SES light blaring, even with the 10% ethenol fuel around here.
If youre only driving a short distance to work, the engine may not even reach full operating temp and that may be why you get such lousy gas milage. Also, simply running a car in 5th as opposed to fourth gear makes the car travel 33% more miles per the same number of revolutions / RPM. It could simply be that youre driving in the city where these engines really suck down the fuel. Once youre cruisingon the hiway, milage should come back up for you.
If youre only driving a short distance to work, the engine may not even reach full operating temp and that may be why you get such lousy gas milage. Also, simply running a car in 5th as opposed to fourth gear makes the car travel 33% more miles per the same number of revolutions / RPM. It could simply be that youre driving in the city where these engines really suck down the fuel. Once youre cruisingon the hiway, milage should come back up for you.
wow i only get around 15mpg and drive WAY more conservativly thatn yall do...i do have a large cam though so i guess that's why...i'm in 5th at 30mph and in 6th at 40...however, this is all city...and a lot of stop and go traffic...why would you ever drive in 5th at 70mph 
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SES light not on, right? MAF plugged in right? Try normal stuff like air filter, fuel filter, plugs, fuel injector cleaner, sea foam, possibly some new front o2 sensors as well. That should tune you up as well as you can be tuned up.
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Originally Posted by cr0y
Just out of curiosity. How does the cars computer know when certain things are wrong such as a bad spark plug, bent valves, etc?
I cruise on the Interstate at 80 - 85 mph in 5th gear at around 3000 rpm and still get 18 - 20 mpg all around driving. I live in West Virginia. This is not a very 6th gear friendly state. I do get better mileage when just cruising for fun at 50 mph in 4th but I can get at worst 17 running 75 - 80 mph on Interstate in 5th & a short city run getting to and after 15 - 20 miles on the Interstate. I see anywhere from 200 to 260 on a tank of gas. It takes 12.5 to 13.5 gal. to fill up. I run Sunoco 94 or Exxon 93 depending on where I am when I need fuel.
Could very well be your o2 sensors. Mine went bad and I lost ~50hp and ~2 mpg. New O2s will cost you about $160 from autozone. PM me if you need a part number, although I know you can find it here with the search function.
