did you do the usual check's for things: fuel filter, air filter, all fluids, fuel pump. ?

 

Check the thermostat. If it's stuck open (like mine is right now) your fuel economy goes to shit. Not to mention economy normally goes down a bit in winter anyway.

BTW.....9.1mpg...wow....the worst I've ever gotten is 11mpg......and that's with a LOT of beating on the car.

 

You might also want to check your ETS (Engine Temperature Sensor). It should sit right on the thermostat housing. Your car maybe stuck in a cold loop so its running rich.

 

How can you tell if it's stuck in cold loop? I put the voltmeter on the battery and it said open loop, meaning something isn't grounded, would cold loop give that reading? It was too cold to take most of the other readings...

 

how much gas do you fill up with? the reason i ask is because the fuel gauges can be inaccurate due to bad sending unit in the tank. check out se-r.net for more info.

 

I know my guage is off, it's been off since I got the car, but computing the mileage, which I do every time I fill up yields different amounts. It's pretty consistent in terms of 180 miles=6.8-7.1 gallons when guage shows quarter tank left.

 

 

If the car has been allowed to run rich(due to bad o2 sensor,exhaust leak before sensor from a cracked manifold or bad gasket that causes the sensor to read lean and richen the mixture(I've had it happen),or some other bad sensor)the Catalytic converter could be plugged which would cause bad fuel economy.You may also want to check to see if you have a fuel leak from a dried out O ring or hose-the car is old enough!I routinely replace all of the rubber hoses when I get an old car because of the chance of failure(especially all the brake hoses!)

 

I have a hotshot header, but when they modified my exhaust to fit the cat, they did a lot of cutting. One of the bolts on the header is stripped from all of the motion of the exhaust. However, this is after the O2 sensor, could it still be giving the bad reading even though it's downstream of the sensor? I don't have any fuel leaks and the cat is less than 20k miles old. I had the problem last year and replaced the cat and the rest of the exhaust.
I think I have narrowed it down to the O2 sensor possibility and the thermostat being stuck open. Although it does seem to heat up reasonably fast. I replaced the thermostat in March and the O2 Sensor in the sumer when I installed the header. I'm gonna end this because it's long and the subject pisses me off...

 

I know my guage is off, it's been off since I got the car, but computing the mileage, which I do every time I fill up yields different amounts. It's pretty consistent in terms of 180 miles=6.8-7.1 gallons when guage shows quarter tank left.

If your getting 180 miles to 7 gal, your getting almost 26mpg...

 

which is significantly down from the 30 mpg gallon over the summer. But lately it has been more like 160 miles on 7-7.5 gallons. Lately as in the last month and a half. granted the weather has been horrible here in lovely Dayton, OH, but then I failed emissions(209 ppm HC where the limit is 147 ppm HC) which is embarassing and could be costly.

 

geeze, i guess my 20-24 bone stock is real shity then?

 

how much is a gallon in litres?

 

I have a hotshot header, but when they modified my exhaust to fit the cat, they did a lot of cutting. One of the bolts on the header is stripped from all of the motion of the exhaust. However, this is after the O2 sensor, could it still be giving the bad reading even though it's downstream of the sensor? I don't have any fuel leaks and the cat is less than 20k miles old. I had the problem last year and replaced the cat and the rest of the exhaust.
I think I have narrowed it down to the O2 sensor possibility and the thermostat being stuck open. Although it does seem to heat up reasonably fast. I replaced the thermostat in March and the O2 Sensor in the sumer when I installed the header. I'm gonna end this because it's long and the subject pisses me off...

You can kill a cat in a matter of minutes with the wrong mixture! All it has to do is overheat once to melt down into a blob of useless material.It may be that the o2 sensor's been bad for a while,and this is what's causing your problem.If it's working correctly,a scan(with a tool most people can't afford) will show it oscillating between rich and lean.Is it possible that you have a headder gasket leak?I had a bad check valve on the headders on the Chevy 350 in my Olds Cutlass,and it caused the o2 sensor to constantly read lean(and go through severe lean out on throttle tip in).Finally,the thermostat stuck open will only cause it to heat up more slowly,and should not severely drop fuel mileage.

 

I didn't think of the header gasket, I'll look at that tomorrow and tighten the bolts. Yea, with all of the cutting and movement of the exhaust it could have jarred the header bolts to the head as well...also, I have a voltmeter and it will finally be warm enough to use it tomorrow, so wuld the voltage read high for lean and low for rich? Or vice versa? Or can't I tell with a voltmeter? Thanks!

 

It should oscillate between rich and lean at a steady rate when operating properly.If it doesn't then either the O2 sensor is bad or there is some other malfunction causing the car to be either rich or lean.A O2 sensor works by producing a voltage in the presence of oxygen(hence the name).I believe it goes higher with more oxygen(lean).The voltage produced is very small,I believe it is measured in millivolts but am not sure.

 

If all your fuel is going through the engine, 8 mpg will be blowing black smoke like a cold diesel. I would look for a leak.

 

1 US gallon is approx 3.5 litres,
1 UK gallon is approx 4.5 litres

hope that helps, Ian.

 

Hmmm wut mpg is 180 miles per tank????

I've started to have bad mpg in my car like 4 months ago, like 250 per tank, but now that its cold i'm getting 180. I went to the dealers to try and get a diagnostic test but they told me i modified my car too much and they can't check it.(didnt really give me a reason why) Is there a way to check whats wrong???

 

I am getting real bad mileage too. I put gas in Monday morning, by Wed. it was down to half a tank, today a quarter. My dad suggested just filling it up and seeing how much it takes, I think my sending unit is bad. If it is, is it in the tank or on the tank? I just replaced the tank, and I don't want to mess with going into it again. Oh yeah, its a 92 SE-R. To figure out your gas mileage, just take the amount of mile you put on, divided by the gas you put in. Its a rough estimate. You may just need a tune up, but cold plays a a BIG factor in on that.

 

I have to throw this out there...if the O2 sensor is before the place where I think my header leaks, would that cause the O2 sensor to send low voltage and make it run rich? That dosen't make sense to me...also, can an EGR problem cause you to run rich? I know it can cause poor gas mileage, but my cat is fried and I gotta figure out why....

 

Running rich will fry the cat.

 

I am certain that it's running rich, this is a fact...the cat is melted and a lump of shit...I am working on why it's running rich and eliminating that problem before replacing the cat. The issue is that the pacesetter exhaust had to be cut to accomodate a hi-flow cat. When the shop cut it, they rattled the bolts and stripped them (the bolts on the flange from the primaries to the downpipe) so now there is a leak at that point. I am hoping that this is why it is running rich, but it dosen't make sense because the O2 sensor is before the leak...