fuel economy vs. O2 sensors

bigcletus94

Registered User
I am sure this has been disscussed millions of times but....I have been getting pretty poor fuel economy for a while now, and its not getting better. My MPG is the same if not a little worse than before with my old motor. Would replacing the O2 sensors be a good place to start? As far as I know, they have never been replaced.
 
it seemed to help on mine, and seemed to give a little power back. is it throwing codes?

you could have that "foot in pedal" problem that is common with these cars.:D j/k
 
I get around 250 miles per tank mostly intown miles. I decided that I should change the O2s since the car is an 89 and I have 100,000 miles. Well I get the same mileage per tank. I had no codes before and no codes now. I have heard people say they get lazy or something over time and need to be changed. I wonder who started that myth? Do you think Bosch?
 
I never mash the pedal to the floor. I drive very conservatively. But it doesn't seem to matter. Either way, I get the same milage. About 250 to a tank. I have seen others post that they are getting over 300 to a tank on the same year as I have(94' Auto) which makes me mad. So that whole O2 sensor thing is a myth huh? I have never changed them. I am not getting any check engine lights either(haven't since I put in my new motor and lots of new parts/sensors). I haven't done a code scan in a while though. Maybe I should start there. Thanks for the responses.
 
I have 3 SCs...1 being a 94 AODE
When I first got the car with 70K on it I did all the scheduled maint. Flushed trans, rear end, tuned up etc...
My first road trip I averaged 250 miles to a tank. NOT GOOD!
We replaced the O2s, IAC,TPS.put on a fowmaster cat-back exhaust, C&L MAF, BBK 70mmTB and then I got about 300 miles to a tank. Recently I had the car throwing codes. We have since replaced every sensor and put new plug wires on.
I'm now happy to report the car got 375 miles out of a tank on a recent trip. with 110K on the odometer.
And this car is a daily driver with every other weekend spent at Julesburg dragstrip running in street class, with my son at the wheel.
Then theres the 92 that Michele races. It only gets 230-250 miles to a tank but its the CMRE S2 running low 13s
 
A weak oxy sensor can impact mileage as it can signal a lean condition when there isn't want causing the computer to increase injector pulse widths when not necessary.

Report your actual mileage rather than miles per tankful.

Check your fuel pressure regulator vacume line to make sure it isn't leaking any fuel into the line.
 
I got 15.1 mpg the last fill up. I drive all intown and about 75-90 miles on the hwy per tank. My car runs perfect and I got the same gas mileage before O2 and after. No codes and in Illinois we have dyno emission tests. I passed emission before installing new O2 sensors.

These cars don't get good gas mileage unless you are on the highway a lot. Even LS1 F-Bodys get 26 mpg on the highway and they are 5.6 L and 320HP.
 
OK, when things were bad in the 94 I got 18-20mpg HWY, when good (NOW) , I get 24-27,17-18 in town. So don't give me that LS-1 does better crap! And I getting at least 260 HP, from a V6, with no internal mods.
I'd say you have some problems somewhere! just as I did!

92%20SC%20Michele%20Topeka%202001%20.jpg
 
suckin money and gas

Im in the same boat only maybe worse, I am getting under 200 to the tank in town( most recently i marked it at 11 miles to the tank, but had been layin on it). before my engine mods i got a solid 220-250 intown, which wasnt great but i was livin with it,,,,Now just like you I am looking for some answers..

PS, I have owned LS1 style, firebird formula, and got pretty bad intown, comparabable to a "normal" SC,,, but its highway mileage was awsome---miss that sixth gear.
 
heres an idea

maybe its not the exhaust side of things maybeits the fuel system, dirty injectors, or maybe its just that you guys try to drive like john force from stoplight to stopligh, ya know if youre at a stop and the light turns green you floor it, that will give crappy gas mileage, or maybe you guys got an a$$ hole neighbor that siphons the gas outta your tank, well but my suggestion is to clean you fuel injectors change fuel filter etc. because if the filter is caked with crap you will also get crappy gas mileage, whatever you choose to do good luck and i hope youcorrect your problems,


another thing maybe but i dont know if this will cause crappy mileage but maybe the electronics for the maf are bad and telling the computer there is more airflow than normal therefore if would pump more gas to compensate for the extra airflow. just a thought

well good luck anyway
Steve
 
Hey SCgraphics guy, do you have a 5 speed?


I used to own a 1983 5.0 V8 T-Bird with AOD and 3.08 gears. I used to average about 16 mpg with mixed driving. When I bought the 90 Cougar LS 3.8 V6 AOD and 3.27 gears my average mpg went to 19 with the exact same driving habits and the same drive each week. While I still had the Cougar I started working about 3 miles from home and mileage fell to 15 mpg. I bought the 89 SC, AOD 3.27 gears, in 2000 while still owning the Cougar, and they got the same exact mileage as I would drive one for a couple of weeks then the other to compare. So I am not saying that mileage is worse than other cars I have owned and compared to the Cougar it's pretty good since one had 140hp and the SC has 210. The best thing about SC is the bypass that allows you to run as if there was no blower which I do about 90% of the time.

My car runs perfect, I'm not bragging it just does. No codes, passes dyno emmision tests that simulate driving conditions, starts in cold weather idles perfect immediately, etc. etc. I get 12 lb boost and 18inch of vacuum. I have installed new Motorcraft PP plugs and motorcraft 8mm wires. The orignal plugs were in the car with 92,000 miles and the car got same mileage. People say I should get better mileage on this board . So I shell out $80 for new Bosch O2 sensors and get same performance and gas mileage. I have a 1994 70mm Ford MAF on the car now and still get the exact same mileage as before.


The statement about the F-Body I made was that they are rated around 18 and 25. The F-Body LS1 is 5.6L V8 and around 3400 lb and has a EPA rating of 18 city and 26 hwy compared to a Lincoln LS with a 3.9L V8 and 3700lb with a EPA rating of 17 and 23 (same as my 89 SC and around the same weight) GM has to be doing something right to get that gas mileage with a 100 cubic inch handicap.
 
As to your comparison the only thing I can say is the newer technology is better! Our cars are primative in comparison!
Still great cars though!
 
Maybe not as new technology but certainly not primitive. Intercooled blower, traction control, EEC V controller, ABS, w/ electronic suspension. If this configuration was selling right now for about 25g's(in adjusted dollars) with the same power/torque and slightly less weight, Ford dealers would be moving them like a freshly escaped convict. Definitly not primitive.
 
These cars are relatively heavy and stop & go driving in town really causes the mileage to drop.

My 1994 SC with an automatic is 100% stock with 105k miles gets about 250-270 miles between fill-up (15-17 mpg) in suburban driving in warm weather using Mobile 1 oil. I took a long trip over the weekend and got 20 mpg averaging 75 mph. I think that's about right.

I also have a 1996 Corvette with a slightly modified LT4 (322 rwhp). I took a trip from Dallas to Houston, averaged 75 mph and got 27 mpg. Around town it gets 16-17 mpg or about the same as the T-Bird.
 
Fuel Economy

I bought my car out of state and on the trip back I got an incredible 27 miles to the gallon. Unfortunately, it was overheating every now and then. So I replaced both coolant temp sensors. It fixed the overheating problem but I have never come anywhere close to getting that fuel economy again. Any thoughts? Brandon
 
mileage

I was wondering the same thing since I got my exhaust done with no cats, all magnaflow stainless resonator and mufflers with 2 1/4 inch pipe. Got 24-26 mpg before work was done and now am lucky to get 20-21. Thought cutting the cats would help mileage and also lost a lot of my low end torque. Hopefully, new o2s will help get my mileage back!

94 5 speed

144,000 miles
 
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