Rotten gas milage, stumped

[Blank-Disk]

In the last month, my 93 ATX's gas milage has gone from about 22 to 15 mpg. When I drove it here from NY, i was averaging 26 mpg. I haven't changed the oil yet, which I'm going to do today. It's been running very sluggish lately. I live in a very high altitude area, almsot exactly 1 mile up, so I understand that the car will suck more gas to coutner the low air pressure, but still, this is kinda nuts. I'd even understand 19, but 15? I had the fuel pump replaced about a year and a half ago. SOmeone suggested that the filter didn't get replaced. For what i paid for the job, it better have. I've also considered 02 sensors, but those also got replaced with the fuel pump, and haven't been a problem, there's no "Check Engine" light activity at all. Overall teh car is running good. The transmission has been leaking lately, oh but that's okay, i only JUST spent $2500 on a rebuild. Looks like a good torque convertor is hard to find. Any Suggestions?

 

[40BelowSummer]

When I got my 93ATX it got 15MPG as well. Now its at 31.4MPG!!!!!!!!! My elevation is 6200FT. I did a top end 60K before it went to 31.4MPG. I changed the O2's and the ECT sensor as well.

Try running your codes. The first thing I would replace is the ECT sensor since it will make your mileage go to **** and is only $18. If that doesnt work, replace the O2's if you dont know the last time theyve been replaced.

Good luck

 

[DHMag]

go to Auto-Zone and purchase a bottle of RXP. its a small orange bottle with yellow label. retails for 6-7 dollars. its a decarbonizer. i ran it thru a full tank of gas with new plugs. after refilling with fuel only, i changed the plugs again (Bosch Super plugs both times). brought my mileage up from 14 city to 20 city. 18 highway to 36 highway. though i did just get 38MPG this past week on nonemissions formulated gasoline.

 

[ratshavefeet]

what octane was your non emissions gas?? thats way nice 38mpg in a sho. I get like 22 but I need a 60k

 

[DHMag]

what octane was your non emissions gas?? thats way nice 38mpg in a sho. I get like 22 but I need a 60k

87 octane at all times. occasionally ill run 92-93 though. i had to work to get 38 MPG though. shifting at recommended shift points is the key

 

[ratshavefeet]

I see, what are the recomended shift points? Anybody ever put racing fuel in there sho? I want to but I am scared of sho boom.

 

[Hack]

I seem to recall reading that a bad charcoal canister can casue horrible gas mileage. It may just be my imagination though.

On the racing fuel, there is no need to use it on a stock or close to stock SHO. As Dale mentioned, the SHO runs fine on 87 octane. Higher octane only gives a benefit if the motor is designed to run on it. Some forced induction SHOs run it, but that is to prevent fatal detonation. If you were to rebuild the motor using really high compression pistons, you would also need it. I am sure that Todd Cook's SHO powered PPHC car runs racing fuel. IIRC he said it runs in the 12.5:1 cr range. (Stock SHO is 9.8:1)

 

[DHMag]

I seem to recall reading that a bad charcoal canister can casue horrible gas mileage. It may just be my imagination though.

On the racing fuel, there is no need to use it on a stock or close to stock SHO. As Dale mentioned, the SHO runs fine on 87 octane. Higher octane only gives a benefit if the motor is designed to run on it. Some forced induction SHOs run it, but that is to prevent fatal detonation. If you were to rebuild the motor using really high compression pistons, you would also need it. I am sure that Todd Cook's SHO powered PPHC car runs racing fuel. IIRC he said it runs in the 12.5:1 cr range. (Stock SHO is 9.8:1)

to follow up: the manual *recommends* premium unleaded for the 3.0/3.2 SHO. when i first bought my SHO, i ran 3 tanks of each fuel grade thru the system. i never noticed any change in performance and therefore, couldnt justify dropping in 12 gallons of premium fuel at the higher cost.

 

[ratshavefeet]

and my silly self was without a question putting in 92 octane because of my fear of ticking. 87 for me now. How do you get nonemissions gas? Whats the difference? It seemed to make a pretty big difference for yer mpg.

sorry for getting off track of the post. I think you have a bigger problem then a oil change if you lost 7mpg, But I got no suggestions.If you don't know about the fuel filter why not just replace it anyway..or atleast look at it, it should be half obvious if its been on there for a long time. I don't think I ever replaced a fuel filter that didn't look like crap on the outside.

 

[DHMag]

and my silly self was without a question putting in 92 octane because of my fear of ticking. 87 for me now. How do you get nonemissions gas? Whats the difference? It seemed to make a pretty big difference for yer mpg.

sorry for getting off track of the post. I think you have a bigger problem then a oil change if you lost 7mpg, But I got no suggestions.If you don't know about the fuel filter why not just replace it anyway..or atleast look at it, it should be half obvious if its been on there for a long time. I don't think I ever replaced a fuel filter that didn't look like crap on the outside.

where i used to live in North Texas, dallas/Ft Worth is known as the Metroplex. in those counties, air pollution is a problem, so the gas is reformulated for cleaner emissions and the emissions testing is stricter. even more strict than the California emmissions, which is the number 1 smog producer in the country. where i live now, in South Texas, air pollution isnt that big of a problem. San Antonio has no major industrial areas therefore the air is cleaner here. but it might change when Toyota opens its doors in a few years. since air quality isnt a major issue here, i can use nonformulated gasoline.

oil viscosity and thermal dynamics will affect your mileage. ive never come across a huge difference like 7MPG though. Blank-Disk stated he hadnt changed the oil yet, so oil change is not the cause of the drop in MPG. id suspect either crappy gas, emissions formulated gas, or driving attitude.