Gas mileage sucks!

[dcraig1000]

I have a 93 Lesabre Limited. 111,000 miles. It runs perfectly. The thing is my frickin gas mileage is horrible (15-16 mpg's). I keep the tires inflated to proper psi, the plugs are in great shape, the air intake system is clean. there are no codes, current or stored. Im a mechanic and know my way around cars pretty well, but I am stumped.. Im not heavy on the foot too much either. I have been battling this issue now for a couple of years and have run out of ideas. If the darn thing was running bad or I drove like an idiot, I could understand the issue. Any other ideas??????

 

[journeyforce]

Can you verify your TCC is working correctly? If it was not locking up then that would hose gas mpgs and it never did set a code or drive differently on my 1989 Century.

 

[dcraig1000]

well the tcc seems to work fine. going around 55-60 on the highway in o/d when I tap on the brake pedal it downshifts to 3rd fine, so Im sure it is working correctly. On another note, I have not checked it yet, but Im going to check my fuel pressure. maybe the pump is putting out to much....hell I dont know.

 

[Hawk]

If you test the TPS and it checks out fine, then I would to a Fuel PSI test and a Fuel Leak down test. Seems more to me that you might have some bad injectors causing your fuel issue.

Had a 93 Century that was doing that, ended up damaging the valves (it was due for top end service anyway). Long story short, the car is still on the road to this day running just fine with 32 mpg freeway

 

[2k2cse]

A lazy O2 sensor can also cause bad mileage, and not always throw a code.

 

[journeyforce]

Perhaps it is your coolant temp sensor (the one that the computer uses to adjust fuel delivery and not the one for the dash) if it is going south then it could be fooling the computer into thinking the car is still warming up so it is causing the car to run rich to warm it up faster? The CTS might be failing but not setting a code?

Perhaps it is crap gas?

Good luck

 

[dcraig1000]

I do understand that there are alot of possibilities here. Kind of why I hate OBD1. Because its not as reliable and in depth as OBD2 as far as coding. Gonna pull the cts and read the resistance across the terminals. Im pretty sure I know what its supposed to read cold and hot. Ill put a heat gun to it and see if it is responding as it should. If thats okay then I will do a fuel pressure test at the rail. 40-47 psi cold. 33-42 once warm at full operating vacuum. If thats okay then I will look at the o2 sensor. If thats okay then I will just shoot the car.

 

[Gold Lesabre]

When my O2 sensor was acting up with a bad ground from the clip loose, my mileage drop 6 mpg and light came on and often would stall when off the gas.

 

[dcraig1000]

checked the fuel pressure. it checked out fine. a little low actually, so its not that. gonna look into the o2 and coolant temp sensor next weekend.

 

[leftoverture]

Have you checked your brakes? Could be one is dragging slightly.

 

[Enslow]

Do you have an exhaust gas analyzer, or access to one? It might give you an idea if you are running rich at idle (or under driving conditions if you have a dyno).

 

[dcraig1000]

I have access to both up at my school(college). Gonna be starting the spring semester in a couple weeks so I can check that then. if it were running that rich I would think there would be other symptoms though. maybe even a c.e.l. ?????????

 

[steppjohn]

Hi,
Probably not your problem, but is it shifting to all gears? My '95 does not make it to 4th.
Around town I didn't even notice it. I did not even realize it until I made a careful check of the shift points. It would affect mileage on highway mainly, and probably not by the amt you are seeing.
Just a thought

John

 

[dcraig1000]

thanks john, it does make it to fourth most of the time. its wierd sometimes coz when its cold out, it will not shift into 4th on the first run of the day, but after it warms up and i shut it off then the next time i get it in and drive it shifts normaly. doesnt happen all of the time. more when its cold out. also, i do do a lot of stop and go driving and i attribute that a little to the bad mpg's, but not to the degree of what it is.

 

[dcraig1000]

okay, this is how bad it sucks....252 miles on a full tank. ridiculous!!!!!!!!!!!!!

 

[Gold Lesabre]

O2 Sensor....

 

[Cadillac_AL]

okay, this is how bad it sucks....252 miles on a full tank. ridiculous!!!!!!!!!!!!!

Something is definitely wrong with that. When I go on vacation I always go 400 miles before looking for a gas station. If compression and vacuum are good i would blame leaky injectors or FPR. My old V8 Seville will go 300 miles on a 18 gal tank. I would be depressed if one of my economy cars couldn't match my Cadillac's economy.

 

[1380Ken]

252 miles / 18 gallons = 14 miles/gallon

The EPA estimate for your car is 17 mpg city.


That would be if you drained the tank to zero. You probably had one or two gallons left

252/16 = 15.75 mpg


You might spend more money chasing the problem than you will save.

I get 20 mpg with my 2005 and it is mostly highway driving, but a lot of traffic on the highway. My car is epa rated at 18 mpg city.


How are you measuring your gas consumption?

 

[dcraig1000]

you are right Ken, I had exactly 2.1 gallons left. I filled it up, drove til it was buried below E, filled it up again and calculated 18 minus the 2nd fill up gallons.

 

[Gold Lesabre]

Craig

Did you find out the issue......now I had my fuel filter and lines replaced and my mileage is down under 15 also....dont get it??? Maybe a dirty fuel filter was better for mileage