Has anyone had problems with a stock s/c 3800 having terrible gas mileage? Mine seems to be at around 12-15 mpg around town. I get on the gas every now and then but I didn't expect to have this bad of gas mileage. One thing I noticed was the last time I filled up my tank completely I smelled gas in the passenger compartment for a few days.
Within the last year I put the evap cannister back in and hooked in the purge solenoid. A few years back I was experiencing closer to 20-24 in town with my swap. All of my connections seem tight and the cannister is in the same place as it was stock. I've been watching my scanner's output and my long term fuel trims are always at or around -2/+2% so I really don't understand where all of the fuel is going. Any help you can post would be appreciated!
What transmission? With an auto or 5 speed I would think you should be at 25 or better... If you're smelling gas there is likely a leak or you are running super rich, you don't have to see any gas to have a leak, vapor leaks really fast and any liquid fuel evaporates really quick.
------------------ 86 Fiero GT 4spd - L67 swap: VS cam, GenV 98 GTP - Some mods
yep my stock engined 87 with the auto is not doing all the great. I did manage to increase it by swapping a 180 thermostat with a 195. The 195 seemed to improve the engine idle. Mileage jumped about 3 mpg. Now getting 17 to 20 city/highway.
I've been watching my scanner's output and my long term fuel trims are always at or around -2/+2% so I really don't understand where all of the fuel is going. Any help you can post would be appreciated!
If the fuel trims are good, you can 99% of th time not worry about the way the motor runs.... Your fueling would have to be wrong, and the o2 sensor would have to be reading inaccurately the oposite direction.
I would look for stuck brakes, tires, alignment, or fuel loss.
I have a 3800 SC Series II that is entirely stock except for a 3.4 pulley. It gets around 25-26 mpg running around 73 mph on cruise control with the A/C running. The transmission is the manual Getrag 282. This specific combination dynoed at 258 HP and 300 Ft LBS of torque at the wheels so it does have some jump when you push the go pedal.
[This message has been edited by hnthomps (edited 05-01-2014).]
I think that I had a fluke recording and my gas gauge isn't reading very accurately anymore. I ran out of gas just above 1/4 tank about a week before I posted this. The fuel pump started whining when I came to a stop and I had about a mile after that and it quit running altogether. I am running a 282 getrag that was original to the car and a 3.4 pulley with a 180* thermostat. The heads and supercharger were recently rebuilt. When I have the car jacked up none of the wheels seem to have brake problems and while it's on the ground I can push it forward and backwards fairly easily. The car was just recently within the last 6 months.
I just measured my gas mileage again at the last fill-up and it was showing 22 mpg with all in-town driving so I'm thinking the one reading I got was a fluke. Thanks for all of the recommendations, if it comes back I will be sure to follow through on some tests to see what's causing it.