Horrible MPG - Third Generation Forum

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Horrible MPG
Monday, March 25, 2013 3:38 PM
So my '98 Z is getting horrible mileage. I have no idea what is causing it. I'm hoping you guys can help me figure it out. I'm getting like 19 MPG. I took a 300 mile round trip and the car took a whole tank plus 10 bucks. My old Cav with the 2200 makes that trip with the gas gauge sitting at 1/4 when all is said and done.

My driving method hasn't changed at all. I did a couple WOT pulls to 108 (both cars), so I'm not driving the Z any harder. I averaged 80MPH on the thruway and wasn't fluctuating speed, tires were at 40+ PSI. I could get almost 500 miles out of a tank on the 2200 Cav, but my Z can barely get 300. I know the motor is bigger so it's going to get less but that's ridiculous. It also doesn't seem to matter whether or not I drive the car hard or not, it'll dip to like 17.

The car is mostly stock, I don't drive with the windows down or the air conditioning on, and I'm not hauling cinder blocks or four fat friends. The car runs great, but I think the thermostat gets stuck open because when I'm idling with the heat on the temperature drops belle the 1/4 mark from operating temperature with the heat on. Might be normal.

Car got new plugs and wires 5000 miles ago, and I run synthetic oil and change it regularly.

Any ideas?




Re: Horrible MPG
Tuesday, March 26, 2013 11:39 AM
if its a 2.4 it doesnt have spark plug wires?


and im in the same boat with my 02 ecotec, runs GREAT but gets 18-22 mpg. grrrr


John Lenko wrote:

It is bad. Stop. Now. Bad. Bad bad. Bad bad bad.

...j

Re: Horrible MPG
Tuesday, March 26, 2013 5:23 PM
Likely the oxygen sensor.



FU Tuning



Re: Horrible MPG
Saturday, March 30, 2013 4:35 PM
could be, mines original, checked it on my to do list, thanks Meth


John Lenko wrote:

It is bad. Stop. Now. Bad. Bad bad. Bad bad bad.

...j

Re: Horrible MPG
Tuesday, April 02, 2013 2:16 AM
Had a similar issue with my 99 z24. It would hardly ever reach operating temp and was getting about 12-16 mpg city. I replaced the thermostat and now it seems to get about 18-20 mpg all city which is epa estimate. The other thermostat was new, but faulty right out of the box. I still kinda feel cheated because I've known people with automatic 99+ mustang gt's getting 17mpg city and that's a 4.6 v8 !!! I'm still going to replace my upstream and downstream o2 sensors just for the hell of it, even though there's no CEL or codes being thrown. o2 sensors and a thermostat should get you back in check.
Re: Horrible MPG
Saturday, April 06, 2013 8:20 AM
Spark plugs. Keeping them changed regularly is a whole lot cheaper than gas....




Ipud wrote:

We put Jap Traps on cinder blocks around here. We don't wave the American flag for novelty


I proudly own American cars, nothing else....



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