Bad Gas Mileage

**2kz** · 08-14-2013, 04:38 PM

This year my 2000 Z28, only has 42,000 miles, has been getting 11-12 mpg. Easy city driving, no flooring it, lol. I'm thinking it's time to replace the O2 sensors? Is it possible they are bad even with no SES lights? Car runs fine. What brand does everyone recommend, AC Delco? TIA!

**tatertot91** · 08-14-2013, 05:52 PM

When is the last time you did a full tune up? New plugs, wires, fuel filter, air filter, I would start there. New O2s probably wouldn't be a bad idea either. What octane of fuel have you been running?

**pajeff02** · 08-14-2013, 06:11 PM

^^ This. May as well clean the MAF while you are at it. I generally recommend Bosch P/N 13111 O2 senders, especially is you have headers as they have a longer harness.

**tatertot91** · 08-15-2013, 02:48 AM

My personal experience has me using denso sensors. Nothing wrong with bosch, I've just noticed that denso o2s read/switch faster. Also when I can its a plus going with the oem brand, especially for sensors imo.

**pajeff02** · 08-15-2013, 02:53 AM

No actual testing to base this on, but my understanding is that the P/N 13111 sensors are faster switching than the P/N 13444. The latter being the Bosch stock replacement sensor for our cars.

**JayTA98** · 08-15-2013, 06:46 AM

I was having bad fuel mileage and I switch my O2 sensors to brand new Boschs. I don't have headers. I did noticed a change in my fuel mileage right away. My car had 110K when I swap them. Also make sure you don't use lower octane fuel it will drink it like ice tea in a hot summer.

**cammed goat** · 08-18-2013, 12:05 PM

Agree with all stated above.

**theorangeguy** · 08-22-2013, 10:36 AM

I've had a few things ruin my mpg in my cars...bad o2's and vacuum leaks are the ones I ran into the most though.

**0rion** · 08-22-2013, 12:46 PM

any mods? Is the car running funny at all? I know you have a '00 which doesn't really have a functioning coolant gauge but is it at least moving up the scale like it should? I would start with maintenance items before just throwing O2 sensors at it. 42k miles isn't a bunch of miles to have on those sensors. That's not to say they still might not be bad because regardless of the mileage they're 13 years old. I would still start with cleaning the MAF, plugs/wires, ect ect since those are normal maintenance items that should be done anyhow.

**cammed goat** · 08-23-2013, 05:29 PM

Plug wires could be degrading given their age and being exposed to heat/cold. Is the car a daily driver? But I agree with cleaning the MAF. Give it a good spray and let it dry completely then reinstall. Do this first then get back to us if there is no change.