Bad MPG, Changing O2's help!

**airmaxon1** · 01-27-2008, 09:45 AM

I have a 99' Trans Am, A4, and i get horrible gas mileage, probably 150 to a tank city driving. I have done everything people have mentioned, except changing my O2's. Now few questions. Would they be makin my engine light come on if they were bad, or no? Also whats the process to change them out? Thanks for any help

**Wheeler99WS6** · 01-27-2008, 10:10 AM

changing the o2 sensors is no sweat. they just unscrew. Are you still running Cats.? If so maybe you have a bad Cat. They can throw a code (engine light) but I have heard of guys having problems and not getting a code also. What mods do you have so I can better help you diagnose your problem.

**airmaxon1** · 01-27-2008, 10:40 AM

Yeah im still runnin cats, damn CA emissions. Is there anyway to tell a bad cat? my mods are only SLP Lid and a cutout thats open full-time.

**Tracker9118** · 01-27-2008, 10:48 AM

By the way you have 4 O2s on the car & a bad cat will smell like rotton eggs.

**airmaxon1** · 01-27-2008, 10:50 AM

oh well than no bad cat for me, exhaust smells fine

**Tracker9118** · 01-27-2008, 10:50 AM

You will also have power loss & your fuel mi, will go to shit.

**Tracker9118** · 01-27-2008, 10:52 AM

When was the last time you put plugs in it????????????

A GOOD SET.

**airmaxon1** · 01-27-2008, 01:07 PM

well i bought the car with 80,000 miles on it, and i looked and saw MSD wires, so i figured that they had just been changed before i got it. Dont know why someone would change wires but not plugs?

**SeVeReDiStOrTiOn** · 01-27-2008, 06:39 PM

Originally Posted by airmaxon1

I have a 99' Trans Am, A4, and i get horrible gas mileage, probably 150 to a tank city driving. I have done everything people have mentioned, except changing my O2's. Now few questions. Would they be makin my engine light come on if they were bad, or no? Also whats the process to change them out? Thanks for any help

You can also try cleaning the front o2's first before replacing them...it's the cheaper option. CRC makes a non-residue eletrical cleaner and that's what I use.

Also driving habits are the main cause of bad mpg....try to keep it under 2000rpms in town. In traffic I leave more room between the car in front and meso that I can do a slow rolling cruise instead of the constant stop and go....it really helps.

**180ls1** · 01-27-2008, 10:29 PM

Originally Posted by airmaxon1

well i bought the car with 80,000 miles on it, and i looked and saw MSD wires, so i figured that they had just been changed before i got it. Dont know why someone would change wires but not plugs?

pull only the easiest plugs to get to and do your best to get a judgement from those. there is a good chance there is bad plugs though thay are somewhat hard to change in our cars. But for mpg i would do o2's, clean maf, seafoam it, and new plugs. Is your engine throwing a code???

**airmaxon1** · 01-29-2008, 06:50 PM

Originally Posted by 180ls1

pull only the easiest plugs to get to and do your best to get a judgement from those. there is a good chance there is bad plugs though thay are somewhat hard to change in our cars. But for mpg i would do o2's, clean maf, seafoam it, and new plugs. Is your engine throwing a code???

dont have a scanner to check out the codes, just seafoamed it yesterday, few nice big puffs of smoke

ill have to check on those plugs tomorrow and see how they are. hoping that seafoam will do some magic without havin to do anything else

**konigandy6** · 01-30-2008, 03:30 PM

Simple maintenance may help

Fuel filter
Air filter
Fuel injection cleaning
Plugs and tune up

Also, I have heard keeping your foot out of the accelerator helps a lot too...