horrible gas mileage

I recently modded my airbox and started to get terrible mileage (15-16 mpg) I had gotten it up to a whopping 16.5 mpg, but something happened and I am back to the 15 mpg's again? Could it be bad gas? Sparkplugs? I just replaced the sparkplugs and wires about 4 months ago. I would liked to get the mileage up to where it was (18-19mpg). I love the power that gutting the airbox has done, but if it means 3 mpg less it may have to be reversed. Has anyone ever had a similiar problem? Or know of a simple solution? :banghead:

I hope that's a lot of city driving, or else you should be up in the low or even mid 20s, not 18-19, much less 15.

Damn I wish the old gmforums was still around at times. I know I've read something about sucky mileage, but I couldn't find it here. Sorry.

yes it is city mileage. A lot of short trip, but even so......15 mpg? That is ridiculous......

you need to replace the Fuel Pressure Regulator. Its a known problem on these auroras and will burn excessive amounts of fuel until you notice some black smoke out the exhaust and it can get bad enough to actually cause fuel to leak. I replaced mine today. Extremely easy to do. Replace every 80K. After you do that. Drive it for 10 miles and then press the instant miles button on the computer readout. Notice the improved fuel mileage you get when coasting compared to what you were getting. If that doesn't work, replace oxygen sensors. These are the two things that will KILL your fuel mileage. I replaced both items at the same time so i can't tell you what one fixed my problem, probably BOTH. Do the FPR first, depending on your year, you either have 2 or 4 oxygen sensors.

I drive my '96 one mile to work each way. It will get the same bad mileage because the computer sees the engine running more than the odometer sees road miles. I get the car out on the highway and I’m back to the mid 20’s (MPG). Real low city miles will kill anything. Now, regular city miles should get you more. I average 20, but that is with 10% ethanol gas (we got to run this crap in southeastern Wisconsin). Real gas gets about 1-2 mpg more. I’d do like tedhontz (http://www.automotiveforums.com/vbulletin/member.php?u=215837) says and check the O2 sensors.

. I’d do like tedhontz (http://www.automotiveforums.com/vbulletin/member.php?u=215837) says and check the O2 sensors.


Is there an easy way to tell if they are bad? like with a multimeter or color or something?

if you pull them out, you might as well replace them. If you need instructions on the job, let me know. After i pulled mine, they have a grey ash looking foggy build up on them. SOme may have black carbon on them.

if you pull them out, you might as well replace them. If you need instructions on the job, let me know. After i pulled mine, they have a grey ash looking foggy build up on them. SOme may have black carbon on them.

Where are the two on the exhaust manifolds?
Are they easy to get out?
Any special tool or socket required?

My scan tool says I have one bad one on the manifold, but I'd like to replace them all at the same time.