Crappy milage, O2 sensor?

[rivet0r]

note : completely stock 90 Laser RST

Well I had my O2 sensor hooked up to a datalogger not long ago when I initally realized my milage was horrible, and it was working properly. Would this mean that the O2 sensor isn't the problem as far as crappy milage? I didn't think I was running rich, but I have black crap in my exhaust, you wipe it with your finger and it comes off.. The thing is, I recently passed smog, but wouldn't I fail if I was running rich? I'm currently getting 12mpg.. and I'm trying to eliminate the problem. My oil smells like gas, so I had my mechanic check the injectors, and although he said there was moisture around them, I still don't believe that would drop my mpg in half. By the way, I just bought this car roughly 2 months ago, and have had crap milage since then. I don't want to have him change the injectors if that isn't the real problem, considering it will be expensive as hell. He said there was gas in one of the cylinders, so the seal will need to be replaced? Something in that direction.. anyways, I'm stumped and I don't know what else to do, the fuel filter is brand new, O2 sensor was working properly when I had it hooked up a datalogger, and although my injectors are leaking a bit, I don't feel that could drop my milage to what i'm currently getting.. that's a big drop for a little leak. If i'm wrong, please correct me, I want to fix this problem. My exhaust smells normal when I smell it, but there is black crap in the exhaust, and my mechanic said that means I'm running rich. Anybody have any ideas? And forgive me for the long post, I just want the problem fixed.

 

[doug]

This may not be the answer, but check to make sure your exhaust ground strap is connected. It's just a braided steel strap that goes from the frame of the undercarriage and connects to the downpipe (I think that's where it goes on 1Gs). It electrically grounds your O2 sensor to enable it to work properly. Many people have reported crappy mileage whenever this ground strap gets either removed or cut during an exhaust upgrade.

 

[rivet0r]

Originally posted by doug
This may not be the answer, but check to make sure your exhaust ground strap is connected. It's just a braided steel strap that goes from the frame of the undercarriage and connects to the downpipe (I think that's where it goes on 1Gs). It electrically grounds your O2 sensor to enable it to work properly. Many people have reported crappy mileage whenever this ground strap gets either removed or cut during an exhaust upgrade.

Thanks for the reply, although I have already checked this and it is in tact. Anybody else have any suggestions? =/

 

[markmakeitso]

Depending on how often you start and stop the car a leaking injector could cause really bad mileage. It will allow drops of gas to drip into the cylinder after you stop the engine. Could also make it run rich when they're spraying.

Actually replacing stock injectors is fairly cheap. DSMtrader and tuners classifieds always have sets of 450s for about $50 to $100, and a decent mechanic shouldn't take more than an hour to swap them in. You could do them too, you only need a couple tools and an affinity for hands that smell like petroleum products.
Heck, you're in California, there's gotta be a performance shop around you that has an injector balancing machine. Pull the 4 plugs, look to see if one is obviously different colored than the others. If so, pull the rail and injectors and have them checked out. You can also check the resistance across each. Hope that gets you started.

 

[rivet0r]

Originally posted by markmakeitso
Depending on how often you start and stop the car a leaking injector could cause really bad mileage. It will allow drops of gas to drip into the cylinder after you stop the engine. Could also make it run rich when they're spraying.

Actually replacing stock injectors is fairly cheap. DSMtrader and tuners classifieds always have sets of 450s for about $50 to $100, and a decent mechanic shouldn't take more than an hour to swap them in. You could do them too, you only need a couple tools and an affinity for hands that smell like petroleum products.
Heck, you're in California, there's gotta be a performance shop around you that has an injector balancing machine. Pull the 4 plugs, look to see if one is obviously different colored than the others. If so, pull the rail and injectors and have them checked out. You can also check the resistance across each. Hope that gets you started.

Thanks a lot, I'm definitely going to take your advice on that.. and it gives me more confidence that it could be the injectors, despite how big of a leak they have.