Thread: MPG??? B chassis

On my 99 SE-L, had bad alighment, bone stock I got 33 mpg highway.

• Installed JWT Pop Charger, 33 mpg highway.
• Installed 91 intake cam, 33mpg highway
• Installed SSAC header, 27mpg highway
• Talked to DC Scotty, found out about grounding issues, switched to 4 wire Bosch 15727 - 33mpg.
• Full 2.5" exhaust - 33mpg
• Reground kit - 33mpg.
• T25 turbo - 28mpg
• T25 Turbo Front O2 sensor shorted out at the Savanah convention, AFR's at 17-18's cruising, driving home 35mpg.
• Fixed front Alignment (was off by 1") and installed new O2 sensor - 32mpg
  

No matter what I did I could never break away from 33mpg, until I went turbo and it got worse . I was OBD2 though, OBD2 is religious on keeping AFR's at 14.7. So if a breather mod worked, then mixture would lean out, thus O2 sensor would compensate with more fuel.

I completely forgot about old gas. But how old would it really have to be to actually affect MPG? The gas was only about 2 months old since I didn't have the need to refuel it. I'll keep an eye on the MPG to see if it gets any better with new gas.

That's probably why. Check this article: Does Gas Go Bad?

Another thing is, it could be like my 99 SE-L was, my tank could never keep it's pressure. Thus when it would stand for a week on a hot day, i would loose close to 1/4 of gas! No leaks that I could find, just seemed like the evap system had some holes in it.

I have an app on my phone called aCar that I input all my maintance records and fillups into and it keeps track of everything for me.

Since 213,019 my car has been averaging 27.1 mpg with a low of 23.464 mpg to a high of 31.131 mpg, it's currently at 228,600. And I do not baby this car at all, it sees redline at least once a day. I think I might have a partially blown head gasket as well, I go through an entire overflow bottle every 3-4 weeks and there are absolutly no leaks and the temp guage never reaches operating temp unless it's 80*+ outside. And yes I've checked the temp sensors they're working properly, I think the HG is letting pressure into the cooling system and making the thermostat stick open, and yes the thermostat is a new OEM stat.

Oh man 42mpg with a VE is mighty nice. Thats the kind of performance I'd like to get with my new NX. I might have to keep the VE I purchased, lol.

All in the tuning, Calum realtime obdII, 15.5-16:1 a/f's on the highway, Plenty of power, good solid 12.9:1 a/f under wot, 14.0-14.5:1 under medium load. All around perfect running 200whp VE with everything you could ask from a street car

O2 disabled or O2 broken? I've tried a ton of things tune wise to get it to lean out cruising, even messing with the fuel pressure. It would still be back to 14.7 afr's.

Running about 15.5-16 afr now on OBD1 ecu with O2 disabled, gas mileage is slightly better but not all that great. I think my O2 sensor is busted it's trying to tune the car to 14.1 thus I disabled it .

rear o2 disabled, front o2 still in with a wideband right behind it.

All i know is his never had a problem with a/f's changing at all. Also was running a lot of timing everywhere. Dont know why yours had an issue but all i know is he was loving the mileage. he would go to tucson which is about 240 miles and use a half tank of fuel. lol

Rear O2 is useless, only tests to make sure the cat works. I'm just saying from ECU stand point, which would not let you get leaner then 14.7 (well technically 14.5-15.3), unless O2 sensor is disabled.

Though when I disabled O2 sensor on OBD2 car, it ran like crap, especially going lean in boost.