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5-6 MPG, no codes, bad 02 sensors?

Old 02-11-2019, 01:31 PM
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mrbears
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Default 5-6 MPG, no codes, bad 02 sensors?

Hey all, didn't really want my first post to be a "help!" one but glad to be a part of the community! I've recently acquired a '05 G35 Coupe (Revup) project/daily and thanks to the DIYs here I've managed to rebuild almost all of the suspension and fix a few other things. I should have a nice intro post soon.

So I've realized I'm getting about 5-6 MPG. I reset my trip meter, racked up about 92 miles and pumped in 16.4 gallons from a full tank. I'll continue to monitor, and the ECU was reset about the time I last filled up. I know the computer has to re-learn the fuel trims and all and my gas foot isn't very light. I'm about a 40/60 city/hwy commuter so I'm expecting around 15MPG.

Car is totally stock except some resonator deletes, rest is suspension work. Alignment is solid and the tires are some 340 UTQG all-season whatevers.
Full tune-up has been done recently including NGK stock plugs (gap checked), 10-30 oil, number of oil leaks fixed including valve covers. I've held a screwdriver up to all the injectors and they seem to operate normally. The back ones are hard to get to so i had to just kinda feel for the ticking.

I'm throwing no codes except for a one-off P1078, which is funny since I just replaced the opposite CAS for a 1084 code. Reset it a couple weeks ago and haven't seen it come back.
Idle is normal around the 750 mark and power feels good, no misfiring or weird noises coming from the pump.

Could 02 sensors tank mileage this bad? Or is this just normal fuel trim learning?

Thanks!
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Old 02-11-2019, 04:12 PM
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jhc
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Originally Posted by mrbears View Post
Hey all, didn't really want my first post to be a "help!" one but glad to be a part of the community! I've recently acquired a '05 G35 Coupe (Revup) project/daily and thanks to the DIYs here I've managed to rebuild almost all of the suspension and fix a few other things. I should have a nice intro post soon.

So I've realized I'm getting about 5-6 MPG. I reset my trip meter, racked up about 92 miles and pumped in 16.4 gallons from a full tank. I'll continue to monitor, and the ECU was reset about the time I last filled up. I know the computer has to re-learn the fuel trims and all and my gas foot isn't very light. I'm about a 40/60 city/hwy commuter so I'm expecting around 15MPG.

Car is totally stock except some resonator deletes, rest is suspension work. Alignment is solid and the tires are some 340 UTQG all-season whatevers.
Full tune-up has been done recently including NGK stock plugs (gap checked), 10-30 oil, number of oil leaks fixed including valve covers. I've held a screwdriver up to all the injectors and they seem to operate normally. The back ones are hard to get to so i had to just kinda feel for the ticking.

I'm throwing no codes except for a one-off P1078, which is funny since I just replaced the opposite CAS for a 1084 code. Reset it a couple weeks ago and haven't seen it come back.
Idle is normal around the 750 mark and power feels good, no misfiring or weird noises coming from the pump.

Could 02 sensors tank mileage this bad? Or is this just normal fuel trim learning?

Thanks!
I won't say "Impossible", but more likely that you have a fuel leak or perhaps someone has stolen your gas. Don;t smoke or Vape around your vehicle until you get this sorted. GL!
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Old 02-11-2019, 04:32 PM
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Originally Posted by jhc View Post
I won't say "Impossible", but more likely that you have a fuel leak or perhaps someone has stolen your gas. Don;t smoke or Vape around your vehicle until you get this sorted. GL!
Lol, getting my fuel stolen would honestly be funny before frustrating. I've never dealt with a fuel leak before, is there a common spot that's prone on these rides? Even a stuck injector would cause 1 bank to run super rich right? I see no black smoke on my bumper, which is something I did notice on an old Eclipse I had when it had a similar issue.
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