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Old 02-20-2020, 05:05 PM   #1
ItalianGuy
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OMGHi2U Sudden massive drop in mileage, neither power nor oil consumption affected.

My mileage has recently and immediately taken a huge dump. I normally average 14-15 around town, up to 20 if I babied the car and 25 on the highway. My last fill-up I noticed I was down 1/4 tank with only 30 miles on the tank. I drove gently until I had time to stop at a gas station and when I filled it back up and did the math, my average was 11.3 mpg and that was with a lot of gentle driving, shifting at 3k at the most.

This came on from out of nowhere, and my oil consumption and power has been just fine. The only thing I can think of is an injector is stuck wide open. Could there be any other issues? Is there any way to check/test for a stuck injector without pulling everything off?

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Old 02-20-2020, 05:19 PM   #2
Homemade WRX
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Do you have a wideband O2 sensor you can read/log?
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Old 02-20-2020, 06:12 PM   #3
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What's your fuel trims at idle/during closed loop? A wideband would be most ideal to see AFR.
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Old 02-21-2020, 06:59 AM   #4
rtv900
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if an injector was stuck wide open your idle would be horrendous
how's the idle?

maybe another tank to check is in order?
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Old 02-21-2020, 12:05 PM   #5
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If the car is running fine, if your AFR is fine, but now you're suddenly consuming a bunch of fuel then I would look for a leak.

If it's not leaking with the car sitting there then I would start to look at the return system. Typically if it's a leak in the engine bay you'll smell it, BUT if you're leaking at the return line further under the car then you may not smell it so much while driving down the road.
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Old 02-21-2020, 04:38 PM   #6
4eat05
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With the car idling you should be able to hear the injectors clicking using a long screwdriver as a stethoscope.
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Old 02-21-2020, 09:38 PM   #7
ItalianGuy
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Quote:
Originally Posted by Homemade WRX View Post
Do you have a wideband O2 sensor you can read/log?

I do have a wideband, and didn't notice just how all over the place it's randomly going until you asked about that. It reads normal for the most part, then randomly reads anywhere from like 8 to 22, then back to 14-ish while cruising, with no abnormalities under acceleration. However, the Accessport logs show completely normal readings with no spikes or dips.


Quote:
Originally Posted by viper_crazy View Post
What's your fuel trims at idle/during closed loop? A wideband would be most ideal to see AFR.
I didn't check log those, I will tomorrow and see.


Thing about that is I just replaced the o2 sensor with a new Denso back in August. Looking at my order history, if it is the o2 sensor then this will be the fourth one I've purchased in five years and I don't even put 6k/year on the car. Any idea what could be sending my o2 sensors to a very early death?

The car is otherwise idling fine and I don't smell any gas anywhere, so now it seems I'm looking at another dead o2 sensor?

Anyone want to buy a Subaru?
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Old 02-29-2020, 03:08 PM   #8
ItalianGuy
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OK I replaced the o2 sensor and it clearly is not the problem. Although the car drives fine, this is what's happening with the readings. This was recorded in idle while going through Costco's car wash.

https://imgur.com/WeXgtTd

Any idea what's causing that?
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