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Old 12-02-2021, 10:01 AM   #1
Fast03Wagon
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Default Fuel smell, then reset ECU, smell gone, but comes back

Hi,

I posted this is Engine Management, but haven't had any replies, so I thought I'd try here.

It's been a while since I've posted here, but I figured you all would be a good source of info (sold my WRX, but now have a 2008 Outback XT.)

The car has been protuned for a few years with no complaints. In the last month or so, I've been getting a bad fuel smell in the cabin. First thing I tried was reset the ECU and just like that, the smell was gone. However, after about 50 or so miles, the smell comes back, almost like it's a result of some ECU learning after the reset. Been through 3 cycles of resetting and solving the smell, only to have it return.

Unfortunately, the tuner (Horizontal Motorsports in OR), is now out of business, so I can't ask them. Any advice?
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Old 12-02-2021, 11:03 AM   #2
pigboat_2
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Standard cold weather intake manifold fuel line leaks is my guess.
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Old 12-02-2021, 12:51 PM   #3
Fast03Wagon
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Quote:
Originally Posted by pigboat_2 View Post
Standard cold weather intake manifold fuel line leaks is my guess.
Thanks for the reply.

I thought so too, (I struggled with that issue in my old WRX) but it doesn't seem to be temperature dependent; the smell doesn't go away when the car warms up but it does when I reset the ECU - warm or cold.
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Old 12-03-2021, 11:33 AM   #4
Max Capacity
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Have you lifted the backseat and checked the fuel pump area for signs of leak ?

Maybe you have a Evap vent hose that has an issue ? Maybe have a smoke test done.

Doesn't make sense to me that resetting the ECU would stop the smell...?

Another idea, if you have air compressor blow air into the fuel filler neck for a few seconds. Maybe you have a vent hose that needs blowing out.

FWIW, once about a month ago, my 2005 Legacy GT wagon had a hard time filling the gas tank, I googled the issue and someone said they had good luck blowing air into the fill neck. I used my tire filling air nozzle and a rag to kind of seal the fill tube, it seems to have worked. I have put 8+ gallons in the tank a couple of times without issue. I'll also note Aug 2017 I had the gas tank and fuel filler tube replaced.

Last edited by Max Capacity; 12-03-2021 at 11:41 AM.
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Old 12-03-2021, 11:59 AM   #5
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You have a leak or a dead o2 sensor. the ecu is learning the lean condition and adding fuel, when you reset it its starts learning again.

You need a tune up
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Old 12-08-2021, 10:16 PM   #6
Fast03Wagon
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Quote:
Originally Posted by Max Capacity View Post
Have you lifted the backseat and checked the fuel pump area for signs of leak ?

Maybe you have a Evap vent hose that has an issue ? Maybe have a smoke test done.

Doesn't make sense to me that resetting the ECU would stop the smell...?

Another idea, if you have air compressor blow air into the fuel filler neck for a few seconds. Maybe you have a vent hose that needs blowing out.

FWIW, once about a month ago, my 2005 Legacy GT wagon had a hard time filling the gas tank, I googled the issue and someone said they had good luck blowing air into the fill neck. I used my tire filling air nozzle and a rag to kind of seal the fill tube, it seems to have worked. I have put 8+ gallons in the tank a couple of times without issue. I'll also note Aug 2017 I had the gas tank and fuel filler tube replaced.
I have not looked under the back seat - I'll do that. The first two times this happened was right after a fill up (no issue getting the tank full), so I wondered if it was something with the evap system.

I understand a smoke test for the intake system, but I didn't know it could be done for the evap / fuel system. Thanks for the tip.

Quote:
Originally Posted by blurred View Post
You have a leak or a dead o2 sensor. the ecu is learning the lean condition and adding fuel, when you reset it its starts learning again.

You need a tune up
The O2 sensor is a good thought, but no check engine light, which I've got before when the front went out and replaced it about 20K miles ago. I've been keeping an eye on the AFR via AccessPort and it doesn't seem to read or learn lean conditions. It really seems to run fine, besides the smell.

A leak wouldn't go away with the ECU reset, do you agree?


Thanks for the replies.
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Old 12-08-2021, 10:28 PM   #7
blurred
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Quote:
Originally Posted by Fast03Wagon View Post
I have not looked under the back seat - I'll do that. The first two times this happened was right after a fill up (no issue getting the tank full), so I wondered if it was something with the evap system.



I understand a smoke test for the intake system, but I didn't know it could be done for the evap / fuel system. Thanks for the tip.







The O2 sensor is a good thought, but no check engine light, which I've got before when the front went out and replaced it about 20K miles ago. I've been keeping an eye on the AFR via AccessPort and it doesn't seem to read or learn lean conditions. It really seems to run fine, besides the smell.



A leak wouldn't go away with the ECU reset, do you agree?





Thanks for the replies.
The leak doesn't go away but your fuel trims will be reset. A failing o2 sensor doesn't throw a light until your trims are beyond limits.

That's why when you reset your car runs correct fuelling, but after driving your o2 sensor is reading a false lean condition and adding fuel which you are smelling.

If the car is in fact not running rich then you have an exhaust leak and the reset is just a placebo. You should log your cruise and figure out if your trims are normal
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Old 12-09-2021, 03:13 PM   #8
Fast03Wagon
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Quote:
Originally Posted by blurred View Post
The leak doesn't go away but your fuel trims will be reset. A failing o2 sensor doesn't throw a light until your trims are beyond limits.

That's why when you reset your car runs correct fuelling, but after driving your o2 sensor is reading a false lean condition and adding fuel which you are smelling.

If the car is in fact not running rich then you have an exhaust leak and the reset is just a placebo. You should log your cruise and figure out if your trims are normal
Ok, thanks - this is making sense. I'll investigate the fuel trim and see what I come up with.

The reset is definitely not a placebo, it's unbearable to drive without hanging my head out the window
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Old 12-09-2021, 03:17 PM   #9
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Quote:
Originally Posted by Fast03Wagon View Post
Ok, thanks - this is making sense. I'll investigate the fuel trim and see what I come up with.

The reset is definitely not a placebo, it's unbearable to drive without hanging my head out the window
that sounds like an exhaust leak then. If it is just before the o2 sensor it will read lean and dump more fuel. You will also get lots of exhaust fumes in the cabin, whereas if you are just running rich you will only smell it when you come to a stop with your windows open.
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Old 12-19-2021, 10:47 AM   #10
Fast03Wagon
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Updating this thread with (hopefully) a solution for anyone that encounters this issue in the future. The fuel smell hasn't come back in a couple weeks with no need to reset the ECU.

I've been logging AF Learning and found it is doing OK, all within +-5% (even slightly pulling fuel) - highest value logged is -1.56% and lowest is -4.69%, so the ECU is not seeing a lean condition. I didn't fix any exhaust leaks, so I don't think that was the issue.

I tried the easiest / cheapest solution first: a new gas cap (OEM from the dealer), knowing mine was old and it didn't feel like it sealed like it used to. I can't fully explain this one other than a bad gas cap caused an EVAP system leak and the leak was coming strongly into the cabin. Fingers crossed this is the fix! If not, I'll continue to investigate and come back with more info.
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Old 12-19-2021, 03:00 PM   #11
Max Capacity
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Good Luck with that.

FWIW, my 2005 GT wagon has had P0457 and P0442 small evap leak a number of times. Turned out the mechanic found the leak at the shut-off valve on the side of the fuel fill pipe when doing the smoke test. I have put two new gas caps on the car in the past few years.

I did not smell gas with my issue.

Only time I smelled gas is when the fuel pump basket had issues or the rusty fuel tank leaked. My fuel tank and fill pipe were replaced in Aug 2017.
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Old 12-30-2021, 02:27 PM   #12
David_Machowski
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Default Fuel smell, then reset ECU, smell gone, but comes back

I had the same issue on my 15 STi. Turned out to be the BOV. I watched a Video by Smeedia, and he changed out his BPV for a BOV and immediately started running rich. I was actually also throwing a P0420 Catalyst System Efficiency Below Threshold (Bank 1). Once i changed out the BOV for a BPV the gas smell and CEL went away. It is known that for a MAF setup that a BOV can cause the car to run rich. The BOV i had was a dual port, which on my 04 WRX caused me no issues at all.



Hope this helps, and hope you solve your issue!


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