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04-26-2021, 08:44 PM | #1 |
Scooby Newbie
Member#: 458787
Join Date: Nov 2016
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P0420 and hard start
Hi folks, posting here because other Subaru forums seem to lack mechanical know-how.
2007 Forester N/A EJ25. Every once in a while it will have trouble firing on a cold start. Usually on the second try it starts. Also once in a while, on a cold day, it would flash a P0420 cat code. I would clear the code and it wouldn't come back for a year or so. Recently the cat code has been coming back consistently, but not all the time. The no-start issue seems to be correlated with the appearance of the code. Any ideas? I know that typically a cat code is consistent with a bad cat, but the hard starting has me wondering. It just seems like more than a coincidence. Otherwise the car has no issues. Front O2 sensor going bad, perhaps? Faulty injector or wire causing the cat to go bad? Any ideas are appreciated. I have rebuilt engines and am mechanically inclined. Thanks. Edit: Oh, I checked the O2 sensor voltage and found the voltage at the upstream sensor to be over 2 volts. The downstream sensor was 0.7 volts. Does that mean high oxygen (exhaust leak), or low oxygen (running rich, bad sensor)? My short and long term fuel trims are fine, in the low single digits, moving +/- around zero.
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Last edited by _rgk; 04-26-2021 at 09:08 PM. |
04-26-2021, 10:42 PM | #2 |
Scooby Specialist
Member#: 495950
Join Date: Jan 2019
Chapter/Region:
South East
Location: Augusta, GA
Vehicle:2011 WRX WRB |
the cat might be clogged?
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04-26-2021, 10:59 PM | #3 |
Scooby Newbie
Member#: 458787
Join Date: Nov 2016
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When I did the 105k service about 60k miles ago, I re-used the exhaust manifold gaskets. Just now I put in new gaskets. I just took the car for a spin and it has plenty of power. I will see whether the code comes back. If it does, I will replace the A/F sensor. At 175k, it's probably due anyway. If the code persists, I'll have a pretty good idea that it is indeed the cat.
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04-27-2021, 08:09 PM | #4 |
Scooby Guru
Member#: 487
Join Date: Nov 1999
Chapter/Region:
TXIC
Location: Houston TX
Vehicle:1998 /2005 STunIcorn Acadia Green USDM 22b |
Screw new cats
Will trip code when cat operating below 90% efficiency I have done this on 3 cars 3 diff manufacturers Same code Code never came back GL |
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