P0420 Diagnosis - Page 159 - Subaru Outback - Subaru Outback Forums
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post #1581 of 1609 (permalink) Old 04-07-2019, 06:45 PM
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This is a log Ive done. I tried to put all units in US so that its easier for you guys to figure it out. I did a single "pull" then decelled and coasted. My car is running like crap and I notice its worse around idle when it heats up. The temperature sensor reads the temperatures correct but could be messing with the ECU. Please let me know what you think and what parameters youd like to see. If it means I can get my car fixed, Ill send even send money

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post #1582 of 1609 (permalink) Old 04-07-2019, 10:49 PM
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4.79psi at idle MAP
12.6psi car off MAP
12.3psi from BAR sensor constant
14.5psi today outside.

Maybe that helps?

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post #1583 of 1609 (permalink) Old 04-08-2019, 08:36 AM Thread Starter
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Originally Posted by samochitwa View Post
This is a log Ive done. I tried to put all units in US so that its easier for you guys to figure it out. I did a single "pull" then decelled and coasted. My car is running like crap and I notice its worse around idle when it heats up. The temperature sensor reads the temperatures correct but could be messing with the ECU. Please let me know what you think and what parameters youd like to see. If it means I can get my car fixed, Ill send even send money
So here's what to log:
Engine RPM
AF sensor 1
O2 sensor
ECT sensor
Atmosphere/Barometer
MAP
Battery Voltage
Knock Correction
Ign Timing
Load



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Originally Posted by samochitwa View Post
4.79psi at idle MAP
12.6psi car off MAP
12.3psi from BAR sensor constant
14.5psi today outside.

Maybe that helps?
So the baro/MAP correlation is a problem. Low pressure readings means the car thinks it's at a high altitude. The MAP sensor scaling in the ECM is what determines the intake manifold pressure measurement and fueling. The MAP measurement is based off the barometer measurement by providing a difference in intake to barometer values. Your Barometer is on the right side strut tower attached to a bracket. Small like the MAP sensor and easy to replace if you can get one. It's attached to the bracket with 2 10mm screws.

Start with a new (or a salvage yard) barometer then look at the baro/MAP values with the key on, engine off and compared to local weather report and to what you have now. I believe this is your problem. When you get that fixed, relog with the data above.
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post #1584 of 1609 (permalink) Old 04-08-2019, 10:18 AM
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Thank you so much!! I’ll pick one from a salvage asap
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post #1585 of 1609 (permalink) Old 04-08-2019, 10:28 AM
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Thank you so much!! I€™️ll pick one from a salvage asap
That makes a lot of sense too because my car used to always buck and throw the code going down hills or at lower elevations! I live at about 4120ft and the highest point in my city, so pressures could screw with it alot
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post #1586 of 1609 (permalink) Old 04-08-2019, 05:25 PM
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Two pulls. Both with a short idle, acceleration, let off the gas - coast to a low speed, then back on the gas for a short cruise. I selected the parameters you suggested.

Got a free used Barometer today and noticed little to no difference! Real life air pressure is up today by a little. Still getting 12.6psi with the engine off compared to todays 14.6 psi air pressure.

Thanks again!
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post #1587 of 1609 (permalink) Old 04-09-2019, 02:25 PM Thread Starter
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Originally Posted by samochitwa View Post
Two pulls. Both with a short idle, acceleration, let off the gas - coast to a low speed, then back on the gas for a short cruise. I selected the parameters you suggested.

Got a free used Barometer today and noticed little to no difference! Real life air pressure is up today by a little. Still getting 12.6psi with the engine off compared to todays 14.6 psi air pressure.

Thanks again!
Then that would mean there's something wrong with the ECM unless your elevation vs local weather report is different. I doubt two different BAROs would result in the same measurement.

I'll look at the logs in a bit and post back.


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post #1588 of 1609 (permalink) Old 04-09-2019, 04:22 PM
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Quote:
Originally Posted by samochitwa View Post
4.79psi at idle MAP
12.6psi car off MAP
12.3psi from BAR sensor constant
14.5psi today outside.

Maybe that helps?
Quote:
Originally Posted by samochitwa View Post
That makes a lot of sense too because my car used to always buck and throw the code going down hills or at lower elevations! I live at about 4120ft and the highest point in my city, so pressures could screw with it alot
At 4100 feet, nominal Atmospheric Pressure would be around 12.6 psi, rather than the 14.7 psi at sea level.

The logs show "Atmospheric Pressure" constant at around 12.6 psi. Were the logs made at the 4100 feet level? If so, the car's barometer and MAP reading with engine off would be correct.

What is the original source of the reported 14.5 psi ATM? Is it in your area, or is it coming from a weather station (i.e., where the actual barometric measurement is being made) at lower altitude?

@cardoc: On this generation, is the "Atmospheric Pressure" data and the MAP data sourced from a single sensor? I seem to recall a discussion where a separate ATM sensor was identified in the ECM, whereas the MAP sensor is the device connected to the intake manifold downstream of the throttle plate.

@samochitwa Could you fill in your car details in the UserCP area, and perhaps where you are located. This way the information will show up in each of your posts, under your ID, and readers will know what car you have.

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post #1589 of 1609 (permalink) Old 04-09-2019, 04:51 PM Thread Starter
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@plain OM

On his model, the BARO is mounted on the strut tower and the MAP is on the intake. The ECM determines air volume by comparing the two. Post 1583 above has the pic of it's location. It's about as small as the MAP, just thinner. They will have a small filter attached (some don't). This Ebay ad has a good pic. https://www.ebay.com/itm/2000-2002-F...MAAOSwCCpcbu~L


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post #1590 of 1609 (permalink) Old 04-09-2019, 05:31 PM
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@plain OM

On his model, the BARO is mounted on the strut tower and the MAP is on the intake. The ECM determines air volume by comparing the two. Post 1583 above has the pic of it's location. It's about as small as the MAP, just thinner. They will have a small filter attached (some don't). This Ebay ad has a good pic. https://www.ebay.com/itm/2000-2002-F...MAAOSwCCpcbu~L
Thanks.

In the quoted measurements, with the engine off, both the baro and the MAP are much the same. The "reported" outside ATM at 14.5 psi is probably a reading that's closer to sea level. I wouldn't worry about the baro or Map sensors unless the car wasn't at 4100 feet when the logs were made.

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