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Discussion Starter · #1 ·
Hello,

I have a 99 Outback AWD and it "Stumbles" during acceleration. I currently do not know why it stumbles but took a OBDII read while driving. If any one can help diagnose this problem that would be great. Here is the reading.

Trouble Code - P0440 (Evap sensor)...... Probably the gas cap.

Fuel System 1:
Closed Loop

Fuel System 2:
N/A

Load Value:
12.0%

Coolant Temp:
186 deg F

STFT - Bank 1:
-14.0%

LTFT - Bank 1:
7.8%

Manifold Pressure:
9.3 in.hg

Engine RPM:
2450 RPM

Vehicle Speed:
42 MPH
 

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Meh.
I has wagons.
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12,372 Posts
Thread moved to correct forum.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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16,277 Posts
Hello,

I have a 99 Outback AWD and it "Stumbles" during acceleration. I currently do not know why it stumbles but took a OBDII read while driving. If any one can help diagnose this problem that would be great. Here is the reading.

Trouble Code - P0440 (Evap sensor)...... Probably the gas cap.

Fuel System 1:
Closed Loop

Fuel System 2:
N/A

Load Value:
12.0%

Coolant Temp:
186 deg F

STFT - Bank 1:
-14.0%

This means the computer is reducing fuel due to the AF sensor reporting rich most of the time. Unburned fuel exiting the engine. Tune up time most likely.

LTFT - Bank 1:
7.8%

Fuel map learning is adding fuel, but this depends on a few factors you don't have listed here. TPS position, MAF and rear O2 are needed for certainty.

Manifold Pressure:
9.3 in.hg

Vacuum is good. This is not indicating a leak anywhere.

Engine RPM:
2450 RPM

Vehicle Speed:
42 MPH
Check the gas cap integrity and that its tight. If its been a while since the plugs were replaced, pull, check and replace if necessary. Check the condition of the wires also. After plug replacement, clear the codes and drive it. If your scan tool can watch the drive cycle monitors, watch them while you drive. All except EVAP should drop off and set to ready after about 25 miles. The EVAP monitor will take 2 drive cycles with a key cycle in between to set.
 

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Discussion Starter · #4 ·
new readings

Fuel System 1:
Open Loop

Fule System 2:
N/A

Load Value:
3.5%

Coolant Temp:
183 deg F

STFT - Bank 1:
-4.6%

LTFT - Bank 1:
0.0%

Manifold Pressure:
10.2 in.hg

Engine RPM:
1987 RPM

Speed:
42 MPH

Ignition Advance:
38.0 deg

MAF Air Flow Rate:
1.5 lb/min

Throttle Position:
1.5%

Bank1 - Sensor 1:
O2S Output 0.015V

Bank1 - Sensor 1:
STFT -4.6%

Bank1 -Sensor 2:
O2S Output 0.020V

Bank1 - Sensor2:
STFT 0.0%


Tell me what you think?
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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16,277 Posts
Do you have a way to get a "stream" of data? About 20-30 seconds of the same outputs?

This is light throttle cruising. ECM is still pulling fuel. But it's also in open loop learning. Did you clear the ECM? Mainly I would want to see streaming of the AF, O2, Temp and Trims. Since both sensors are showing lean in what you posted, a relationship cannot be established. As for vacuum, its still looks good.
 

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How new is the air intake filter and are there any cracks in the intake? Is the EVAP hose going over the fuel filter cracked?
 

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Discussion Starter · #9 ·
I checked the filter at the beginning of Jan. It was good and clean. There weren't any cracks that I saw.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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16,277 Posts
I cleared the ecu too. Why?
In the last set, the engine temperature was up but the system was still in open loop fuel. The ECM was "learning" it's fuel trim map.

What codes were on the ECM?

You don't have a vacuum leak. The computer is pulling fuel due to a Rich condition.

Clean the throttle body. Run down the tank of gas you have and put a bottle of Sea Foam in with a good gasoline; no Murphy stations or mom & pop gasolines. At the same time run Sea Foam through the intake to clean the carbon out of it and from the valves. Then, if they haven't been replaced prior, put a new set of plugs in.

If that doesn't correct it, then you can look at the front sensor or what that code(s) were.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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440=EVAP is not functioning proper or there is a leak in the EVAP circuit. Check the condition of your gas cap. If its iffy, replace with a Subaru cap. Otherwise, the system will need to be checked.

As for the stumble, try the previous suggestions I posted and see if it improves. Something is causing the rich condition in combustion or incomplete burn. It may also be a failed AF sensor that's sending improper data to the ECM.
 

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The intake is the air intake. Fuel is shot into the cylinder head via the injectors. No fuel in the intake manifold, only air and oil particulates from the PCV system.
 

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'99 Outback 2.5 GT auto & '97 LegOB w/ grossly insulted 2.5
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141 Posts
Seems,to me anyway, that the '99 MY has a preponderance of the fuel filler necks rusting through. That may cure your PO440, but listen to cardoc's counsel regarding the fuel trim issue.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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you could try this;

 

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2003 LL Bean 120k
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135 Posts
I am opening this back up, my H6 seems to stumble around until the RPM gets up in the higher end, then it starts pulling like a train, no CEL, have not had it on a scanner, new plugs, filters, 129k auto.

thanks Dar
 
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