need some diagnostic help: MAF vs 02 sensor
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AudiWorld Super User
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need some diagnostic help: MAF vs 02 sensor
<i>This isn't actually about my TT, but my daughter's '00 A4 1.8t has started acting up and a lot of ppl on this board are knowledgeable about these things...</i>
Symptoms: at higher rpm's, her engine will run stumble, run roughly, lose power, and may -or may not- turn on the CEL momentarily. There appears to be no symptoms when the engine is cold and therefore running on the built-in default ECU maps.
Befor testing it, I scanned it with my ProDiag and found these faults.
17522 P1114 163
Bank 1 - Sensor 2: internal resistance too large [Sporadic]
16795 P0411 163
Secondary Air Injection System: Incorrect FLow Detected [Sporadic]
After the car warmed up, I made a full throttle run in 2nd gear. While data graphing and logging, I noticed the air mass reading climb up to about 120 g/s at 5000 rpm <i>(which is as high as it should get in her unmodded 150hp 1.8t),</i> then abruptly drop to 65 g/s, then up to 213 g/s... then dropping and fluctuating from 70 g/s down to 7 g/s... all in 5 secs, before I lifted off the throttle. During these readings the car ran very roughly with no power. The check engine light binked erratically for a few seconds afterwards, then things settled down and I was able to drive home gently without other symptoms...
A scan following this run added the following fault codes:
16486 P0102 163
Mass Air Flow Circuit -G70: Low Input [Sporadic]
16684 P0300 035
Random/Multiple Cylinder: Misfire Detected
16688 P0304 035
Cylinder 4: Misfire Detected
16686 P0302 035
Cylinder 2: Misfire Detected
<b>So, what's the diagnosis?</b> Bad MAF? Could this be linked to the original sporadic 02 sensor problem?
TIA, ~john
<i>PS: sorry about the cross-post in the A4 forum, but I know you guys and I don't know them! </i>
Symptoms: at higher rpm's, her engine will run stumble, run roughly, lose power, and may -or may not- turn on the CEL momentarily. There appears to be no symptoms when the engine is cold and therefore running on the built-in default ECU maps.
Befor testing it, I scanned it with my ProDiag and found these faults.
17522 P1114 163
Bank 1 - Sensor 2: internal resistance too large [Sporadic]
16795 P0411 163
Secondary Air Injection System: Incorrect FLow Detected [Sporadic]
After the car warmed up, I made a full throttle run in 2nd gear. While data graphing and logging, I noticed the air mass reading climb up to about 120 g/s at 5000 rpm <i>(which is as high as it should get in her unmodded 150hp 1.8t),</i> then abruptly drop to 65 g/s, then up to 213 g/s... then dropping and fluctuating from 70 g/s down to 7 g/s... all in 5 secs, before I lifted off the throttle. During these readings the car ran very roughly with no power. The check engine light binked erratically for a few seconds afterwards, then things settled down and I was able to drive home gently without other symptoms...
A scan following this run added the following fault codes:
16486 P0102 163
Mass Air Flow Circuit -G70: Low Input [Sporadic]
16684 P0300 035
Random/Multiple Cylinder: Misfire Detected
16688 P0304 035
Cylinder 4: Misfire Detected
16686 P0302 035
Cylinder 2: Misfire Detected
<b>So, what's the diagnosis?</b> Bad MAF? Could this be linked to the original sporadic 02 sensor problem?
TIA, ~john
<i>PS: sorry about the cross-post in the A4 forum, but I know you guys and I don't know them! </i>
AudiWorld Super User
Joined: Mar 2000
Posts: 13,200
Likes: 2
how are your plugs? I think the MAF wacky readings are a result of backfire or reverse flow..
If you can see the MAF read fairly linearly before it stumbled, there's a good change it is ok.
The 2nd O2 maybe confusing the ECU, but I am not sure how because it is usually just a monitor for cat performance. Check to make sure it didn't come unplugged. I doubt it is causing this problem.
How I would attack this is suspect misfire from plugs.
Then intake leak (like BPV, IC, any hose)
then MAF.
If the plugs are good, the misfire could be due to running lean, which could then point to intake leaks or MAF
The 2nd O2 maybe confusing the ECU, but I am not sure how because it is usually just a monitor for cat performance. Check to make sure it didn't come unplugged. I doubt it is causing this problem.
How I would attack this is suspect misfire from plugs.
Then intake leak (like BPV, IC, any hose)
then MAF.
If the plugs are good, the misfire could be due to running lean, which could then point to intake leaks or MAF
AudiWorld Super User
Joined: Mar 2002
Posts: 2,082
Likes: 0
or, the ever popular coil pacs!!
I don't know if the 2000 A4 even HAS coil pacs... but your description is very familiar. Mine crapped out at 90k with similar symptoms.
All four were replaced with the latest revision codes, purchased from the local VDub dealer. Now, one of those just crapped out after 17k miles of use! No spark at all...
I did learn something though!! a "coil pack" is a coil that serves more than 1 cylinder, typically 2. A V6 will have 3 coils, 2 cylinders per... So a "pack" is a group of three centrally located coils, and uses traditional plug wires to carry the spark to the plugs.
The "PC" term for our gizmos is "coil on plug"...
yeah!! I know.. I know.. that and 5 bucks will get you a cup of coffee...
All four were replaced with the latest revision codes, purchased from the local VDub dealer. Now, one of those just crapped out after 17k miles of use! No spark at all...
I did learn something though!! a "coil pack" is a coil that serves more than 1 cylinder, typically 2. A V6 will have 3 coils, 2 cylinders per... So a "pack" is a group of three centrally located coils, and uses traditional plug wires to carry the spark to the plugs.
The "PC" term for our gizmos is "coil on plug"...
yeah!! I know.. I know.. that and 5 bucks will get you a cup of coffee...
AudiWorld Newcomer
Joined: Apr 2011
Posts: 1
Likes: 0
<i>This isn't actually about my TT, but my daughter's '00 A4 1.8t has started acting up and a lot of ppl on this board are knowledgeable about these things...</i>
Symptoms: at higher rpm's, her engine will run stumble, run roughly, lose power, and may -or may not- turn on the CEL momentarily. There appears to be no symptoms when the engine is cold and therefore running on the built-in default ECU maps.
Befor testing it, I scanned it with my ProDiag and found these faults.
17522 P1114 163
Bank 1 - Sensor 2: internal resistance too large [Sporadic]
16795 P0411 163
Secondary Air Injection System: Incorrect FLow Detected [Sporadic]
After the car warmed up, I made a full throttle run in 2nd gear. While data graphing and logging, I noticed the air mass reading climb up to about 120 g/s at 5000 rpm <i>(which is as high as it should get in her unmodded 150hp 1.8t),</i> then abruptly drop to 65 g/s, then up to 213 g/s... then dropping and fluctuating from 70 g/s down to 7 g/s... all in 5 secs, before I lifted off the throttle. During these readings the car ran very roughly with no power. The check engine light binked erratically for a few seconds afterwards, then things settled down and I was able to drive home gently without other symptoms...
A scan following this run added the following fault codes:
16486 P0102 163
Mass Air Flow Circuit -G70: Low Input [Sporadic]
16684 P0300 035
Random/Multiple Cylinder: Misfire Detected
16688 P0304 035
Cylinder 4: Misfire Detected
16686 P0302 035
Cylinder 2: Misfire Detected
<b>So, what's the diagnosis?</b> Bad MAF? Could this be linked to the original sporadic 02 sensor problem?
TIA, ~john
<i>PS: sorry about the cross-post in the A4 forum, but I know you guys and I don't know them! </i>
Symptoms: at higher rpm's, her engine will run stumble, run roughly, lose power, and may -or may not- turn on the CEL momentarily. There appears to be no symptoms when the engine is cold and therefore running on the built-in default ECU maps.
Befor testing it, I scanned it with my ProDiag and found these faults.
17522 P1114 163
Bank 1 - Sensor 2: internal resistance too large [Sporadic]
16795 P0411 163
Secondary Air Injection System: Incorrect FLow Detected [Sporadic]
After the car warmed up, I made a full throttle run in 2nd gear. While data graphing and logging, I noticed the air mass reading climb up to about 120 g/s at 5000 rpm <i>(which is as high as it should get in her unmodded 150hp 1.8t),</i> then abruptly drop to 65 g/s, then up to 213 g/s... then dropping and fluctuating from 70 g/s down to 7 g/s... all in 5 secs, before I lifted off the throttle. During these readings the car ran very roughly with no power. The check engine light binked erratically for a few seconds afterwards, then things settled down and I was able to drive home gently without other symptoms...
A scan following this run added the following fault codes:
16486 P0102 163
Mass Air Flow Circuit -G70: Low Input [Sporadic]
16684 P0300 035
Random/Multiple Cylinder: Misfire Detected
16688 P0304 035
Cylinder 4: Misfire Detected
16686 P0302 035
Cylinder 2: Misfire Detected
<b>So, what's the diagnosis?</b> Bad MAF? Could this be linked to the original sporadic 02 sensor problem?
TIA, ~john
<i>PS: sorry about the cross-post in the A4 forum, but I know you guys and I don't know them! </i>
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