Engine stumble/hesitation around 2500 RPM?
#721
07-18-2023 | 02:59 PM
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I was trying to eliminate the air cleaner or the tuning flap change-over values as a cause.....especially considering all the COV related issues mentioned on the forums plus I am seeing lumpiness on the graph for air flow (could be throttle body though..)
Last edited by Sajan; 07-18-2023 at 04:47 PM.
#722
07-29-2023 | 07:09 PM
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@Bruce in Philly
I am going to change out the camshaft adjustment solenoids to see if they make a different. my testing with a piwis has lead me to this path..
will let you know next week what happens.
these solenoids are part of the varicam triad...
I am going to change out the camshaft adjustment solenoids to see if they make a different. my testing with a piwis has lead me to this path..
will let you know next week what happens.
these solenoids are part of the varicam triad...
- Camshaft Actuator - 9A1-105-304-05
- VarioCam Lift Valve Solenoid (VVS) - 9A1-105-308-03
- Hall sensor / camshaft position sensor / variocam sensor - 997-606-106-03
#724
08-05-2023 | 10:19 AM
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No bueno... didn't solve it but now I feel like it's more obvious..
Will start with the next cheapest item from the triad lol..which is the position sensors. Browsed through the thread and didn't see anyone mentioning replacing those.
Will start with the next cheapest item from the triad lol..which is the position sensors. Browsed through the thread and didn't see anyone mentioning replacing those.
#727
06-10-2024 | 11:34 AM
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reposting what I posted there:
well. I ordered a oil cap because I needed to drill a hole in the current one to measure the crankcase pressure...to test out the AOS.
I discovered my current oil cap is missing an o-ring! I could hear a little leak near the cap and when I held the cap tight, it stopped.
With the new oil cap (no sound/leaks), the car seemed to idle a little better when warm. Will report back in a few days after further observation.
Now here's the main point: I got a reading of -12inH2O.
According to LN engineering, the correct reading is
so the car is driving A LOT better. the low end torque is there (and it pulls!) and the stumbles are less prominent or non-existent. I will occasionally feel it, ever so lightly but not enough for me to care.
I would even say if I didn't spend months chasing this down and had just gotten this car, I wouldn't even think there's anything "wrong".
So maybe the low crankcase pressure was the issue? My theory is that these are transition points in the variocam tech and less than ideal readings/sensor data/pressure values make them more obvious. after all, look at precise nature of these engines..
the crankcase pressure is affected by higher altitudes which probably explains why the stumble was gone when I was in the mountains..
well. I ordered a oil cap because I needed to drill a hole in the current one to measure the crankcase pressure...to test out the AOS.
I discovered my current oil cap is missing an o-ring! I could hear a little leak near the cap and when I held the cap tight, it stopped.
With the new oil cap (no sound/leaks), the car seemed to idle a little better when warm. Will report back in a few days after further observation.
Now here's the main point: I got a reading of -12inH2O.
According to LN engineering, the correct reading is
- MA1 Nominal crankcase vacuum is -15.0” (-14.0” to -16.0”) of H2O (not HG).
so the car is driving A LOT better. the low end torque is there (and it pulls!) and the stumbles are less prominent or non-existent. I will occasionally feel it, ever so lightly but not enough for me to care.
I would even say if I didn't spend months chasing this down and had just gotten this car, I wouldn't even think there's anything "wrong".
So maybe the low crankcase pressure was the issue? My theory is that these are transition points in the variocam tech and less than ideal readings/sensor data/pressure values make them more obvious. after all, look at precise nature of these engines..
the crankcase pressure is affected by higher altitudes which probably explains why the stumble was gone when I was in the mountains..
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