I did a plug swap a few days ago (factory plugs had 115,000 miles on them) and the car really pepped up (go figure right…). Well ever since then, I have noticed that at around 3500RPM there is a very abrupt “surge” in power at 3500RPM under mid-throttle condition.
With the M54 engine having an adaptive manifold (DISA valve), I began wondering if that is what I’m feeling (the vane switching from short to long setting). So I read about the DISA valve going out, went ahead and pulled the unit, and found the vain flapping around free (the hex spline was entirely worn off). So with that in mind, there is no way it want being "controlled" at all. I pulled the vain out (would need to rebuild it anyways) and installed the unit (less vain), then went for a drive. I did not notice any lost of low end torque but did notice a good bit more top end. My guess is the vain was in a semi-open state thus not building torque but hampering high RPM airflow.
However, I'm still getting that hard "surge/spike" in power at about 3700 RPM. It's very abrupt but only shows up under mid-throttle. So what to look at next? With the M54 having variable cams, when do they kick in? Do they go to full advance under WOT condition (thus why I don't feel a "surge/spike" WOT)?
I really hate this as it makes smooth application of power in a corner impossible.
With the M54 engine having an adaptive manifold (DISA valve), I began wondering if that is what I’m feeling (the vane switching from short to long setting). So I read about the DISA valve going out, went ahead and pulled the unit, and found the vain flapping around free (the hex spline was entirely worn off). So with that in mind, there is no way it want being "controlled" at all. I pulled the vain out (would need to rebuild it anyways) and installed the unit (less vain), then went for a drive. I did not notice any lost of low end torque but did notice a good bit more top end. My guess is the vain was in a semi-open state thus not building torque but hampering high RPM airflow.
However, I'm still getting that hard "surge/spike" in power at about 3700 RPM. It's very abrupt but only shows up under mid-throttle. So what to look at next? With the M54 having variable cams, when do they kick in? Do they go to full advance under WOT condition (thus why I don't feel a "surge/spike" WOT)?
I really hate this as it makes smooth application of power in a corner impossible.