Diagnosing Problems


How they work          diagnosing problems          porting and polishing          rebuilding nosedrives          Swaps and upgrades          Adding a boost gauge         

replacing needle bearings     adding a nosedrive drain          supercharger oil change          pulley size suggestions          links, references, and sources


Diagnosing problems with superchargers usually puts you into one of two categories.  A mechanical noise, or not enough boost indicated on the gauge.  Let's break them out and deal with them seperately:

NOISES

A rattling noise at idle is almost always a worn supercharger coupler inside the nosedrive.  Refer to How they work  for a description of it's function and purpose.  The noise comes from the 6 holes in the coupler being worn into more of an oval shape than round.  Don't confuse this noise for a noise from the harmonic balancer (dampener).  The balancer makes more of a loud clattering noise at idle.  To determine if the rattling noise at idle is your problem, remove the supercharger belt (by releasing the belt tensioner) and rapidly turning the supercharger coupler back and forth rapidly by hand (back and forth in the direction the belt normally spins the pulley).  If you 'feel' any slop or movement without feeling the immediate resistance of the weight of the rotors spinning, your coupler is worn and should be replaced.  Generally, if you notice the problem is just beginning, it's not critical that you replace it right away, but plan on it soon.  Refer to rebuilding nosedrives  for procedures on changing the coupler yourself.  This is a good time to totally rebuild your nosedrive if you feel you're up to it, but isn't always necessary unless you have bearing related problems also (great preventive maintenance, I suggest a nosedrive rebuild if you're changing the coupler).  For M62's, you'll need to remove the entire supercharger from the car.  M90's can pull the nosedrive without removing the supercharger.

In these pictures, you'll see the good coupler (left) and worn coupler (right).  If you look closely, you'll s that the holes are oval on the worn coupler, in the direction of rotation:

 

Grinding or excessive whining noises are generally a bearing issue (or your kids in the back seat).  Sometimes this can be caused by the wrong lubricant, so make sure you ONLY use GM Supercharger Oil or another supplier's oil that is the exact same content.  Use a mechanic's stethoscope to determine where the noise is coming from.  Keep in mind that some whine from the supercharger is normal due to the straight-cut gears in the nosedrive.  This can become more prominent after changing to a smaller pulley or building a custom air intake.  The supercharger or something nearby?  Refer to Google for a typical warnings.  Try a Google search on "how not to get your stethoscope tangled in the belts of a running engine".  If the grinding or whining does seem to be coming from the supercharger, you'll need to remove the belt to diagnose further.  After removing the belt, gently and slowly turn the pulley by hand, feeling for any roughness or grinding.  Also move the pulley in and out if you can (as if you were trying to pull the pulley off the shaft or push it back on).  Any slop or play in this direction is another indicator of bearing problems.  If you find any bearing failure indicators with these tests, plan on either getting a rebuilt nosedrive/supercharger or rebuilding it yourself.  Even if you're sure it's only the nosedrive bearings, it's a good idea to go ahead and replace the needle bearings in the supercharger itself also.

 

LOW BOOST ISSUES

The greatest tool you have for identifying low boost issues is your boost gauge.  If your car didn't come with a boost gauge, or if you don't trust it, you can add one.  Most owners have a good idea of what boost levels to expect in certain situations, and when that drops, the wondering begins.  Different factors can affect this.  Temperature, atmospheric pressure (altitude), vacuum/boost leaks, etc.  In a nutshell, low boost issues CANNOT be caused by the supercharger itself unless there is a catastrophic failure that should be very obvious.   95% of the time, it's an issue with either the BCS (boost control solenoid) or BCA (boost control actuator):

M90 Gen3 BCA/BCS.BCA in yellow, BCS in blue.

M62 Gen3 BCA/BCS.BCA in yellow, BCS in blue.

 

If these are determined to be working properly, the most likely issue is a problem with your boost gauge.  Either the MAP sensor or a vacuum line.  The first thing to test is the BCA (boost control actuator).  It should move quickly, smoothly, and full travel from retract to extend.  Open the hood, and remove the engine cover or supercharger cover (depending on series).  Start the car and leave it to idle.  Locate the BCA and verify that the arm is fully retracted, forcing boost bypass.  Remove the top vacuum line and verify that the arm fully extends until it touches the stop on the base flange of the supercharger.  Do this several times:

VIDEO

If you determine your BCA is not travelling fully, check to make sure you have good vacuum and no leaks at the lower fitting.  Consider putting some light oil like 3in1 in the two vacuum ports and on the shaft (actuator) seal, and manually actuate it in and out to re-lubricate the insides of the actuator.  This may free it up.  Also check to be sure the bypass valve shaft on the supercharger moves freely by hand with the BCA removed.  It can be difficult, but this can be lubricated on the car by oiling the bypass shaft.  You can only do this on the end facing the front of the motor.  If the bypass still feels sticky to you, it may require removing the supercharger to clean and lubricate it.

 

The next thing to check is the BCS (boost control solenoid).  It'll be easier to check if you remove it from the BCA.  Disconnect the electrical connector and remove the bolt(s).  Once it's in your hand, use an Ohm Meter to check the resistance across the two pins.  I've seen BCS readings vary from 500K ohms to 1.5M ohms.  Anything in that range is good.  If you get infinite resistance or a dead short (0 ohms), you'll need a new solenoid.  These don't fail often, so getting one from a wrecker is a good option.

If you suspect vacuum leaks at a vacuum line, or possible vacuum leaks in the BCA or BCS, or even around the vacuum ports or the base of the supercharger, you can find  them easily by using carburetor cleaner (never use this on sensors).  Start the car and let it idle down to normal warm idle.  Gently spray carb cleaner on each fitting, hose, tube, around the base of the supercharger, and on the BCS and BCA.  If there is a leak, it will draw the carb cleaner into the combustion chambers, and you'll hear your idle RPM's rise.

 

 


How they work          diagnosing problems          porting and polishing          rebuilding nosedrives          Swaps and upgrades          Adding a boost gauge         

replacing needle bearings     adding a nosedrive drain          supercharger oil change          pulley size suggestions          links, references, and sources


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