On my way home from work last night, while sitting at a red light, my engine suddenly started making a whine similar to a supercharger. The whine was accompanied by a noticeable alternator whine from my speakers. My radio was on (iPod input) but idle, e.g. my iPod was not playing. The alternator whine changes pitch with RPM but is not affected by volume (the alternator whine is the same volume whether the radio volume is at 0 or full blast) . I searched around the engine bay, the supercharger whine is very noticeable but the source isn't.

I can tell no difference in performance and everything that worked before continues to work. The serpentine belt is in good shape and tensioned properly, the alternator appears to be working correctly (volts range from 12.5-13.5 on the gauge), both the clutch fan and e-fan spin freely and are unimpeded. The only work done (recently) was replacing the ignition lock cylinder on the steering column. That was done last weekend, four days before the weird noises started.

 

There's a ground strap above the back of the valve cover going to the firewall that, if I've read correctly, is to eliminate radio noise from the engine. Might be worth checking to see if it's in good condition

 

Remove the belt and start rotating pulleys.

You've done all the ground refreshing, right?

 

Yes, grounds were done last year. I'll pull the belt and spin pulleys... it's got to be coming from somewhere.

 

I would suspect the alternator but, with the serpentine belt removed you can run the engine (for a max of two minutes) to see if the noise goes away. If it's still there check the crankshaft harmonic balancer condition and for rubbing on the timing chain cover. This is a very long shot but worth eliminating in your troubleshooting steps.

Before removing the belt, use that mechnic's stethoscope to touch the alternator body while the engine is running and see if it's the bad guy.

Also, touch the base of the distributor to see if it's running dry and making that noise. That bonding strap on the firewall is there to help in radio noise suppression. Sources of noise are the distributor, spark plug wires, alternator, and even from the distributor rotor tip.

 

Thanks Ken, that's really valuable information. I pulled the serp belt and all pulleys are smooth as butter. I will for sure get a stethoscope on the distributor.

I noticed some bare wires in the harness that runs under the exhaust manifold (from injector harness). I pulled that part of the harness to re-wrap/re-loom and in the process, broke the tip off the sensor that bolts into the middle of the block just above the oil pan (manifold side). Any idea what that is? It's not identified in my Haynes. I thought I'd ask here before starting a new thread.

 

I'm not a Renuts expert but I think that's a Knock Sensor.

 

Coolio. Word on the Interwebs suggest it's not necessary or, at least, not critical. I'm thinking about epoxying the whole thing back together and sticking it back in. Just the shell is broken/cracked. Cruiser? Thoughts?

 

Hey! Mechanic's stethoscopes are fun! I think I've narrowed the whine down to my alternator. It feels fine if I spin it by hand but my stethoscope definitely says the alternator is whining.

On the plus side, my stethoscope says everything else is purring like a happy kitten. Thanks again for your help Ken and Cruiser.