93 400SEL Air Injection Pump question
 

Car: 93 400SEL (83K miles) When my car's Air Injection Pump is ON at cold start, it makes a "raking metal" sound. It is not loud by any means but it was troubling at first because I originally thought that the sound was coming from the timing chain. The sound eventually goes away after 2 minutes and the engine sounds fine afterwards.

Is the "raking" sound normal for the Air Injection Pump?


thx

Yes, it is pretty much normal. If you have a noise that persists once the pump shuts down then you have trouble.

You shouldn't hear the pump inside the car. It only works for the time you are hearing it so it is not exactly OK. I think you have a belt driven pump with a clutch similar to a AC compressor. Depending what your plans are, if it fails you might wish to investigate before it does.

With a 93 you probably don't have a diagnostic module so removing the belt will only affect emmisions. If it goes to failure the belt may take out others. If the clutch is the problem it can be replaced if done before total failure. If the solution is a rebuilt unit taking it to failure isn't a problem except for the risk with the belt.

Duxthe1 and Stevebfl, thanks for the quick replies. I only hear the noise when I have the hood up and standing right in front of the engine. The raking sound eventually goes away after the pump clutch disengages so I know it is still doing what it is designed to do. l definitely keep an eye (and ear) for anymore degradation of the pump. Thanks again for the help.

You can hear that pump on our 300E for a couple mins on startup too....sounds....like an air pump.....I think that sound is normal....

Thanks for all your help.