RPM related clicking - tachometer cable? - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 03-21-2012, 03:14 PM Thread Starter
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RPM related clicking - tachometer cable?

I'm getting a clicking sound that can be heard best at idle, inside the cockpit with the roof up.

I thought it was a pulley bearing but I've changed out all I could on the front of the engine--supercharger, idler, tensioner, and AC. My car has 80k miles so I'm glad I did it for preventative maintenance, but the clicking is still there and driving me crazy.

It's most noticeable at idle with the car in neutral. Sometimes turning the AC on lessens or stops it. Sometimes turning the AC OFF does the same thing. So, I figured it was the AC bearing, but I just changed that and the sound persists.

It's usually there, but not always. Sometimes the clicking is completely gone, but that's rare.

I can't really hear it in the engine compartment with the hood up. But inside the car it seems to be coming from in the dash or near the firewall.

I'm thinking maybe the AC clutch itself, or maybe a sticking tachometer cable.

Do the R170 and/or Slk32 use conventional type analog tach cables? Or is the tack electronically controlled?

Anyone ever have a noisy tachometer cable?
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post #2 of 8 (permalink) Old 03-21-2012, 03:20 PM
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SLK uses CAN bus electronics to do the tach signal. no mechanical wire

- ASP pulley kit
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post #3 of 8 (permalink) Old 03-21-2012, 03:31 PM
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Are you sure it isn't the purge valve? It's marked MOT off to the side of the engine and cycles to process gas vapor from the tank/evap canister.




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post #4 of 8 (permalink) Old 03-21-2012, 03:45 PM Thread Starter
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Quote:
Originally Posted by Subby_ View Post
SLK uses CAN bus electronics to do the tach signal. no mechanical wire
Ok, so much for that idea--unless it's the tach itself. Thanks Subby!



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Are you sure it isn't the purge valve? It's marked MOT off to the side of the engine and cycles to process gas vapor from the tank/evap canister.
No, not sure, but that's a good thought. I'll check, thanks!


I appreciate all suggestions.
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post #5 of 8 (permalink) Old 03-21-2012, 03:51 PM Thread Starter
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Noisy injector?

Any experience with injectors getting noisy?

Do they sometimes make an audible click or clack kinda sound when they go bad?
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post #6 of 8 (permalink) Old 03-21-2012, 04:24 PM
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Originally Posted by brusby View Post
Any experience with injectors getting noisy?

Do they sometimes make an audible click or clack kinda sound when they go bad?
They're electronic, so I can't imagine them making noise. I have not heard of it either.

Another idea is to pick up a mechanic's stethoscope and use it to isolate the noise. They are cheap and very easy to use, obviously be careful around the front of the engine and be sure to let go and turn away quickly if the probe gets yanked by the belt.




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post #7 of 8 (permalink) Old 03-27-2012, 12:29 AM Thread Starter
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Found it

Of course, it would be the bearing in the very last pulley I changed that was causing the problem.

After swapping out the supercharger bearing, 2 idler pulleys and bearings, and the A/C bearing, I finally changed the tensioner pulley and bearing, and that stopped the clicking. Strangely I couldn't hear it with a stethoscope placed directly on the pulley nut.

This engine is inherently kinda noisy, but now it's a good noise and it sounds appropriate for such a powerful beast.

At 80k miles, I'm really glad I changed all these things. The SC bearing was getting pretty raunchy and raspy sounding and one of the idler pulleys was also obviously developing problems. All in all, the bearing and pulleys were pretty inexpensive. I changed 'em all for what it probably would have cost to have the dealer change just one.

A lot of that inappropriate, trashy sound is gone and now it's a real delight to drive this great car again.
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post #8 of 8 (permalink) Old 06-15-2013, 12:53 PM
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Funny I'm getting the same ticking, I thought it was the heater blower motor (which makes the same sound in my w210) but it wasn't. Same thing: can hear it when roof up inside pass. compartment, but not

How does one go about checking the pulley bearings for wear? Play? Or just noise? At 37k miles should I even worry? Harbor Frieght just opened a store nearby - I'm going to head up there to grab a $2.99 stethoscope just to have one at hand ... I've got to figure out which of my cats is rattling in by w210 anyway ...
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