What is this? - PeachParts Mercedes-Benz Forum

markho · #1 10-28-2009, 06:37 PM

This is making a ticking/tapping noise and it seems to be associated with my tachometer.

When my tach reaches 10k rpm, the needle seems to get stuck, and then I hear a ticking noise from this unit under the hood (see attached). Its on the driver's side and attached to the inner fender wheel/well. The engine runs fine, and the tach eventually pops out of 10k rpm and bounces back to normal. What is this? How do I fix this?

DeliveryValve · #2 10-28-2009, 06:46 PM

It's a vacuum convertor. It supplies vacuum and atmospheric air to your EGR and transmission. Other than replacing it with a quieter unit, You can disconnect and plug the line to your EGR from it. But for the trans you'll need to rework vacuum lines if you choose to disconnect it.

Do a search there is a vacuum diagram here.

..

markho · #3 10-28-2009, 07:08 PM

Quote:

Originally Posted by DeliveryValve

It's a vacuum convertor. It supplies vacuum and atmospheric air to your EGR and transmission. Other than replacing it with a quieter unit, You can disconnect and plug the line to your EGR from it. But for the trans you'll need to rework vacuum lines if you choose to disconnect it.

Do a search there is a vacuum diagram here.

..

the only thing it seems to affect is the tach. My transmission shifts smoothly as before. Can I buy this part new? What your telling me sounds a bit complicated.

#4 10-28-2009, 07:15 PM

Are you sure that's where the noise is coming from, I don't see haw that would affect the tach. On the other hand, the tach amp is mounted on the fender a few inches away.

techguy512 · #5 10-28-2009, 07:19 PM

Quote:

Originally Posted by Craig

the tach amp is mounted on the fender a few inches away.

There is no tach amp in the '85s.

I imagine that when the engine hits 10K rpm, lots of things are ticking....like time bombs...

markho · #6 10-28-2009, 07:23 PM

Quote:

Originally Posted by Craig

Are you sure that's where the noise is coming from, I don't see haw that would affect the tach. On the other hand, the tach amp is mounted on the fender a few inches away.

yeah i'm pretty sure. I put my hand on it i can feel the ticking as I hear it.

#7 10-28-2009, 07:23 PM

Quote:

Originally Posted by techguy512

There is no tach amp in the '85s.

I imagine that when the engine hits 10K rpm, lots of things are ticking....like time bombs...

You're correct, I didn't notice we were talking about an '85. I still don't have a clue how a vacuum issue would affect the tach.

markho · #8 10-28-2009, 07:26 PM

anyone know the part number for this?

DeliveryValve · #9 10-28-2009, 07:31 PM

Quote:

Originally Posted by Craig

Are you sure that's where the noise is coming from, I don't see haw that would affect the tach. On the other hand, the tach amp is mounted on the fender a few inches away.

Actually if it did have a tach amp, it would be on the other side.

Quote:

Originally Posted by Craig

... I still don't have a clue how a vacuum issue would affect the tach.

The Vacuum converter (#84 on the diagram)is controlled by the EGR computer (#80 on the diagram). The EGR computer also controls the tach. Perhaps the EGR computer is getting a false reading from somewhere or perhaps it is malfunctioning or Possibly connection issues.

Try unplugging the power to the vacuum converter and see what happens.
.

#10 10-28-2009, 07:35 PM

Quote:

Originally Posted by DeliveryValve

Actually if it did have a tach amp, it would be on the other side.

The Vacuum converter is controlled by the EGR computer (#84 on the diagram). The EGR computer also controls the tach. Perhaps the EGR computer is getting a false reading from somewhere or perhaps it is malfunctioning or Possibly connection issues.
Try unplugging the power to the vacuum converter and see what happens.

My '82 W123 tach amp is on the left fender.

That makes sense if they are both connected to the same computer.