[BogdanBxl]

Tachometer pop up at my W124 300D when I turn the key and goes to 7000 rpm and turns back slowly to 2000 rpm and stay there - when I continue to turn the key to start engine and after engine starts the tachometer indicates corect the rpm during all the period when engine is functioning. After I stop the engine the tachometer goes normally back to zero. The pop up issue is only when I turn the key and goes out when engine starts.
Any ideea why this is happening this when normally the tachometer should stay at zero when the key turns and only to go up when the engine starts to function?
Thank you in advance for your replies!

 

[ianrandom]

Tachometer pop up at my W124 300D when I turn the key and goes to 7000 rpm and turns back slowly to 2000 rpm and stay there - when I continue to turn the key to start engine and after engine starts the tachometer indicates corect the rpm during all the period when engine is functioning. After I stop the engine the tachometer goes normally back to zero. The pop up issue is only when I turn the key and goes out when engine starts.
Any ideea why this is happening this when normally the tachometer should stay at zero when the key turns and only to go up when the engine starts to function?
Thank you in advance for your replies!

Welcome! Can I recommend putting your car details (model and year are helpful) into your profile for us please?

Complete your Profile

Click on ACCOUNT SETTINGS, and scroll down to 'Vehicle Details' , and Location, then click 'Save' on bottom. At least a State would be good, and will show when a member hovers his cursor (arrow) over the flag next to your post.

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[BogdanBxl]

Welcome! Can I recommend putting your car details (model and year are helpful) into your profile for us please?

Complete your Profile

Click on ACCOUNT SETTINGS, and scroll down to 'Vehicle Details' , and Location, then click 'Save' on bottom. At least a State would be good, and will show when a member hovers his cursor (arrow) over the flag next to your post.

www.benzworld.org

Done!

 

[ianrandom]

Thanks! I can't help on your tach problem, not familiar with the diesels. But I'm sure someone will know.

 

[Floobydust]

Since a diesel engine have no ignition system, the electronic diesel system synthesizes a tach signal from a CPS on the flywheel. There could be an issues with this system, but since you get the correct RPM reading while running, I would suspect and issue with the tachometer itself.

 

[BogdanBxl]

Since a diesel engine have no ignition system, the electronic diesel system synthesizes a tach signal from a CPS on the flywheel. There could be an issues with this system, but since you get the correct RPM reading while running, I would suspect and issue with the tachometer itself.

Tks. I still wait for more ideas on this matter. Best

 

[Floobydust]

There is a simple test for this. Pull or the OPV relay or Fuse 7 and turn the key on. If the tach still swings to 7K, etc. then the issue is in the tach. If not, it is with the EDS or possbily the Klima relay.

 

[BogdanBxl]

There is a simple test for this. Pull or the OPV relay or Fuse 7 and turn the key on. If the tach still swings to 7K, etc. then the issue is in the tach. If not, it is with the EDS or possbily the Klima relay.

OPV I know where it is - Fuse 7 is the one in the fuse box or the one on the top of the OVP? Where is located and what is EDS? Klima relay where is located? I will try this when I will search and find their location. Thank you very much for your suggestion which I hope will clarify my problem.🙏

 

[Floobydust]

EDS = Electronic Diesel System (I'm not sure of the location)
Klima - your A/C control relay, located behind the battery.
Fuse 7 is in the main fuse box near the master brake booster.

Also, check/replace Fuse 5 as this powers the tach.