My '87 300 SDL is doing a very strange thing. When I first start it, for the first few to several minutes, the tachometer doesn't register and the the "Antilock" warning light is on. While it's doing this, it seems to be running fine. After a little bit, the engine will make a noise like one cylinder missed, then the tach will work and the anitlock light goes off. After that the car again runs fine.

Anybody have any idea what might be going on here? I'm not even sure where to start. Thanks.

Put a volt meter across the battery with the engine off. Start the engine and record the voltage while it goes through this cycle. Please post the voltages.

Check your OVP relay then test the ELR system.

Look for a link to the w124 maintenance manual - you will find a procedure there.

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This is a classic example of a failing OVP. The only valid test is to replace with a new OVP.

Test or cure?

Both.

Nobody diagnoses these little relay assemblies, if it is malfunctioning (as it appears to be), replace it.

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Gone to the dark side

- Jeff

Over the years my SDL had same. Also AC may cut out.

I've also found that new aftermarket OVP can also be bad out of the box.

So if you try a new one and you have the same symptoms, try another OVP.

I keep a spare OVP in the glove box now primarily because a bad one can cut the AC out...and I often travel the desert south west in summer.

Weird part is temperatures (engine bay) seem to affect the OVP failure. Or Partial failure i.e. tach ok but idle will jump around, or idle ok but no tach.

Also check the fuse box (maybe #17) & fuse contacts. Check the reference sheet under the fuse box lid. On occasion gets corroded and cuts the tach out.

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1986 300SDL 440,xxx

I had a feeling somebody would say that this is "a classic example of" something. Thank you. I'll replace the OVP and we'll see what happens.

How about, if alternator voltage is indeed going high and the OVP is doing it's job?

Check the battery voltage as I described in post 2.