Intermittent problem: Tach dies and idle drops, gets rough. - Page 3 - PeachParts Mercedes-Benz Forum

hcciv003 · #31 07-02-2008, 02:25 PM

Got the ovp from a dealer. Installed yesterday and the problems fixed. ('95 E300D)

Jhoulihan · #32 07-04-2008, 07:16 PM

I have a 1993 300D with the same symptoms...ABS light On, no Tach and no A/C. I tried cleaning all the contacts on the OVP relay and while the problem got better, it was not cured. Today I peeled away the aluminum casing of the relay and resoldered all the connections. I wrapped the whole relay with electrical tape to keep the moisture out and plugged it back in. So far it looks like it worked. I also scraped down the fuse contacts on the inside and they did have quite a bit of corrosion on them.

Finster · #33 07-26-2008, 09:27 AM

I have a 87 300D with the same tach and ABS problem. Tach stops working ABS light comes on, idle speed drops and it's rough to start. The manual says if the ABS light comes on, but the brakes work, it's the alternator not putting out the required voltage. A voltage check confirmed this. 14.2v when everything is jake and 13.5v to 13.7 when tach stops and ABS light is on? Any thoughts on the voltage regulator or alternator being the culprit?

babymog · #34 07-26-2008, 09:51 AM

Voltage is fine. Most likely culprit and the common denominator is the OVP / Overvoltage Protection relay.

Jhoulihan · #35 07-26-2008, 10:43 AM

Just a followup....it's a few weeks later and I seem to have fixed the OVP relay by resoldering it. I wasn't able to figure out how to remove the aluminum cover so I just peeled it off, resoldered everything and then taped it all back up with heavy electrical tape.

gsxr · #36 07-27-2008, 10:21 PM

Quote:

Originally Posted by Finster

I have a 87 300D with the same tach and ABS problem. Tach stops working ABS light comes on, idle speed drops and it's rough to start. The manual says if the ABS light comes on, but the brakes work, it's the alternator not putting out the required voltage. A voltage check confirmed this. 14.2v when everything is jake and 13.5v to 13.7 when tach stops and ABS light is on? Any thoughts on the voltage regulator or alternator being the culprit?

Finster, it's the OVP. If the regulator was kaput, you'd either get no charging, or voltage in the 15-17 range.

TheDon · #37 09-18-2013, 01:49 PM

I'm going to be a thread digger but this seems to be the definitive OVP thread.

Sister texted me: RPM gauge is dead and the car is shaking when I stop at lights.

Soooo, no tach and a low idle. Must be the OVP. Haven't heard back if she gets an ABS light. But I am picking up a new OVP on the way home from work and will swap it out.

Update: no ABS light. I find it weird that the rpm sensor would die randomly. The tach is intermittent apparently. Ill replace the OVP anyways since its probably old.