Does the OVP Affect Charging? - PeachParts Mercedes-Benz Forum

DieselPaul · #1 12-13-2013, 06:27 PM

Does the OVP affect charging? On the 92 300D the battery was dead because the dome light got left on. Jumped it, it was idling very low, AC wouldn't come on, and the tach was dead.

Drove it around for 15 minutes, idling smoother but still low, tach was still dead.

ABS was working, blower fan was working but acting strange. I did not have a spare OVP on hand so I didn't try swapping them.

My dad called me a few hours later he went to restart it to move it and the battery was flat again.

No tach, low idle, etc I thought were OVP symptoms, but the dead battery says bad alternator to me.

Any thoughts?

zorecati · #2 12-13-2013, 06:44 PM

Quote:

Originally Posted by DieselPaul

Does the OVP affect charging? On the 92 300D the battery was dead because the dome light got left on. Jumped it, it was idling very low, AC wouldn't come on, and the tach was dead.

Drove it around for 15 minutes, idling smoother but still low, tach was still dead.

ABS was working, blower fan was working but acting strange. I did not have a spare OVP on hand so I didn't try swapping them.

My dad called me a few hours later he went to restart it to move it and the battery was flat again.

No tach, low idle, etc I thought were OVP symptoms, but the dead battery says bad alternator to me.

Any thoughts?

I can only comment on my 87. OVP doesn't effect charging on my car.

Jeremy5848 · #3 12-13-2013, 06:56 PM

OVP should have nothing to do with charging unless the fuse is bypassed and the internal Zener diode has shorted. In that case you will have a permanent short-circuit across the battery whenever the ignition is on and charging will be weak if not impossible. I see this as a very unlikely possibility; there are many other things to check first.

Jeremy

JamesDean · #4 12-14-2013, 02:49 PM

Yep sounds like dead alternator or low output voltage to me.

I would put a meter across the battery and see what you've got. Then start it up and see what the alternator is putting out. Rev the engine a bit and see where the voltage goes.

If you're going to end up replacing the alternator I strongly recommend upgrading to one of the higher amperage units. 143 or 150A.

sixto · #5 12-14-2013, 04:31 PM

Might be just worn brushes in the voltage regulator.

Sixto
87 300D

DieselPaul · #6 12-14-2013, 10:58 PM

I've got a new in the box Bosch voltage regulator hanging around so I'll try that.

The car is 100 miles away from me in Cincinnati at my dads house so I haven't done any more diagnostic work. Ill mess with it next time I am down there.

DieselPaul · #7 12-21-2013, 10:11 AM

Put in a known good regulator, no change. Car idles at 13.7-13.9 volts, bring it off idle and it holds solid at 14.0. Edit been letting the car idle while I do some googling and it is now idling at 13.9-14.1.

Used OVP, no change. I can't find anyone locally that sells OVPs so Ill probably have to order one online.

Edit realized my correctly functioning 88 190D has the same style ovp, swapped relays, no change.

DieselPaul · #8 12-21-2013, 10:57 AM

Found this
Crank speed sensor - '93 300TD [Archive] - Mercedes-Benz Owners' Forums

Put a multimeter on the two pins to measure resistance and got no resistance.

AC compressor doesn't come on which also makes me think crank sensor because doesn't the Klima compare the crank speed to the AC compressor speed and decouple the clutch if they are spinning at different rates.

Jeremy5848 · #9 12-21-2013, 11:08 AM

Klima does look at the crank sensor so that is a possibility. The sensor itself is just an electromagnet "running backwards." It is unlikely to fail but the wiring from it (down under the engine somewhere) is worth suspecting. That would explain the tach and the compressor but your charging issue may be a completely separate problem.

DieselPaul · #10 12-21-2013, 11:53 AM

I don't think I'm having a charging issue. I think my dad left the dome light on.

Jeremy5848 · #11 12-21-2013, 03:02 PM

I'm not sure Klima looks at the compressor speed--that may be a separate device. There were changes over the years. In any case, Klima has several inputs and must be happy with all of them or it won't allow the compressor's clutch to engage.

DieselPaul · #12 12-21-2013, 03:12 PM

My concern is the low idle and dead tach, my thought was the AC not coming on is another thing pointing towards the speed sensor.

Bio240D · #13 12-21-2013, 04:27 PM

Hi Diesel Paul and everyone else,

When you say you checked the crank sensor and got no resistance, what do you mean exactly? Do you mean it was "open" ie it had Infinite resistance, Or did it have zero resistance like a piece of copper wire has zero resistance?

If it measures "open" then I would think the sensor has gone bad. This would explain the dead tach because it uses the signal from that sensor to figure out how fast the engine is turning.

It would also explain the a/c compressor because the climate controller would think that the engine was not running. It would make sense for the controller to disengage the compressor because you don't want to try to start an engine with the additional load of the ac compressor.

The 14 or so volts the alternator is putting out sounds fine to me.

I hope this helps!
Cheers,
Chris

DieselPaul · #14 12-21-2013, 05:27 PM

I'm sorry it measured open. I've been posting from my phone so I haven't been as detailed as I should be.

Sensor is around $67 from the dealer. $101 aftermarket. Go figure lol.

sixto · #15 12-21-2013, 06:08 PM

Rather than resistance, test the crank signal for AC voltage. I don't know what it should read but it should increase linearly with engine rpm.

Sixto
87 300D