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  #1  
Old 02-18-2002, 02:01 AM
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E320 '94 Intermittent starting (OVP again?)

My '94 E320 exibits intermittant starting problems. It has happened with both cold and warm engine. Last time I cranked until the battery was almost dead. I waited 10 minutes and tried one last time, and it started up normal. It runs normal for weeks, and then it happens again.

After reading hundreds of postings it sounds like it could be the Over Voltage Protection relay (OVP). Mine is the original type (Siemens p/n 000 540 52 45) I took it out of the car and checked the zener diode with a DVM. It reads 0.56V in the forward direction. That's normal for a diode. I did not check the reverse direction. I think it's supposed to be 22V. I connected +12V to pin 30z and minus (gnd) to pin 31. I then connected +12V to the control pin (15U). I could hear the relay inside switch when I connected power to 15U. The relay contact between pin 15 and 87M ohmed out fine (0 ohms when contacts are closed). I then checked the voltage on pins 87UG and 87E when these relays were closed. 87E has +12V on it, but 87UG is sometimes about a volt low (11V). If I tap on it I, it jumps back up to +12V. It tells me that the contacts may be slightly burnt or the connection inside is not 100%.

Does anybody know what the relay between 87UG and 30z controls? I tried to open the relay by bending out the metal tabs on the bottom, but it won't pull out. Does the plastic cap on the top have to come off?

Am I on the right track with my troubleshooting, or could it be something else?

Thanks again for an excellent forum.
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Old 02-18-2002, 02:28 AM
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I forgot to mention another clue. When I crank (and the engine is not starting), the RPM needle jumps up to about 2000 rpm and shakes.
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  #3  
Old 02-18-2002, 05:06 PM
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Typically, the Siemens unit has solder joints that over time have come apart, causing sporatic problems.

Might be easier to just replace it...
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Old 02-18-2002, 08:07 PM
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You also may want to check the wiring harness for broken insulation. Had the same problem with a 94 E320 a few years ago, turned out the harness was bad and had it replaced under goodwill warranty at the dealership.

Good luck...
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  #5  
Old 02-19-2002, 02:43 AM
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I have the OVP on order from the Mercedes Shop. Price was $62 + $5.25 shipping. I should have it in a couple days and I should now at the end of the week if it fixes the problem. Stay tuned....
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  #6  
Old 02-19-2002, 09:48 AM
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Does anyone have a pic of the OVP?

It has been discussed mahy times but I have never had a problem with it in 4 MBs. Just as an insurance policy, I would like to know what it looks like.

Also is there a GM type of fuse in tere?

I ordered that fuse but got a assotment package of GM type fuses.

TIA.
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Old 02-20-2002, 11:16 AM
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Sorry, no pic...

...it is a silver rectangular relay (twice as tall as it is wide). The top is white (where the fuse(s) reside) and there is a clear cover to protect the fuse(s).

The OVP uses the standard AN-type fuses (like the GM cars) and it should be either 15 or 20 amps.
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  #8  
Old 02-21-2002, 12:05 AM
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I took some pictures of it, both outside and inside. I just need to figure out how to put them one here. The insert IMG button does not seem to work.

I received a new "improved" part from PartsShop. I ordered the replacement p/n 000 540 67 45. I received a part that is made in Hungary with p/n 89 7219 000 stamped on it. Is this the regular Mercedes replacement part?
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  #9  
Old 02-21-2002, 12:09 AM
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roarbj:

Use the browse button as shown in the attached pic. Thanks.
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E320 '94  Intermittent starting (OVP again?)-image1.jpg  
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  #10  
Old 02-21-2002, 11:30 AM
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Here's a picture of the OVP (original Siemens part)
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E320 '94  Intermittent starting (OVP again?)-ovp1.jpg  
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  #11  
Old 02-21-2002, 11:34 AM
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This shows the three relays inside
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E320 '94  Intermittent starting (OVP again?)-ovp2.jpg  
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  #12  
Old 02-21-2002, 11:36 AM
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This show the circuitboard inside. The solder joints can sometimes go bad and have to be resoldered.
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E320 '94  Intermittent starting (OVP again?)-ovp3.jpg  
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  #13  
Old 02-21-2002, 11:37 AM
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roarbj:

Thank you very much for the pics. Now I can try to locate it in my cars.

I heard there is a 30 A (?) fuse in there but I could not see it in the open pic.
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  #14  
Old 02-21-2002, 11:38 AM
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This is the new part I got from PartsShop
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E320 '94  Intermittent starting (OVP again?)-ovp7.jpg  
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  #15  
Old 02-21-2002, 02:39 PM
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The relay is located on the passenger side behind the battery. The 15A fuse is on the top under a clear plastic lid that flips up. You can see the fuse when the OVP is installed in the car.
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