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Old 02-18-2002, 01:01 AM
roarbj roarbj is offline
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Join Date: Feb 2002
Posts: 20
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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