OVP relay 1991 300TE 4matic - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 08-09-2019, 01:40 PM Thread Starter
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OVP relay 1991 300TE 4matic

Hello All
I have just replaced the ignition lock assembly in full as the old one failed. The car now is hard to start and won't idle. I think I shoot myself in the foot when I had a brain fade. I was jump starting the wagon with my truck and almost hooked up the leads at the wagon backwards. Of course large spark and chest pain. The car seemed OK though and the two 10 amp fuses on the top of the OVP relay were also
OK. Can the relay still be toast if these fuses are OK? The car does start but not easily like it used to and doesn't want to idle at all. Runs smooth at higher RPMs but I haven't driven anywhere as I am afraid of getting stranded.
Thanks for your help.
G
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post #2 of 10 (permalink) Old 08-09-2019, 06:41 PM
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Replace the OVP. If member Sbaert is out there, I am sure he can explain well why this is the next best step.
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post #3 of 10 (permalink) Old 08-10-2019, 04:37 AM Thread Starter
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Will do. Thanks for the help. I guess the OVP internals are not always protected by the two fuses on top?
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post #4 of 10 (permalink) Old 08-10-2019, 12:43 PM
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Originally Posted by gozody View Post
Will do. Thanks for the help. I guess the OVP internals are not always protected by the two fuses on top?
Probably not when you reverse hook it even momentarily. The electronics in there (especially the Zener diodes) are not going to like being reverse connected.

I would buy a new one and replace it. If no change at least you have a spare for the future.

- Cheers!
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post #5 of 10 (permalink) Old 08-11-2019, 03:18 AM Thread Starter
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Part is on order and I will update thread after I install it
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post #6 of 10 (permalink) Old Yesterday, 01:43 PM Thread Starter
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I installed the new KAE OVP today. It started with some difficulty and won't idle below 1,000 RPM ( that's with me holding it there with the accelerator pedal). Won't hot start. What's your next suggestion or tip? I amgoing to try and test the old OVP to be sure its dead but that's for another day.
Thanks
RG
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post #7 of 10 (permalink) Old Yesterday, 03:54 PM
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Maybe one of the 2 fuel pumps is shot or your fuel pump relay is now a dud?
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post #8 of 10 (permalink) Old Yesterday, 04:16 PM
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Does this car have a standard old school Bosch Jetronic with ECU? Or is it the later model fuel delivery system?
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post #9 of 10 (permalink) Old Yesterday, 09:47 PM
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CIS-E....all first gen 4Matics up to and through '93. M103.....

Kevin
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post #10 of 10 (permalink) Old Yesterday, 10:53 PM
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In that case, since your idle is shot, I would recommend starting to make some voltage measurements starting from the IACV.
As the car is idling see what the average voltage (in DC mode) is at the IACV connector with the car idling. Should be in the 4V-5V range.

If you do not have a voltmeter, as the car is idling, disconnect it. In an operational system the idle would shoot up to 1000-1100 RPM.
If you hot plug it during idling the engine would immediately stall.

See if you have this expected behavior.
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