Help!! Need OVP plug schematic! - PeachParts Mercedes-Benz Forum

Cap'n Carageous · #1 07-11-2002, 04:05 PM

Does anyone have a schematic for the OVP connector for an 89 300E. I spent about two hours in the service CD and could'nt find it!!

Mick J · #2 07-11-2002, 04:31 PM

This any good?

Cap'n Carageous · #3 07-11-2002, 04:40 PM

Looks good to me. Thanks Nick!! BTW, where did you get that if you don't mind my asking?

Arthur Dalton · #4 07-11-2002, 05:16 PM

On the CD
go to wiring schematics/diagrams
go to page 117
go to frame 43

Benzwood · #5 07-11-2002, 05:33 PM

Here's a photo of one too, and by the way, if you want to buy it I'd sell it $20 + postage. Guaranteed working or your money back.

I replaced it trying to fix an intermittent fuel pump problem, turned out to be the MAS control unit instead.

It's from a '92 300E, PN #201 540 32 45

Cap'n Carageous · #6 07-11-2002, 10:46 PM

My goal here is to try to bypass the OVP to see if I can determine a way to test one. That would answer a lot of questions and save a lot of money for members. Instead of just going out and buying a new one every time a car hiccups, we could have a test to verify the OVP is/is not working. I bet there have been a million of these things purchased unnessesarily. I know I bought one and the car actually ran worse when I installed it!

Benzwood · #7 07-12-2002, 12:07 AM

Someone should start an OVP rental service.

I believe there's a test procedure outlined on the MB 124 CD-ROM somewhere, seem to recall reading it.

vrsmith · #8 07-12-2002, 07:42 AM

I was told that if you have power between the fuse posts, then the ovp was working. I was also told that you can remove the ovp and try the car briefly without it. It was worse without it on my car. (Although worse than dead is hard to imagine.)
I would like to know how to test the air flow meter rather than pay the big dollars to replace that part.
Good luck, (to us all).

Cap'n Carageous · #9 07-13-2002, 08:46 AM

What is the function of pin 30a?

stevebfl · #10 07-13-2002, 09:29 AM

One must ask ones self what does by-pass mean. Then one must find what an OVP does. AND, then it becomes obvious.

The OVP is simply a fuse like any other fuse except it is designed to blow on voltage changes not current changes.

It's most basic purpose is to connect various control units to the battery.

Based upon that concept what determination can be made of the case Stephen points out? That case being that a new OVP made the car run worse.

Its most likely that the old unit was bad. Think about it and tell me how I can be right. Unless you understand why I can be right you are not understanding how things work. I'm going to let someone else explain it. This is a challenge! All you techs take a break.

stevebfl · #11 07-13-2002, 11:05 AM

You got the by-pass right, but that wasn't my question.

Of course this isn't my thread, but my question is: why do I believe the original OVP bad if a new one makes the car run worse?

This question goes to the heart of the original question. The need to by-pass is dubious if the results of by-passing are misunderstood.

stevebfl · #12 07-13-2002, 11:38 AM

Nope.

Maybe some extra credit for true statements, but not the diagnostic insight I'm seeking.

Gonna give you another try, while we wait.

And BTW sixth post down last sentence:

"I bet there have been a million of these things purchased unnessesarily. I know I bought one and the car actually ran worse when I installed it!"

stevebfl · #13 07-13-2002, 12:25 PM

See now we are getting somewhere, but you flunk.

Let me correct a few misconceptions and see if we get some diagnostic hints from that special sentence.

First: With a good OVP a warm car set properly will notice no difference when the OVP is unplugged!!!!! can we say "limp home" While warm starting will not be affected.

Second: With a dead controller the idle valve goes to it's "limp home" position which is a little faster (on a 300E) than a proper running car at idle untill put in gear and the A/C turned on at which time the fixed setting is not enough for full idle speed.

I'd love to spell out my conclusions but think more time should pass to let others think this through. If you can't wait write me and I'll tell you how I see it. steveb@atlantic.net

stevebfl · #14 07-13-2002, 12:53 PM

Haven't got the email yet but to keep things from being too confused, one more point. I just read the cars you have and I must point out that we are NOT talking about your car!

Your car is a HFM SFI car and the OVP functions differently. You do not have an idle valve and because the system is electronic your car will not run without the OVP.

Arthur Dalton · #15 07-13-2002, 01:01 PM

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I have read that this is one of the faulty parts that caused problems on the original and was replaced in the new style relays. For what it's worth...