Help!! Need OVP plug schematic! - Page 3 - PeachParts Mercedes-Benz Forum

Cap'n Carageous · #31 07-13-2002, 04:52 PM

[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.]

So, in MY case OVP is not telling cold start mechanics to operate and may be screwing up the warm operation mode too?

Oops! That's not a valid question. I should ask is it possible and/or likely for the OVP to cause the controls to behave ths way?

stevebfl · #32 07-13-2002, 04:58 PM

Come on now Stephen.

The OVP doesn't tell anybody, anything, ever. Think of it as a fuse. Its either connected or it isn't or somewhere in between.

The car we have been talking about uses electronic control of a mechanical system that does pretty well without electronic help.

Your system on the other hand absolutely needs electronic help as thats all there is. No connection to the battery and you don't go period.

Cap'n Carageous · #33 07-13-2002, 05:31 PM

Now before you get perturbed with me, remember I'm the student seeking knowledge

! Most of this thread is way over my head, so I have to shoot in the dark on ocassion. And I'm sure I speak for everyone in thanking you for you're participation here. I hope this thread becomes a reference for the function of the infamous OVP.!

So, with the mindset of the OVP as a resisted fuse, what would be the results if it wasn't there at all? Assuming there would never be a spike in voltage.

stevebfl · #34 07-13-2002, 05:41 PM

Its needs to the system could be provided with a hunk of wire untill time came where protection was needed. Then the control unit could suffer.

The point to remember is that the device plays no part in decisions. It only powers up the system. Think of it as a UPS for the cars computers. As far as running the PC a wall outlet would be just as good, but we use UPSs to protect the thing from lightning/etc. Our software is totally not concerned with whether the power came from the wall socket or the UPS. Same holds for the OVP.

Cap'n Carageous · #35 07-13-2002, 05:53 PM

Now we're at a level I can understand. (sorry to have to bring you down here)

One last question and I'll go home, why is this thing blamed for so many conditions? It seems that every time the word "stall" or "erratic' comes up, the first "answer" is to replace the OVP.

stevebfl · #36 07-13-2002, 06:12 PM

Probably the key to most of its problems comes from the fact that the systems it powers on the KE and K-jet w/lambda cars work so well without any control at all. This leads to some weird, intermittant problems, especially if the OVP problem is intermittant as often is the case. The extent to which you see problems with it are probably also to to the many systems that get affected and the many ways things are affected. It pops its ugly head in where nobodyexpects all the time.

MB has so few bad connections and thats what this really turns out to be. If the car totally died everytime it went out like on the later cars it would be easy especially if it stayed broke long enough to look for it.

stevebfl · #37 07-13-2002, 06:18 PM

OK now its time to slap the teachers hand.

Go back a couple posts, I mistook who I was taking to when I stated: "Your system on the other hand absolutely needs electronic help as thats all there is. No connection to the battery and you don't go period."

The system I was refering to was the later HFM system not yours. I figured that mistake would really confuse everyone set on learning this so i needed to make the correction. I probably should go edit it. Hopefully anyone reading this as archives will read this far or they are going to quit.

Cap'n Carageous · #38 07-13-2002, 06:26 PM

Mr. Brotherton, my thanks for your perseverence. I know you had better things to do on a summer Saturday afternoon than to educate us about OVPs!! As promised, I'm through!

I will however, monitor this thread in case someone else asks a question like "which terminals do you bridge to test the OVP?

As best I remember, the only other answer was wrong and the student that submitted it had to stand in the hall for 15 minutes!!:p :p

stevebfl · #39 07-13-2002, 06:36 PM

Its been raining all day and I was set to go out to the local stock car races tonight (haven't done that in years and they have improved the track this year). Just seemed like the day to do it, but now its rained out.

Oh well, I had fun.

Cap'n Carageous · #40 07-13-2002, 07:25 PM

I wish I was there. I would take you and your family up to Alachua to Sonny's BBQ. You deserve something for all this!!

Mick J · #41 07-14-2002, 03:42 AM

Well you guys across the pond have been busy while I've been asleep! A couple of observations.

1. The function of the OVP is to shut off power to the ABS and fuel computers to protect them if the car system voltage gets too high (for example if the alternator's voltage regulator screws up).

2. As Steve said, the KE fuel injection system is a mechanical one with electronic aids. If the engine and ignition system are in good condition it will run without any of these aids - I know because my 230TE (UK petrol prices are such that most of us can't afford to run 6 cyl cars) ran with a failed OVP on and off for months 'till I fugured it out. My project this sunny Sunday morning is to see if the HFM equiped E220 will run without it - I guess it won't.

3. The car that ran worse when the OVP was replaced must have had the mixture and idle (I think earlier ones had manual idle adjustment?) when the electronics were not working.

4. The common problem with the OVP is bad soldered joint on the PCB. It is easy to repair, just open it up and run a hot solder iron over all the joints.

Mick J · #42 07-14-2002, 04:04 AM

Another couple of thoughts!

1. Checking voltage at the fuse terminals will not tell very much as this is on the 'live' side of the relay.

2. To bypass the relay bridge the 30, 87l and both 87e terminals. Beware, the ingition switch may not shut off the engine if you do this. You could use the 15 instead of the 30 but this may overload the ignition switch.

Cap'n Carageous · #43 07-14-2002, 08:51 AM

I was playing around with this old OVP and noticed that there is no continuity from side to side of the black resistor in the pin 15 ignition circuit. Car wouldn't start when this one was in. Another cause for failure? This one would be immediately noticeable since the car won't start. It's the black one in the middle of the picture.

Arthur Dalton · #44 07-14-2002, 10:01 AM

<<
I was playing around with this old OVP and noticed that there is no continuity from side to side of the black resistor in the pin 15
??>>

I believe that is a diode, not black resistor...

Switch your meter/leads polarity and re-check for foward bias...

Cap'n Carageous · #45 07-14-2002, 10:15 AM

Current will pass through it but it doesn't have continuity either way polarity is checked. Does that mean it's ok?