R129 OVP relay - Come out come out wherever you are...

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E55BOF

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If you've seen my other threads, you know that the R129 I've acquired has running problems. Terry at Wayne Gates suggested that as the car has had plenty of jump starting, checking the OVP relay/Base Module would be a good next step. As usual, I can't find it on WIS...

Worse, I can't find the wretched thing either! Unless I've gone selectively blind, it's not under the black plastic cover left rear of the engine compartment, and it's not in the relay compartment behind the fuses right rear of the engine compartment either. Could some kind soul tell me a) whether the 1994 model R129 has the relay or the module, and b) where I should look for it? Please help...
 
I'm not sure that it has an OVP relay as such .

From memory there are a couple of 'multipurpose relays' under the cover on the passenger side of the engine bay , one performs the function of the fuel pump relay and some other stuff , I read about them somewhere ....
 
This is it on a 1994 W202, passenger side.
It may have a fuse on top.

Dec
JumpLeads.jpg
 
Thank you, Derek, but there are no relays under the passenger side cover at the rear of the engine bay. I am looking for either a tall silver relay, or a black plastic box (see the pics below), with one or two fuses on top of it (or possibly four if it's a Base Control Unit). I can't find either relay or unit, either on WIS or on the car, and I'm getting more and more p****d off as time goes by...

I've spent hours on the internet, but not found an answer. Really, REALLY frustrating...

Thanks Dec; that's the little b*****d I'm after, but I can't find it. In fact, I don't even know if the '94 M119 model has one, or the later Base Module. I do hope somebody can help with the info I need, before I go berserk and start breaking things. Oh for a Haynes manual....
 

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Is your Vin WDB129066-------? if so...

Found this on the EPC which suggests it's in the 'Apparatus Case'.

EPC #54 Electrical Equip.
080 Apparatus Case and Control Units.
scroll to page #6.
Part No 92.





.
 
Spooky !

I was just about to post the same image , 2nd down on the page below , which suggests it's under the cover on the passenger side , where the ABS control unit is on mine - I took a few snaps of mine and definitely no OVP there , but I'm sure I read somewhere that the function on some cars is integrated into another unit ?

Apparatus case and control units for Mercedes-Benz 300 SL-24 parts catalog

I'll post some pics of this area on mine in a few minutes .
 
Here's a few pictures of the same area on my car - I know it's a 300 and not a 500 , but a lot of the stuff is the same . No OVP that I could see there !









 
2nd picture down Derek. The thing with the red cap bottom right.

And in 3 & 4 half hidden behind the thing with the control knob on the top .

Edit. Is this not it?





.
 
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The VIN is WDB129067.

Yes, Druk, that is indeed the OVP relay; but my underbonnet is nothing like that. The early SL500's was (I have a hard-copy Mercedes partial service manual printed in 1989), but my 1994 is not.

However... I rather think my car has a Base Control Unit, not an OVP relay, and that it is part no. 77 in the first diagram which Derek's link brings up - SL 280/320/500 to 09/95. I have an 'apparatus case' exactly like that, and it looks to me as if item 77, which also appears in the 09/95-on diagram, has slots on the top for four fuses.

I'll take another look in the morning, but I'm hopeful...
 
Derek - yes - well spotted .

It was pitch dark outside when I took those , but it is cunningly hidden there too !

Hopefully the 500 will be similar .
 
On a '94 you're looking for the base control module, which incorporates the OVP.

311831d1275638930t-overvoltage-protection-relay-base-control-module-img_3016_.jpg
 
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Thank you Doodle. Mine's a '94, too, but not the same as yours. Go figure...

See the pics below. My Base Control Module was inside the 'apparatus case', not outside it like yours. There's the little blighter at the back, just as I hoped. Two of the fuses were blown. I replaced them, and Hey Presto! it runs!

:bannana: :bannana: :bannana:


It was still lumpy, but much better than before. I ran it up to 80 degrees, then drove around the block a few times for a couple of miles, and when I parked it, the idle was steady at around 600-ish rpm, and the oil pressure sat at 1.8 bar, and rose to 3.0 bar as the revs reached about 1200 rpm. All the gears are there, both automatically and with manual selection, they change smoothly, and kickdown works.

I think there's still a slight misfire, but if that doesn't go away once I can take it for a run, I can sort it; probably one or two plugs are still a bit sooty. What plugs do people prefer, by the way? NGK, Champion, Denso? I don't see the point in Platinum or Iridium plugs for this old-tech car, but I'll take advice on that.

Gentlemen, thank you all. I got there is the end. Result? You betcha...
 

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Plugs make sure they are non resistor. I have champion in mine from green plugs or something can't remember now but old plug specialists.
 
Just go to MB for plugs. They are not expensive and you will get the right non-resistor type.
 
Thank you Doodle. Mine's a '94, too, but not the same as yours. Go figure...

See the pics below. My Base Control Module was inside the 'apparatus case', not outside it like yours. There's the little blighter at the back, just as I hoped. Two of the fuses were blown. I replaced them, and Hey Presto! it runs!

:bannana: :bannana: :bannana:


It was still lumpy, but much better than before. I ran it up to 80 degrees, then drove around the block a few times for a couple of miles, and when I parked it, the idle was steady at around 600-ish rpm, and the oil pressure sat at 1.8 bar, and rose to 3.0 bar as the revs reached about 1200 rpm. All the gears are there, both automatically and with manual selection, they change smoothly, and kickdown works.

I think there's still a slight misfire, but if that doesn't go away once I can take it for a run, I can sort it; probably one or two plugs are still a bit sooty. What plugs do people prefer, by the way? NGK, Champion, Denso? I don't see the point in Platinum or Iridium plugs for this old-tech car, but I'll take advice on that.

Gentlemen, thank you all. I got there is the end. Result? You betcha...

What I do now is disconnect the battery for 20-30 mins, reconnect and allow the engine ECU to readapt/calibrate over the next 200 miles.
 
Why do you need to disconnect the battery? Whatever the ECU parameters are now, will they not adapt to my style of driving anyway once I actually start running around in it?
 
What I do now is disconnect the battery for 20-30 mins, reconnect and allow the engine ECU to readapt/calibrate over the next 200 miles.

Not sure it's quite that advanced if I'm honest.

There's certainly no gearbox adaptation to take place, given that it's a 4sp hydro unit.
 
I did rather wonder. He's perhaps thinking of the five-speed fitted to the later cars?
 
I'm talking about engine ECU not TCU on the 5sp auto. Nothing got to do with driving style. It may not work but in the 90's a lot of M-B's had engine ECU's that would adapt or readapt after the battery was disconnected. May be your car is not one of them thus it was only a suggestion. It might be worth finding out. Can't assist anymore other than to say it worked on both my W202's and my W210. Anyway you've nothing to lose disconnecting the battery...
 

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