Ovp

[vincemacca]

How do you test the OVP relay.
Is it safe to remove it and start the car without it to see if it runs any differently. Or is it a diagnostic machine job only?

 

[television]

How do you test the OVP relay.
Is it safe to remove it and start the car without it to see if it runs any differently. Or is it a diagnostic machine job only?

If you unplug it the car will not start or run. If you carefully remove the plastic cover, (you may have to cut welds) it needs soldering up. if you are not used to soldering, give it to a TV guy who works from home. Many of these relays were faulty when made, bad soldering.
It can be tested on the car, pin 30 will have 12volt on it, and the output on pins 87 (may be two)should also have 12 volt, in the fault condition this drops to 7.5 volt.

malcolm

 

[Stevie A]

And ABS Light comes on when voltage drops below 10 volts so protecting ABS system by shutting it down. So this is why you can tell when OVP is faulty when ABS light is on. It's about 50 quid for a new OVP relay.

 

[tom7035]

Rough idle.

Vincemacca,
Re. your rough idle, if you've checked out the OVP OK, clean out the crud from your throttle body around the butterfly valve with carb cleaner or similar (removing it to do this makes a more thorough job) and take out your Air Mass Sensor (plugged into the side of the air intake ducting after the filter box, with wiring attached) and do the same with the wire sensor. A small artists brush and some care with this. Also add a bottle of injector cleaner (follow instructions) to your next couple of tanksful of fuel.

 

[veedweeb]

Vincemacca,
Re. your rough idle, if you've checked out the OVP OK, clean out the crud from your throttle body around the butterfly valve with carb cleaner or similar (removing it to do this makes a more thorough job) and take out your Air Mass Sensor (plugged into the side of the air intake ducting after the filter box, with wiring attached) and do the same with the wire sensor. A small artists brush and some care with this. Also add a bottle of injector cleaner (follow instructions) to your next couple of tanksful of fuel.

I might be speaking out of turn here, but I am quite experienced with VWs and their faulty and temperamental MAFs...

The only thing you should clean your MAF with is Isopropyl Alcohol (available in a big aerosol from Maplins for a fiver. Spray it all over the MAF and let it dry naturally - don't blow it, or dry it with a cloth or compressed air. The element in these things is very sensitive and you MUST NOT touch it with anything, except the alcohol.

Like I said, this applies to the Bosch MAFs fitted to VWs, but I can't see why it would be any different to the MAFs fitted to Mercs.

Steve :smile:

 

[television]

Like I said, this applies to the Bosch MAFs fitted to VWs, but I can't see why it would be any different to the MAFs fitted to Mercs.

Steve :smile:

You are right :smile: they must all be handled the same way, you do not touch it with anything.

Malcolm

 

[tamrsoft]

You can also get the spray from Halfords (Electronic Component Spray), it's about £3.99. Glad to see someone else has the sense not to use Carb or Brake cleaner when cleaning these units.

 

[tom7035]

Sorry I spoke!

 

[television]

Tom it always nice to have your practical expert advice, you know these cars inside out. what you and I can do, is often hard to get across to someone else when you have no idea of there technical competence. I used to tell people to solder up there OVR, then one guy sent me one that he had soldered. the mess was unbelievable, from that time onwards I tell them to take them to a TV service man who works from home.

Best regards. Malcolm

 

[turnipsock]

at the end of the day, it's just a RELAY. The contacts burn out due to the current being fired through it at switch on. You can open it up and clean up the contacts, there are various things you can get from Maplin to do the job.

One way of increasing the life of this is to switch off as many things as you can before turning on the ignition.

 

[television]

at the end of the day, it's just a RELAY. The contacts burn out due to the current being fired through it at switch on. You can open it up and clean up the contacts, there are various things you can get from Maplin to do the job.

One way of increasing the life of this is to switch off as many things as you can before turning on the ignition.

Sorry Turnipsock, the point in question here was cleaning the MAF.
I only mentioned the OVR as an example of what can happen when giving advice. Incidently The OVR produced for the 124 were all badly soldered, MB admit this and I is number one on the hit list for faults, as you know that if you alter the contacts, the current characteristics will change as this is a sensing relay.

Malcolm

 

[tamrsoft]

TOM7035 - I meant Electronic Component Spray only for the MAF, Carb cleaner for the throttle body by all means. I have seen suggestions for cleaning the MAF with carb cleaner - dangerous practice.

 

[vincemacca]

ABS Poor starting & OVP Testing

Thanks folks for all your efforts, it is very much appreciated. Problem now sorted.

For those who may experience this, here are the symptoms and cure (with pictures)
Mercedes 200e 1989
Symptoms
ABS Light permanently on
Poor starting and rough running when cold. Feels like the old carb setup without the choke not working properly - you try and blip the throttle and it dies until it warms up.
Check OVP Fuse first
OVP is behind the plastic panel behind the battery, and can be covered by it own cover
Check fuse in the top OVP. If not blown then you will have to check the OVP operation

To test: connect pin 30 to pin 87L (thereby bypassing the relay switching). To do this you will need to remove relay and insert a couple of partly bared wires into 30 & 87L sockets. Replace the relay it jamming the wires in the socket, so you can join them together without shorting anything out. If the OVP relay is faulty the engine should run smoother and the ABS light will go out.

If faulty you can take the relay apart. First remove fuse. Splay the bottom of the container moving it from the relay inside. You should be able to remove it. Check soldered joints (see picture of centre contacts) and redo them all if any look suspect. And try to clean the contacts especially the top of the coil. Mine had a bit of dirt trapped, keeping the copper plate from pulling the contacts towards each other. But I also re-soldered all the connections in place as some looked like they had dry joints

So after cleaning the contacts and re-soldering the connections did it work ……… Nope, I checked the operation of the diodes and the resistance of the coil etc and while there appeared to be no apparent fault with the circuitry it didn’t work properly – only partly energised. However, I had proved it to be faulty so it was off to the scrap yard for a new one….£2 . Fitted it and it worked perfectly.
Hope this helps

 

[television]

Thank you for putting up the answer, this means that the relay gets out of spec. I see by the part number that it is not the original.

Malcolm

 

[turnipsock]

It sounds like the coil was damaged.

How are measuring the resistance of the coil? What resistance did you get?

The diode is there to kill the back emf.

 

[television]

It sounds like the coil was damaged.

How are measuring the resistance of the coil? What resistance did you get?

The diode is there to kill the back emf.

Problem with a coil is that you cant measure one short turn.
Re the Diode in this case is not to kill the back EMF, the output in overload condition comes through the diode hence the 7,5 volt in the over voltage state. I am sure that I have read that it is a zenor, its certainly a 50-100 amp device. I will refund the postage.


Please Vincemacca Post it to me and I will do a write up

Malcolm