300sl engine problems

[nevilledoreen]

I have a 1993 R129 300sl, it starts and runs perfectly for 4 weeks then all of a sudden is very dificult to start ,when it does it runs roughly for 5 kilometers until I switch it off.
I start it again and it goes fine for several weeks then the same problem .
Also I have had the electric radiator fan running when the engine is cold ,next time I start it is ok.The roll bar warning light has come on but the roll bar had been up for weeks moving the roll bar up and down did not switch off the warning light ,next time I started the car it was ok.
The car has had new high tension leads distributor cap and plugs fitted.
Can anyone give me a clue to the problem as the car at present is unreliable.
Neville

[nevilledoreen]

In addition to above over the last 6 months I can hear a clicking sound on some days coming from under the dash.
The car starts ok and runs ok when cold only after it has been run for about 5 kilometers and it has sat for half an hour does the problem occur and only accassionally.
ie hard to start cuts out when it does start and when it run it runs very rough even at idle and cuts out when I increase revs.
Can anyone help as I am desparate.

Thanks
Neville

[grober]

First port of call might be the OVP relay? Sounds as if you problem might be voltage level related. Low voltage can cause lots of voltage sensitive units to malfunction or come up with warning lights/ faults. Check the alternator is charging OK the battery is in good nick and all major earthing points are making good contact including the engine earthing strap. R129's can leak a fair bit check some of the electronics are not getting soaked - particularly those at floor level.

[nevilledoreen]

Thanks Greame ,it has a new battery and never driven in the rain so water at floor level should not be a problem . I am in Australia so it is start of summer dry but not hot.what is the OVP valve ?Where is it located ?
I am on old engineer and have restored MGB , MG midget ,Riley ,Sunbeam talbot and an early Benz ect but anything made after 1972 and I am lost .
I look forward to your reply as I am stumped.
Regards
Neville

[grober]

Right sounds as if corrosion/ damp is not going to be problem unless you live in an area of high humidity. The OVP relay supplies quite a few units including the engine ECU, Motorised idle valve and ABS controller. Its a large relay located behind the battery located close to the bulkhead. Its normally hidden behind a flexible black plastic cover behind the battery which covers the abs and engine ECU's It can be identified by having 1/2 fuses on the top. They can sometimes be repaired by resoldering the internal circuit board if dry joints are the problem-- lots of posts on here if you key in OVP in the search box.

[IBN]

Hi Neville

I've got a 300SL too. I'm not technical but when I was having all sorts of electrical problems, someone on here suggested that I might have a problem with fuses. When
I checked them they were all oxidised (covered with white powdery deposits). I changed the lot and hey presto ... all the problems disappeared.

Might be worth a try.

[nevilledoreen]

I appreciate that you both took the time to answer me I will now follow up on your advice.
Warm regards and an enjoyable christmas to you
Neville

[Ian B Walker]

Might be worth checking the temperature sensor near the thermostat. If it is throwing a wobbly then the engine ecu will either be over fuelling or under fuelling the engine.

[nevilledoreen]

Hi guys I still have problem I have fitted a new ovp relay and all new fuses.
The car starts and runs OK when cold but after running a short time and then switching the car off leaving it for half an hour it is hard to start and when it does finally start it is not running on all cylinders.
The clicking is coming from the left side under the dash or near the ovp relay it sound like a relay trying to operate but I cannot locate exactly where it is coming from .
Can anyone please help as the car is unreliable and I am stumped.
Thanks
Neville

[ray_hennig]

Originally Posted by nevilledoreen

The car has had new high tension leads distributor cap and plugs fitted.

Did it have a new rotor arm?

If not, finish off the HT side with that and DONT economise - MB original is my choice having had misery with cheaper replacement.

RayH

[nevilledoreen]

Hi yes rotor arm was replaced,can anyone give me any idea what the problem is ?
This is becoming an issue as I cannot rely on the car.
Also any ideas on the clicking I can hear could it be a relay ?
If so which one ?
All ideas appreciated
Neville

[nevilledoreen]

Still got the problem can anyone please,please help.
Neville

[neilrr]

Sounds like you need to take it to an MB indy. Your location?

[stwat]

Check the temp sensor as Ian stated. The one for the ECU is at the back on the engine on the right hand side. The wires going to the two connectors can crack and break causing all sorts of problems. I have had to replace them on 3 of my MB and my 300SE has had them replaced in the past too.
Also check the pins on the OVP plug as they cam become loose over the years. I have also been having running problems and found all the pins to be quite loose.
You have to dismantle the plug to release the idividual pins and then gently crimp them to close the gap.
My car instantly ran better and smoother and so far hasn't cut out(touches wood)

[nevilledoreen]

Thanks fellas car is at mechanics now so if he cannot find the fault I will pass on your comments I thought I might get the crankshaft positioning sensor checked as well,
What do you think ?

PS I went thru 300 posts on this site and this sensor showed up as a potential problem.
Thanks again to all that have helped me
it is appreciated
Neville