1991 500Sl Starting Problem

[GregE240]

Hi folks,

Wonder if anyone can shed some light on this for me?

I've just got back from a 1700 mile tour of Germany, including visits to RUF and the Schlumpf museum (highly recommended). My partner and I took the SL, and it performed faultlessly, aside from an occasional starting issue, which I thought I'd had fixed.

The problem is this: every so often, you go to start the car, turn the key and you DON'T get all the dash lights come on. If you continue to turn the engine will turn over, but will not start. You then have to turn the key back to 0 and try again. Next time it might start.....or it might not. During the trip it was mostly okay, just a little heart in mouth "will it start" moment every now and again.

I've had the sleeve that the ignition barrel fits into replaced, and this seemed to do the trick, but alas, the problem surfaced again. Another mechanic has cable tied the main ignition power feed to the switch as they thought it might have worked loose, but that hasn't done the trick either.

The problem occurs regardless of whether the engine is hot or cold.

Any ideas? I'm open to suggestions!

Thanks,
Greg

 

[jberks]

Based on the way most of these work (unless the SL is different), the system is a barrel with integral switch. In the case of a ford, the barrel simply had a pin at the end of the barrel and this slotted into a small plastic rotating switch. The key turned the barrel, the barrel turned the switch and the approrpiate contacts were made at the appropriate time. This is why a ford was so easy to steal. You pushed in a screwdriver, just flicked the switch off the end of the barrel and popped a small screwdriver in the end of the switch completely bypassing the barrel.

If the lights don't come on, then the ignition setting on the switch isn't making contact or the power isn't getting away from the switch. The starter piece may still work, after all, its only energising the solenoid switch wire but without power to the ignition circuit, the fuel pump, coil etc won't be energised so it won't start.

I imagine its either the switch or a dodgy connection somewhere in the loom. These can be nightmare problems because you can't really trace it until it fails completely. However, if it occasionally refuses to start, but runs fine when running, I'd suspect the switch rather than the wiring, as a loose connection or broken wire will move as you drive and should cause the car to stall. Also, replacing the sleeve would have disturbed the switch which may have caused the problem to go away for a while. I'd go for a new ignition switch.

 

[television]

Yes the ignition switch on a SL is a big problem, due to the amount of electrics on the car. Mine was replaced at 33k for the same reason as yours. and I know of a least 50 others. Some people take them apart and bend the contact

Malcolm

 

[kieron1]

Ignition Switch

Hello again Television
I am mb club member and you helped me out in the past re a dodgy key fob
But this time my problem is that my 500 SL 1991 has an intermitant problem in starting
All the dash lights come on and I can hear the fule pump whir but nothing else happens and the after about 20 mins it might start.
The other night I was towed home and it started as soon as it came of the transporter !!!
So I have an auto electrician coming to look at it tomorrow pm.
So are you saying that the most likely problem and solution is to change the ignition barrel ?? How can I get the auto electrician to prove or not that this is where the problems lie?
Also should I be checking anything else out?
The local Merc service manager suggested that it might be the relay between the merc alarm and the starter motor.
What do you think ??
Is it easy to change the ignition barrel / switch
Cheers Kieron

 

[television]

If it is the ignition switch,you only replace the electrical switch part, but on the 129 they can have a K38 starter lock out relay that is wired from the alarm, it is a well known thing that the spade push on connectors can make poor contact, this K38 sits behind the radio if fitted.

A voltmeter would soon tell you what the fault was

I remember you well from the MB club forum