R129 starting problems

[Alan M]

I am getting an intermittent starting problem with my SL320 V6.

The first once or twice it happened I thought it was my fault letting the key go too soon even though I know it should automatically crank the engine until it starts even after letting go of the key.

The starter motor engages for a split second, the rev counter needle flicks 3/4 of the way around the dial as the starter disengages before the engine turns and fires. Sometimes it will fire immediately on the next turn of the key or sometimes it will repeat the non starting 2 or 3 times before it will fire. It will then be fine for several days before this happens again.

I would like to get to the bottom of this before it gets worse and I'm left stranded, so any help pointing me where to look would be appreciated.

thanks in advance.

 

[Neebo]

112 engine's starter motor jam's on ring gear ,when it eventually starts lubricate the ring gear with a copper grease spray not too much though.you can apply it through the bell housing or remove plastic gromet at the rear of the sump.

 

[Alan M]

112 engine's starter motor jam's on ring gear ,when it eventually starts lubricate the ring gear with a copper grease spray not too much though.you can apply it through the bell housing or remove plastic gromet at the rear of the sump.

Thanks for reply. I have always got the car started (so far) - just sometimes takes 2 or 3 goes before it does.
When you say it jams is this the drive gear on the motor jamming so it doesn't fully engage on ring gear?

Do you mean that the engine needs to be started and running while spraying in grease which would make sense to distribute grease around whole of the ring gear.

 

[alexander patie]

Do you mean that the engine needs to be started and running while spraying in grease which would make sense to distribute grease around whole of the ring gear.

that is exactly right, and will effect a miracle cure, though you may be sceptical at this stage. any clinging spray grease will do (eg chain lube), although MB advise removing the starter and applying a special MB paste direct this is not necessary. enjoy.

 

[Alan M]

Thanks guys for the replies - I will get hold of some spray grease and get it sorted.

though you may be sceptical at this stage.

Not sceptical at all. Although my first thoughts centered around the smart start system and with the rev needle registering I was thinking it might have been thatthis tells the starting system the engine had started and, hence cutting power to the starter, but glad it sounds simple and cheap to repair

 

[alexander patie]

you were thinking right about the rev needle. this is an interesting fault where friction between starter and ring gear sets up a strong enough signal in the crank sensor to be seen by the ecu - obviously this signal is read as, say, 3,000 rpm and the starter is cut as the engine is running. so many have had this before, but few think to mention the rev counter.