1999 SL320 occasional start problem

DubW129

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1999 SL320 V6
Hi, Have this car a couple of months drives like a dream, yesterday and on one previous occasion a couple of weeks ago had a starting problem. both times had been driving in city traffic for about an hour stop start stuff, parked the car in multistory returning 2 hours later. Turned key and she made the noises you would expect for that first split second but the engine just would not take, started on around tenth try on both occasions. In between, and since, no problem. Was willing to put first time down to some transient gremlin, second time has me thinking something expensive may be brewing. No technical knowledge myself as you have gathered, just wanted opinion before making the dealers day..thanks
 
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Alex Crow

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if you are saying that the engine was 'turning over' correctly for several seconds this sounds like a crank shaft position sensor fault.

if you are saying that when turning the key you got a split second of cranking and no more then it sounds like the ring gear needs greasing. if the latter then watch the rev counter needle next time it happens, if it immediately sweeps upwards above 1000rpm just as the starter cuts out this confirms it.
 
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DubW129

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Thanks a lot, certainly could not describe "several seconds" of turning over, the thing just seemed ready to start for as long as i had the turn on the key then stops, more like a second. will be watching for counter if, or rather when, it happens again. can i assume the second greasing solution is the lesser of 2 evils? thanks for tip.
 

Alex Crow

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yup, greasing the ring gear is a magical and seemingly impossible fix. basically the friction that can build between the starter and ring gear on this model is capable of generating signals in the cps that are interpreted by the ecu as the signals from the flywheel trigger plate. it reads it as high rpm and immediately cuts the starter, asuming it has started.

best way to grease is through the inspection cover at the bellhousing with the engine running. MB recommend a special paste for this but just use a spray grease with good fling resistance, eg chain lube and give it a really good blast. good luck.
 
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DubW129

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Problem sorted

Hi , Had car plugged in and garage managed to replicate my problem came up as crank shaft sensor alright, replaced and hopefully thats the end of current woe..cheers
 

Alex Crow

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happy days dub, glad you got it sussed.
 
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