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Discussion Starter #1
I have perchased a 1975 450 Sl, sadly! The car will run for 50 or 60 miles. It might be parked for a few moments, and then will crank but not start. Last Monday, after the dealer had told me it was fixed, I drove out of the dealership in a pouring rain to have the motor quit and refuse to restart. The mechanic, a service manager, and I pushed the dam thing back into the delership!!<br>
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It has been the problem child of an Audi dealer in Richman, VA. who passed it on to me as fixed. It now sits in a Mercedes dealership in Salisbury, Maryland and quite honestly is baffling them! <br>
It has had a new brain, all inition parts for tune up,a modulator for the fuel injectors, something under the dash which is inition related, and many other parts which have cost me a small fortune but have not solved the problem.<br>
If anybody out there has had experience with this model and year which could be helpful in solving the problem, your help would certainly be appreciated
 

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Jim<br>
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There are many reasons why the engine would be difficult to start, the fuel filter and fuel accumulator may be at fault or the pump may be the cause.<br>
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The problem occurs particularly after the engine has been running due to the pressure relief valve located at the back of the pump inside. It is activated by a small spring and a metal cone which in time it sticks and do not allow pressure to be relieved.<br>
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As the pump is driven by a permanently excited electric motor the pressure is reduced. After stopping, the fuel accumulator maintains pressure in the system to facilitate starting and with this pressure if the valve is stuck it develops an inner leak.<br>
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If you tap the pump firmly it releases the pressure valve and the engine starts again. When the tapping becomes frequent, is time to replace the pump.<br>
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Mercedes know this and they provide a Check Valve which to be installed by replacing the existing hollow screw to the pipe connection to the pump, effectively providing a secondary pressure relief valve and avoiding having to buy a new pump. <br>
 

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Why do you think MB's are so expensive to run ? Because the damn dealers never fix them properly !<br> <br> I think this is a common problem on SL type models from the late 70's - 80's.<br> <br> IS it erratic, intermittent ? Possibly re-create a stall by reversing (hammer lock turn) quite sharply - again NOT every time. After a cut out Might crank for 1 min or 30 minutes before restarting as if perfect ?<br> <br> Cut out can occour at speed, momentarily (all dials go dead and spring back to life)<br> <br> Then this is down to the wiring loom. The MB dealers would like to replace your ECu and this may appear to work but only because a new ECU (especially upgraded components) can defy poor wiring for a while.<br> <br> MB dealers have no idea how to fix this one. My car had had £6k spent on it to fix this problem with Alan Day and a good independent ex GWR MB mechanic and it cost me a £30 cable (and many hours).<br> <br> It is most likely to be the coax type lead from the ECU. This is an expensive MB type lead. anything else may wreck your ECU so buy an MB one - about £30 <br> <br> I jiggle mine and it works. very difficult to get it to fail because of the nature of the lead. It needs a certain resistance etc. wet it warm it up and it may fail.<br> <br> hence this fault Can be working (not necessarily engine) temperature specific.<br> <br> Unfortunately once fixed, this may indicate the life of the loom is approaching. I inferred this but have no proof other than observation of other SLs with similar problems...<br> <br> You may notice old SLs that have had new wiring looms. This type of fault is why.<br> <br> lovely car indeed. but is it worth it ?<br> <br> I wish MB's could just master Jap level of reliability.
 

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You are welcome. This kind of thing makes the internet useful !<br> <br> I had a good one owner, genuine 65k miles example. But it had had a front end crash and the front steering bushes, I think, were worn (un cat like over 90 mph). Again dealers couldn't fix and wanted between £1-3k to just rebuild the front suspension in order to cure the problem.<br> <br> The car had no other faults and was otherwise very reliable and good fun. I especially like the lifetime cam chains which mean that servicing is cheap and you don't have to entrust a mechanic to change the cam belt properly.<br> <br> I would have kept it had I not wanted to spend £££ getting a (car other than a Porsche) up to a decent condition.
 

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It sounds like vapor lock. 75 and 76 models were known for this. Check out this article from this board. Not sure what can be done about it.<br> <br> http://fly.hiwaay.net/~gbf/107/rt.html
 
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