Mercedes Benz SL W107 (1971 - 1989) - 1987 300SL- running rough | Technical matters | Back Room Forum

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Fri 23 May 2008 18:51

1987 300SL- running rough - Mikeym1

Hi,
My friend owns a 1987 Mercedes 300SL. During startup (cold or warm) the car is difficult to start, then hunts for a few seconds before sorting itself out. The car also very harsh
during speeds of 40 - 50 miles an hour but if ran in sports mode it seems o.k.
Someone advised the head needs rebuilding due to blown gasket at £2000. I have checked for water from the exhaust and in the oil but there is no trace (although I haven't ruled it out) and added a component called K-seal just in case. Someone also advised the harshness at 40 mph is due to a wheel baring. I am considering checking the plugs, filter and wheel baring this weekend. Although I have some mechanical experience I do not know a lot about these cars. I think this model has a carburettor fitted. I was thinking it could be a choke problem? Any advise please?
Mike.

Edited by Pugugly on 23/05/2008 at 18:58

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Fri 23 May 2008 19:10

1987 300SL- running rough - Screwloose

Mike

It's Bosch KE-Jetronic electro-mechanical injection. Check the cold-start injector is functioning at initial cranking; but resist the temptation to adjust anything - these systems are not forgiving....

Define "harsh?" Noise; vibration; from where?

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Fri 23 May 2008 19:20

1987 300SL- running rough - Mikeym1

There seems to be lack of power during those speeds and there seems to be some vibration dues to this. I can only describe the lack of power like the handbrake has been applied on and the car is struggling to pick up speed. I would probably be able to give more detail if I drove the car.

Edited by Mikeym1 on 23/05/2008 at 19:23

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Fri 23 May 2008 19:30

1987 300SL- running rough - Screwloose

Could be a misfire; I've seen a lot of distributor cap troubles on those. If all the obvious things, plugs, leads etc. are OK; have a good look at the cap.

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Fri 23 May 2008 19:37

1987 300SL- running rough - Number_Cruncher

>>Could be a misfire; I've seen a lot of distributor cap troubles on those. If all the obvious things, plugs, leads etc. are OK; have a good look at the cap.

Fully agree - leave KE jetronic well alone unless you know your onions!, and I second the advice about checking out the ignition system.

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Sat 24 May 2008 10:52

1987 300SL- running rough - Roger Jones

I agree with the suggestions above. Fixing a head gasket on an M103 engine should cost no more than about £700 if done by an independent; pointless giving such a job to a main dealer, who have fewer and fewer staff familiar with the older models.

You may find similar problems described and solved at any one of these places:

www.benzworld.org/index.php?page=active_topics

mbca.cartama.net/

www.mercedesforum.com/

forums.mercedesclub.org.uk/

www.mercedes-benz-club.co.uk/public/home.htm

www.mbclub.co.uk/

www.mercedesshop.com/shopforum/index.php

forums.mbworld.org/forums/

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Tue 22 Jul 2008 19:44

1987 300SL- running rough UPDATE - Mikeym1

Hello again,

I was recently on this site for problem my friend had with her Mercedes 300SL
Thanks for the information regarding this problem.

Since then the distributor cap has been replaced and the car has passed an mot but
there is still a problem. I expect this type of car due to the weight is not going to be high performance but it is really struggling to go and there is a vibration through the front wheels which I can only describe as trying to drive the car with the front wheels seized on. very sluggish.

Any ideas please?

Mike.

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Fri 8 Aug 2008 19:05

1987 300SL- running rough UPDATE - BenG

Binding front brakes and/or warped discs? Failing front wheel bearing/s? Front wheels out of balance?

Jack up front of car and check if wheels rotate freely to see if brakes are binding. If so, check if the brake calipers are frozen by removing them and gently pumping the brake pedal (not to the floor) and check if the pistons move in and out on both sides.

Also check the brake pads for unneven wear, check the discs for warping by measuring the side-to-side run-out when the hubs are rotated. Also check the brake pads can slide in and out freely when the caliper is mounted to the hub, and is not gettting stuck due to corrosion of the pad and/or sliding contacting surfaces.

If wheels are running freely, grab opposite sides of the front wheels and try to rock them from side to side and top to bottom to check if the wheel bearings are worn.

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