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Marty, Bosch Certified Master Technician
Category: Car
Satisfied Customers: 54829
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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I have a 1989 Mercedes 300 SL ( 107 ) series I cannot start

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I have a 1989 Mercedes 300 SL ( 107 ) series
I cannot start it in cold weather It will start no problem when warm In cold weather it will turn over no problem and when you release the key from the Turn engine position it will try to fire up but will not do so
Hi, it sounds like you may have a bad overvoltage protection relay or a blown fuse in the relay. The relay is located on the relay panel above the fuse box. I'd also check the ignition system. Worn spark plugs, a bad cap and rotor or a weak coil or low voltage to the coil could also cause the problem. I'd start by checking the relay since it is essential for the cold starting. The fuel mixture should also be checked and adjusted as needed.Let me know if you have any questions.Please be sure to click on a rating for my service.Marty
Customer: replied 2 years ago.
Do you have any photo or sketch that would indicate this relay switch
It's located above the fuse box. I've attached a picture below. It' the relay with the red top.
Customer: replied 2 years ago.
Thank you for that
I have located the relay switch and the fuse in it is intact. Unless of course the relay itself is faulty
Taking off the distributor cover is a major operation as it is located at the front of the head and the radiator may need to come out first to get access to an Allen key bolt underneath at the base of the distributor
I am wondering if it is more a fuel issue as when you succed in getting it started you have to leave it just tick over at idle speed until it is completely warmed up as if you try and give it any throttle whatsoever it will just cut out
It could be fuel or ignition. You need more fuel when it's cold and you need hotter spark when it's cold. You might try replacing the relay and see if it helps. I'd also check the fuel mixture.
Customer: replied 2 years ago.
Last question. How do you check the fuelixture
To check it properly you need a gas analyzer or you need to connect an ammeter to the EHA valve on the side of the fuel distributor to measure the current draw. A simple way of testing the mixture is to remove the air cleaner and gently press down on the air flow sensor plate and see if the engine rpm increases. If it does it tells you that the mixture is too lean. Do this both cold and hot to see if the mixture is off. You don't need to press very far when doing the test. About 1 - 2 mm is enough.
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