'90 300SL Warm Start Problem

[rbgreen2]

1990 300SL, 60k miles: Cold starts fine, runs smoothly, no missing is apparent at any RPM. Once up to normal operating temperature, continues to perform smoothly. BUT, if stopped and the engine turned off, can not complete a successful warm start unless left to rest for about 30-45 minutes. Without the wait it sputters, coughs and then dies. But, after waiting another half hour it starts instantly and runs smoothly until turned off again. Then the same wait is required for the next start. It has good spark and acts and feels like a fuel mixture problem. Online I have learned that somewhat similar symptoms have been attributed to coolant temperature sensor issues, rotor and cap problems, vacuum leaks or the fuel pump relay. This car is in a remote location 250 miles from the nearest Mercedes mechanic. So, its up to me to fix it. Where is my best bet to start for a fix based upon these symptoms? I am not a serious mechanic but am capable of replacing parts. Any help or direction would be appreciated.

[rocky raccoon]

On my 89 560SL, that specific problem was the engine temperature sensor. The fuel pump relay would prevent the car from running at all. The engine temperature sensor is by far less expensive than the distributor cap so I would start there. Be sure you replace the right one (there are three on my car). The one you want has two wires attached.

Do you have a manual or CD that will help you isolate the fault using voltage tests? If not, go ahead and replace that $40 sensor. It is a sma ll gamble.

[rbgreen2]

Thanks Rocky, I'll add that to my parts list.

[lymlyt]

Hi, do a search on my latest post, serach lymlyt. Sounds somewhat
similar to my current problem, runs good cold until hot, then hesitation, occassional miss, but mine doesn't die. On my way to pick it up-indy
says it fixed. I'll post when confirmed.

[Archunt]

You may want to check your wires for arcing, although the symptoms are usually reversed.

[billtei]

I have the EXACT same problem with my '91 190E ... hopefully it is just the engine temperature sensor as suggested

[Paratroop]

I have a 95 e320 with 111000 miles.Warm start problem also.Turned
out to be the Crankshaft Reference Sensor.Crankshaft Sensor is located
at the rear of the engine,drivers side,above the starter.The sensor located on the front of the engine is the CAMSHAFT SENSOR.They are
two different animals.

[tecqboy]

Do a forum search for "crankshaft position sensor" issues.

The Crankshaft position sensor on this vehicle is located on the front of the engine and mounted on a small piece of flexible aluminum. It's just a coil of wire in a metal shell about the size of a .45 calibar bullet with a cable coming out the top. Look for it near the water pump. It's easy to acidentally bend the mounting piece if someone has done any maintenace work in the area. ( fan belt or water pump ) So check that the pick-up end of the coil is close, but not touching the flywheel. Too large a gap can cause erratic operation.

In my car ( 300sl) , I can hear the fuel pumps run ( there are 2 ) when I turn on the ignition. When your car won't start, can you hear the fuel pump?

[sldan]

Had the same problem with my 91 300SL ay abot 55K miles. Injectors were leaking with the engine off.

I have not had any engine problems in three years after replacing ignition coil, rotor, cap, and plugs.