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Discussion Starter #1
My 300E does not start when it is cold. Runs fine once it gets warm. Have to crank it a few times till it slowly starts stumbling and have to keep my leg on the gas padel. Takes a while to pick up rpm. After about 4-5 cranks, it starts but hasitant to rev up till it warms up. New fuel filter, air filter, spark plugs, distributor cap, rotor and set of ignition wires. Has 180000 km. Any help will be appreciated.
 

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My 300E does not start when it is cold. Runs fine once it gets warm. Have to crank it a few times till it slowly starts stumbling and have to keep my leg on the gas padel. Takes a while to pick up rpm. After about 4-5 cranks, it starts but hasitant to rev up till it warms up. New fuel filter, air filter, spark plugs, distributor cap, rotor and set of ignition wires. Has 180000 km. Any help will be appreciated.

If you have a M103-12V engine then possible cold start valve or engine temp sensor.

If I recall cold start valve comes in for about ten seconds if the engine temp sensor is below 50 or 60 degrees F. ?

It gives a shot of gas to the intake which is enough to start and stabilize the idle.
 

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Discussion Starter #3
Thanks RBYCC. I checked the 10 amp fuse behind the battery on the right and is fine. Where would the cold start valve and the engine temperature sensor be located? I have a rough idea for the cold start valve ( between 3 rd and 4 th fuel injector, but I could be wrong.
 

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remove the intake box and u should see it it looks like a big injector and if i ware u i would replace all the injectors they are not expensive u bought mine for 180$ total new
 

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Thanks RBYCC. I checked the 10 amp fuse behind the battery on the right and is fine. Where would the cold start valve and the engine temperature sensor be located? I have a rough idea for the cold start valve ( between 3 rd and 4 th fuel injector, but I could be wrong.
Cold start valve is in the area of the fuel distributor...follow the fuel line from the fuel distributor to locate it.

The engine or coolant temp sensor is on the left side of the engine, threaded into the upper surface of the cylinder head, should be toward the back of the engine.
This is different from the temperature gauge sender unit.

You can test the coolant sensor with a voltmeter.
The cold start valve must be removed to test.

The fuel pump relay may also be defective as the it controls the cold start.
If you put a voltmeter on pin 12 ( terminal 50 ) of the relay and ground you should read 10 volts when you activate the starter, if you don't see the 10 volts, then the relay is bad.

You also need to check out all the wiring between these components.
 

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Discussion Starter #8
I pulled the ignition coil wire and removed the plug from the cold start valve. With the digital meter, I get steady 4 volts and when I crank it, I get 7 volts.

There are two sensors on the cyl head on the right side near the back, one with only one wire and the other with two wires (screwed like sparkplugs). Which one would be the temperature sencor? I get readings in ohms (resistance).

Mine is a 1990 6 cyl, 3 liter, 300E. Behind the battery, there is only one relay with 10 amp fuse. The rest are big black modules. Could not find the fuel relay unless the relay with the 10 amp fuse is the one.

Can you help please for cold start problem. Rund great when warm, but stumbles after a few cranks when cold.

Thanks
 

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I pulled the ignition coil wire and removed the plug from the cold start valve. With the digital meter, I get steady 4 volts and when I crank it, I get 7 volts.

There are two sensors on the cyl head on the right side near the back, one with only one wire and the other with two wires (screwed like sparkplugs). Which one would be the temperature sencor? I get readings in ohms (resistance).

Mine is a 1990 6 cyl, 3 liter, 300E. Behind the battery, there is only one relay with 10 amp fuse. The rest are big black modules. Could not find the fuel relay unless the relay with the 10 amp fuse is the one.

Can you help please for cold start problem. Rund great when warm, but stumbles after a few cranks when cold.

Thanks
If you are seeing 4-7 volts at the cold start valve, then go back and check voltage at the fuel pump relay.

Should be behind the battery where you are looking.
The forward relay with the ten amp fuse is the OVP.
Behind it is a black module which is the fuel pump/kickdown control.
The furthest back is the KLIMA or air conditioner module.
 

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Discussion Starter #10
Mine has 1) OVP with 10 amp fuse.

2) Behind it, there is a silver relay.( 0015420219 )

3) MAS black module on the left with a release knob on top with
20-22 pins.
( 007 545 6532)

4) Computer with lots of wires pluges on top.

I did break the silicon and opened the MAS relay but all solder joints
were intact. I still used the soldering gun and made the joints
stronger.

Still would not start in the morning without 6-7 cranks. Ran fine
after having been warmed.
 

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Mine has 1) OVP with 10 amp fuse.

2) Behind it, there is a silver relay.( 0015420219 )

3) MAS black module on the left with a release knob on top with
20-22 pins.
( 007 545 6532)

4) Computer with lots of wires pluges on top.

I did break the silicon and opened the MAS relay but all solder joints
were intact. I still used the soldering gun and made the joints
-b= stronger.

Still would not start in the morning without 6-7 cranks. Ran fine
after having been warmed.

More then likely the silver relay.
Pull it out and see if it has nine active pins.

Below is the troubleshooting flow chart from the Mercedes M103 engine manual:


 

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bringing another dangling thread to life... I have this same scenario on my 190E 2.6 with a MAS, trying to find out if anyone's had resolution to this problem? my car's been tuned up.

furthermore, RBYCC, your post in this thread has been the most informative thing I've been able to find on this problem... I've been scouring the internet for a week. We'll see how the above procedure works on a 190E :)
 
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