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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 49175
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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it turns over but the spark from the distributor to the coil is weak.

Resolved Question:

it turns over but the spark from the distributor to the coil is weak. what do i need to do to fix the problem?
Submitted: 5 years ago.
Category: Mercedes
Expert:  Marty replied 5 years ago.

Hi George, can you give me a little more history of the problem? Has the car been running fine and just quit? Do you have a voltmeter?

 

Marty

Customer: replied 5 years ago.
the car was running fine. i stopped at a store shut the engine off. when i returned it would not start. this problem happened once before, but the next day the car started.
Expert:  Marty replied 5 years ago.

Ok, can you verify that the fuel pumps are running by listening to them at the right rear of the car while a helper cranks the motor? You may need to actually put your hand on the pumps to feel them working. Do you have that voltmeter?

 

Marty

Customer: replied 5 years ago.
fuel pump is working. no i do not have a voltmeter.
Expert:  Marty replied 5 years ago.

Ok, spark comes from the coil and goes to the distributor and on to the ignition rotor back out through the cap to the individual spark plugs. If you have weak spark from the coil to the cap the problem could be a bad coil, coil wire or ignition control module. You will need a voltmeter to perform some tests or you will have to have the car diagnosed by a Mercedes technician familiar with the ignition system. I don't recommend replacing anything without proper diagnosis. Let me know if you have any questions.

 

Marty

Customer: replied 5 years ago.
what test do you want me to perform with the voltmeter?
Expert:  Marty replied 5 years ago.

The first thing I'd like you to do is to turn the key on and test for voltage at each terminal of the ignition coil. Then I'd like you to connect your voltmeter from one terminal to the other and measure the voltage. Let me know what you find.

 

Marty

Customer: replied 5 years ago.
when i measure each terminal it shows good. when i measure the two together it shows no reading.
Customer: replied 5 years ago.
did you get my answer? both terminals show positive, but when i test the both at the same time i get nothing at all.
Thanks.
Expert:  Marty replied 5 years ago.
Hi George, I was away this afternoon. Those readings are what we want to see. How do you know you have weak spark? How did you test it?
Customer: replied 5 years ago.
i tried to start to car while a friend of mine pulled off the wire that went to the distributor which goes to the coil. he used a screwed driver and said the spark is weak. he has a litlle knowledge about american cars.
Expert:  Marty replied 5 years ago.

Ok, if he is correct then the procedure would be to replace the coil wire and then the coil. If he is incorrect I would check the spark at the spark plugs. If no spark is present I would replace the ignition rotor and possibly the distributor cap. I would see if you have spark at the plugs first. Let me know if you have any questions.

 

Marty

Customer: replied 5 years ago.
thanks i will try this tomorrow and get back with you. thanks!
Expert:  Marty replied 5 years ago.

Ok George, I'll be around if you need anything.

Customer: replied 5 years ago.
i changed the coil wire and the coil. it is acting the same way. the ignition modular cast $2300.00. what do i do ?
Expert:  Marty replied 5 years ago.

Hi George, if you have some spark from the coil I would change the rotor first. Let me know what happens.

 

Marty

Customer: replied 5 years ago.
we got plenty of spark. the mechanic sprayed ether in the carb and the vehicle started right up. again he checked the fuel pump and it is running fine. he thinks it might be the fuel filter.
Expert:  Marty replied 5 years ago.

Ok, at least we know the problem is lack of fuel and not spark. I doubt that the fuel filter could be the problem based on your description earlier but you could give it a try. To diagnose it properly the fuel pressure and flow should be checked. Also make sure the car isn't out of gas. You may have a problem with low fuel pressure or with the fuel distributor. I'm assuming that when he stops spraying the ether that you can't keep the car running.

 

Marty

Customer: replied 5 years ago.
your right its not the filter. he clean the connection and got a lot of gas out of the fuel pumps. on this model i have two pumps. he thinks i got low on gas(which i did) and stuff on the bottom of the tank got into the fule pumps. the car seems to be running fine. i probably need to put some sort of cleaner in the tank. have any suggestions?
thanks,
george
Expert:  Marty replied 5 years ago.
I wouldn't bother with any cleaner. Your fuel tank has a very fine screen inside which filters out debris. Anything that could have gotten through the screen would have gotten through long ago. So I assume the car is up and running now? It sounds like the mechanic isn't really sure what happened to me.
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 49175
Experience: Bosch Certified Master Tech. Over 35 years experience.
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