Ignition troubleshooting

ignition
mercedes-benz
c-class

#1

Hi guys. I have 1976 Mercedes 280 with gas staight six cyl. The engine turns over, but won’t fire. I have no spark at the coil. I replaced the coil. I have 12v on positive side, and 12v on negative side of coil to the ground. Is that a sign of a good ignition module or not? What else I should check or do? Thank you for your help. Alex.


#2

How many miles since the last tuneup? When is the last time you replaced the points, plugs, spark plug wires?

Check to see if you have spark at the plugs. Get a spark plug tester at your local auto parts store ($5.00-10.00). You should see a bright blue spark. If you don’t, pull the cap on the distributor and make sure the rotor spins when you turn the engine over. Check the rotor and cap. Look for rust and crud. Look for excessive wear on the cap contact points and rotor. Check spark plug wires for cracks and burned spots. Always check the stupid stuff first. If rotor doesn’t move, you have a broken distributor. You may need t time the engine. The gap maybe beyond specs. Has the distributor been out of the car or been moved? Hope this helps


#3

If the negative side of the coil doesn’t show a pulsing the voltage while cranking the engine then something is wrong with the module. The negative side of the coil has to make a ground connection and then open the connection in order for the coil to generate the spark. The module should do that function.


#4

Thank you. I’ll check that pulsing. I suspect it’s a module too. Is there a such thing as a generic module? or it has to be for that specific car?


#5

Using a test light probe tied to ground and probing the minus side of the coil while craking the engine is a good way to test for the ignition pulses.

The ignition module will be specific to the car and possibly the year also. You might be able to get a replacement at a parts store if you need a new one.