1997 C180 no spark on two centre cylinders
I assume you have already checked your spark plugs to make sure they are properly gapped and are not worn or broken.
If your engine has a mechanical distributor, you probably need a new distributor cap and rotor, or at least you need to clean the high-voltage contacts. It's also possible you have bad spark plug cables. If you have an ohmmeter (one of the functions of a digital multimeter), remove one of the cables and check the resistance. If it's a wire cable, it should be no more than a couple of ohms. If it's a resistive (radio interference suppression) cable, it should not be more than a couple of thousand ohms (compare with a known good cable such as one going to another cylinder). If the cable reads very high resistance, is open, or you can't get a consistent reading, I recommend changing the entire set of cables - if two have gone bad, the rest are probably also approaching failure.
If you have separate coils for pairs of cylinders instead of a distributor, the coil feeding those two cylinders may be bad. You can test the coil secondary by reading resistance from the spark plug cable terminal to ground and comparing this to the other coils. If the ohmmeter test doesn't show anything significantly different between the good ignition circuits and the bad ones, or you don't have an ohmmeter, continue to the steps in the next paragraph. Note 1: prolonged engine operation with bad spark plugs can damage the coil. Note 2: on engines with multiple coil packs, an ignition module failure can prevent one of the coils from working, but usually the engine computer diagnostic system can identify this specific problem.
If you don't have an ohmmeter, it's more difficult to identify the problem. Try parking the car in a very dark place, open the hood, then start the engine. Turn off all artificial lights and watch the engine to see if there any visible sparks or corona discharge (the air near the part has a faint purple-blue glow) around the high voltage components. A spark from a cable indicates the cable has bad insulation. A spark or corona around the coil indicates a bad coil (broken-down insulation).
If you still haven't found the bad parts, try swapping spark plugs and cables (be careful not to mix up the firing order!) to see if the problem moves to a different cylinder, or if your time is more valuable than your money, replace the plugs and cables (and distributor cap/rotor, if your engine has them).
May 12, 2014 |
2002 Mercedes-Benz C180