Help with 71 mercedes 250-no start - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 03-07-2010, 05:36 AM Thread Starter
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Help with 71 mercedes 250-no start

Bought a 1971 250 Mercedes sedan. Will not start. When tested, no spark. Everything appears to be grounded both sides of coil and breaker points, no power. Has a ignition control module that doesn't seem to belong. Cannot find an accurate wiring diagram. Any help to lead in the right direction???
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post #2 of 3 (permalink) Old 03-07-2010, 07:34 PM
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Did it run when you bought it? As a starting point, I'd start by closely examining the points, cap and rotor. Make sure the points are gapped properly and not excessively pitted. If they're badly pitted your condenser is either bad, or the wrong impedence. Make sure the rotor center contact is good and making contact with the cap when installed. You'll see the wear witness marks. Make sure the little graphite "tit" is in place and in good shape. This is the contact for the rotor. If all is good there, put the cap back on and pull the coil wire at the distributor cap. Holding it about 1/2 in. from a good grounding point and have someone crank the engine. You should get a nice blue spark. If you have spark, plug the coil back in and then pull one spark plug wire at the plug and do the same. You should get the same kind of blue spark. If all is good there, check for fuel, too little or too much. I had a problem with the points on mine. I had put a brand new set in a while back and it fired right up. Backed it out of the garage and it stalled and wouldn't restart. A little troubleshooting discovered that the points were grounded out at all times. I put the old points back in and it fired right up. I couldn't see anything wrong with the new points, but took them back and got another set. Replaced them and it's worked fine since. You can check by hooking a dwell meter or timing light up. Then crank it over. The dwell meter should flucuate in the range of the dwell angle, unless the points are grounded out, or the timing light should flash every time the cylinder that you're hooked up to fires, unless the points are grounded out. One other thing, if the electronic module is stock, it is triggered by the points. In that case the points would normally not wear very much, except at the rubbing block where it rides on the distributor cam.

Good luck and let us know what you find out.

Last edited by mbbuff; 03-07-2010 at 07:51 PM.
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post #3 of 3 (permalink) Old 03-09-2010, 09:07 AM
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Try to use another same coil to make sure if there's problem in the ignition.

W123 280 1979
W115 200 1976
W124 300E 1991
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