help with ignition problem - PeachParts Mercedes-Benz Forum

Gurunutkins · #1 03-02-2008, 06:49 PM

Hi folks need some insight into an ignition problem.

I have a 76 450sl with cis injection that wont start. I tested plug cable to cylinder 1 and found I have 20KV plus using a voltage tester so assumed the problem was fuel and have spent the last week playing with the injection system, tested everything and it is all at spec.

car still didn't start so I played with the timing all in spec for static timing still no start.

finally pulled the spark plugs today to test the compression (yep I was starting to go a little loco) whilst the plugs were out got a friend to crank the engine to test the compression and had one of the plugs in the wire resting on the engine, there was no spark!

tested another plug on a different plug wire and as the distributor turns I get a little puff of smoke from the plug but no spark. test it with the voltage tester get 20KV plus spark. put a different spark plug in just a tiny spark or a little whiff of smoke as the plug is supposed to fire.

I have 12vplus at the coil, 13.5 at the battery, the distributor is turning and will fire a timing light or a spark tester at 20KV. The plugs are autolite 64 (recomended replacement for the car) and have done about 80 miles. all the cables ohm out as per spec (less than 3K ohms)

any thoughts appreciated
thanks
Barri

Tims450SL · #2 03-02-2008, 07:44 PM

well, I hate the auto lite plug-Please get the Bosch non resistor replacements I looked but cannot find the number. DO NOT USE PLATINUM. Also have you tried the old starting fluid in the intake to see if it even bumps? It sounds like a breaker point issue to me. I am not a tech, but as I have lots of troubleshooting experience (i.e. buy something - hope it fixes it) They have high compression and the slightest spark anywhere should give it alittle chance of firing. It really seems like the issue could be the fact that your coil is really not as strong as it reads and that the breaker points are not being feed and or are not working correctly. Good luck I will keep an eye out-let us know when you get it working and what the prob was ok! :0)

Robert Squires · #3 03-02-2008, 08:30 PM

* What is the condition of the cap and rotor, resistance of the coil wire? How did you measure the output of the coil, to get the 20KV?
* I believe that by '76 all the US export M117s were solid state ignition, i.e. no points or condenser.

Gurunutkins · #4 03-03-2008, 09:36 AM

thanks for the thoughts
it is solid state, the rotor and cap are new and all wires are between 3 and 5 k ohm. I will be replacing the plugs today with something else but cannot see how 8 plugs (with just 80 miles on them) fail at the same time. I measured the 20KV with a spark tester where the spark jumps a calibrated distance between the end of the cable and earth. I was getting a nice blue/purple spark at 20KV.

just when I plug the sparkplug into the wire and earth it to the engine and a tiny little spark or just a small puff of smoke. there is not even enough to ignite starter fluid.
cheers
Barri