Failed Pertronix Install - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 05-05-2012, 05:48 PM Thread Starter
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Date registered: Apr 2012
Vehicle: 1971 Mercedes-Benz 250C
Location: Toronto, Canada
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Failed Pertronix Install

So I've spent most of the day "re-wiring" the transistorized ignition of my 1971 250C in order to fit the Pertronix igniter. I've done this already on my other classic car with much success ... Well not so for the 250C.

I think I've done it all correctly but the car just won't run ... it starts, barely, and then struggles to keep on running. Pertronix guys confirmed that I have the right kit: 1867A. In the catalogue this is for the 1970 250C, which I am guessing had the conventional ignition set-up so I sort of doubt that I have the right part. My distributor number is 0 231 187 003 with both advance and retard functions.

I really hope that some of your may be able to shed some light here. I read this forum for the past week and had gathered a lot of info but I guess it just wasn't enough So how I tackled the "re-wiring" of the ignition is as follows: I connected the wire coming from the ignition to one end of a 0.4 ohm resistor (I have the 1.8 ohm red bracket resistor to go with the red Bosch coil that I purchased but decided to try it with a 0.4 ohm since the coil has 2 ohms of resistance to begin with), then at the other end of the resistor I connected the wire that goes to the starter and the wire that now goes to the positive terminal of the coil. Pertronix red wire to the start of the resistor, with the ignition wire (as per Pertronix instructions) and the black wire to the negative coil terminal. Tested the voltage and it came in at 9.5. Tested the red Bosch coil and the resistance came in at 2 ohms, hence the amperage was now 4.75. With the original set-up the amperage was 3. To make sure that the RPM switch works, so the advance / retard functions of the distributor work fine, I ran a wire from terminal 7 of the transistor (where the green wire from the distributor used to be) and ran it to the negative terminal of the coil.

When I started the car first, I did notice a weird noise and upon opening of the dist cap, noticed that the rotor was rubbing against the Pertronix unit! I tried a different rotor that I had (much thinner), this time no rubbing, but the car still does not run. Like some of you with certain distributors, I did not have to modify the bracket as the magnetic sleeve seemed to go on without any issues and lined up properly with the unit. Could I have installed it incorrectly??

I think that there could be so many factors here ... At this point I considering leaving the points in and dealing with them ...

Any thoughts / ideas / guidance would be much, much appreciated.
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post #2 of 2 (permalink) Old 05-06-2012, 08:00 AM
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Date registered: Jun 2007
Vehicle: '70 280S-'73 450SLC-'81 380SL-'84 500SEC Euro-'92 300SL24-'95 E320
Location: Northcoast of Ca in Eureka
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I recently had similar issues with my '70 280s. The problem was getting the magnetic ring to seat down properly on the distributor. Take a socket from your tool box that is of a slightly smaller diameter that the ring, set it on top of the ring and give it a gentle but firm rap with a small hammer and be sure that puppy is fully seated. Mine now runs like a chump....I mean champ

1973 Mercedes 450SLC (PineGreen/MahoganyLeather)
1981 Mercedes 380SL FORSALE (LtIvory/PalominoMBTex)
1984 Mercedes 500SEC Euro (040Black/BlackLeather)
1992 Mercedes 300SL-24 Signal Red/Black Leather
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