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Old 11-24-2013, 12:19 PM
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Location: Vernon, CT
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Need help!!! 74 450SL misfires 3 cyls, also just cuts out.

I am posting this on 3 different forums. This one, the Vintage and the Tech forums to get the most exposure.
The is for a friend's '74 450SL that I have worked on and know fairly well, but not everything.
First some background on the car. The valves and timing have been set to spec. The wires (Beru), cap and rotor (Bosch) are relatively new. The coil (Bosch) appears to have been there a while. The distributor has the old points system.

The car has a loping idle as if she is misfiring. Using my timing light, I found that there is a pause is strobe light pattern on cylinders 1, 2, and 8. The other cylinders didn't miss a beat. We checked un der the cap and there is no corrosion on any of the tips, they all look the same, clean. We did however notice that the rotor itself has a lengthy crack in it. It runs almost the whole length of the rotor, meaning from the center point out to the edge. It's a hairline crack, but noticeable.

Now, this car as I said has the old points ignition system and this is where my knowledge is a little thin. At the base of the rotor shaft, on one side is a metal tab which is secured to body of the distributor that has what appears to have felt on it. This however appears to be very old and the felt part that touches the rotor shaft is all worn down. It looks as if the metal may be touching the shaft. On the opposite side there appears to be what I guess would be the "points". There is a spring load device and clearly there is a "make or break" contact point on it. I also notice near this and a hair away from the shaft, what appears to be a magnetic sensor which I assume senses the position of the rotor as it spins. We noticed that this part of the shaft has evidence of surface rust/grime/dirt.

The other and probably related issue, is that the engine at times just ups and dies. The engine would be idling and suddenly just die. No stumbling, just cuts out, yet it would start right back up and be fine. This also happened yesterday as we pulled into a gas station. It has also happened while underway. We were driving along at about 35 mph and the a fleeting second the engine cutout but fired back up on her own.

Any and all tips would be greatly appreciated.

1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
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Old 11-24-2013, 05:01 PM
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Join Date: Jan 2012
Posts: 7,515
I posted info in the tech section.

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