Cleaned distributor cap, engine turns but won't start - Mercedes-Benz Forum
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post #1 of 3 (permalink) Old 10-23-2018, 07:40 AM Thread Starter
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Date registered: Oct 2018
Vehicle: Mercedes W116 280SE '78
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Cleaned distributor cap, engine turns but won't start

Hi guys, I'm hoping you can help point me in the right direction here. I had nothing to do one day (usually how it starts, right?) and I thought I'd open up, check and possibly clean the distributor cap on my '78 280 SE K-jet. Worth mentioning I took out the wires first and one of the wires wasn't exactly looking great, possibly damaged by me when I pulled it out of the cap, the metal filament was cracked but it was still making contact so I took a note to replace that wire next.

My distributor cap looked rough on the inside with the contacts having plenty of carbon deposits but my car was starting pretty decent prior to doing this. I cleaned the contacts and noticed the plastic housing for one of the contacts was missing a side but the contact was held OK in place (not wobbly) and because the car started fine prior to this, I took a note to change the distributor cap as well at the next self-service interval which was due in 2 month's time.

All in all, the distributor cap and one of the wires were not in great shape but as I said before, the car was running fine before with recently (3months) replaced injectors, fuel filter, fuel pump and spark plugs as part of a major overhaul that helped with rough idling, loss of power and so on, the car was running decently for the first time!

I cleaned the cap the best way I could, made sure there are no carbon deposits on the contacts and put the wires back in (double, triple, quadruple checked that they're in the right order and match the markings on the cap) but when I placed the cap back on, I must have installed in a wrong way because as soon as the engine turned, I heard a loud pop. I stopped and looked, the rotor contact broke because the cap wasn't seated properly.

I ordered a new rotor and thankfully got it delivered the next day so I thought it'd be just a straight swap but I wasn't entirely sure if the rotor needs to be twisted in a certain direction and I did not make a note of the original rotor direction - I assumed the timing does not need adjusting for just a rotor swap. I simply twisted clockwise until it fell into place, put everything back together and gave it another try. Made sure, by the way, that the cap was seated properly now and the cap screws fell into place on the side of the distributor screw mounts.

As soon as I tried to start the engine, it cranked for a couple of seconds and then made another pop under the hood, only this time smoke came out and it smelled like burned plastic.

I took out the cap, it looks OK, so does the rotor. No obvious melting stuff at least at the surface. What have I done wrong, what should I be looking for? Could it be the ignition coil, or one of those cables that got damaged as I took it off the cap? How can I check the coil without being able to start the engine now? I don't want to go down the route of throwing parts at it (cap, rotor, spark wires, distributor, coil??) because the car was starting fine before all this so I'm trying to take the logical approach here but I'm out of ideas.

Any suggestions are highly appreciated, thank you!
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post #2 of 3 (permalink) Old 10-25-2018, 08:59 PM
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post #3 of 3 (permalink) Old 10-26-2018, 01:09 AM Thread Starter
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Thank you, very useful, helped me to figure out that I put my cap back the other way around!
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