Help, 1981 380SL the coil gets hot and car shuts off - PeachParts Mercedes-Benz Forum

Dlandis · #1 10-10-2011, 08:08 PM

I have a 1981 380SL and the coil gets hot and car shuts off. I bought a new coil and still have the same problem. Any suggestions?

meltedpanda · #2 10-11-2011, 10:22 AM

1. low quality plug wires drawing to much resistance
2. wrong plugs
3. short in the wires ( coil)
4. If you have points ( cant remember on that car) make sure they are not stuck closed or too narrowly gapped

did you do some sort of service and this occured or just happened?

Dlandis · #3 10-11-2011, 08:38 PM

I just bought the car about two weeks ago. I will try some new spark plugs. The plugs are a bit different than normal plugs. They have a sharp point on them and they were not normal plugs like champion or AC. The spark plug wires are new at least they look it. They are Bosch wires. I don't think there are any shorts in the wires. I did put a new coil on it and it got hot after driving for few hours. I am also going to replace the resistance unit that is made of ceramic. It could be shorting out there. I also checked the voltage on the coil and I got a reading of 11 volts which is okay. Thanks for the advice.
dlandis

Genbiltstein · #4 10-12-2011, 05:27 AM

A coil will get hot. If the coil is getting too way too hot you might want to check your dual ballast resistor with a DVOM. One resistor is for starting and the other is for running.

RadioTek · #5 10-12-2011, 12:32 PM

An '81 wouldn't have points, the last year for D-Jet ignitions was '75. I would suspect that you should check out the ballast resistors as mentioned above.

Then verify that you have the correct combination of plug wires and spark plugs. The system was originally designed to have non-resistor spark plugs, with a resistor in the connector of the wire. That's why the connector at the plug end is such a big one. If you are running resistor plugs, it can cause problems.

Next, verify the distributor cap and rotor, making sure they are correct and in good shape.

Then check your timing, to make sure it is properly set. If you are set wrong, when the engine gets up to temp, the automatic timing changes could be bringing things out of the 'run' area.

There is a possibility that the ignition module in the distributor could be bad, and could be messing up the signal to the coil, also.

There are a whole lot of things that could cause trouble like this, some not even mentioned above. I've just talked about ignition-related things, you could have a fuel related problem. Trying to trouble shoot over the 'net is difficult; you always seem to have too little info, so any suggestions are merely guesses at best.

Please keep up with the hunt for the fix, and let us help you with it. The hunt can be as much fun as driving the car. There is a unique satisfaction to fixing a problem yourself.

Best wishes,
Scott

meltedpanda · #6 10-12-2011, 04:48 PM

Sounds like you are using platinum plugs. Not good. Cross new with old original for matched specs

Genbiltstein · #7 10-13-2011, 05:32 AM

Scott: I know when I hear good advice.

Dlandis · #8 10-15-2011, 07:39 PM

Thanks for the advice. I'll continue to try these options and will post my results. Just need some time to work on it. I did replace the resister but it didn't make a difference. It could be that the coil may be weakened from all the times it overheated. I will have it tested.

meltedpanda · #9 10-15-2011, 08:11 PM

cross check those plugs, may be that simple

Dlandis · #10 11-03-2011, 07:13 PM

I have done most of all the advice given and it seems the coil is not as hot as it was before. I have a 1985 190E also which the coil doesn't get hot at all. Maybe I shouldn't compare it with the 380SL which is a much bigger engine as well.
I have been driving it and it hasn't shut off like it did. I bought new ballast resisters, new copper plugs, rotor and cap and another new coil. I double checked the wiring for a short. Set the timing as suggested also. I am carrying another coil in the trunk in case it would cause the motor to shut off like it did before. I have one more thing that I was going to try. What would happen if I switched the wires to the coil by placing the positive on the negative and vice versa? It could be possible that someone before me installed them backwards. I read an article about switching them and it implied that it wouldn't make a difference. Any more advice?

meltedpanda · #11 11-03-2011, 10:54 PM

older ones are marked SW" for Switch and "CB" for Contact Breaker. Later issue ignition coils are marked "+" and "-" on the primary terminals. it will run reversesd but not well

Dlandis · #12 11-04-2011, 06:22 PM

Thanks again. I will look at them more closer over the weekend.

Dlandis · #13 11-10-2011, 06:52 PM

I am still having the coil get hot. I bought another coil from the Mercedes dealer to make sure it was OEM. I replaced the rotor and the cap. Put new ballast resisters on it. OEM new plugs also. Checked the wiring and it all seems good. The only thing left to do is replace the spark plug wires. The wires that are on the car are Bosch Ultra Premium 7mm opti-layer copper coil wires. Any more advice about the plug wires? I am almost about to give up and take it to a professional.

meltedpanda · #14 11-10-2011, 07:41 PM

it would seem to me with all that you have done, that the grounding may be the issue, have you checked all the major ground junctions, and the grounding from the coil?

Dlandis · #15 11-10-2011, 08:08 PM

I will recheck them all again this weekend. Thanks.

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