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  #1  
Old 03-04-2017, 11:43 PM
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M-100, 6.3 1970 no spark

Dear forum,

engine is cracking, fuel is coming,( tried start ether also,)

5.5 volts on the coil, between its plus and minus,

12 Volts between + and other grounds,

cleaned the grounds,

coil resistance, 1.8 ohm,primery, 12K secondary,

did not check wire to ignition switch,

tried a spark plug outside the engine, nothing,

anybody has any clue,

thanks in advance,
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  #2  
Old 03-05-2017, 09:02 PM
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Several things to try, all of them are cheap.

Pull the plugs wires from the distributor cap one at a time. Look for blue powder. This is evidence of arcing and will build up enough resistance to shut down the spark from the distributor to the plug. Start with the wire from the coil as it is usually where this starts. Check both ends.

Check your coil wire with a continuity tester to see if current is passing through it. The coil wire can break down internally and not pass voltage from the coil to the distributor.

Check your rotor cap. OK, on the 6.3 this is a bit expensive so clean the black off the end of the rotor and file off the arcing. Also check the inside of the distributor cap for carbon build up. This can be knocked off with a sharp tool or scraped off with a flat tip screwdriver.

(You may consider buying a new distributor cap if yours is cartooned inside. But when you see the price of such a cap you might want to try scraping the carbon off one more time!)

Then pull a wire from a plug and hold it next to a valve cover. Have someone crank the engine. If the ignition system is firing you should see a spark jump from the end of the wire to the cylinder cover. If not then you will know there is no spark to your plugs.

You can also check the wires and see if they are passing current. There is no need to buy a new set of wires as each part of each wire can be replaced. You can check the plug caps, the wire itself and the distributor plug. I have found that all three can go bad independently of the others.

You can buy everything you need from Peach Parts. If not then the dealer could surely provide the individual parts.

If you find some used wires then be sure to check the ohms on the metal plug connector. They vary from car to car but the ohm level is indicated on the side of the metal cap.

And don't forget to check your points. Both sets should look good and have some contact metal left. If one or both is burned down to just the arms then that is probably your problem.
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  #3  
Old 03-06-2017, 12:40 AM
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Thank you Idle

I did have a new distributor cup, no help,

cleaned the ground, no spark,

I had a spark for 2 seconds, and gone,

did start for 5 seconds, and only smell of fuel,

will take a closer look at the points,

at the leads,


thanks for the response,

will keep posting hopefully with results,
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  #4  
Old 03-06-2017, 07:37 AM
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Do you have spark coming directly off the coil? 5.5V for cranking seems low. Your resistor may be bad or the coil itself may be bad. IIRC, the 6.3 has the same spark setup as the 3.5 and 4.5, meaning one resistor is bypassed during cranking. Pretty sure the coil, wires, cap & rotor are the same as those engines as well.
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  #5  
Old 03-06-2017, 08:39 AM
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Quote:
Originally Posted by rreeuuvveenn View Post
I did have a new distributor cup, no help,

cleaned the ground, no spark,

I had a spark for 2 seconds, and gone,

did start for 5 seconds, and only smell of fuel,

will take a closer look at the points,

at the leads,


thanks for the response,

will keep posting hopefully with results,
The starting for five seconds is telling me that the system is working and then breaking down.

This is beginning to sound like bad plug wires. If it will start again for even the five seconds then a test from those days is to see if you can see the electrical pluses running down the wires.

This method is at least ninety years old. Back in the 60's we thought we were smart for knowing how to do this.

The method is to be in a dark garage, or on a dark night, and to raise the hood. Then you just look at the engine, which you will not be able to see because of the dark, while a helper starts the car. It only needs to run for a few seconds.

If the wires are totally shot you will see blue pluses of electricity running down the wires. They will move quickly, looking like a lot of very fast blue worms.

Yeah, I know this sounds crude but when you are a thousand miles from a repair shop you do what you must to figure out a problem.

I have seen this several times. I can't explain what you would be seeing but it is quite impressive to see. It is also a sure indication that you need new spark plug wires.

(And back then the wires were not always kept apart from each other like they are now. When the wires would wear you would get what was called 'crossfire' where a spark from one wire would jump to another and fire the wrong plug. Or ground out on the block.)

And if you are really hardcore you can just grab a plug wire and hold on. You will know in less than a second that you need new wires. And yes, I once saw someone do this since they could not get their shop dark enough.
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  #6  
Old 03-06-2017, 08:48 AM
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You might just start with changing the coil wire to the distributor. The coil wire always breaks down first.

Check the resistance in the coil wire with an ohm meter. It should pass current with only a little resistance.

Also: Have the battery checked. It may be breaking down.

Also: Have the ground wire checked, and the grounding strap. Both can break down internally and look great but pass little or no current.

And clean your connections to the battery. I have seen a little bit of build up on a battery terminal shut down an entire electrical system.
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  #7  
Old 03-06-2017, 11:21 PM
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Dear friends,

Thanks for your input and support,

The car is running,

cleaned the the points,

oiled the distributer,

the advance plat was stuck, teflon oil helped

thanks again,
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  #8  
Old 03-06-2017, 11:29 PM
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What was stuck? Do not understand.
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  #9  
Old 03-06-2017, 11:34 PM
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in the distributer the plate the carry the two set of points,

and moves back and force by the vacuum from the engine, advancing the ignition,

got lubed, with moving back and force,
Attached Thumbnails
M-100, 6.3 1970 no spark-20170304_131550.jpg   M-100, 6.3 1970 no spark-20170304_131550.jpeg  

Last edited by rreeuuvveenn; 03-06-2017 at 11:53 PM.
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  #10  
Old 03-07-2017, 12:52 PM
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The best repairs are the cheap and easy ones.

There are so many little things that can trip up these older cars and all it takes is one part of the system to stop functioning like it should.

Thanks for sharing the results.
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  #11  
Old 03-11-2017, 01:36 PM
GGR GGR is offline
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I had a similar issue long time ago. With heat and metal dilatation, one set of points was grounding. The car would start missing, then would run on 4 cylinders and then would stop working all together. the car would then start again just by letting it cool long enough. I pulled all the hair out of my head before identifying the problem.

A blocked advance plate shouldn't prevent the car from starting. Assuming your issue was similar to mine, you may have solved it by fiddling with the points. If symptoms similar to the above start (re)appearing, you will know where to look.

Another issue I had a number of times on older MBs is the rubber/insulating washers deteriorating around the screw where it goes through the body, to which the points connect.
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  #12  
Old 03-11-2017, 02:10 PM
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you probably right,

could be I fiddled around so much,(like a mad dog)

that the insolation to the points got away from grounding the high voltage,

thanks for your kind input,
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  #13  
Old 03-11-2017, 07:26 PM
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that's a very expensive distributor (compared to the mearly expensive ones on other benzes ). If you are going to keep this car long, consider an electronic ignition conversion.

There are kits for it that basically swap out the points for an optical trigger and keep the car very intact. Search threads here. Also look for the international m-100 group on the web for their site and it's pile of threads.

-CTH
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