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  #1  
Old 09-20-2015, 08:56 PM
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Fintail Tune Up

I'm trying to troubleshoot some hard starting with my fin and have found the following so far:

1. The resistance on the plug wires was measured with the multi-meter set to 20K resistance.
Cylinder#
1: 5.11
5: 1.24
3: 1.29
6: 1.5
2: 1.27
4: 1.31
Coil Wire: 8.55

Jumped plug 1 and then 2 to ground from the plug wire to metal, cranked the engine and by my perception observed that #1 spark seemed a lot weaker than 2.
Removed the air cleaner and pushed the throttle linkage and observed strong fuel flow from the accelerator pump of the firewall side carb only (which appears to be normal). Car runs great once started, plenty of power though I don't have an experienced enough ear to detect slight miss, although there is very slight inconsistency to the idle.

I purchased a timing light and having been a diesel head all my life, took my first ever timing readings. Attached to plug wire #1, the reading on the balancer seemed to read 1.5 ATDC. If I'm reading the markings right, they look like 1, 2, 3, 40. Does each digit on the balancer indicate a factor of 1 or 10? I don't suppose the car could run at 15 ATDC!?
The spec is 2 ATDC if I recall. Any reason to advance it .5 degrees? 93 octane is used.

Questions:
Does the data indicate abnormal resistance in plug wire 1?
Is the coil wire reading within normal limits?


Thanks for the replies. I plan to replace the points, cap & rotor at the very least.
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Last edited by joshhol; 09-21-2015 at 06:12 PM.
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  #2  
Old 09-21-2015, 06:56 PM
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Checked the primary side of the coil ~ 1.3 ohms
Secondary side shows 14.34K which by what I gather looking at random searches, is much too high.

Also, what are the two doohickeys in the picture to the right of the coil that connect into the + side of coil?

Thanks
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Fintail Tune Up-coil.jpg  
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86 300E 5 speed
2010 VW Jetta TDI M6
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  #3  
Old 09-21-2015, 08:11 PM
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The two items to the right of the coil are a condensor (next to the coil). The purpose of the condensor is two fold -cut down the static in the radio and store excess voltage to help reduce pitting on the ignition points. The second item is a ballast resistor. The resistor is designed to provide a full 12 volts to the coil during starting and to reduce the voltage to the coil to approximately 10 volts while the engine is running (non starting). Both of these items are generally pretty inexpensive - I would go ahead and replace them during your tune-up as they look like original parts.

Last edited by BWhitmore; 09-21-2015 at 10:01 PM.
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  #4  
Old 09-22-2015, 04:02 PM
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Thanks BW.
Went ahead and ordered all the parts except the condenser directly to the right of the coil. I located it in the EPC and an initial search showed a possible lead, but that may be a ghost track/hard to actually acquire. Since there is a condenser at the distributor, seems like an odd system to have 2.
Also noticed something odd, the plug wire for #1 is a right angle tip with 5K Ohms R while the other 5 are straight tip with 1K Ohms and a different Bosch part number. Sloppy mechanic work? Possible contributor to hard starting?

One other question: Does a reading of 1.3 ohms R on the primary side of the coil indicate that a resistor is built into the coil already, making an external ballast resistor redundant? The coil I ordered looks like the same one (Bosch Green Label) but based on the plug wires, don't know if I can trust the current setup.
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previously-
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  #5  
Old 09-22-2015, 04:37 PM
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I am pretty certain that the coil requires an external resistor. Most coils do not have internal resistors. The reason for the external ballast resistor is to increase the life of the coil by reducing the voltage to the coil during running. The external condensor is to prevent static in the radio. The condensor located inside the distributor (attached to the points) is to lessen point arcing. It appears from your pictures that the ignition parts on your car are original or were installed several years ago. Any new parts that you can obtain is a good idea and use the older known good parts as spares. I am not sure of the proper resistance values of your spark plug or coil wires. You might also want to consider the installation of a Pertronix electronic ignition system. With this system you never have to replace the points again and get a better spark. Pertronix has a web site. You will need the number stamped into the side of your Bosch distributor.
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  #6  
Old 09-22-2015, 06:00 PM
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Thanks again. I will look into the condenser, see if it's available. I noticed that there were little condensers sprinkled all over the place in the epc.

And I'm sure you're right about the external resistor, I'm just over thinking it.

I will take a look at the Pertronix system, heard a lot about it, but I like the fact that my fin is virtually all stock. However, I like hard starting much less than altering the ignition system.

Still need to do a compression test and evaluate the fuel system some more. Valves were adjusted recently.
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76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6
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  #7  
Old 09-30-2015, 08:20 AM
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Got the ignition parts and all the plug wires had resistance values of around 1.00. The coil wire was less than 1 and the (identical) coil was 2.2 on the primary and 14.63 on secondary. I guess I can keep the current coil in service or just keep it as a spare. The plug wires should help improve spark quality. This mild fall weather is calling for some fin driving for sure.
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  #8  
Old 10-01-2015, 01:40 PM
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For whatever reason some of the replacement wire sets have a 5K socket for plug #1 and 1K socket for the rest. You want a 1K socket.

What are the hard starting problems?
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  #9  
Old 10-01-2015, 10:32 PM
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The new wire set is good to go. The car has always been a little difficult to start, more so when it's been warmed up and you stop for a little while but lately it seemed more and more difficult and I was almost stranded the other night. Always thought it was the carbs and coming from a diesel background, I'm not accustomed to suspecting ignition parts.

Been doing some reading on coils and ballast resistors and after becoming more confused, I think I've sorted it out. The 3 bosch coil types: blue, black and red correspond to: no external resistor, .9ohm external, and 1.8ohm external resistor respectively. My set up right now is the black coil but someone configured it with the red (1.8ohm) external ballast resistor. The coil is actually silver with a green label but it says to use a .9ohm ballast resistor, so it is the modern version of the old black coil.

Butthat shouldn't affect starting if the ballast resistor is supposed to permit maximum voltage to the coil during cranking. The thing that confuses me is that the power to the + side of the coil comes through the external resistor, there is no other way, so how can it distinguish between cranking and running? Is just a function of the material of the resistor progressively increasing resistance as voltage passes through? I was checking voltage on either side of the resistor and at the + side of the coil and readings were all over the map. For a while it seemed like the whole system was dead because I couldn't get any reading and I couldn't get a spark to jump from the plug wires to ground.

Head scratching. But, I suppose I should put in all the new parts and then take readings and then maybe try switching out the ballast resistor for a lower one. Or run a red coil.
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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Last edited by joshhol; 10-01-2015 at 10:44 PM.
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  #10  
Old 10-01-2015, 11:10 PM
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Not having owned a gas vintage Mercedes for a few years and not having a sharp memory, a few questions: how many separate wires are connected to the positive side of the coil? If there are two separate wires that would mean that while cranking the coil is receiving a full 12 volts directly from the starter solenoid. Once the engine has started and the key released to the run position, the power is routed through the ballast resistor thus reducing the voltage to the coil while the key is in the run position. If you have a multi meter you can check the voltage at the coil while cranking and then again while running. The coil will operate on a full 12 volts for a period of time but will run hotter thus reducing the life of the coil. When checking for spark it is best to attach a spark plug wire to a spark plug and ground the spark plug to the engine. Crank the engine and you should see a bright orange/blue spark at the spark plug gap. Only use this procedure if you have a point type ignition. Doing this with an electronic ignition can potentially damage the ignition system. A point type ignition system consists of both primary and secondary parts. The primary parts utilize low voltage (12 volts or less) and consist of the points, condensor (both internal and external), the primary windings of the coil, the ballast resistor, the ignition switch, the primary wires (small wires) and in most cases the starter solenoid. The secondary parts are the spark plugs, plug wires, distributor cap, distributor rotor, and the secondard windings of the coil. When everything is working properly, 12 volts goes the the primary windings of the coil (while cranking), as the points are closed the primary windings of the coil are allowed to saturate and when the points open the primary windings of the coil collapse and jump to the secondary windings of the coil creating up to 20,000 volts which travels through the coil wire to the center tower on the distributor cap, through the rotor, and then to each spark plug wire in a certain sequence (firing order). As stated before, while running the 12 volts is routed through the ballast resistor thus reducing the voltage going to the positive side of the coil. The reason for this is two fold: to provide a hotter spark during starting and to lengthen the life of the coil. A good check of the coil and points is to attach a spark plug to the coil wire (the distributor cap side of the coil wire) and to crank the engine. You should see a constant spark at the gap of the spark plug. Your idea of replacing the points and condensor is a good starting point. With a vintage car there is also the possibility that the distributor shaft bushings or distributor cam lobes (causes the points to open and close properly) are worn which would result in the points not opening and closing at the correct time. When installing the new points be sure to lubricate the distributor cam lobes with a VERY small amount of lubricant such as a high temp grease ( quite often new points come with lube contained in a small capsule). High temp grease can also be purchased specifically for distributors.

Last edited by BWhitmore; 10-02-2015 at 12:14 AM.
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  #11  
Old 10-02-2015, 12:08 AM
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Just to go down a slightly different path in parallel, I have a few questions:

1. Manual transmission?
2. Dual solex carbs?
3. How does it idle when cold? When hot?
4. Do you use the choke to start the car cold? And then shut it off in a little while?

Based on your answers to 3 and 4 I might have more comments.

Scott
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  #12  
Old 10-02-2015, 06:29 PM
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On the pic you can see the wire coming from the resistor going to + coil and then the wire that goes to the condensor on the same side. But the condensor leads terminate on the side of the cylinder head and they look like braided wire or something. The same kind of wire departs the brake booster and terminates on the same spot on the head. So, there's only one path for power to the + side of the coil, right?
The EPC does show an external resistor, guess I need to find a wiring diagram.

Scott: Manual, dual solex, will stall when cold if don't maintain high idle (worse in winter), idles awesomely when warm, I use the choke as you describe.
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Fintail Tune Up-img_20151002_072454_020.jpg  
__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6
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  #13  
Old 10-02-2015, 06:55 PM
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It is hard to tell from the picture. As you said it is best to get a wiring diagram. As stated before,an electronic ignition system Pertronix) is an option. The Pertronix system will eliminate the ballast resistor, eliminate forever the need to replace the points and condensor and provide a better spark. The Pertronix system MAY also require new spark plug wires. From the pictures, many of the parts shown appear to be original to the car. Probably best to see what Scott has to say about your carburetors, etc.
before buying any new parts, however, from a reliability standpoint you will need a strong ignition system.
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  #14  
Old 10-02-2015, 08:46 PM
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Wiring diagram confirms that power travels through the resistor to coil + and no other way. Will take a hard look at Pertronix but it may not happen right away.
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76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6
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  #15  
Old 10-03-2015, 10:23 AM
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Quote:
Originally Posted by joshhol View Post
Scott: Manual, dual solex, will stall when cold if don't maintain high idle (worse in winter), idles awesomely when warm, I use the choke as you describe.
Regarding start when cold - do you pull out the choke, crank the engine, and it fires right up and then runs high until you push the choke half way end, then runs fine, then eventually you push choke all the way in? If you have easy cold start then I am not sure why you would have difficult hot start related to spark/coil/etc.
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