Cool..

When you have time , I would still do the simple groud verification test I mentioned as a high percentage of electrical faults on these systems is poor ones............. Specially intermittants.
Being a neg grounded coil circuit, a poor ground is as bad as a poor feed.

So I did some yard stuff, ate lunch, and decided I would venture out for the first extended drive. Cranks, no start, but would chug every once in a while like it wanted to start.

Pulled two plugs, bone dry. So I dicked with the CSV, no change. Looked at the voltage at the coil and points, it was OK. So I invented a new test. I hooked up my timing light pointed it at myself, and pressed the trigger while I cranked. Discovered no spark. Then on another try it flashed and the car started. So I have discovered that even with dry plugs, I have an ignition problem.

So then I checked the switch box and distributor plate grounds per Arthur, and both were fine. So then I squirted some contact cleaner on a Q-tip and swabbed the points, finding that some dirt/grease came off. Put everything back together, and cranked. Flashing timing light, instant start.

Summoned up some courage and took it for its first extended drive, which went fine.

Personally, I don't think the points were dirty enough to cause the problem, but time will tell. I believe that switching unit is flakey and it's time too look for a Pertronix or Crane unit.

BTW - I did check the resistors (in car). The .4 is showing 1.8 and the .6 is 1.2.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

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An easy test for point conductivity is to hook the ohm meter on the wire going into the dist. and then measure to ground when the points are closed .. there should be trace, if any, resistance through the points. The problem with these transistor ignitions is they went to low voltage on the points to give them longer life, but in doing so, any R factor from wear, corrosion, dirt/oil on them will result in No spark.. whereas the old ignition systems had so much current going through them [ due to them being the switching source for the coil triggering] that the high current actually burnt of any corrosion/oil, etc.
So, the fault of these systems still always comes down to the common faults of Mechanical switching.. so , I too recommend dumping them for a Full electronic set-up. { you mention Randys referral to "Breaker" controlled transistor system.. the Breaker part is referral to the points, whereas full electronic is the same transistor switching along with hall effect or optical triggering of the transistor, thereby replacing the points with electronic switching....the new units still use the transistors to carry the coils load, it is just that they are no longer triggered by mechanical points -Thank Goodness]
If you decide on Pert, do get the correct coil, as yours will not work with their set-up

Seeing that this post is an ignition related post , I am going to throw this tid-bit of info in on this one for et al.........

As CT mentioned , he used a timng light.. not to time his car, but rather to verify spark.
Well, techs have been using this tecnique for years and if any here remember the OLD timnig lights, these can be found at yards sales , etc a $1 b/c no one wants them anymore... but, they are the perfect ignition spark observation tool for your toolbox.
These are the ones that do not have an Inductive pick-up, or leads that go to the battery to power a bright light, or any of that new stuff.. these are just a simple Neon lamp in a plastic housing and two spark plug high tension leads coming out that have connectors on the ends so you can remove a spark wire and insert this light In SERIES with the spark plugs wire. They don't even have a trigger on them..they were so bad you had to put the shop lights out when you timed a car !!! But , for quick spark verification , they are the tool.
The advantage to these is you can now check for spark at any plug or even better yet, right out of the coils center tower [ secondary ignition]..and B/c it takes the plug power to light this lamp. a weak spark will result in a very weak lamp [ whereas, with an inductive type light, this is not the case as the lamp is battery powered]
So, a nice tool to have hanging around for ignition output testing without having to hold plugs wires close to ground or laying plugs on the manifold, and all that Jazzzzz...
Get one .. they are even cool for lawn mowers and chain saws , etc. Like 'da man says .. " Hey , it's gotta be spark or gas, Man..can ya dig it ?"

chuck, The advice I got from Frank Mallory about cleaning the points is to use a dollar bill. If you have to do this more than once, that means you have oil leaking up from the engine into the distributor and probably more shaft wobble than is good for you. Get it rebuilt some day. -cth

__________________
- cth350@gmail.com
http://www.111lakeside.com/

I guess what the esteemed mr Mallory meant was..." use a dollar bill and buy an new set of points..." .
Read my reply up further regarding the need to start with the basics,And I mean real basics ,no fuel No start,No spark no start.....etc etc .Messing around measuring ohms and things are things you do once the engine is running and you have a running fualt, and Charlie is right on the button,the Distributor shaft seals wear and oil leaks up ,but do you still have the plastic points cover in there? , If so, remove it and throw it way because it will hold both oil fumes and moisture in the Distributor cuasing problems with the points.

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Yeah, Right..
..Ohms and Volts and schematics .. Scope patterns..all NO GOOD when it comes to electrical diagnostics.

.. just do the basics... jumper 12v over to the coil .... right????

I've been working on these for close on 40 years and i have found that advising people to read schematics etc is extremely counter productive.
When you are dealing with a cash paying customer,who is only interest is to have the mercedes back on the road,you don't have time to read some diagram ,especially when the average mercedes from 1954 through to 1984 had an almost identical wiring layout with the same plugs .lead colours etc .
More on this later...I've work to .

.. But these are not cash paying customers .. these guys are Forum members seeking out technical info on there Pride and Joys..
So, we tech them for FREEEEEEEEEE........... from schematics postings to hands on circuit, step by step, fault tracing ... and even a few electical tips of the trade thrown in....for good measure.

Many of these fellow members [ specially on the Vintage Forum] didn't just fall of a turnip truck, ya know...........they are bona-fied DIYers ... not customers.

Which is exactly why I post on here ,I feel I have spent enough time under these older mercs ( and a lot of new ones) to be able to say to someone,"just run a hot lead to the coil,crank the engine and see if it starts...".
OK?
Whilst reading a schematic is fine for those who need to know wherew a wire leads to,it's not going to get a car running with a minmum of fuss.
Meredes owners are fortunate in that the wiring is near bullet proof with fualts being related to the components on the ends of those wires.
Bythis I mean that there are no firewall plugs to corrode etc etc ( as per Fords and Volvos ) and given that,the fualts are nearly always simply and quickly found.So looking for earth connections ,while being a basic job,it really isn't neccesary to search them out.
Go back through my post on this topic and you will notice I mentioned the 'points'...Did the owner check his points??,did he check the "condition" of the spark?...again I said the spark should be 'loud and clear blue' otherwise the car won't start.
Well it did start but because he chose not to check the points the spark was insufficient to run the car properly and it stopped on him.
CTH mentioned a common mercedes Fualt as being the cuase of dirty fualts and I respect his opinions on this as he has a far larger collection of Older mercs than me,so he knows one or two things about them.
I see that far too much time is being spent telling Merc owners to do things which will not get a car running such as I have said already,things like looking for the resistance in the ballast resistors.
For instance ,the owner who started this topic was worried about a crack in a resistance....well that is not going to stop a mercedes running,it may not look very good but as long as the Circuit is "not open" it will run.
A car will run with a tired resistance and will only fail to start when the resistance burns out,something I have yet to see on a mercedes.(In that case the engine will fire while the engine is cranking on the starter but won't continue to run when the key is released.)
The spark plug test I mentioned is quick ,easy,takes about 3 seconds to do and gives a far better true indication of ignition conditon than any timing light method,which I did many years ago till experience tuaght me better.
I mention this because normal practice is to just hook my Repco test bench and let the machine tell me whats wrong...but no private owner has these( or the Sun equivalent) So I let people know the quickest easiest way to get a car running or what ever else they would like to know and you know what??? I do it for free from the back of my turnip truck/keyboard...

All I can say is that occasionally in your near-rants there was some useful advice. But your basic message was "if there is gas and spark, the engine will start and run." Well, DUH, even I, who you obviously think just fell off the turnip truck, know that.

The problem was that there was no spark and I was trying to figure out why. And I was working through the recommended tests and getting some very odd numbers.

And for this system, with the positive side of the coil being switched and negative grounded, you gave some extremely poor advice when you suggested hooking up battery voltage to the positive side.

From the turnip truck,

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

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.. WRONG... which is what we have been trying to tell you ..
The coil on this version of Transistorized Ignition is wired directly to ground on the Neg side , meaning it is not a switched ground circuit. [ Which the SCHEMATIC clearly verifies] ..SO. bringing your 12v pos. jumper to the coil WILL NOT START THIS CAR , come hell or high water.
get it ???????????????

I hear ya..yada.yada,yada,..rant ...

MY point was you were giving WRONG info..info that not only would not solve the problem or start his car..., but could, in fact, fry the guys coil.
That was the point..but you , in you 40 years of expertise, just would/could not comprehend. But . he did ..so that's all that matters.........

I am also from the school of KISS, and I do grant you that a jumper to coil pos on a STANDARD system is a quick trick of the trade to eliminate the possibilities of ignition sw feed, BUT, that is NOT the case on THIS post and makes that trick not only invalid, but dangerous.
Something you may want to consider next time you jumper an ignition with direct 12v to the coil is to first see if the coils neg side is GROUNDED.. a very KISS observation.




END !!!

My 4.5 burned out TWO boxes. One just plain died, another went when the key was left in the "Run" position with the engine off and the points happened to be closed.

Ignition boxes can and do fail. Now, relax, both of you. It's a simple misunderstanding, so don't drag it out into drama

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

MercMad -

I think that everyone would agree on at least a couple of things. 1) we are here to help solve problems and offer advice, and 2) that we don't ever ever get rude like you were in your last post.

This is your warning. If you ever post anything like that again, either I or your co-moderator will ban you from this forum.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe