M189 ballast resistor

[OzBenzHead]

Am I permitted a non-116 question here?

I have ordered new coil and condenser for my 300SE coupe's M189 engine, as the old ignition system is playing up. (Have already replaced plugs and points, and the HT leads were replaced just before I purchased the car 3.5 years ago; it has hardly been driven since - like less than 200 km. The dizzy cap was also replaced with the HT leads.)

The original coil is no longer available, and has been replaced by M-B with a different one (different part number and different specs). Trouble is, the previous ballast resistor (1.8 ohm) is no longer appropriate for the new type of coil.

MB Spares has been unable to source the new type ballast resistor or to discover its resistance; they have supplied the following part numbers:

0001581485
and, alternatively
0001581285.

The local stealership seems uninterested in being of assistance (surprise, surprise!) and claims to know nothing about M189 engines anyway.

Does anyone here have relevant experience or knowledge of this matter, and can they advise me of the new ballast resistance and/or a supply source for it?

TIA

Gordon

PS: The nature of the ignition systems misbehaviour is this:
Start car from cold, drive a few hundred metres and all is fine. Then, as soon as it has gained a bit of warmth (like the temperature needle starts to move from cold) it starts to misfire.

Replaced the original coil with a spare (old used Bosch of unknown provenance or capacity) and there was an improvement of about 60%, but still not right.

Then replaced the ballast with another old one of 1.8 ohms an another, slighter, improvement was noticed.

I don't want to fit the new coil/condenser combo with the 1.8 ohm ballast, as that would likely destroy the $100+ investment in those two new parts.

 

[WGB]

I apologise in advance if I am teaching you to suck eggs OBH but here is my understanding of a ballast resistor circuit.

As far as I know the the reason for a ballast resistor is so that it can be bypassed while using the starter circuit to allow full battery voltage (which may be lowered in cold weather) for only a short time while starting.

Then when the motor starts and the full charging voltage (about 14v) hits the wires the coil supply is reduced to 8 or 10 volts (or whatever is specified) by the ballast resistor being pulled into the power supply circuit.(There are usually two power supplies - one from the ignition switch direct and another connected via the ballast resister.

The coil should have it's rated voltage somewhere on the case I would think and when put in series with it's ballast resistor the voltage should match the rating.

It doesn't matter who makes the resistor so long as the output voltage is correct for that particular coil hence I would think Bosch/Fomoco/(wash your mouth out)Lucas would all potentially make something correct. An auto sparkie should know what to use as there must only be a handful of different spec resistances that are used.

My differential diagnosis of your problem would include
1) Faulty coils - all of them(Maybe even tracking insulation).
2) Faulty wiring - are you connecting the correct circuits to the ballast resistor circuit and to the open circuit.
3) Mismatched coil and ballast resistor.
4) There is nothing wrong with the coil and the problem is in the H-T leads or other part of the ignition (Unlikely considering all te worlk you have done).

Bill

 

[OzBenzHead]

I apologise in advance if I am teaching you to suck eggs OBH but here is my understanding of a ballast resistor circuit.

Not at all, Brother Bill. I'm learning on the run with this one, as its specs are so different from all my other Benzes - and other cars I've owned.

[...]
My differential diagnosis of your problem would include
1) Faulty coils - all of them(Maybe even tracking insulation).

Yes - I really do suspect that the old coil (it's the original 43-year-old one as far as I can tell from the car's service history) is dying, and the spare - which came out of a lucky-dip box of stray parts at my mechanic's workshop - is also dying, just not quite as dead yet. Hence my having ordered a new one ($71 from MB Spares) and a new condenser ($13).

By "tracking insulation" do you mean current leaking over the outside of the wires or the coil casing like as happens with grotty leads? I've looked at it at night with no lighting and the engine being revved (including whilst in gear with all the brakes on - and not standing in front of the car!) and not been able to see any "lightning" running along the wires or between elements of the system.

2) Faulty wiring - are you connecting the correct circuits to the ballast resistor circuit and to the open circuit.

The wiring is as it came when I bought the car - and it was all working fine then. It had been serviced for the previous 15 years by MB Spares, so presumably everything is correctly connected. It also appears to conform to the diagrams in the workshop manual.

3) Mismatched coil and ballast resistor.

As it's the original (or at least original-spec) coil and ballast, I assume they are matched; their part numbers seem to be correct according to the parts catalogue. The existing ballast (looks original, as it's extremely discoloured) measures at only 1 ohm resistance; it should be 1.8, so I suspect it's dead or dying. The tolerance range is quoted as 1.7 - 1.9 ohms.

4) There is nothing wrong with the coil and the problem is in the H-T leads or other part of the ignition (Unlikely considering all te worlk you have done).

As I now have replaced - or ordered replacements for - everything else bar the ballast and the leads, I'm leaving the leads until last. A set of the correct Beru HT leads for an M189 is outrageously expensive.

(I should also hope the distributor cap is okay; it was barely months old when I acquired the car, and has seen little use. A new one of those caps is worth the price of a secondhand car - well anything other than a W112 coupe!)

The search for enlightenment - and correct performance - continues. If I can discover the correct resistance rating of the new type ballast to complement the new type coil, I'm not too fussed what brand it is if the Beru / Bosch / Hella variety is unavailable or unaffordable.

 

[WGB]

I have heard of coils failing slowly but my experiences are

1) Overheat and rupture when 12v is applied to an 8v coil for too long.
2) Tracking from the insulation to earth - usually there will be a faint crack and sometimes just a carbon track.
3) Sudden stop with an open circuit internally.
4) I have heard of others where the coil gets hot and then misfires but I don't think this is very common.

Tracking can best be seen at night with the lights out (as are many things in life) when even the slightest leak will show up as a blue glow.

It can often also be heard as a ticking or low cracking sound but can be hard to hear over the general din.

Have you tried http://www.autohausaz.comfor your Beru cables - a set for my 6.9 was US$100 and were all shiny and genuine.

Bill

 

[WGB]

I have just realised that we are back in the 50's with your 300 not in the 60's.

There must be some similarity between all the 300 motors- Adenaur, Gullwing and 1960's 300 - at least in size of motors and layout of ancillaries as I undertstand they were all based on the same original design with different block materials.

The plug lead set for a 1960's 300 motor is US$41 at Autohausaz.com.

I guess this car has points and condensor and there is a chance of an intermittent short in the distributer wiring which comes on when hot - just a thought.

Bill

 

[Styria]

Hi Gordon, first thing to clear up is posting details on 300Se Coupe and its associated M189 engine - absolutely no problem.

Now, as it is 30 years or thereabouts since I have owned a 300 long wheel base saloon, my memories are a bit sketchy. First of all, could you let me have a pic of the ballast resistor ? Is it the white rectangular ceramic bit ? (Pardon my ignorance - Auto Electrics are NOT my forte). Next, the original coil - was it black in colour - I may still have one but will need to check. I may also still have the internals of the distributor but, again, will need to check. I also have a set of non-genuine 300 leads that I can let you have free of charge - they are just about brand new and are just sitting in the bottom of my box together with other sets of leads.

I assume that your problem is purely one of an electrical nature. Now, how about fuel ? M189 engines are very susceptible to have a good and strong supply of fuel. I got stranded once by a dirty fuel filter. Car always started okay, but would gradually start missing the further one drove.

Another potential source of problem - fuel tank. There is some internal gizmo (coiled tubing ?) that deteriorates with age and clogs up, severely restricting the fuel supply being fed to the pump. Also, how good is your pump ? Remember, if it is an original unit, chances are that it is tired. Many 6.3 pumps, for instance (and probably similar if not the same) have been replaced by units for the 116's. I well remember a guy with a 1967 250 SE who spent probably close to $2000.00 chasing a similar sounding problem to yours - in the end, replacement of the fuel tank (!) was the end solution. Anyway, keep us in touch on the discussion board - there is always something there to learn from. Regards, Styria

 

[koan]

Have you measured the volts at the coil (old one) after startup and again when the problem is evident?

Is the misfire evident on a waem idle?

Coils certaily die but my experience is that they work or they don't.

Just check the points and condensor are screwed down and the connections are tight, I got caught with a loose condensor years ago. Symptoms were OK at idle but misfire when driving due to the vacuum advace moving the breaker plate and affecting the connection.

koan

 

[OzBenzHead]

Styria, Bill, koan: Thanks for your input. I now appear to have the issue sorted. Not even the CA Classic Center guru - who is, allegedly, an expert on the M189 - could answer the question, but it turned out to be quite simple: the new coil had the ballast resistance printed on it!

Here are the new numbers and specs:

COIL: (replaces original part number - original part no longer supplied by M-B)
Beru ZS 109 (coloured red)
0 040 100 109
Ballast resistance required: 1.8 ohms (same as previous - against advice given elsewhere)

CONDENSER:
Beru ZK 106
0 030 100 106

Given that the original ballast resistor was supposed to be 1.8 ohm but had deteriorated to barely 1.0 ohm resistance, and given that the genuine replacement part had to come direct from Germany on order and was the ridiculous price of $130 , I used an after-market ballast ($11) for test purposes.

The ignition is now working beautifully.

Thanks to all who assisted in sorting this out.

 

[WGB]

Pleased it was that simple and you didn't get to see the inside of the Petrol Tank!!!!!

I guess the coil must have been overheating or the ballast resister had an intermittent open circuit.

Bill

 

[OzBenzHead]

Pleased it was that simple and you didn't get to see the inside of the Petrol Tank!!!!! [...]

I'm glad I attended to that earlier.

When the car was first laid up, I figured it would be inactive for quite a while, so I removed the tank, gave it a thoroughgoing treatment with POR-15 fuel tank solutions, sealed it, and stored it dry, out of the car.

You should have seen what came out of it in the first flush! It was petrol-perfumed red mud! I flushed it thrice until the drainage was clear and clean.

Of course, that didn't stop the fuel lines developing some internal rust during the intervening years, and I have now, for two days since putting the car (sort of) back on the road - at least for testing and refining purposes - experienced random fuel blockages. It eventually rights itself, only to have another series of kangaroo hops farther down the road. It might be one km or 10 km between them, but it's happening.

I have so far replaced the fuel filters (fore and aft) twice; the first time they were all red mud, the next was still red-mud coloured but mainly liquid. I figure on having to replace those filters at least twice more before it comes completely clear - but that's okay. If I don't have to dismantle the injection pump (six-plunger job) I'll be happy.

This weekend I might venture out with the coupe on a car club outing - only a short run of about 60km each way. If I get into strife, there should be plenty of other clubbers to help me out - although I expect it will be okay. An Italian tune-up might be the medicine required (though I have to nurse the new rear axle along for the first 500 km and not exceed 80 km/h).

Even after two different blockages halted the car completely, a few minutes of sitting seemed to cure it and the car ran well again.

 

[WGB]

Is it worth (or safe) adding some injector cleaner or alcohol to pick up any last bit of water that might be hiding in the system?

Bill