Ignition trouble, but it's not the coil. WRD?

[Cees Klumper]

I tried searching but did not find what I was looking for, hence this new topic.

Symptoms are that, starting recently, the car misfires a bit when cold. This has gotten progressively worse, and now the car also misfires and hesitates when getting a bit warmer. So I went to troubleshoot when it happened again this morning on a glass run (taking empty glass bottles to the recycling collection point here in the village):

- checked to see whether the CSV had perhaps started to drip causing overly rich condition - removed the small screw on the side, turned on ignition - no drip
- pulled the plugs and noticed they were all black. I was running NGK BK7ES and swapped them for clean BP6ES to see if that made a difference
- then measured the plug wires'  resistance - all a hair under 1K ohm
- measured the coil primary resistance, which came in at around 1.9 ohms
- then proceeded to check the ignition timing with my timing light

That's where I noticed something odd: the timing light was 'skipping' every couple of seconds, indicating misfiring. Strange thing was that the engine did not seem to really stumble, although it did not run as smoothly as normal either. I checked the wiring to the timing light, and the other wiring to and from the coil and the (1-2-3= distributor, but no change: haphazard misfiring. After some more running, it slowly seemed to go away, and the timing light was firing consistently.

I installed this coil probably 15 or more years ago. Have been running it without the 1.8 ohm Bosch resistor since that is what the 1-2-3 ignition installation instructions suggest you can do, so long as the coil's primary resistance is at least 1 ohm (which it is). 

Checking on-line it appears that these are the symptoms of a failing coil. So have decided to replace it, and on the SLS site saw that they advise to, for 1-2-3 installations, use the BERU ZS 115 coil together with the (for that coil apparently mandatory) 0.9 BERU resistor. SLS did not have either in stock, so I bought those on two different other car parts sites. Supposed to come in later this week, and I will report back when I have swapped them with the current coil. Fingers crossed...

[mdsalemi]

Cees,

You indicated ~1K ohm resistance on the plug wires? Was that with the Beru or Bosch connectors on the end of the wires? The wires themselves should be essentially zero resistance, and solid copper core.

You don't have a resistor in the circuit, right? If you did, I'd check that since these are ceramic and have been known to crack and cause intermittent resistance. (been there, done that...)

Have you checked your rotor and cap? I've seen (though not necessarily with your setup of course) evidence of wear on the conductive end of the rotor as well as the receptive conductors inside the cap.

Here's what the USA website says for 123:

For 6 cylinder engines we advise to change your coil to a high performance coil because of the short load time in the higher rpm range. Make sure you use coils with a primary resistance of at least 1.0 Ohm. ( 1,0 Ohm or more ) For standard street engines we advise a "Bosch Blue" or "Beru ZS106" coil. For high rpm engines a "Bosch red (0 221 119 030)" or "Beru ZS109" is much better.

[fosdicke]

Check the points.

[Cees Klumper]

Thanks Michael,

Since I installed the 123, maybe ten years ago, I've had no resistor in the circuit. I kept it though, in case I wanted to go back to my earlier electronic ignition, it's a red bracket (1,8 ohm) Bosch ceramic resistor.

The plug wire 1K ohm resistance is including the connectors, so 'all-in'.

I've several (used) distributor caps and rotors on the shelf in case the new coil doesn't solve the issues. The current ones look fine, but I guess faults could be tough to spot.

I went with the BERU ZS115 because the SLS website suggests it. Will chech the primary resistance but whatever it is, I will put the new 0,9 ohm BERU resistor in there as well.

@ fosdicke: the 123 distributor is electronic, no points, so that and the dwell angle are out iof the equation,

[450sl]

Distributorcap hairlinecracks?

[waltklatt]

Check the wires for secure and clean connections.

[fosdicke]

@ fosdicke: the 123 distributor is electronic, no points, so that and the dwell angle are out iof the equation,
[/quote]
Was unaware of your Distrib. mod so then I would suspect the triggering device for the system .

[ja17]

Sounds like a coil failing. I heard some techs say that a ballast resistor should be used even with the 123 dist.

[Cees Klumper]

Thanks all, all good points (pun intended). As soon as the new coil and resistor arrive, I'll follow the process of elimination. I do hope it's not the distributor itself, but I think that is unlikely. We've not heard of a 123 failing yet on this forum, to the best of my knowledge.

@Joe: the new BERU coil I ordered says very explicitly not to use it without a 0.9 ohm resistor, so that is what is going in.

[ejboyd5]

Unfortunately, for the past ten years or so, it is no longer safe to assume that new electrical parts straight from the box will work as intended.  Keep some known "good" common components around for test purposes so as to preserve your diagnostic sanity.

[wwheeler]

Cees,

When I bought my 123 several years ago, the vendor made the comment that many people keep the original distributor in the trunk just in case the 123 goes out. Apparently when the 123 goes out, it is totally dead and you are stranded with no warning. That does not sound like your situation luckily, but thought I would mention it.

FYI, I have had absolutely no issues with my 123 in seven years or so. BTW, I liked the pun and they are always welcome.

[BRYANH815]

last year i too suspected the coil also replaced the resistor. This helped for a while but periocially it would sputter also. i replaced the distributor and the symptoms are gone. check for correct resistor OHM rating ..good luck

[Cees Klumper]

Thanks for all the additional pointers, much appreciated. The new BERU coil came in today, now I only need the 0,9 ohm resistor to arrive, hopefully tomorrow otherwise next week.

[Cees Klumper]

Update - yesterday I tested the new coil and resistor by taking the car for a spin. Unfortunately, the same symptoms occurred: during the warm-up cycle, the car ran rough, missing on several cylinders and smoking. However, when the engine was warm, the symptoms went away. So this morning I decided to remove the thicker shim I had placed under the 'coolant tower' as part of the WRD. I had been trying to remedy a long-standing issue where, about half-way through the warm-up cycle, if you came to a stop, the car would stall. I figured it needed a thicker shim, to prolong the functioning of the WRD until the engine was properly warmed up. I now believe that that extra shim made the car run way too rich during the warm-up cycle, essentially flooding the engine and causing the misfiring. I measured the total shims thickness and it came out to around 2.7 mm. I decided to drastically reduce that, to .7 mm. Indeed the car ran flawlessly during the warm-up cycle, however again, mid-way through, would stall when coming to a stop: the old behavior. Clearly i need to read up on the WRD again. What I also found odd is that I had to adjust the Constant Speed Solenoid with a fully warm engine, as that no longer kept the car running in idle. I had not thought that reducing shim thickness under the WRD would affect the fully warmed up running characteristics. To be continued.

[Tyler S]

Double check the constant speed solenoid circuit for proper operation. A weak solenoid, intermittant operation, or one that is not fully extending will cause an engine stall in gear at stops.
You may also need to raise your base idle.

[wwheeler]

Cees,

I have a similar problem with the warm up cycle at mid point. My engine runs lean at that point also, but it doesn't stall. The engine just runs more rough and at a slightly lower RPM. Yes, adding a oval shim fixed that problem, but it made the cold idle terrible and way too rich. I decided to compromise with a slightly richer cold idle and somewhat still lean mid point.

The other thing I did was to use a higher temp coolant thermostat to speed through the warm up. I had previously used the coldest thermostat Mercedes had because of the heat here in Texas. But it was too cold for my engine and prolonged the warm-up. The final improvement was to add more round shims in order to reduce the time the WRD was open and hence, reduce the time of the mid point warm up. These cars don't run now in sub freezing weather as they did when they were daily drivers, so that extreme WRD range may not be necessary. It isn't perfect, it is better.

Oval shims change the cold running mixture and the round shims in the air valve change the time/temperature in which the WRD operates. And you probably know, if you remove too many round shims, the WRD may never completely shut off. I also changed my driving habits while the engine warms. I minimize idling until the engine is warm enough to be past that ugly mid point.

BTW, I have also found some change in mixture when swapping oval shims at full hot. Not suppose to, but it did a bit.

[franjo_66]

I've also got the same mid-point issues with the warm up cycle. Mine doesn't stall but definitely runs rough and has lower rpm idle.

I've learnt to live with it similar to Wallace by minimising time spent idling etc.

Just wondering if anyone has managed to solve this issue or is it too minor to worth worrying about?

I have had the pump overhauled, new coil, new 123 distributor etc but this symptom perseveres. 

[Cees Klumper]

Thanks, sounds like it is the WRD after all. My car started to have this mid-cycle stalling/hesitation issue many years ago, and I finally decided to tackle it last Fall by swapping out the coolant tower and adding oval shims. The issue went away, but now it runs way too rich during the warm-up, causing misfiring if I let the car sit and idle for one or two minutes; that's when it starts fouling the plugs and the veru rough running starts. So long as I can just drive away from cold start, it's ok (although probably still very rich). I probably removed too much oval shim, by going from 2.7 to .7. I will add a bit at a time until it seems optimal. First, though, I will re-set the idle mixture when the engine is warm with my Gunson CO meter, to make sure that basic setting is ok. Probably will need to be re-set with every shim added, as the WRD setting does seem to influence the fully-warm running mixture. Will report back. At least the car has a nice new coil and resistor! The CSS works fine, it is relatively new and just needed to be adjusted a bit.

[Pawel66]

Cees, I was following this thread and hope you can tune the warm up cycle ok.

If I may: you mentioned your CSS is relatively new. Can I ask - did you buy it anyhere, rebuilt it or installed a new coil inside?

The thought of CSS going bad one day is not a pleasant one.... I find it difficult to drive without it...

[Cees Klumper]

Yes Pawel, I got it new at Van Dijk in Holland some years ago. I can look up the invoice, but I am afraid that we will learn it was a fraction of today's cost, like so many parts. For example I remember getting the hood badge new for maybe $25, and it's not all that long ago.

I kept my old CSS (which functioned, but had lost its oomph) and have been following that particular thread with interest. Looking to open it up to clean and hopefully restore to its former glory.

[Pawel66]

Thank you! I have also noticed spares prices going steeply up even over the last 2-3 years.
It could be, perhaps, wise to have a couple of components at hand now...