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...