W111 123 ignition – part 2

In the first part of this series, I installed the 123 ignition distributor and got the car running.   This part focuses on test driving the car and fine tuning the install.    I should note that the 123 ignition distributor has nothing to do with the W123 Mercedes.  A couple of people assumed I was fitting a distributor from a W123.    The 123 ignition is a brand new electronic distributor that fits many makes and models.

My first step was setting the correct advance curve for my engine.   Luckily the workshop manual has all the specifications I needed.    The first specification covered the static timing value for the ‘047’ distributor my car was equipped with.

This distributor was shared with the 250SE saloon and coupe, as well as the 250SL and some versions of the 230SL.      Next the manual also covered the advance curve.     The ‘047’ and ‘051’ distributors are a little different in this regard.   While they have a normal advance curve, they use a vacuum retard curve.   As far as I can tell, this was not emissions related, just a quirk of these engines.    It’s quite odd, as the curve for related engines like the 250S is totally different and does not use this vacuum retard.

I used the centre of the curve for my initial setting, adding 5 degrees for the static timing value.    Setting the vacuum retard was a little more tricky, as the add actually doesn’t really allow it, but there are settings you can use to ‘fool’ the system into doing retard, not advance.    The 123 ignition company provides such an example on their website, which I used.

The car started up fairly well, although idled quite high.    I took the car for the first test drive since fitting the new distributor.    The test drive showed a lot of promise.    I had none of the missing, stalling or stuttering that I had experienced before.    On the other hand, the car was pinging quite a lot under load.   I tried a few minor adjustments to see if that would help.   I used the app to set up the advance curve to be the bottom of the curve rather than the centre.   It helped a bit, but the car still pinged.

A couple of days later when I had more time, I started by checking the timing with a timing light against the values in the distributor.  To make sure I was checking static timing, I zeroed out the advance values in the app below 3,000RPM. Immediately the error was apparent.   I really should have checked this first.   I had assumed my static timing was at TDC, but actually I was between 15 and 20 degrees BTDC.  No wonder the car pinged.   I loosened and rotated the distributor until it was at 5 degrees BTDC, per the factory setting.    A byproduct of this was the idle went down a bit too.

Based on this, I then set the advance curve per the centre of the curve on the page.     I took the car on another test drive.    This time, the pinging was gone.    Since this test drive was at 10pm, and it was only 15C out, I left the settings where they are.   In the future, I will take the car for a longer drive on a hot day, and experiment with advancing the timing a bit, for example to the top of the curve.

During these test drives, I was able to have the 123 ignition app up on my phone to see what the distributor was doing.    It’s quite useful!

The other positive thing was that the car ran well on this test drive.  Again, no missing, stalling or stuttering.   While the problem was intermittent, it would have normally manifested itself in the two drives I have done so far.   Things look extremely promising.

The car is having a power steering leak fixed next week, so after that I will be able to take it for a longer test drive, and further adjust the settings on the 123 ignition distributor.    So far, the 123 ignition has exceeded my expectations.    I also need to mount the coil properly and tidy up the leads.    Separately,  I found out that the residue around #5 spark plug is likely just grease coming out of a fitting on the side of the head.     Based on that, and since the car is running well, I have not changed the spark plugs so far.   My next step is really to put some more miles on the car and make sure the problem really is gone.