123 Ignition and Distributor Vacuum Issue

[Nicolas Aristodemou]

I have a late 1970 US spec 280SL automatic and I have recently replaced the distributor with an 123 unit, set the mapping switch to position “8” as and connected the throttle body vacuum connection directly to distributor bypassing the  vacuum solenoid valve as the emissions control system of the car is in uknown operating condition. I have tried various timing settings, the car idles properly but when the throttle is opened it hesitates before picking up again at higher revs. I have read that the location of the vacuum pickup point on the throttle body might be an issue. I have been through many posts on the subject but there isn’t any clear answer. I would appreciate any help.

[teahead]

Did you replace your throttle body with the early style?

Need to do that if you bypass the emissions stuff.

[Nicolas Aristodemou]

Thanks for the response.

No, I haven't replaced the throttle body. The emissions control system is still intact apart from the 17 deg, 100 deg stats which have been disconnected (I can trace their wiring and restore it), as well as the vacuum solenoid which has been disconnected but still operational, if the power connector is restored to it. I can re-activate the vacuum solenoid and pass the throttle vacuum hose through it and then to the distributor and reset the 123 to programming position E from position 8 that is currently set at since that setting (E) would correspond to a car with an emissions control system.....

Maybe this would sort out the problem. The car used ti run fine with the old Bosch distributor, but I prefer  to have the 123 unit installed; it runs much smoother at idle....

[Benz Dr.]

If your old system is still working hook everything up as before or it will never run right. If it's not working then you should find a throttle valve from a vacuum retard system.

[teahead]

Did you read this thread?

https://www.sl113.org/forums/index.php?topic=23210.0;all

BTW...

I think for one, this thread is in the wrong section.

Announcements?

[dirkbalter]

We just had this discussion.

https://www.sl113.org/forums/index.php?topic=23210.25
It is believed that the 123 can be programmed ignoring the vacuum from the throttle body and advance or retard strictly based on rpm's.
Tyler (a member here) seems to be the expert on the subject and you might want to contact him.

Dirk
 

[Nicolas Aristodemou]

Yep, thread in the wrong section.... my first post and got it wrong......

I am going through the suggested post ...... a lot of information to digest....... I think for me easiest thing to accomplish would be to reconnect the vacuum solenoid valve and from that vacuum to the distributor and set the 123 curve back to position E.  I will try that next weekend and see how it goes..... thanks for valuable advice

[PeterW113]

Mine is a 68 Euro car so may not be relevant,  but I just attached the vacuum pipe  to the 123 distributer’s body as it had a tube to connect it to. I didn’t disconnect anything and all seems fine.

Maybe all will be fine if nothing is disconnected or bypassed. 

As I said probably not relevant for a US spec car.

Peter

[dirkbalter]

Yep, thread in the wrong section.... my first post and got it wrong......

I am going through the suggested post ...... a lot of information to digest....... I think for me easiest thing to accomplish would be to reconnect the vacuum solenoid valve and from that vacuum to the distributor and set the 123 curve back to position E.  I will try that next weekend and see how it goes..... thanks for valuable advice

Based on what you said in your earlier post, it looks like your emission control system had problems already and someone tried to bypass it. Once the system acts up, and since there is no real benefit of keeping it, people including myself chose to remove it and revert back to the earlier style. In order to do that, you will need a different distributor and an earlier style throttle body.  Your throttle body has vacuum over the whole rpm range. The vacuum is controlled with a valve (that may or may not work). The earlier style bodies have max vacuum at idle which than breaks down as the rpm’s increase.
The 123 will definitely work with an earlier throttle body. If it works with a later (70/71) throttle body with a non-operating switch-of valve is to be determined.

[Tyler S]

In experimenting with the 123 “tune” version, it appears it will work on a later 70-71 setup. The key here is it needs to be the “Tune” or “USB” version of the 123 in order to be able to modify the vacuum advance curve to work with the existing later style throttle body.
The preset curves of the standard 123 wont work with inop emission controls without changing the throttle body.

[Nicolas Aristodemou]

Thanks very much, all is clear and understood. I will either have to re-commission the vacuum switch and connect the 123 distributor (which I have already installed and it is the normal type - non USB or TUNE TYPE, hence not programmable- ) and see how it works or I will look for an earlier throttle body to take from there direct vacuum to the 123. I will post my findings in by next weekend.

One thing that puzzles me though, if someone could answer this for me, would be why instead of changing the throttle body or drilling it in another place - which seems very difficult and needing a lot of precision- , one could not simply drill a small hole and tap a small port on the intake manifold itself as close as possible to the throttle body. Surely that would provide variable versus constant vacuum with maximum vacuum when throttle is closed to minimum when throttle is fully opened. Then possibly from this tapping one could  provide variable vacuum directly to the 123 without the need for a vacuum switch.

[Tyler S]

naristodemou,  Using intake manifold vacuum would have the same effect as the late style throttle body. In fact, That is how I did my testing. But with the tunable version of the 123.
The earlier system used a vacuum (Retard) system in that the port on the throttle body was located immediately behind the throttle plate. There is vacuum present at idle and it falls off quickly to zero when the throttle is opened. This system kept the distributer retarded at idle/decel and spring pressure advanced the timing as the throttle plate is opened/vacuum lost.

[Nicolas Aristodemou]

Thank you Tyler, everything is clear now. Shall be restoring my vacuum valve switch next weekend, set the 123 distributor to position E and hope everything will be ok. Will put up a post on the results. 

[Tyler S]

Just an FYI to everyone. It appears the curve settings have changed on the updated 123 distributors. Be sure to check your production date for the correct chart. Distributors built after 04/25/2019 use the new values. I'm going to do a little more digging into these changes and see if and how the updated curves effect the late 280sl system.

[Paul & Dolly]

Interesting, I am a bit confused now.

Tyler : Which is the "new" chart please,as my data seems to be in conflict with your heading in red ?

I have just bought a 123 Mercedes 6-R-V to fit to my early UK 250 SL this coming week.
My current  distributer is a Bosch 0231 185 009 JF U6

The new 123 body is marked as follows:

Mercedes 6    30-07-2019

and the data given in the book supplied with it  seems to be the same as your first table, with the Red Heading - production date before  25-04-2019.

My table is shown here. It suggests Position  8 for my 250SL with the 009 Distributer.

Paul

[Tyler S]

Paul, setting 8 is the correct setting for the 250sl. However the curve data has slightly changed. There seems to be some conflict between the production dates. Im still looking into it. My best guess is the newer units were shipped with old instructions. You can double check to see which unit you have with a good timing light. Disconnect and plug the vacuum port on the throttle body. Then check the mechanical advance at 3000 rpm. It will be 19 for the newer production and 22 for the previous production. Either way there is only a 2 degree difference in total advance. (Mechanical and vacuum). You can always advance (turn) the distributer a few degrees to make up for the difference.

[Paul & Dolly]

Tyler

I suspect you are correct, the 123 website gives the new chart you have shown,
I have Emailed both 123, and the UK supplier for their explanation

Thanks
Paul

[Nicolas Aristodemou]

Can I ask where the speed relay shown as no 50 on the electrical schematic for the late US spec  280SL gets its signal from in order to determine the engine speed? If it is from pin no 4 which goes to the old transistorised ignition pin 7, what happens when this component together with both ballast resistors is removed to install the 123 distributor? surely if pin no 4 connects to the +ve coil terminal (in the schematic it shows connection to terminal no 7 of transistorised ignition or +terminal of coil),  then it would constantly sense 12V hence could not determine and count the pulses. Maybe connecting pin 4 of the speed relay to the coil -ve terminal would be a better bet so that the speed relay becomes once more operational? I suppose that  I can check the operation of the speed relay by feeling the vacuum solenoid valve coming on at about 2200 rpm.

Any thoughts on these?

[Tyler S]

The problem is the speed circuit, temp sensors and ignition coil were power side switched. Not ground side switched like the older system. It could possibly be made to work ground side switched but it would take heavy modification. Have a look at this video. He gives an excellent explanation of the circuit and wiring diagram.
https://youtube.com/watch?v=-PzvtA03RGA

[Nicolas Aristodemou]

I have seen this very informative and well presented video several times before; unfortunately it does not answer my question since it does not discuss the mods done for an 123 ignition installation.

I think that, since the 123 units have only two connecting leads ground and power (123's electronic circuits are taking ground from the body of the unit which is in contact with the engine which is in turn earthed) the only way it can be provided with +12V is from the coil +ve terminal which is also connected in parallel with the +12V power from the ignition switch.

Now this +12V power cannot be uninterrupted else the 123's electronics would not function (earth provided by the 123's chassis).  Also the power to the coil has to be constantly switched on and off for the coil to produce High Voltage since the power is DC. Hence the only way that this power is switched on and off to the coil by the 123's electronics is through switching on and off the connection to the -ve terminal of the coil via the black cable of the 123 unit going to the coil.

I understand that as per the original configuration of the vehicle (late 280SL auto) prior to the installation of the 123 distributor, switching of the coil was accomplished via the on/off action of the +ve terminal of the coil, which is no longer the case with the 123 ignition for the reasons explained. That is why the speed relay's pulse counter (pin no 4) was connected to the coil's +ve terminal.

Hence my original question is if the speed relay's terminal no 4 will accept and operate properly counting pulses when connected to the -ve coil terminal since the +ve coil terminal has constant power. If not how was it possible for other late 280SL owners with emissions control to keep their speed relay operating and use 123 ignition under mode E where vacuum solenoid valve controlled the retard to the distributor?

Surely I am missing something here....... 

[Tyler S]

I think I understand what you are trying to do. Remove the existing transistor unit but have the speed relay signal being switched by the 123. I think originally others were leaving the old transistor unit in place and hooked up (except for coil connections). The speed relay connection was left connected to the transistor box pin 7. The lead from the transistor box that originally went to the points was connected to coil negative so that the 123 could provide the signal it needs.

I don't think you could hurt anything by test connecting the speed relay signal wire directly to coil negative with the 123 as in the original setup it would have received both ground (through the coil during dwell) and power during operation. The only caveat being the original circuit had ballast resistors in series. 

[Nicolas Aristodemou]

Thanks Tyler, your help is much appreciated.

My car doesn’t have the transistorized ignition installed. Some previous owner must have  removed it. All other emissions control parts are present though.

I will try to connect pin 4 of the speed relay directly to the coil negative hoping that it would receive correctly the appropriate number of pulses and operate the vacuum solenoid  at about 2200 rpm. If that fails to work then I will scrap the emissions control all together, drill my throttle body from the underside  adjacent to the throttle butterfly (towards the inlet manifold) and set the 123 to the 051 setting which is position 8.

Will post my results early next week when I get the chance to work on the car this weekend. Thanks once more for all your help.

[Tyler S]

No problem 👍🏻. Sounds like a good plan.

[Nicolas Aristodemou]

Finally curiosity got the best of me...… I have connected pin 4 of the speed relay to the coil negative and everything seems to work fine now. Vacuum valve operated as intended closing the vacuum at about 2200 rpm. I didn't have time to set the timing with a timing light (will do that later) only set in a position where the car seemed to idle smoothly without too much advance. The car revs now effortlessly, no hesitation whatsoever... I think that is the beauty of the 123 ignition.

Another milestone reached..... Since this summer I have renewed the AC system (new Sanden compressor, condenser, condenser fan, filter/dryer, high pressure hoses- only original evaporator was kept), installed a period Becker Mexico which I had salvaged years ago, installed headset guide rails and headrests in seats, valve adjustments, linkage adjustment, chrome trims with rubber inserts all around which were missing, 123 ignition, emissions control system recommissioning..... to name but a few.

Thanks to all the people who have guided me through this latest 123 ignition installation exercise on a late 280SL US spec.

Nicolas

[ctaylor738]

Beckmann Technologies (electronics rebuilder) told me that connecting the speed relay directly to the coil will quickly fry the speed relay.