1970 M130 US two-way switch problem

[bracurrie]

The car is a manual 4-speed and I have the stock ignition setup with ICM, speed relay and two way advance switch. When starting cold I will hear an audible relay click and engine RPMs increase, but then I hear the relay click again and the RPMs go down. This may happen 3 or four times but then it will stop with the engine RPMs lower and I assume that is a non-advanced state. The speed relay does trigger the two-way switch on when you rev the engine up and off again when the RPMs drop again

I tried driving the car with the two-way switch un-plugged but the engine drags just a bit at an RPM when the when the speed switch would trigger the advanced state and idle is too low when first starting the engine cold, so that isn't acceptable.

So clearly the system needs diagnostic attention. What experience has anyone had working with this ignition setup?

My first idea was to un-plug everything and clean contacts.

I have a spare new speed relay(in-hand) and trigger relay(on the way).
Thanks for any input.
Brad

[Markedes]

I am very happy that you posted this. Mine is a ‘71 280sel with the 4 speed automatic. Same symptoms: audible click or “tink” with a change in power that I assume is due to a change in timing.

I too am planning to pull and contact-clean all of the associated connections. Have you seen any progress on the problem yet?

This is my second Mercedes, my first 108 and I love it.

Thanks again for posting.

Mark M

[Idle]

Are these fuel injected cars with air conditioning? If so the click is the lifting magnet snapping out to increase the RPM when the compressor kicks in.

These things can be rather loud as they get older and a bit out of adjustment.

[strelnik]

Originally Posted by Idle

Are these fuel injected cars with air conditioning? If so the click is the lifting magnet snapping out to increase the RPM when the compressor kicks in.

These things can be rather loud as they get older and a bit out of adjustment.

This acceleration for increased load was a common feature in late 60-early 70 US and Euro cars.


It was used on US police cars to offset AC load on cars, especially those with police pursuit packages. I used to deal with those at Chrysler.


Citroen used the same thing on their Citromatic-(AT)-equipped cars to increase pressure in the accumulator as vehicles shifted under "extreme" circumstances.

[Markedes]

AC compressor is inop on my car. Also it occurs sometimes rapidly. I’d like to know which component is doing it.

[bracurrie]

No AC either in my case. Also the changes are too rapid to be normal. Haven't yet cleaned all pin contacts in system which multiple techs have suggested as a first step.

I have been told that the problem could be eliminated by going around the system, but I like the retard feature when the car is above 100 C.

Could someone here explain the Timing change-over detailed in the Service Manual 00-74. I have had no training or experience with ignition systems other than what I have read. As a result I am confused by terms like "intake vacuum will act on ignition distributor" and "distributor is charged with atmospheric pressure". does vacuum increase when throttle is opened up?

What throws me is that some systems have a feature to actively retard timing and some to actively advance. So I believe in the case of a 1970 280 SE w 6 cylinder MFI I believe the two-way switch when activated it allows vacuum to advance ignition. But I am unsure of this.
Brad

[Mike D]

Retarding the timing will actually increase the engine temperature due to a longer "burn" of the combustible fuel mixture. The retard feature is for emissions control.

[bracurrie]

Originally Posted by Mike D

Retarding the timing will actually increase the engine temperature due to a longer "burn" of the combustible fuel mixture. The retard feature is for emissions control.

How is the retard done?
Thanks
Brad

[Mike D]

Depends on the distributor.

Single or dual diaphragm?

Vacuum retard or advance?

Ported or manifold vacuum?

Yeah, yeah, I know, more questions than answers but it matters which distributor you have as to how the solenoids affect the ignition timing.

The very most basic explanation is that the retard/advance mechanism is enabled/disabled depending on whether the engine is under load or at idle/cruise. This is selected by the solenoids allowing or blocking the vacuum supply to the timing mechanism.

[Frank Reiner]

Originally Posted by bracurrie

How is the retard done?

Originally Posted by Mike D

Depends on the distributor.
Single or dual diaphragm?
Vacuum retard or advance?
Ported or manifold vacuum?
Yeah, yeah, I know, more questions than answers but it matters which distributor you have as to how the solenoids affect the ignition timing.

bc:

Some pics of the distributor, and of the point on the intake manifold (or carburetor) where the vacuum line originates will be helpful.

[Benz Dr.]

The system is vacuum retard and is under constant vacuum from a port near the throttle body. The vacuum control valve remains opened allowing the distributor to go to full retard below 2,200 RPM. Above that speed ( or near it ) the vacuum with be switched off and the distributor will advance about 20 degrees all at once. Below 2,200 the only advance is with the distributor flyweights. This system was designed so that the as the mechanical advance ends the vacuum takes over.

There are often two thermo switches on this system: one to advance the ignition below 140 degrees F and another to advance the ignition above 212 degrees F. In my opinion, a 200 degree switch would have been much better because once you get your engine above 100C it won't cool off by advancing the ignition timing if you are in stop and go traffic. Retarding the ignition at idle will make your engine run hotter which is why I have no use for AC in these late model cars; 280SL's in particular.

The most common distributors used on this system during this time frame is the 062 or 064. Sedans may have used different units.

[bracurrie]

Originally Posted by Benz Dr.

The system is vacuum retard and is under constant vacuum from a port near the throttle body.

Thank you Benz Dr. Between your post and a little digging on the Pagoda SL site I think I understand my system a lot better now.
I do use the AC as my car is a daily driver. I am re living issues from the mid 70s all over again.
Am I correct to say the retard system is ONLY an emissions limiting feature? If so then should connecting the vacuum from throttle body to distributor around the two way switch be a simple fix for a wonky speed switch and relay? Eventually I will fix the original setup to preserve originality, but not use it.

I have connected the vacuum as described above and the car cold starts well and seems to run well. Are there any adjustments to distributor timing needed to accommodate the elimination of the retard feature?

Thanks again.
Brad

[bracurrie]

Originally Posted by Mike D

Yeah, yeah, I know, more questions than answers but it matters which distributor you have as to how the solenoids affect the ignition timing.
This is selected by the solenoids allowing or blocking the vacuum supply to the timing mechanism.

Thanks Mike for the reply. In a subsequent post exchange with Benz Dr the reality that my car has a simple retard feature driven by a switch relay and speed switch that simply blocks vacuum advance for limiting emissions.
When you say solenoids do you also mean relays? If not then I humbly ask for enlightenment. I am not a mechanic/tech so my knowledge is limited.
Brad

[Benz Dr.]

Originally Posted by bracurrie

Thank you Benz Dr. Between your post and a little digging on the Pagoda SL site I think I understand my system a lot better now.
I do use the AC as my car is a daily driver. I am re living issues from the mid 70s all over again.
Am I correct to say the retard system is ONLY an emissions limiting feature? If so then should connecting the vacuum from throttle body to distributor around the two way switch be a simple fix for a wonky speed switch and relay? Eventually I will fix the original setup to preserve originality, but not use it.

I have connected the vacuum as described above and the car cold starts well and seems to run well. Are there any adjustments to distributor timing needed to accommodate the elimination of the retard feature?

Thanks again.
Brad

If you were to disconnect vacuum part of the system you would only get 10 degrees of ignition advance. If you hooked the vacuum line directly to the distributor you would still only get 10 degrees of advance. It's when the vacuum is switched off on a running engine that you will then see 20 -22 degrees of advance all in one movement. If your system is still working be happy that it does.
The only way to effectively change this system is to find a 051 distributor and an earlier vacuum retard throttle body to go with it.

[Mike D]

Relays are electrical control devices. Solenoids are mechanical devices which are usually activated by electrical controls such as relays. Activation of the solenoid opens or blocks vacuum flow depending on whether the solenoid is normally open or closed.

Either of them can "click".

Benz Dr. is sending you down the right path.