Electronic Ignition System For W115

[racing3000]

Hi, finally we have achieved to convert the oem ignition system of my 1974 W115 230.4 M115 engine to electronic ignition system of original W123 M102 230E engine. However, we used the oem M115 ignition spark plugs and cables, except the main ignition cables (the green one and the black central one connected to the distributor cover). I would like to ask for the recommendations regarding the 4 ignition cables and spark plugs in order to reach the best acceleration and smooth running.

Thanks in advance,

[Mike D]

Please clarify the situation.

Are you using the M115 engine with the M102 ignition?

Did you install the M102 into your W115?

[racing3000]

Yes, I am using the M115 with the M102 ignition. The result is better than I guess in terms of performance, but I used the oem cables and spark plugs of M115. So, I am still thinking of squeezing more power if I change the cable-spark plug set. Is it a good idea to use the oem set of M102 or any better recommendation?

[Mike D]

I'm not that well informed on the M102 ignition set-up. How is the spark controlled? Electronically through an ECM or mechanically using contacts/trigger inside the distributor assembly? What controls the timing curve? Mechanical advance or through an ECM?

I'd use the wires from the M102 and NGK BP6ES plugs.

Have you considered using an aftermarket ECM and a 36-1 trigger-wheel to operate the ignition?

[racing3000]

The technician used the contacts and some other parts, I don't know which ones exactly, inside the distributor. The timing curve is controlled by mechanical advance. The ignition coil is smaller, but produces higher voltage and there is a simple electronic ignition control unit.

[Mike D]

Well then, you've basically changed nothing. You are still using the Kettering system. The standard plug wires will suffice.

The advance curve might be a bit off using the M102 distributor. Check it using a timing light. Should be about 10 degrees BTDC at idle with vacuum disconnected and advance to apx. 32 degrees at about 3500 RPMs.

[Benz Dr.]

Originally Posted by Mike D

Well then, you've basically changed nothing. You are still using the Kettering system. The standard plug wires will suffice.

The advance curve might be a bit off using the M102 distributor. Check it using a timing light. Should be about 10 degrees BTDC at idle with vacuum disconnected and advance to apx. 32 degrees at about 3500 RPMs.

Why would you want to disconnect the vacuum line when the engine normally runs with it on? That's only for testing.

I would leave leave everything connected and set timing to roughly 40 degrees BTDC or it won't make good power. If it pings knock it back a couple of degrees. Make sure there isn't any carbon core wires in your high tension system.

[meltedpanda]

timed hundreds of time , for me I listen for the sweet spot ,fine it and set it-then - drive it , if good great , if not listen some more with increasing and decreasing revs. I use the standard setting as a starting point , then "listen " from there, never has failed me

[Mike D]

The point of initially setting the timing at 10 degrees BTDC and then increasing the RPM's is to determine the advance curve and its properties.

The original poster mentioned he replaced the OEM M115's distributor with one from a M102.

Wouldn't it be nice to know if the advance curve of the M102 is the same as the M115?

[Mike D]

Found this for you. Might be of some help.

https://www.benzworld.org/forums/w201-190-class/1186701-anyone-have-ignition-timing-specs-2-a.html

[Benz Dr.]

Originally Posted by meltedpanda

timed hundreds of time , for me I listen for the sweet spot ,fine it and set it-then - drive it , if good great , if not listen some more with increasing and decreasing revs. I use the standard setting as a starting point , then "listen " from there, never has failed me

I do that too while test driving and then I check it against the stock specs after I'm done. In most cases, the stock specs are going to be where it runs best. V8's are a different story and I find most of the 4.5's run best at about 8 - 10 degrees BTDC.

[97 SL320]

Originally Posted by Mike D

Well then, you've basically changed nothing. You are still using the Kettering system.

Maybe. Perhaps the mechanic used a Pertronix or is using the points just to send a trigger signal to the electronic ignition module.

In any event, spark gap dictates what voltage the wires will see not type of ignition module. If the gap is the same as stock, the voltage will be the same as stock. I'd feel safe increasing plug gaps 0.010 inches over stock even with point type ignition wires.