electronic ignition-some help needed

[n/a]

I really don't want to throw in the towel (or I guess the shop rag) on this one just yet.  Can Tom, and others, who have installed the Pertronix, tell me exactly how they did the wiring?  Did you run a wire from the negative terminal on the coil to ground?  Any ground wiring that needs to be done to the distributor?
The tech support guy at Pertronix told me that almost all complaints they receive are related to voltage issues.  One problem that I have is that the wiring on my car is a bit weird because of the transistorized MB ignition.  I'm not 100 percent sure about proper wiring.  I am bypassing all resistors.
Can anyone offer suggestions about getting the timing closer to spec by just cranking the engine?  I can't get it started to properly do the timing.  I've been tinkering around with the timing and I fear that it is now way off.
Thanks,
Don

[Benz Dr.]

Dwell angle is the amount in degrees that the points are closed. As the shaft turns the points are closed until the cam opens the points. Once the points close again the coil builds up a charge ( coil saturation ) until the points open again and the coil releases the high tension voltage to that part of the system ( cap, rotor, wires, spark plugs)
If you have points you have a dwell angle. Electronic systems do this , well...... electronicly and so there is no dwell angle but rather a point of fire that lets the coil build up a charge in the same way as a points coil system. This is a very similar idea to dwell angle done by points except this is done by induction pick up or some other means and is basically service free.
( I bet no one can make sense of this)

Dan c
SL Barn

Daniel G Caron

[Tom]

Dan,

I think I actually did follow your line of explanation regarding dwell!

Don,

Let me try this with a focus on the coil, which of course has two terminals, one positive and one negative.  Under the Pertronix system, two wires connect to the positive coil terminal and two connect to the negative terminal.  The first two wires (red and black) come from the Pertronix Ignitor unit contained within the distributor housing-red to positive terminal and black to the negative terminal of the coil

The third wire is the hot wire with switched power that was once the lead wire to the first ballast resistor.  This should be attached to the postive terminal of the coil.

So now you have two wires connected to the postive terminal and one wire connected to the negative terminal of the coil.  Once these three wires are connected, your system should work.

The fourth wire that is not connected is the RPM feed.  The RPM relay that feeds the 2 way valve with an RPM reading to turn your vacuum on and off needs the wire to feed the RPMs.  The wire that does this emerges from the wiring harness that runs along the fender.  The wire emerges from the larger sheathing as a smaller sheathing with two wires.  I am now questioning my original indication that it was the green wire and will need to verify this and get back to you.

However, I left that 4th wire unattached for months until I figured it out and the car ran fine.  It just runs better and allows you to set your timing and get the proper overall ignition advance curve.  So work with the three wires until I can figure out the 4th wire and report back.

Best,

Tom


____________________________________

1971 280sl Tunis Beige Metallic
1971 280sl Tobacco Brown
1994 E320 Cabriolet, Smoke Silver
1999 E320 Wagon 4 matic, Brilliant Silver
____________________________________

[hands_aus]

Hey Dan,
That makes a lot of sense to me. (ex electrician)
On my 250 SL the Magnets in the Pertronix rotating collar allow approximately 38 degrees equivalent Dwell angle. I believe this is right on spec.

Don,
The ground wire to the negative side of the coil should not be there.
On my 250 SL there is no speed relay and no 4th wire.
Just the switched positive wire plus the red wire of the Pertronix unit go to +ve terminal of the coil, then the Black wire from the Pertronix unit goes to the -ve terminal of the coil.

There is a small ground wire inside the distributor that goes under the screw that holds the  little bracket that I had to modify so that the magnetic collar could rotate freely and holds the base plate in position to the vacuum rod. (I remember you saying that you did not need to modify that bracket).

I am not sure if that ground connection does anything now that the Pertronix unit is installed still it won't hurt to have it in place.

You are not far off now.

Bob (Brisbane,Australia)
early 250 SL, RHD

[Naj ✝︎]

Brisbane Bob,
Should the red wire not be on the switch side of the ballast resistor - giving it full 12 volts?
naj


65 230SL
68 280SL

[Cees Klumper]

OK Dan - that's what I had always assumed. Still, your explanation of the dwell (duration of impulse) being determined electronically makes a lot of sense also. Maybe the only way to find out for sure is by asking one of the manufacturers of these electronic units or reading up on the subject somewhere. Electronic ignition ins-and-outs may be a good topic for a Pagoda World article actually.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[hands_aus]

Hey Naj,

I checked my set up and you are right, I do have the red wire of the Pertronix unit connected to the switch side of the ballast resistor, so yes it does get 12 Volts.

Bob (Brisbane,Australia)
early 250 SL, RHD

[n/a]

Being at wits end, I decided to pull the pertronix and re-install my old system.  The car started right up and idled fine with my old points ignition!  I set the timing with my strobe and adjusted the idle.
So, I guess that narrows my problem to pertronix.  But, how and why is still a mystery.  
Don

[zambo]

Hi Don

I came to this thread very late and ended up here accidently looking for info on pertronix for my 3.5 108 BUT, having read all the details on your problem and some of the other comments on the thread, I am thinking they simply suggested the wrong kit!

Elsewhere on the thread folks refer to the 1864LA unit as correct for a 280SL - now even though your distributor isn't listed, I would think that getting the 1864LA - which is different than the one they supplied you - was worth a try. Did the dealer suggest the one you fitted because it matched your distributor number, or they just took a guess.

I don't know if this is worth a try, but good luck in solving the problem anyway.

Regards

Richard

[n/a]

hi don just some info, your ign. system is the one put on the `107chassis starting in 1972. it was on my 450sl & others i worked on. i think you have the wrong kit.
                   vincediver

[Richard Madison]

Not sure what this was...was not posted by me. I was "retired" in mid 2007.

I erased the message...it was in HTML code and was full of dead links.

Richard M, Feb 29, 2008