Pertronix I vs II

[berfinroy]

I just had an old Mercedes hand install a Pertronix II electronic ignition in my 1972 4.5 D Jetronic. I have had cold start roughness for some time and hoped this would help.
It didn't. Let me add that I know its not the AAV valve as it has been restored with a new thermal element and tested. What other part should I be looking at?
Incidentally, I have used a Pertronix I on my old Rolls Royce I6 with great success, with a noticeable improvement in quick starting and general performance. Is there any reason to think that the original Pertronix I system is actually better than the more "advanced" system II?

[Mike D]

No significant difference for stock application.

The II has a couple of added features such as the power is cut if the key is left in the "run" position without the engine running. Has a built-in "dwell advance" feature for initial start-ups.

Both, in fact all the Ignitors, require the use of "suppressor" wires as opposed to the "solid core" wires your Benz has.

I have used them with the standard MB wires (solid core with the resistor ends) and had them work fine but the company recommends suppressor wiring.

[berfinroy]

I did use suppressor wire....

[Graham]

Originally Posted by berfinroy

I did use suppressor wire....

The recommendation to use suppressor wires with the Pertronix in place of the OE copper wires only appeared after the v II came out. Many of us run the early Djets with Ignitor 1 and copper wires. The OE wires had resistors at each end for suppression purposes (about 6kohm total). Newer sets of wires have resistor at just one end are 1kohm. Maybe because the think we should use resistor plugs?

I have used both resistor and non-resistor plugs with Ignitor 1, Bosch 1K wires, original switchgear and coil since 2008. No problems at all (despite what some say about the resistor plugs!)

Did you use the suppressor wires with the OE type connectors? Could be that you have a weak spark if you are still using the OE switchgear and coil?

It may not be your problem, but staying with the proven to work Ignitor 1 on our old Djets, makes most sense to me. They do have a new model 1887LS for the 74-75 djets, but the 1885 is correct for the 72.

Cold start roughness? Some suggestions:
- Check temperature sensors resistances are to spec. Check all injection harness wiring and connectors. (I rebuilt my harness)
- Check that throttle position switch is correctly signalling to ECU to run on idle mixture control. Then set ECU idle mixture knob in middle of it's range and try different setting with a burst of rpm in between.
- Set ignition timing to 0BTDC (with vacuum). Then check to makes sure it advances to about 27BTDC when revved to 3000rpm. (better than factory spec)
- retard at idle can cause rough idle - Try with A/C turned on (it should disables the retard id the switch on line from throttle body to distributor is working.)

Too much info? Sorry!

[Tomguy]

Can you clarify cold start roughness?

The cold start valve ("Injector") dumps a ton of fuel in until the thermo-time switch turns it off. A test you could do I suppose is unplug that valve during the roughness and see if it smooths out or not. It could just stall out, of course, but only one way to know.

If your system is on the edge of being too rich the CSV might be dumping too much in, or if your system is on the edge of too lean and the CSV is not dumping enough in due to being plugged or faulty it could also be the cause.

That being said, the thermo-time switch has (as the name would indicate) a designated time it is supposed to be on for, and then turn off. If the thermo-time switch is faulty it could be causing an issue. One way it could be faulty is it turns off too quickly, the other way is that it does not turn on at all, or it stays on too long. These are all things you would need to measure accordingly based on the temperature it reads from the coolant it's in, the 12v heating applied to it to cause it to turn off, and the open or closed signal it sends in response.

[Graham]

Good point.
CSV injecting too much fuel or not enough could be the problem.

I think the thermo-time switch only allows CSV injection up to a coolant temperature of 35C. If working, problem should go away once engine has run for a short period (maybe longer in the weather we have -11C at the moment!)

[berfinroy]

Graham and Tomguy:

A belated thank you for your thoughtful suggestions...

Berfinroy

[Adv_rider]

Anybody knows where can I get suppressor wires for a W108 4.5?

I dont quite understand how to identify them.