Unkle

Hi

I want to test my leads, distributor and coils with a very basic procedure i found on here but can't remember it . I think it was: if i pull a coil lead on each distributor in turn, their should be no change, is that right?

I think mine runs slightly differently on one or the other. Any help is much appreciated

sml

Not sure, but I do know that you should not simply disconnect the lead on top of one of the ignition coils!

Laker

Was it the mist test? Spray Down the engine with a little water and start the engine in complete darkness and look for arcing. Also I believe you are referring to pulling the center lead off the main (right) dist cap to check for a broken belt which drives the secondary (left) distributor. If the belt is broken it won't run at all. If not broken it will run but roughly.

Rocket Rob

Maybe this thread will help

https://rennlist.com/forums/964-foru...pdate-iii.html

Bertrand

The ignition coils do not like having their secondary disconnected while having their primary switched on/off (like any transformer).

What I do is to disconnect the primary (low voltage) which feeds the coils. They are on the left side: 2 flat connectors near the coils on a flat heat-dissipator. Pull a wire retainer and the connector slides downwards.

I try to start the car with only one connected, then with the other one. If it runs smooth in both cases, everything is OK as far as I'm concerned.

Unkle

Hi, thanks for that.

Yeah it was the test of just disconnecting each coil to dist in order to see how it runs. I think it ran slightly differently on each individual coil dist and 6 leads, so didn't know if that was right. It wasn't really bad but could signify a single lead or coil issue as i have new plugs rotor and caps, in the last 6 months

rarebear

I would like a switch as in a plane, but I think that is not possible because the P does not have magneto ignition.

sml

you shouldn't do this. it's the same as just pulling the lead off the coil.
follow the advice of Bertrand.
does the same thing but safely otherwise you can fry some components.

darth

It's safe to disconnect the coil lead at the distributor provided one grounds the lead. If the electrons can't find a path to ground that's when problems arise.

Steve Weiner-Rennsport Systems

Nossir,..that principle works perfectly,...

The RPM drop on single ignition occurs due to differences in ignition advance needed for proper combustion so it doesn't matter whether you use CDI, Kettering, or magneto ignition systems..

Lorenfb

"The RPM drop on single ignition occurs due to differences in ignition advance needed for proper combustion"

Actually both coils 'fire' at the same time, as the DME ECM triggers both
ignition modules from a single output pin. The RPM increase results from
a more complete combustion of the fuel charge when both plugs ignite
the charge, thus releasing more energy.

The twin plug setup on the 964/993 was used because of the single spark
location (offset) of the of the 911 air cooled engine. Having twin plugs
allowed Porsche to run greater timing advances without having detonation
problems. With the 996 engine and its center plug position, twin plugs
were no longer necessary.

Unkle

If steve is right that would explain the slight difference in idle running while carrying out the test.


If Lorenfb is right i should notice a drop in idle stability but it will be the same if i remove/disable either dist.

I'm i am reading these explanations right.

Lorenfb

"i should notice a drop in idle stability but it will be the same if i remove/disable either dist."

That is correct, unless there is:

1. bad spark plugs (or plug) on one side, or
2. one side has bad spark plug wires (or one), or
3. one side has a weak coil, or
4. one side has a bad rotor/dist cap, or
5. the belt timing in the distributor is not set correctly.