bricem13

Hi gents

I'm running a new issue on my 90 C2. Few days ago, I came back home for a small trip with my son. I wanted to check the oil level, so I let the car run and I noticed a clicking noise coming from the engine.
Definitively a kind of arcing/electrical noise.

So i went for a test sequence: disconnected the ignition modules one after the other (switching engine off): car starts and run over both so no belt issue.
The clicking noise can be heard when the bottom spark plugs distributor is connected.
I inverter both coils and still the noise is coming from the bottom plugs.

I did not noticed any arcing in the dark after having sprayed some water around the double distributor.

So I decided to clean the spark plugs: disassembled and clean 11 out of 12... the cylinder 6 top spark plug being difficult as you know.
clicking noise still present even if the car ran smoother after the cleaning.

I decided to change the spark plug wires by the original Beru reference. So far I changed 11 cables out of 14 (top cable for plugs 4-5-6 are still unchanged).
Clinking noise is still here...

I inverted the cap and fingers.
Clicking noise still here.

Now honestly I don't know what to do next.

964/air cooled Porsches are by essence very loud mechanically speaking and sometimes I feel confused with all the noises but at my last trial it is undoubtedly coming for the bottom plugs. Before cleaning the plugs and changing the wires I tried to have run the top plugs from the second distributor and change some plug by the bottom one in an attempt to identify a faulty one but none was clearly identified as faulty.

When the car runs from single distributor: it runs OK from the top plugs, rougher from the bottom even dying attempting to catch the idle after giving a bit of gas.

I'm running out of ideas now.

r-mm

Sometimes the most helpful thing with troubleshooting is having your presumptions challenged so I'll ask: how sure are you the sound is electrical? As you note, its a noisy engine. With a famously noisy valvetrain. I've never found arcing to be that loud a sound. A very loose valve or rocker that walked off its shaft comes sooner to mind.

cjoenck

A couple of questions: Does the clicking noise you hear change with engine RPM or is it constant? Is it more pronounced with a cold engine vs hot or does it stay the same?

You can use an automotive stethoscope to pinpoint mechanical noise. Electrical clicking / arcing can be caused by faulty coils, broken ignition wires or improperly seated spark plug wires.

More likely you need a valve adjustment. How many miles since your last adjustment? Valve "clicking" would be rpm dependent obviously.

You sometimes get a clicking noise from a failing alternator. What's your voltage at the battery with the engine running and under load?

There is a bunch of mechanical stuff rattling around in the engine bay so try to eliminate one step at a time without any preconceived notion of cause.

bricem13

I take the challenges


I already had the stethoscope around and cannot identify a clicking (well more a clack) noise. Valve job was done by myself last winter using the rennline version of the Kirk tool. Both cylinder banks make the same noise and with the stethoscope I can hear the valves, for sure the noise is not related to what I hear.

I classified the noise as electrical from start on and so far it is not rpm dependent, not always here but very often. It is related with distributor II (bottom plugs, not belt driven) and as mentioned not linked with distributor cap and/or finger. I had one plug with light burn marks on the ceramic insulator (cyl 5 bottom if I recall correctly) when I cleaned them but I stupidly did not inspect the ceramic of all. The bottom one showed more deposit on the thread than the top ones. I re-installed them with on y tiny spray of contact cleaner to lube a bit the thread.

Spark plugs are less than 10kkms, alternator has been rebuilt too 15kkms.

Spyder_2011

Spark plugs can fail prematurely, I had one fail in a DI car a few thousand miles after installation and toasted the engine. Maybe worth revisiting that if you’re confident its electrical

bricem13

The bottom plugs are my last guess... I ordered 6 Champion ones and will change them, hoping they are the culprit.

bricem13

Well that's it, the 6 spark plugs are changed.

To make matters worse, it was difficult to unscrew spark plug 6: I found a sort of rubber ring around it of unknown origin (neither the old spark plug nor the new one nor the socket I used), even though I'd cleaned the plugs a while ago.

In the end, it's running without the banging, so it seems to be the spark plugs (or the cables) ! I'm going to take it for a spin in the next few days to be sure that nothing's coming back (I heard it when I opened the hood with the engine running to check the oil level after 1 hour's driving). Air-cooled engines are pretty noisy, mechanically speaking, and I've been listening to it a lot lately.

I'll see if there's a spark plug tester somewhere at work...

r-mm

Rubber ring sounds like it could be the retaining ring from an old socket. BTW this is why I like the magnetic ones. Could it have been preventing the wire from seating on the plug?

bricem13

pretty sure it was not there when I cleaned the plugs and none of the sockets I used misses the rubber ring, neither the SP cables... So no clue where it comes from. It could have effectively prevented the wire to seat properly.

anyway problem seem solved now. so I can enjoy back the car!!