Robert Dean

I recently installed a different turbocharger in my '88 930. I now have audible pinging under certain boost, load, temp. conditions. Timing is at factory spec. Stock waste gate. Fuel quality is good. My distributor's vacuum advance/retard, works smoothly when 'bench' tested.
Vacuum retard is connected to electric solenoid and looks at throttle switch?? and works when throttle closed?? (for emissions??)
Vacuum advance is connected to a thermal switch that is open when cold??
Is ignition retard while on boost controlled by positive pressure thru this thermo switch and acting on the diaphragm??
How should the thermo switch be working ?
I hate to just 'bail' and replace something on a guess or worse take some timing out of it if all I need is a working thermo switch. And I am very reluctant to trial and error this for fear of doing engine damage.
thanks

Robert Dean
Rennlist Member

Robert Dean

Here is an update on the ignition timing retard questions. I was working with some information a read in a 'technical article' from a very good author found on another site. It must have been one of those left/right camber/castor mix-up deals, anyway here is what my problem was. The thermal switch was stuck closed, preventing the timing from retarding under boost. This is kind of important ( I took the hint from Porsche; red vacuum lines with crimped on clamps) so I thought it might warrant a heads up to anyone with a 930 ( I have read that '83-'95 use the thermal switch) You can check it easily with vacuum gage or timing light; should be open (have vacuum and allow positive pressure) with engine at operating temp. The vacuum port is above the throttle plate so you might have to open it( rev engine )to test it.