Barry,

What is ther scientific principle tha causes the GP to generate a voltage? The filament of the GP is probably made of a nichrome like metal. I never heard of that type of material generating a voltage from heat.

Should the engine be hot when the test is being conducted?

The reason I asked about using an occiloscope was I thought maybe some of the voltage might have been generated by the pressure changes in the engine like a piezo-electric effect.