Just a quick question which is slightly off on a tangent but I am after some help and have searched without success. Ive recently tried checking the ignition coil primary trace on a few different cars with varying success. Can anyone tell me if I'm doing something wrong. On some training courses ive used a Pico scope (which is excellent) and had no problems but (until I can get some money together for a Pico) I personally use a small handheld unit the same as this http://www.autodiagnos.com/en/products/autoscope/

The most recent car was a Renault Megane (with the troublesome pencil coils). When I connected the scope I get a missfire on that cylinder but do get a reasonable scope trace????? The car before which is a Datsun 280ZX Just stops as soon as I connect the scope??? I wonder if the scope is not suitable??? Maybe there's a breakdown in the coil signal due to the scope??? can anyone give me any pointers/advise or tell me what im doing wrong??? I have connected the Negative to the battery Negative and the Positive to the Coil, I cant see as its possible to do anything wrong here, Can anyone confirm?.

Many Thanks.
Steve.