Random misfire

DESCRIPTION : 97 chevy silverado 5.7 litres vortec fuel system.

PROBLEM: Random misfire on all cylinders, it was at a shop where they changed, distributor,cap, rotor, plug wires,fuel pressure regulator and spark plugs.

Uscope capture below was on a plug wire snap throttle. Can anyone shed some light on this waveform please.

Does this occur for all cylinders?

Why is there no spark line?

Is there only ~7v?

Not for all cylinders, that was cylinder 3. I was looking at the misfire counter on the scan tool and I saw cylinder 3 misfiring so I went for it. There was a spark line at idle but when I snap the throttle, that was what I captured.

I think that 7v would convert to killo volts base on the scope settings.

Love the uScope capture. Just curious, which ignition probe are you using?

This looks exactly like a short to ground in the secondary ignition circuit. Either in the cap and wires, or across the plug gap itself. If this waveform is isolated to cylinder #3, then your list of suspects is very short.

Recheck all the secondary ignition parts they replaced. If you find no issues, check the #3 plug for insufficient gap, or a possible head gasket failure on that cylinder.

Thanks a lot for the input, it is really appreciated. Am using the secondary pickup lead that comes with the uscope.