Portable oscilloscope?

[c1steve]

I would like to measure the coil output on my Merc. 350 MAG MPI engine. A portable oscilloscope would probably be best. Any recommendation on buying one?

I notice that there are some portable gap jump test tools for very low cost. They might work satisfactorily.

 

[Scott Danforth]

and what would you gain by this information?

coil output on the secondary side is between 45,000 and 65,000 volts depending on the dwell time of the primary side and coil windings

a good portable oscilloscope will be $3500+ for a Fluke 190 series

again, I ask, what would you gain by spending this much money. what problem are you trying to solve?

 

[62cruiserinc]

Oscilloscopes won't tolerate anywhere near those voltage levels directly into a regular probe that comes with them. Most will only handle about 500-1000V. You will have to buy a high-voltage adapter (expensive) or make your own resistive divider with a couple of Megohm-value high-voltage resistors.

You can buy a high-voltage probe that will read the voltage for a lot less money than a scope. The only thing the scope buys you is being able to see the actual voltage waveform.

If you really want to do it, buy a low-frequency (<10MHz) used scope (they should be cheap these days) and build the voltage divider.

Steve

 

[JustJason]

Buy a GTC505. It will show you your spark output voltage as well as showing you a waveform on your coils secondary winding. Very useful for checking for bad plugs, bad plug wires, bad coils, finding ignition misfires.

 

[c1steve]

The GTC505 sounds like the ticket. I went salmon fishing on Sunday, but the engine was missing on the way out. So we turned around. At the dock I found that the spark coming out from the distributor cap was much weaker than from the coil itself.

Cap and rotor are about 2 years told, so have about 250 hours on them. Apparently it is time for a tune up. The weekend before the engine ran correctly, and am surprised at the quick change. I did not have the Torx bit to remove the cap, so did not do a visual check.

The spark from coil wire to ground would jump a 3/16" gap with a mostly yellow spark. That seems weak to me, but the coil has less than 500 hours on it. I did notice recently that there is a .5 volt drop from the starting battery to the ignition switch, I will check into that as well. Might be from the ground wire or the positive.