testing coil packs

[proguide]

I have a 1999 40 horse merc. It s not runing well. How do oyu test the coil packs to see i they are goog???? Help

[chovy]

I have a 1999 40 horse merc. It s not runing well. How do oyu test the coil packs to see i they are goog???? Help


I've replaced coils on a 1970s 7.5 merc. If I remember correctly when one of the coils (two total - one for each cyl) went bad the motor would still run but power was way down and motor ran rough. Both coils ended up failing within a two yr span with a lot of hrs on motor (1000+). When one goes bad the rest will probably fail in a yr or two. The easy way to check is pull one plug at a time and check for spark (make sure gas is out of system! Ground plug against block and pull cord or turn engine over in a dark room. The coils generally fail/short completely. You can also use an ohm meter (check all coils - the bad one will be obvious).

Jeff

[Just-in-Time]

If it is CDM you need a test harness, but there is ways around it
for normal coils
you go + and - with your ohm meter, you want less than 1 ohm
for secondary you go from - of coil to spark plug end , should be around 5K ohms