mariner/mercury 75 no sprak on No1

[raptorheli2]

hi people, 1st time on the forum and looking for some help.

have a 1997 mariner 75 3 cylinder model and i'm not getting any spark on the top cylinder.

it was running fine and it just died in mid use a couple of days ago.

i have replaced a faulty cdi unit as the one already there had gone, either by this fault causing it or some strange coincidence.

i now can get spark with all 3 cdm's using the wiring loom from numbers 2 and 3 cylinders. but number 1 cylinders loom is dead and doesn't spark on any cdm's.

i know i'll need to pull the flywheel off and check for bad wires etc, that will be done but what else can i check and what should i check? how do i check the stator, switch, trigger to find where the fault lies.

thanks for your help.

 

[wbblc87]

Re: mariner/mercury 75 no sprak on No1

hi people, 1st time on the forum and looking for some help.

have a 1997 mariner 75 3 cylinder model and i'm not getting any spark on the top cylinder.

it was running fine and it just died in mid use a couple of days ago.

i have replaced a faulty cdi unit as the one already there had gone, either by this fault causing it or some strange coincidence.

i now can get spark with all 3 cdm's using the wiring loom from numbers 2 and 3 cylinders. but number 1 cylinders loom is dead and doesn't spark on any cdm's.

i know i'll need to pull the flywheel off and check for bad wires etc, that will be done but what else can i check and what should i check? how do i check the stator, switch, trigger to find where the fault lies.

thanks for your help.

You've most likely got a bad CDM. The CDMs are interconnected on the stop circuit. If a blocking diode in one CDM is bad it can cause another CDM not to fire. Using a spark gap tester with everything put back in place and connected. Crank the engine and view the spark in the tester. No spark #1, unplug the wire harness from #2 CDM. Does the spark come back on in #1? If so, #2 CDM is bad. If not, you will need a DVA voltmeter to test the trigger output and stator output to CDM #1. Mercury also makes a harness that plugs into the CDM harness to make it easier to test. You should have about 2-10 Volts DVA on your trigger wire and 200-300 Volts DVA on the stator wire while cranking the engine or running. You MUST use a DVA for this test. A regular DVOM or VOM are not fast enough to show a valid reading.