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Coil and plug cap questions

A

Aladon

New member
1998 merc 40 3 cyl 4 stroke. Popping occasionally from the exhaust at idle with the muffs on. On the lake wide open only 4100 rpms. and Missing and bogging will stall on rapid deceleration. When I perform the resistance tests on the coils and plug caps as per the mercury manual On the plug caps(vdfp caps) I am seeing about 1.5 ohms on all 3 and manual says should be 0. On the coils the primary test numbers are withing spec but on the secondary test I get no reading at all on all 3 coils. Am I missing something? What are the chances of all 3 of either being bad? Also what is the purpose of the diode on the ground from the coils to the fuel pump block bolt? When I measured resistance from the coils to the ground I expected none but there was something like 6 ohms. Does this diode go bad?
Thanks
Alan
 
Last edited:
Diodes stops reverse current flow. All electronics go bad eventually,Excessive heat destroys them. Are u disconnecting components before testing with ohm meter.
 
johnnygjr said:
Diodes stops reverse current flow. All electronics go bad eventually,Excessive heat destroys them. Are u disconnecting components before testing with ohm meter.
Click to expand...

Yes coils were unplugged and removed for tests. It just seemed funny to me to have resistance on a ground wire.
 
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