No spark on #5 cyl part II

[Merc90HPnewbie]

Recap: 90 HP inline 6 tan band 1985. No spark on #5 cyl.<br /><br />I swapped the plug wire (with the same spark plug stuck in it) over to the #4 coil and it sparked. Then I put it back on the #5 coil and ran the #4 trigger wire to the #5 coil and it sparked. So I think I proved to myself that the #5 coil and plug wire are good. I went through the Mercury service manual to test the stator and trigger assembly. Everything tested right smack dab in the middle of the acceptable range. I tested the coil even though it obviously works, and it was in spec. I am unsure how the inputs and outputs of the switchboxes correlate, but am I right in assuming that I've isolated the problem to the switchbox?!?<br />Is there some way to move stuff around on the switchbox so I can make sure the switchbox is bad before I replace it? (I hear they're expensive).<br /><br />The book goes on about how you need some special tester for the switchbox (hmm sounds suspicious- need a special mercury-only test tool or else you can't replace the mysterious black box that you can only get from....Mercury?)<br />Anyway thanks for reading this.

 

[The Marine Doctor]

Re: No spark on #5 cyl part II

If you swap the trigger leads and spark was still apparent on the #4 cyl...the trigger works.<br /><br />The fact that you have spark on the other cyl's proves the stator works.<br /><br />This is how you can test your pack without test tools.<br /><br />TMD

 

[Merc90HPnewbie]

Re: No spark on #5 cyl part II

Thanks TMD. I guess I forgot to say;<br />I swapped the trigger from the #5 to the #4 and I did NOT get spark. So does this prove the switchbox is dead (as the service manual ohmmeter tests of the trigger assembly and the stator checked out good and the #5 coil and plug wire tested good and worked when I subbed then into the #4 position)? I guess one way to check is to sub in a known good switchbox. However part<br />332-7778 A1 (which has been substituted with 7778A12) is $202.40 according to Mercurypartsexpress.com!! Anyone know where to get used but tested good switchboxes?

 

[The Marine Doctor]

Re: No spark on #5 cyl part II

Just remember, if you take something that is working and apply it to something that is not working and it then does not work. It is the latter that is the problem.<br /><br />TMD

 

[Merc90HPnewbie]

Re: No spark on #5 cyl part II

-I have read in other posts about switchboxes just 'going bad'. Is there anything else I need to verify to ensure that when I install a new switch box, I won't blow out a circuit in that one, too?<br /><br />-Any idea where I can get a used one that tests good or has a return policy?<br /><br />Thanks

 

[The Marine Doctor]

Re: No spark on #5 cyl part II

Your best bet is to check here on Iboats for a place that sells switchboxes.<br /><br />Switchboxes wear out just like any other electronic gizmo.<br /><br />TMD

 

[Merc90HPnewbie]

Re: No spark on #5 cyl part II

Did a search on iboats and they sell it for $166. Thanks for the tip!