200 HP - No spark at random cylinders

[jc_mako]

ENGINE INFO: <br />1993 2.5L Mercury 200 (0D271065)<br />INITIAL PROBLEM:<br />My engine had no spark on all 3 cylinders (1,3,5) on one bank.<br />DIAGNOSIS:<br />I swapped the ignition coil leads to the switch boxes and the problem moved to cylinders (2,4,6). From my knowledge this meant that one switch box was bad.<br />FIX:<br />I replaced the bad switch box with a brand new Mercury switch box (The Parts Dealer tested and confirmed that the switch box was bad)<br />I connected all the leads to the switch box including the ground lead. I did not however attached them to the engine block with the 2 screws and spacers<br />NEW PROBLEM:<br />I cranked the engine and I now have no spark at random cylinders.<br /><br />According to the Service Manual I need it to ground the Switch Boxes (Attach to engine block) before cranking the engine or they will be damaged. Keep in mind that all my spark plug wires are connected to a gap board so the engine never actually turns on. Also the problem is inconsistent and just right now I cranked the engine and all 6 cylinders had spark. However this was not the case just last weekend after replacing the switch box. It seems however that cylinders (1,2) are the ones that have no spark.<br /><br />Are both of my switch boxes bad now? Did I damage them both by not attaching them to the engine block before cranking the engine? Could another part be causing the issue?

 

[andy6374]

Re: 200 HP - No spark at random cylinders

Your first diagnosis was right on, bad switchbox.<br /><br />Yes, the switchboxes need to be grounded to the powerhead before cranking.<br /><br />An ailing switchbox can damage the other. That's why it's recommended to replace both at the same time. This time save some money and get switchboxes from CDI/Rapair. They are much better and cheaper. www.seilermarine.com sells them.<br /><br />If you want, here is a troubleshooting guide<br /> http://rapair.com/support/Portals/0/downloads/TroubleshootingGuide.pdf

 

[jc_mako]

Re: 200 HP - No spark at random cylinders

Thanks for the recommendation andy6374. <br /><br />I was planning on replacing both switch boxes with CDI boxes. However I want to be sure before doing so since these parts are not cheap.<br /><br />I'll take a closer look at the trouble shooting guide but I won't be able to check for resistance or DVA readings since I don't have the equipment and really never done this before.<br /><br />What are the chances that the problem is with my switch boxes? Should I be checking the stator, trigger, ignition coil or anything else?

 

[KCLOST]

Re: 200 HP - No spark at random cylinders

You may want to test the trigger also...<br /><br />You can do this easily by switching the "switchboxes"!!!! This requires you to remove every lead on both boxes and switch them around, reconnect the leads as they were before. If you see the same cylinders losing spark after this test, you most likely do have a trigger problem. If the no-spark condition moves it's the switchboxes as the problem. Your previous test didn't rule out the trigger, because all you did was switch the coil leads. But you do know now that all the coils are working ok...