1977 115 HP Misfire (Power Pack)

[wgolz]

Motor Specs: 1977, 115 HP, 4 cyl. Johnson. Single power pack.<br /><br />Symptom: First there was a weak spark at cyl. #3 and now there is no spark at cyl. #3.<br /><br />Tried so far (Result): <br />(i) Checked and cleaned all the grounds. (Result-No change).<br /><br />(ii) Switched the primary ignition coil leads and the plug wires for #3 & #1. (Result-#1 still fires, # 3 does not, so it is upstream of the coils.)<br /><br />(iii) Traced all the sensor and coil wires back to the stator and timer assemblies. (Result-No problems there).<br /><br />(iv) Took the power pack cover off and switched sensor leads #1 & #3. (Result-#1 coil still sparks and #3 does not, but when I unhook #1 sensor lead, which is now in the #3 position, the #1 coil no longer fires. With the switched sensor leads, it does not fire correctly on #1, but if I switch the plug wires, it fires well on #3)<br /><br />Question: It seems like a power pack, but how likely is it that it is instead a stator/charge coil assembly or timer base problem?

 

[mcginleyc]

Re: 1977 115 HP Misfire (Power Pack)

Bill, I like to do the reverse of what you did when trouble shooting electrical systems. Starting with the stator and working down to the trigger, rect/reg (if equiped), powerpack input then output, ignition coil primary, and then secondary. I would suggest getting a manual and a multimeter instead of switching stuff around. Do resistance test on the trigger and stator. Has your engine overheated? This is the cause of many omc stator and cap charge coil failures. See if there is any black stuff dripping down from underneath flywheel. This is just a thought. Use the VDC setting on the mulimeter and test each component. good luck

 

[wgolz]

Re: 1977 115 HP Misfire (Power Pack)

Thanks for the thoughts. It did heat up one time, but I shut it off right away and it started up fine. I have since had the heads off and replaced the diverters. No black stuff dripping down around the stator potting under the flywheel.<br /><br />Wouldn't a bad stator affect the spark on all 4 cylinders and a bad charge coil the spark on cyls. 2/4 or 1/3? So with only #3 not firing wouldn't this leave only a possible bad timer base (the trigger) or the power pack? <br /><br />I would like to go through the full diagnosis, but my Johnson Factory Manual and a Clymer both cover the diagnosis procedure using an OMC neon load tester. I don't have one of those and don't see a way to translate the procedure into something that could be done with my multi meter. How would I do that?<br /><br />Appreciate your advice.

 

[ledgefinder]

Re: 1977 115 HP Misfire (Power Pack)

Bill, you are correct that one set of stator charge coils is used for all four cylinders.<br /><br />There are two sensor (trigger) coils. One for cylinders 1&3, the other for cylinders 2&4. I know the leads say 'sensor 1', 'sensor 2', etc., but that's just labelling - there are just two sensor coils in the timer base.<br /><br />So, sounds like your powerpack.

 

[wgolz]

Re: 1977 115 HP Misfire (Power Pack)

Thanks ledgefinder. That would explain why, when I switch the #1 and #3 sensor leads at the power pack, the firing on the #1 coil is correct for #3 and there is still no fire from the #3 coil.<br /><br />By the way, I edited the previous post that you replied to, to make it more precise. <br /><br />Thanks again for the thoughts.

 

[wgolz]

Re: 1977 115 HP Misfire (Power Pack)

Conclusion:<br /><br />After reading the manual, it became clear that EVERYTHING UPSTREAM OF THE POWER PACK IS SHARED (as "ledgefinder" affirms). Thus, a miss on only one cylinder indicates a bad plug (already eliminated that), bad coil (already changed the coil with a working cylinder), or A BAD POWER PACK. <br /><br />I changed the power pack, and it started firing on # 3 right away. Boat runs great!<br /><br />[Note: Based upon the symptoms stated in the first post on this topic, there never was a reason to go through the whole test procedure specified in the manual, which begins with the stator/charge coil and works down to the coil and spark plug (as suggested by "mcginleyc"). It is important to be careful to weed through the advice one gets on this board very carefully: a ten-second reply from someone whom means well but is unfamiliar with your particular motor can result in an investment of needless hours in wrench time.]