Can a single bad (shorted or open) coil cause no spark on all cylinders?<br /><br />I had started having trouble starting my 1977 115 the last couple of trips previous to my troubles, and had to use starting fluid some. Once started, it was running great and would re-start very easily for the rest of the day's boating activities. After a long run of a couple hours (during which the motor ran great), I had the motor off for about 4-6 hours until ready to return to the ramp. This time the motor would not start.<br /><br />The next day, I started trouble-shooting. There was no spark at any of the plugs and voltage while cranking was above 10V (so weak battery or bad starter voltage drops shouldn't have caused problems).<br /><br />All resistance checks were within specs and the kill switch was OK.<br /><br />I don't have a DVA meter but I do have a digital storage oscilloscope (DSO) with 10X probes which allow me to see the waveform peaks. I believe this method should perform the same thing as a DVA meter (if I understand the DVA meter correctly).<br /><br />The DSO measured 1.2 V peaks on the trigger coils (both sets of wires) with a nice waveform with no irregular spikes or inconsistancies. The charge coils measured well over 100V (160V peak if I remember correctly), again with an acceptable looking oscillating waveform. However, the DSO measured 0V (no output at all) on all 4 of the ignition coil outputs (which confirmed the spark tester showing no spark).<br /><br />Therefore I assumed it was the power pack, so ordered a new one. However, the new power pack had the exact same symptoms. I then decided to do resistance checks on the ignition coils (which I did not do previously). The specs call for a very low R on the primary, so the difference between a good coil and a shorted primary is only a few tenths of an ohm. All looked good except the #4 coil which had a 0.2 ohm resistance the first few times I checked it. After taking the #4 coil primary lead out of the wiring harness and removing the coil from the engine (to ensure none of the external wires were damaged), the coil checked out OK (with a primary resistance of .5 to .7 ohms or so). I am not sure if taking the coil off fixed a "loose wire" type problem or not. However, with the #4 coil disconnected I tried cranking again, and to my surprise, there was spark on the other 3 cylinders. I then re-connected the #4 coil and no spark anywhere. So #4 coil was causing a problem?... not so fast! I then connected the #4 coil to the #3 coil output from the powerpack and all three connected cylinders sparked (this was with the #4 coil output on the powerpack disconnected still). Then, connecting the #2 coil to the #4 output caused no spark (all of this was done with plugs out to increase starting RPM's and reduce starter load, so I wasn't concerned with timing issues).<br /><br />Therefore, with the brand new powerpack, when any coil was connected to the #4 coil output terminal of the powerpack, it seemed to disable the powerpack. Because all the coils sparked on the other 3 terminals, I figured the new powerpack was either dammaged when I got it or I had somehow destroyed it. So I put my old power pack back on and tried one more time before giving up for a while, and it had spark on all 4 coils! Put the plugs back in and it fired right up and has been running great for a couple of weeks now.<br /><br />Needless to say, I am slightly uneasy to go far since the problem appears to have magically fixed itself. <br /><br />I have considered replacing all of the coils in case a "loose-wire" condition caused the problems (if perhaps the #4 coil was shorted or arcing to ground before I removed it and replaced it). Is it possible that a faulty #4 coil could have destroyed the new powerpack (keep in mind it never even fired with the new powerpack, so there were 0 running hours on it) and I then jiggled a wire to "fix" the #4 coil upon removing it? If so, why would it not have also destroyed my old powerpack which is not back on the motor and working great?<br /><br />I hate to spend the money on new coils if it's unneccesary, and I'd especially hate to do that if there's a problem somewhere else in the ignition system. However, until I can figure out what caused all of the problems I will be scared to go far without a chase boat. <br /><br />Any thoughts or ideas would be greatly appreciated as it seems that I'm always the one who ends up troubleshooting my friend's motor problems too.... so I always interested in hearing different symptoms
