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OMC Troubleshooting Diagnostic (Tree) Diagram

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Woodybelle

Contributing Member
Looking for copy of referenced "troubleshooting diagram." I have three different service manuals and could not locate the diagram that I’ve been told exists. If anyone would like to share a copy, I’d appreciate it. Thanks.
 
Motor cranks. Won’t fire unless using starter fluid. Then motor starts/runs for a few seconds.

I bought the boat/motor thinking it was a project…not a disaster. Initially diagnosis was ignition problems (first weak spark, then (no spark). Discovered bad flywheel, stator & timing sensor. Also replaced power pack, coils, plugs/wires (correct OMC replacements) and VR/rectifier, key switch, and link/synch using OMC analyzer tool. Also checked neutral safety switch.

Got engine to fire and would run, but only while applying intermittent cold start at key switch or by manual partial enrichment of cold start switch.. If not enriched, motor would quit. Diagnosed issue as lean condition. Could be fuel restriction or air leak.

Been thru many, many subsequent procedures and replacement parts. Compression good; by-passed onboard fuel tank using new auxiliary tank with fresh gas and new primer bulb and fuel,line; new egr hoses; new intake manifold gaskets; leaf valves looked great; new throttle body seals; carbs rebuilt; rebuilt VRO/fuel enrichment switch; vacuum switch, check valves tested; link/synch again performed with OMC analyzer tool. Although fuel is in carb bowls, now the engine WON’T start except when using starter spray…then runs for a few seconds until spray is combusted.

I am now redirecting my focus to ignition testing, thinking a component may have gone bad during this 2-year process. I checked spark yesterday and thought it may be suspect. Had spark on all cylinders, but color was orange, not blue/white. Could be batteries are down a bit from testing/cranking. So, will recharge battys today AND recheck spark with correct adjustable 7/16" gap spark tester. Last time used a fixed gap tester.

So, I’m starting the diagnosis from beginning AGAIN! Given that I’m EXTREMELY frustrated, and thinking I may have overlooked something, I thought the OMC diagnostic troubleshooting tree diagram might help keep me on track.
 
Follow-up: Using an adjustable spark tester (7/16" gap) produced no spark at any cylinder, although a blueish/white spark was observed at normal gap width of .030" at all cylinders. That said, I don’t know if that test should be considered a "no spark" condition. Certainly, it’s not a "good spark" condition, if the 7/16" test gap requirement is truly accurate. In either case, it seems to rule out any potential issue with the stop circuit.

I proceeded to the power coil test. Ground test passed (no ground indicated). Output test exhibited about 35 volts, less than the 50V minimum required in the manual. Ohmmeter test exhibited 53 ohms, within 55+/- 10 ohms required.

Timing sensor was "good" using OMC analyzer tool.

Power pack test exhibited 0 volts at all primary leads to ignition coils, obviously below the 100V minimum required.

Question, can spark occur at plug, however weak, if power pack is bad. Since a new power pack was previously installed, what may have caused subsequent failure.

Lastly, my original (‘95) tach has never really operated correctly since I’ve owned the boat. It continually displayed a "check engine" light, even when motor was not running. RPM’s displayed erratically and finally quit altogether. Since, I was hopeful engine would run after last repair attempt and would need tach to determine idle speed, I installed a new tach a few days ago. Although warning system now seems to function, the RPM’s do not display (stay on zero) when engine starts. Proper impulse setting was checked with manufacturer. Since I think the tach works off the rectifier signal, I doubt there may a connection with the tach and why the engine doesn’t run. That said, it does seem VERY coincidental. Could there be a common connection?

Baffled!
 
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