How to test if motor is running on all cylinders?

[fsutim]

78 Johnson 70HP. How do I test to make sure it is running on all cylinders. How would you check if it has a bad coil?

 

[R.Johnson]

Re: How to test if motor is running on all cylinders?

Simply pull one spark plug wire at a time,, and note the difference.

 

[rodbolt]

Re: How to test if motor is running on all cylinders?

hello<br /> if you pull a plug wire use a wire puller or it will nail ya. if you do and I really dont reccomend it, imediatly grond the end against a bolt head. the system can generate a lot of voltage and it will go someplace. think of voltage as water pressure in a pipe. you can always use a spark tester set at 7/16 and watch for spark. test compression if you must drop a cyl then short the coil primary to ground.the plugs will tell the story if combined with a spark test and compression test. I can usually<br /> spot dead cylinders with my snapon KV tester as well.<br /> good luck and keep posting

 

[AUGIDAWG]

Re: How to test if motor is running on all cylinders?

Use an ordinary automotive timing light.<br />Move the sensor from wire to wire.<br />If you don't see the light flashing, it is not firing.<br />If you see it flashing, but it misses a few times, then you know that is the cylinder that needs research.

 

[jtexas]

Re: How to test if motor is running on all cylinders?

Rodbolt,<br />I've seen alot of posts advising pulling one wire at a time for this kind of diagnosis and yours is the first recommendation I've noticed to the contrary. Lectricity is a bit of a mystery, & I hate to think of all those electrons stirred up & no place to go, so if I can ask this without sounding like a smart-a$$ - how strong is your recommendation? What's the danger & the probability of a bad outcome? Am I risking a battery/voltage regulator/fire/early death by electocution? Or is it just a shortcut to be avoided when tools are available? <br /><br />thanks,<br />jtw<br /><br />p.s. what did we ever do before we had all this accumulated wisdom at our fingertips?

 

[dcolpitts]

Re: How to test if motor is running on all cylinders?

jtexas, I believe with any cdi ignition(power pack) that a ungrounded lead can damage the power pack module $. My 1986 140 had a plug lead burn out and had to run it for 15 minutes to get back to dock, had to replace power pack the next week. Just my experiance.

 

[NEECAPRS]

Re: How to test if motor is running on all cylinders?

I press a straight pin into each plug wire then go for a ride and ground them-one at a time. The small hole made by the pin closes tight enough to hold several PSI of water pressure- just like chem lab septums.

 

[jtexas]

Re: How to test if motor is running on all cylinders?

Thanks okam - it makes sense, operate outside the tolerances of some electronic components, they heat up & fail prematurely.<br /><br />neecaprs - you mean you ground from your pin to the engine block with a jumper or something? that kills the cylinder?<br /><br />thanks,<br />jtw

 

[rodbolt]

Re: How to test if motor is running on all cylinders?

hello Jtexas<br /> man I lived in Cleburne for 8 years. oneday I want to move back to lake whitney. man that was some good fishing. anyway no worries about death by electrocution. but there are many shortcuts that will work on a 55 chevy that can fry a modern outboard. just say no. use common sense and the proper tool. or to quote the service manual( a suitible tool) <br /> good luck and keep posting

 

[hagarwc]

Re: How to test if motor is running on all cylinders?

The idea of sticking a straight pin through the cap is brilliant!! I have always struggled by putting a thin bit of wire under the cap and shorting that out... when I put the cap on it normally pulls the wire free and I try again.. and again... But this is my second preference in shorting the coils out. I normally see if I can disconnect each coil out on the low tension side but you can only do this if the coils are visible and have connectors to the loom that are visible.<br />Anyway, connect a lead to earth somewhere and short it to each plug (pin)in turn. You will get a more noticible effect if you are actually on the water under load. <br />I DO NOT recommend pulling the leads off as this can definitely fry the ignition box. The older motors that had a distributor/points/coil system would survive this method but you definitely run the risk of damaging your box by just pulling the leads off.