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  Impulse Hour Meter with Coil-on-plug Spark Ignition

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Author Topic:   Impulse Hour Meter with Coil-on-plug Spark Ignition
capg2000 posted 10-19-2010 10:00 PM ET (US)   Profile for capg2000   Send Email to capg2000  
I have been a mechanic for all my life. I have a 2007 Montauk with a [Mercury] 90-HP FOURSTROKE. I am going to install a SenDec impulse hour meter on the engine. It says to wrap the impulse wire around the spark plug wire. I can't find the plug wires--ANYWHERE! Any ideas?
dbrown posted 10-20-2010 12:17 AM ET (US)     Profile for dbrown  Send Email to dbrown     
There are no spark plug wires on your engine. The "pencil" coils are mounted directly to the spark plugs.
Graumann posted 10-20-2010 12:42 AM ET (US)     Profile for Graumann  Send Email to Graumann     
Please post again if you do get the hour meter to work. I've never figured it out on my 2007 Mercury 115 FOURSTROKE.--Keith
capg2000 posted 10-20-2010 05:10 AM ET (US)     Profile for capg2000  Send Email to capg2000     
So the four coils on the back end of the engine are the pencil coils that fire the plugs. Cool. Now a way to [unclear] a pulse wire. Gotta be able to somewhere. I'll do more research and post when I have an answer.
jimh posted 10-20-2010 08:31 AM ET (US)     Profile for jimh  Send Email to jimh     
[Moved to SMALL BOAT ELECTRICAL.]

The entire point of having a coil-on-plug spark ignition system is to eliminate spark plug wires. Since the fundamental application of the device you want to use is to produce inductive coupling from winding turns around a spark plug wire, the device is fundamentally unsuitable for use in a spark ignition system that has no spark plug wires.

Use an hour meter that relies on oil pressure. Install an oil pressure switch to actuate the hour meter.

Chuck Tribolet posted 10-22-2010 05:04 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Coil on plug is also to eliminate misfires. If the coil
only has to produce a spark every two revs, rather than four
or six times per two revs, it can make a badder spark, esp.
at high revs.

You might be able to get the hour meter to run by wrapping
the wire around the spark plug or the base of the coil. It's
worth a shot.


Chuck

jimh posted 10-23-2010 09:39 AM ET (US)     Profile for jimh  Send Email to jimh     
If the Mercury outboard is of a design that is so modern that it uses coil-on-plug spark ignition, I suspect that it is also so modern that it has the Mercury Smartcraft instrumentation system. According to Mercury, the Smartcraft system can:

"Depending on the gauge system you choose (System Monitor, MercMonitor, System Tach & Speed, or VesselView), you may be able to access the following information: basic engine parameters (oil pressure, coolant temperature, voltage, total run time, sea water pressure)

http://www.mercurymarine.com/service-and-support/ storage-and-maintenance/faqs/mercruiser/?category=smartcraft#SC-features

While the above leaves the ability of Smartcraft to display total engine hours somewhat in doubt, I would be astounded if you couldn't find engine hour information on a minimal installation of Smartcraft. Perhaps some of our long-time readers who have long touted Smartcraft for its ground breaking outboard digital technology could let us know if you can see engine hours on a basic Smartcraft gauge with a 90-HP FOURSTROKE.

mikemdd posted 10-23-2010 09:56 AM ET (US)     Profile for mikemdd  Send Email to mikemdd     
I have the 115 HP Fourstroke with the Smartcraft MercMonitor. Engine hours are clearly displayed....one of the reasons I installed it.
jimh posted 10-23-2010 11:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Mike--Thank you. I was certain you could see engine hours, but it is always good to have confirmation.
jimh posted 10-24-2010 09:28 AM ET (US)     Profile for jimh  Send Email to jimh     
From the coil-on-plug assemblies I have seen, I get the impression that they are designed to fit snugly into the deep recess in which the spark plug is installed, and the purpose of that snug fit is to keep moisture and debris from getting into the recess. For this reason, trying to run another conductor down into the recess between the coil-on-plug assembly and the wall of the recess does not seem like a good idea. It could create a path for water to enter the recess.

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