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Old 08-06-2009, 05:28 PM   #1
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Country: SOUTH WEST UK
Location: WESTON SUPER MARE
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Boat make: PHANTOM 19
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Mercruiser Ignition 6V Coil Wanted

I think I've found the cause of my persistant missfire,Does anyone know of a cheap supplier for an ignition coil, it is 6 volt for a mercruiser 140, pattern or original would do ?,mine has a 12 volt fitted and it should be 6 volt,a 6 volt feed to a 12 v coil doesn't work,any help appreciated
Regards Nic
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Old 08-06-2009, 05:53 PM   #2
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Mercruiser Ignition Coil

The original coil on the old M/C 140 should be a ballast coil that normally runs at 9 volts through a ballast wire but it is possible that the ballast wire has been removed and it is running a 12 volt coil. check coil feed voltage on the + terminal it should be 9ish volts if its same voltage as battery ballast wire has been removed. From memory there are 3 wires on the + terminal but i cant remember all the colours grey is tacho, purple/ yellow should be switch feed and the other wire is jumper from the one of the small terminals on the starter , not the yellow/red that is start wire.
If the ballast wire is still fitted and voltage is lower than 9 volts remove it, cut it out of the loom till you find the join, check for 12 volts on the join and fit a new ballast coil with external ballast resistor. A good automotive supplier should be able to help, I wouldnt bother with Halford type stores as they wouldnt know what you were talking about if you can't give them a make and model of car.
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Old 08-06-2009, 06:24 PM   #3
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Country: SOUTH WEST UK
Location: WESTON SUPER MARE
Occupation: MERCEDES SALESMAN
Interests: POWER BOAT RACING
Boat name: BIG AIR
Boat make: PHANTOM 19
Engines: 200XS
Cruising area: BRISTOL CHANNEL

Join Date: Mar 2008
Location: WESTON SUPER MARE
Posts: 792
Quote:
Originally Posted by BILL BROWN View Post
The original coil on the old M/C 140 should be a ballast coil that normally runs at 9 volts through a ballast wire but it is possible that the ballast wire has been removed and it is running a 12 volt coil. check coil feed voltage on the + terminal it should be 9ish volts if its same voltage as battery ballast wire has been removed. From memory there are 3 wires on the + terminal but i cant remember all the colours grey is tacho, purple/ yellow should be switch feed and the other wire is jumper from the one of the small terminals on the starter , not the yellow/red that is start wire.
If the ballast wire is still fitted and voltage is lower than 9 volts remove it, cut it out of the loom till you find the join, check for 12 volts on the join and fit a new ballast coil with external ballast resistor. A good automotive supplier should be able to help, I wouldnt bother with Halford type stores as they wouldnt know what you were talking about if you can't give them a make and model of car.
Hi Thanks for info,its 9 volts when cranking and drops to 6 volts when started aparently supposed to do that to aid cold starting,had thought of changing it to 12V but concerned of damage to condensor and burning out points.If a 6 Volt coil is expensive then I'll change the wiring Cheers Nic
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Old 09-06-2009, 09:03 AM   #4
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Country: UNITED KINGDOM OF GREAT BRITAIN
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Boat name: No Boat
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Quote:
Originally Posted by NIC SURRY View Post
Hi Thanks for info,its 9 volts when cranking and drops to 6 volts when started aparently supposed to do that to aid cold starting,had thought of changing it to 12V but concerned of damage to condensor and burning out points.If a 6 Volt coil is expensive then I'll change the wiring Cheers Nic
Your ballast wire is shot, you will probably find it drops lower as it gets warmed up and resistance increases. The principle of a ballasted ignition system is indeed to aid cold starting, the coil is 9 volt the ballast wire or external resistor drops battery voltage to 9 volts and the jumper from a seperate terminal passes starter voltage direct to the coil so it is constantly running on 9 volts as the starter drops the voltage down to 9 volts when cranking. The same system was used on early Range Rover 3.5 v8.

Go for an external ballast from memory they are 1.7 omh and a new 9 volt coil but don't forget to remove the ballast wire from the loom.
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Old 09-06-2009, 09:06 AM   #5
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Quote:
Originally Posted by BILL BROWN View Post
Your ballast wire is shot, you will probably find it drops lower as it gets warmed up and resistance increases. The principle of a ballasted ignition system is indeed to aid cold starting, the coil is 9 volt the ballast wire or external resistor drops battery voltage to 9 volts and the jumper from a seperate terminal passes starter voltage direct to the coil so it is constantly running on 9 volts as the starter drops the voltage down to 9 volts when cranking. The same system was used on early Range Rover 3.5 v8.

Go for an external ballast from memory they are 1.7 omh and a new 9 volt coil but don't forget to remove the ballast wire from the loom.
Also forgot to mention that model has problems with the rotor arm, gives same symptoms as low coil voltage usually when hot.
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Old 11-06-2009, 04:19 PM   #6
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Country: SOUTH WEST UK
Location: WESTON SUPER MARE
Occupation: MERCEDES SALESMAN
Interests: POWER BOAT RACING
Boat name: BIG AIR
Boat make: PHANTOM 19
Engines: 200XS
Cruising area: BRISTOL CHANNEL

Join Date: Mar 2008
Location: WESTON SUPER MARE
Posts: 792
Part Indentification

Thanks Bob for your info,I'm getting somewhat confused aparently there was either a 6 volt or 9 volt ignition coils used,I can't indentify what would be the correct one for my engine the engine number is 6923256 Mercruiser 140,3.0 litre 1985,I called Barrus twice but get no calls back,any help in confirming this would be appreciated.Regards Nic
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Old 12-06-2009, 09:07 AM   #7
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Country: UNITED KINGDOM OF GREAT BRITAIN
Location: Southampton
Occupation: Marine engineer, Senior Bosun RAFYC
Interests: Boating, Eating, Fishing.
Boat name: No Boat
Cruising area: South coast

Join Date: Jan 2006
Location: Southampton
Posts: 55
Quote:
Originally Posted by NIC SURRY View Post
Thanks Bob for your info,I'm getting somewhat confused aparently there was either a 6 volt or 9 volt ignition coils used,I can't indentify what would be the correct one for my engine the engine number is 6923256 Mercruiser 140,3.0 litre 1985,I called Barrus twice but get no calls back,any help in confirming this would be appreciated.Regards Nic
As far as I know there was only 9 volt coils fitted to the 4 cylinder Mercruiser engines, for more information on available parts try Keypart 01923 221490 they do the Sierra parts that are as good if not better than original and they will supply direct and they are amazingly quick, they will probably have the external resistor as well.
Since I retired I don't have access to the electronic parts books I know there are some B/M members who have access maybe they could help.
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