Installed new gauges, cleaned up some terminals, now no spark

natemoore

Master Chief Petty Officer
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Jun 13, 2009
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I picked up a set of NOS Medallion gauges that were meant for a 1990 Four Winns with a Mercruiser sterndrive. Since my boat is a 1987 Four Winns with a Mercruiser 3.7L and Medallion gauges, I figured the switch over should be pretty easy.

I labeled every wire as I disconnected them from the old gauges. The new gauges were practically identical, except for the face plate. Installation was straight forward. In addition to this, I also cleaned the coil terminal connections, ignition switch connections, and put some dielectric grease on the plug wires at the distributor. I'm positive that no wire got mixed up because I cleaned all terminals one at a time.

This engine usually starts in about one crank revolution, but today, no spark. I used my timing light to check the coil by placing the sensor on the coil wire going to the top of the distributor. Turned it over. Flash, flash, flash, flash. Then I put the sensor on #1 plug wire, turned it over, nothing!

One weird thing that happened was that the tachometer needle was spinning like an airplane propeller. I'm thinking I've got it on the wrong setting. The label said position 1 for 4 cylinder, but the old was was in position 2. Has something to do with the tach signal coming off the coil, so the 4 cylinder position doesn't apply?

I've got a Pertronix ignition and Flamethrower coil.

Help.
 
Last edited:

alldodge

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Mar 8, 2009
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40,582
I picked up a set of NOS Medallion gauges that were meant for a 1990 Four Winns with a Mercruiser sterndrive. Since my boat is a 1987 Four Winns with a Mercruiser 3.7L and Medallion gauges, I figured the switch over should be pretty easy.

I labeled every wire as I disconnected them from the old gauges. The new gauges were practically identical, except for the face plate. Installation was straight forward. In addition to this, I also cleaned the coil terminal connections, ignition switch connections, and put some dielectric grease on the plug wires at the distributor. I'm positive that no wire got mixed up because I cleaned all terminals one at a time.

This engine usually starts in about one crank revolution, but today, no spark. I used my timing light to check the coil by placing the sensor on the coil wire going to the top of the distributor. Turned it over. Flash, flash, flash, flash. Then I put the sensor on #1 plug wire, turned it over, nothing!

One weird thing that happened was that the tachometer needle was spinning like an airplane propeller.

I've got a Pertronix ignition and Flamethrower coil.

Help.

Ya might be positive but there is a negative impact here. Try starting with removing the wire feeding the tach.
Next remove the distributer cap and see why your coil works but not through your distributer
 
Joined
Feb 17, 2012
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2,906
go back and check the insulating bushings on the brackets they are the same brass studs that the wires bolted to. If you missed or dropped a insulator especially on the tach than you may have a weak ground which can result in a poor spark/no spark. I have seen the spring loaded center pin fall out of a distributor but that will only happen if you have removed the cap. It may be just a real weak spark/mistimed spark that the timing light doesn't see. (this leads back to the tach being the problem)
 

natemoore

Master Chief Petty Officer
Joined
Jun 13, 2009
Messages
844
go back and check the insulating bushings on the brackets they are the same brass studs that the wires bolted to. If you missed or dropped a insulator especially on the tach than you may have a weak ground which can result in a poor spark/no spark. I have seen the spring loaded center pin fall out of a distributor but that will only happen if you have removed the cap. It may be just a real weak spark/mistimed spark that the timing light doesn't see. (this leads back to the tach being the problem)

Bushings are there. I wondered "what difference does it make at this point," but just now I took a flashlight and checked my tach wiring. There are two brass studs coming out of the back. One is ground, and the other is 'S' (sender, signal). So these two must not touch, hence the insulating bushings. There is also a terminal marked 'I', for the purple wire, off to the side.

I also realized that I plugged the grey wire onto the 'I' stud. The bracket blocked my view of the big 'S' I drew in black marker on the back of the tach. So that's why my tach was spinning like a propeller. It must have been soaking up enough juice from the coil to keep it from firing.

Hope I didn't fry my tach. Probably not since the 'I' stud takes 12-14.6 volts, and the voltage signal from the coil is probably less than 12V.

Thanks for helping me get it unscrewed.
 

NYBo

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Oct 23, 2008
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7,107
That doesn't explain why you have spark from the coil wire but not from the spark plug wires.
 

bruceb58

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Mar 5, 2006
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30,454
At the coil, take off the wire that eventually goes to the tach. My bet this that wire is wired to a wrong terminal up to your dash. You could take the wires off at the tach at the dash but you never know if you accidentally wired that wire somewhere else.
 

natemoore

Master Chief Petty Officer
Joined
Jun 13, 2009
Messages
844
I put the grey wire on the tach 'S' terminal, the purple wire on the 'I' terminal, where they belong, and the engine fired up in half a turn. All gauges work fine. Mahogany dash looks great, although the forum software is being a royal PITA.

Thanks for the assistance, everyone.
 
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