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Only 3 cylinders are getting spark 1978 150 hp

A

aquaholictom

New member
I have a 1978 - 150 HP V-6 -Mercury Outboard - Stopped running. When I checked spark found out I only had spark on the right bank, nothing on the left bank. Checked each spark plug for spark and none available??
 
Re: Only 3 cylinders are getting spark

I believe you model did NOT have an idle stablizer module, so a bad switchbox would be the leading contender.

You have 2 switchboxes, one for each cylinder bank...

I believe the advice you would get from most guys who work on these would be to replace both switchboxes, one often follows the other when they go - but at a little over 200 bucks a piece (list price), it is a little pricey...

Should have added - to confirm it's a bad switch box, simply swap the wires around (from the trigger and stator, not the spark plugs) - if the bad bank starts firing and the good bank goes dead, then it's definately the switchbox...
 
Re: Only 3 cylinders are getting spark

The stator is probably dead. There is no power going into that box anymore. Replace both boxes at the same time.
 
Re: Only 3 cylinders are getting spark

Thank you for your help. I just looked at the engine and it appears that the mercury switch is disconnected. The ground wire from the switch is connected to the block but nothing else. If I connect it back to the switch box could that possibly correct the problem? Is there only one mercury switch for both switch boxes?
 
Re: Only 3 cylinders are getting spark

The Mercury switch is not the problem.

It's designed to either kill the motor if running or not let you start it if you have the motor tilted up in the trailer position.

With it being disconnected, that's a sure sign that it's not causing this - and yes, the one switch would ground out both boxes - so if it was connected, and it was the problem, you would have no spark anywhere...
 
galamb said:
Re: Only 3 cylinders are getting spark

I believe you model did NOT have an idle stablizer module, so a bad switchbox would be the leading contender.

You have 2 switchboxes, one for each cylinder bank...

I believe the advice you would get from most guys who work on these would be to replace both switchboxes, one often follows the other when they go - but at a little over 200 bucks a piece (list price), it is a little pricey...

Should have added - to confirm it's a bad switch box, simply swap the wires around (from the trigger and stator, not the spark plugs) - if the bad bank starts firing and the good bank goes dead, then it's definately the switchbox...
Click to expand...
Which wire is the trigger wire?
 
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