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Old 30-10-2011, 09:12 PM   #1
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Country: UK
Location: Surrey
Occupation: Motorsport Development inc Engine Managment
Boat make: 21ft
Engines: Various
Cruising area: Solent / Kent / Cornwall

Join Date: Oct 2011
Location: Surrey
Posts: 375
Mercury Oil warning module - failure investigation!

I thought I'd share some info on this I discovered earlier this year. I know most don't keep the oil injection system, but thought all the same this was interesting.

I have a Mercury 220Xri and always suspected that the previous owner of my engine failed to maintain it effectively. In fact when I first got it, turning on the ignition made no noise. I thought it was normal!! When I found this was not the case I looked into it to see why.

So a few months ago I traced the wiring for the alarm (A small Piezo sounder in the engine controls) and I then grounded its supply and in theory it should then start beeping. It did - kind of intermittently, and then it started to stay on. So today I decided to look further and pull sounder out and test it on the bench. Normal operational range is 5-15 volts, so I gave it ago and sure enough it was playing up. No problem found another on ebay.

So on I went this time looking to see when there should only be a short beep from the alarm the warning module on the engine was in fact putting out a continuous signal now I had the buzzer working.

So I did some tests on this rather pricey module only to find that as suspected its defective.

I then decided to do what any self respecting techno nut would do and then try and pull the unit apart without destroying it and try to establish the cause of failure.

Now this is harder than it seems in this case. Mercury have potted the module in a little plastic case with all the electronics covered in a hard setting rubber compound. Down side is chances of serviceability = almost none.

I did however make an amazing discovery... With a bit of careful prying and pushing I managed to pop out the potted electronics as a single lump without destroying it in the process.

I also immediately noticed something rather strange. There was signs of moisture in the bottom of the supposedly totally sealed case, in fact before this picture was taken, it was wet. Not only that I could see cracks along the potting compound where I could tell by looking closely the PCB sits, and now we have a way for the moisture to get in and quite possibly kill the module.. Now to see if its possible to see this..

I then carefully stuck a small (!) screwdriver just below where I could see the PCB end, I levered this slowly up and to my amazement the whole lot started to come away from the pcb revealing the entire face of the lower side.

This almost NEVER happens and only happened for me as the potting compound mercury use is quite flexible.

Check this out. I believe I've just solved the mystery why these modules fail so often for so many people:

Water damage anyone!?!!!

Reason is surprisingly simple. They sit on the outboard engine in the same orientation as the first image above. Water/moisture whatever sits in it and cant go anywhere. Give it enough time and it makes its way into the electronics. Had they been fitted to the engine the other way up I'm almost certain it would never have been a problem!

I did make further attempts to clean and fix it, but unfortunately it was damaged beyond any hope of repair, I'm now just starting on making my own replacement as I will not be handing 200 mercury for something thats so poorly made...

I thought it was interesting anyway
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