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Power and Ignition Problem

D

duckfan

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"I have a 1992 Mercury Mariner

"I have a 1992 Mercury Mariner 60hp that I am having power and ignition issues with. The problem only seems to exist when I have been running the motor for a long period of time and working it hard such as running out in the ocean. The problem acts like a fuel demand issue. The motor will run along fine but then after a while 30 min or so, it will hiccup and stop. Then it I will start it back up again and hit the throttle only to have it sputter and die. Then I will start it up again and ease the throttle to about 1/4 but then when I give it any more it will sputter and die. I have completely gone through the fuel system including filter, pump, and even drained the tank. It seems to be getting plenty of fuel. I put brand new spark plugs in for this last trip out where it acted up again. I am wondering if it might be related to the coil or other ignition parts. It only seems to do this after it heats up and has been running for a while. If I let it cool down and get cold I can run it again for a period of time (30 min) before it starts acting up again. I have only experienced this problem in big water such as the ocean or large bay. Is there a way to check the electrical components to see if that is the problem? Could the issue be electrical or is there an other possible cause to this issue that I have missed?
Thanks"
 
"You need to test for spark wh

"You need to test for spark when it stumble (timing light works well).

It's not an uncommon problem to lose spark when it's heated up. The problem is most often a cracked bobbin (winding) on the stator which loses it's connectivity when it heats up and expands.

So test for spark and if it's a spark loss causing the stumble, it's most likely your stator that is cracked."
 
OK thanks for the advice. I h

OK thanks for the advice. I have a question related to that. As I understand the ignition system on this model has several components. Could it be any of the others such as the coils or switch box? How would I check those?
DF
 
"Yes, there are quite a few co

"Yes, there are quite a few components and thats why you need to determine if you are losing spark and how many cylinders it's affecting - the results will tell you the "most likely" component that is failing.

The ignition works as follows:

The stator is like a generator (and produces AC) - has low speed, high speed ignition coils plus charge coils.

The low speed windings feed the ignition below about 2500 rpms. After 2500 rpms (give or take a bit) the high speed windings kick in and both feed the igniton.

These feed the switchbox which rectifies the power (coverts the AC to DC) and stores it in capacitors.

The charge coils provide power to the regulator, which coverts the AC to DC and regulates the voltage to charge the battery.

You also have a trigger (sometimes called a Sensor). It provides an AC pulse to the switch box to tell it to release it's power to the respective cylinder according to the timing of the motor.

When the switchbox receives it's trigger pulse it releases the stored power to the individual cylinder coil for whichever cylinder.

The coil up converts the power (about 250-400 volts or so from the switchbox) to 45000-55000 volts to fire the sparkplug.

The stator, trigger and coils can be tested with an ohm meter to see if the windings are intact (a quick test to see if they should work).

The switchbox is checked by proving everything else is working since there is no way to test it's internal components.

If you lose spark to a single cylinder it's "normally" a coil. If you lose spark to 2 cylinders it's "normally" a trigger but maybe a switchbox - no power anywhere is "normally" a stator or switchbox.

That's why initial troubleshooting is required to determine where to check next..."
 
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