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2004 Mercury XR6 150 - OT932824 - won't run over 4200 rpm - Can you guess the solution?

7

78dave

New member
I posted this issue many months back. Motor would not exceed 4200 RPMs. Over time I replaced the control module, voltage regulators, shift sensor, and oil reservoir cap and battery. Carbs had been rebuilt and the fuel pump was rebuilt. Temp sensors ohm'd correctly. None of these corrected the issue. What was confusing was I could unplug the sensor plug from the control module and the motor ran perfectly to 5300 rpm. But when unplugged I had no sensors, so I installed a pressure gauge and a temperature gauge to make sure I knew what was going on. I tested the voltage at both idle and 2500 rpm and noticed that it exceeded 16V with is the limit for this motor. These were CDI voltage regulators. I also replaced the control module with a CDI module. No change. Ended up replacing the control module with OEM module and voltage regulators with OEM.

No of these fixed my issue. In the end what was it that fixed my motor? Can you guess? I only post this because I have noticed many time people post their problem, but then we never know if they got their issue resolved.
 
If the voltage was running that high with CDI, did it come down with OEM? Secondly, how were you checking the voltage? Thirdly, did you get 12.65 volts with motor shut down? Fourthly, did you check cranking voltage? Then I may be able to answer your question. It does sound like a battery problem. I always start with the simple thing first......not parts replacement. I don't get rich, but my customers get happy.
 
Voltage did come down with new OEM regulators. I had replace the originals with CDI, but they did not fix the issue and then also reul;ted in hiogher voltage. Per Mercury service for this motor over 16V is not acceptable. But 15.5V if ok. So has high voltage. Checked it on the purple wire both with the yellow wires plugged in and unplugged. At idle and at 2500 rpm. Yes, battery was fine at 12.5 - 12.8 when turned off. Cranking voltage was fine and the battery was later tested and detremined OK. I did though after talking with CDI replace the battery with one that was not maintenance free. No change. I was all over the battery thing as I understand from CDI a maintenance free battery (not a gell cell just one you could not remove the top) may bot be able to "boil" off high voltage when a flooded cell will.
 
timguy said:
Only thing left is the trigger. Or does this have a water sensor?
Click to expand...

You are correct! That'a a winner. Big issue was the sensor plug. When you unplugged it the motor ran perfectly. Hard to trace to trigger.

Hope this helps others with a similar issue. My 2004 was sort of a hybrid as this was the last year for it and it did not have switch boxes. The control module does it all. My thought is now I have a new OEM module, but the old one is still good perhaps.
 
I am confused??? Did the overcharging cause the issue or was trigger the problem the whole time? Sound like two separate problems....
 
faztbullet said:
I am confused??? Did the overcharging cause the issue or was trigger the problem the whole time? Sound like two separate problems....
Click to expand...

The over charging was the voltage regulators and even though this was an issue, replacing them with oem regulators did not resolve the problem of not running over 4200 rpm. I know sounds like a guardian or rev-limit issue, but this engine has neither.
 
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