2005 Johnson 140HP RPM Surging

Nodnerb

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Jun 21, 2011
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I have a pair of 2005 Johnson J140CX4SOR. RPM's get to 2800 and surge between 2800 and 3000 either at idle at the dock, in gear at the dock or on the water under load. All fuel lines, filter, primer bulbs and clamps are new and everything is tight so there's fuel getting to the engines. Both engines are doing the exact same thing and they share a fuel filter, Racor S3232, which is why I suspected a fuel delivery problem at the beginning.

I'm starting to think this is not a fuel delivery problem and something else.
 

hidef

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Aug 22, 2009
Messages
1,465
Re: 2005 Johnson 140HP RPM Surging

Have you checked the screen on fuel pickup in the tank and the vent? Very uncommon for both engines to act up at the same time.
 

Nodnerb

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Jun 21, 2011
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Re: 2005 Johnson 140HP RPM Surging

That's tomorrows project, to back blast with air the tank outlet line and the vent line. I agree it's very uncommon for a pair of engines to have the same problem, that's why I suspected fuel delivery considering the engines share a fuel filter.
 

Nodnerb

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Joined
Jun 21, 2011
Messages
4
Re: 2005 Johnson 140HP RPM Surging

Not fuel. Waiting on software and cable from my Johnson dealer to run diagnostic tests, it's going to be a sensor or the ECU. I'll update when I find the problem and solution.
 

Nodnerb

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Jun 21, 2011
Messages
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Re: 2005 Johnson 140HP RPM Surging

Beginning to look like a bad wiring harness or multiple failed sensors.

Apparently the boat sank last summer... upside down... for 2 days... in salt water.
Engines were pickled immediately, wiring harnesses from helm to motor were replaced, gauges, controls, spark plugs, starters, but not the ECM's or engine wiring harnesses, or any of the sensors. Owner didn't want to spend the money at the time, well he's going to spend it now.
 
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