2012 mercury 115 4 stroke surging

[sjord]

I have a 2012 mercury 4 stroke 115 hp. The boat and motor were bought new last Sept. 2012. When the boat was used for the second or third time the motor would idle between 8 and 9 hundred rpms. It would surge up and down but ran fine otherwise. The dealer checked it out spring 2013 and found no codes. The boat is still surging but around 1000-1100 rpms more when cold but does it sometime when the engine is warm. When starting the engine for the first time after trailering it will start after the second or third attempt. Today I unloaded the boat lowered the engine and turned the key on for 5 minutes or so then started it. The engine had to go through 2 starting cycles then started on the third attempt. Does the low pressure fuel pump run until the high pressure pump chamber is full or will it only run for a set time?
Any thoughts on if this is normal for this engine or is something wrong.

The engine was checked again with no codes but the mechanic said the ground nut on the battery was loose causing the surging. The engine is still surging?

[staylor]

You mentioned it still surges so I'm assuming that it now starts on the first try. It sounds like you have a problem in one of the fuel pumps. Merc wants you to have the dealer test the pumps with their own special tools so they are kind of evasive in the manual about how the system actually functions- but it appears that the low pressure pump runs on demand when you turn the key to first position, but after starting it may run all the time since it has a bypass circuit with a relief valve. In any event, in the shop manual for my 150 FS they note that the engine control module does not monitor the fuel pumps and will not throw a code if there is a problem in either pump. Thus, you can have an air leak in your system which is causing the surging- and it won't throw a code. Tell you dealer to get his shop manual and go thru the factory diagnostic procedure with the factory special tools.
Doug

[sjord]

No it still does not start until third try when cold. It starts on first try when motor is warm. Still surging at 1000 rpms.

Thank You for your Reply.
Scott

[DLM10]

I have a 2012 merc. 4 stroke. It starts and runs well and it has always had a light surge at 1000 rpms, never at idle, never above that speed. Saw this thread last night and remembered it as we were going through a 1.25 mile no wake zone just above idle today. Always thought it was a little odd being injected but never caused any problems.

[sjord]

Thank you for your reply. It must be the nature of the engine.

Scott

[Tundrarx1]

mine does the same too its a 2013, not always, sometime between 11-1200 rpm.

I put the fault on the throttle wire, it take time to have it there, not really an exact science on mine to have a certain RPM between idle and 1400 rpm.

[sjord]

The mechanic that checked out the motor for surging said he contacted Mercury technical support and they stated that the aggressive cam shaft on this engine may result in surging at the upper end on the idle range. So the surging appears to be nothing to worry about.

The starting procedure I was using may have been cranking the engine over to long after the initial fuel was injected into the intake resulting in failed starts or stalling after start up. I will have to try and crank the motor over after the beep when ignition is turned on and not wait. The injectors also put fuel into the intake when the ignition is turned on.

[CrestSuperHawk]

Originally Posted by sjord

The mechanic that checked out the motor for surging said he contacted Mercury technical support and they stated that the aggressive cam shaft on this engine may result in surging at the upper end on the idle range. So the surging appears to be nothing to worry about.

The starting procedure I was using may have been cranking the engine over to long after the initial fuel was injected into the intake resulting in failed starts or stalling after start up. I will have to try and crank the motor over after the beep when ignition is turned on and not wait. The injectors also put fuel into the intake when the ignition is turned on.

I have the same engine and it is a 2013. I have also noticed this surging at the high end of idle. My solution is to back down the throttle slightly. As for starting the engine I crank it as soon as I hear the beep. It fires very quickly. Good luck!

[sjord]

My 115 mercury is still hard to start in plus 4 - 6 degree Celsius temperatures. It takes at least 3 tries before it will start. The engine will also surge at 800 - 850 rpm when cold.
The amperage on the depth finder shows that it is dropping to 10.5 volts when cranking the motor. Is this normal voltage or is it low?

Thank You
Scott

[Hot Runr Guy]

Originally Posted by sjord

The amperage on the depth finder shows that it is dropping to 10.5 volts when cranking the motor. Is this normal voltage or is it low?

Thank You
Scott

Your motor requires a starting battery rated at 1000 MCA / 800 CCA, double-check to see what your's is listed as. The dealer might have scimped on it.

HRG