200 Mercury rpm fluctuations

[Salmonkiller01]

New guy here and my first post , thanks for allowing me aboard

2020 Mercury 200 rpm is fluctuating 20-100 rpm at idle , 40-50 at cruise speed
Wonder if someone else has had the same issues, started about 2 months ago

full service
plugs, double checked gap all burning the same by color
new Racor and engine filter
no fuel restrictions, replaced all hoses fuel flows easily
fuel pressure at 45 psi

what I noticed yesterday was that my voltage is now moving .1-.3 volts also where it would hold at 14.2 normally now 14.2-14.5 fluctuating
Rpm used to hold steady at 600 at idle
engine is not a smooth as it used to be, vibration

any insight would be great as dealers are 2 weeks from looking at it

serial 2b692965

[Salmonkiller01]

If someone can tell me if their digital gauge fluctuates at idle that would be helpful

[IDCI07]

If someone can tell me if their digital gauge fluctuates at idle that would be helpful

I have a 2020 250 Pro XS fourstroke and I noticed my motor is not running as smooth as it used too. It has a vibration or a small twitch at idle in neutral and when I put it in gear. As soon as I give it gas and running on pad it runs fine. It will twitch again when I come off pad. I have noticed on my smartcraft gauge the Rpms fluctuate from around 580-610 at idle. I had it serviced last fall at a dealer and they said they couldn’t find any issue with it but the motor never did it when it was new. I’ve been wondering about this myself.

[thommo59]

My 200 pro xs has always since new had idle rpm movement according to my smartcraft of 580-620. It runs fine otherwise but I have never taken any notice of voltage. It used to on occasions also do what you suggest when just on plane say anywhere from 3500 to 4000 and if I tapped the pedal it would be fine. It just stopped by itself however I have been running 87 grade gas where before I ran higher octane

[Salmonkiller01]

Thanks for the info, it definitely is not smooth at an idle, noticeable vibration. Even when I put in troll control is jumps around. It used to be steady.

[EuropeanAM]

If you would, please take a moment to review the Announcements at the top of the Forum, and be sure to provide the REQUIRED info when posting (serial number). Thanks!

Make sure all of your plug wires snap firmly onto the spark plugs. Have seen a number of wires damaged from improperly grasping them to remove.

Most of the variations you are describing are actually quite normal.

[Salmonkiller01]

I ordered a new set of plug wires and another set of plugs, going to try that as plugs usually fix this issue from what I have read Maybe I got a bad plug and or damaged a plug wire

[Salmonkiller01]

Fixed. Added aerial to original post

[IDCI07]

Salmonkiller01 I sent you a private message

[Salmonkiller01]

Replied

[Salmonkiller01]

The dealer is taking it in tomorrow. Hopefully have it fixed and will let everyone know what the issue was.

[EuropeanAM]

[Salmonkiller01]

Update. Dealer found o2 sensor failed and ecm had an update to do with fuel calibration.
I will launch tonight and let everyone know as it sounds like I am not alone with this issue
Engine has 208 hours and always had a rich exhaust smell idling. Plugs looked a bit rich so hopefully a good run will make it perfect


not fixed runs the same. Uhg

[Salmonkiller01]

When key is turned on is it low pressure pump you hear or high pressure? Or both?


you tube showing cruise and idle
fluctuations
https://youtube.com/shorts/eSjO9c6lVL4?feature=share


fuel pump squeel
https://youtube.com/shorts/qMg2OIktsWg?feature=share

[EuropeanAM]

Hard to diagnose "sounds" from videos, but I don't hear anything disturbing.

RPM fluctuations occur all the time. 20-70 RPM's variance is rather common.

So... let's get some specific info:

-Did you replace BOTH the spark plugs AND the plug wires?

-Do you have PRINTOUTS and a RECORDING from the G3 Diagnostic System? (I could review if so)

-Have they tried a Cylinder Misfire Test on the water, under load to monitor the RPM loss for each cylinder?

[Salmonkiller01]

Talked to my dealer today and they want me to run the boat for an hour and see what it does
when I get home putting in the 2nd new set of plugs and all new wires( genuine mercury and reasonable)
no printout given to me just work order saying what they did.

if the problems persist loping idle as I can not hear a miss and engine roughness the dealer wants it back to take for a run and have computer on it to see what the problem is while talking to mercury

Mercury rep is going thru the engine history data also

Starting to think it is me being paranoid but I swear it never ran this poorly before and troll control was solid. This motor smoothness is not even close to my old Verado

I do appreciate everyone’s input. Great community here

[Salmonkiller01]

IMG_2579.jpegTook the boat out for a good run idle to wide open throttle
Rpm fluctuates 50 rpm at idle now
wide open throttle 5850rpm
runs smooth and good
still has an idle vibration

Put new wires on today and put a new plug in to see how it is burning( other plugs are all gray/white 15 hours)
After 2 hours variable rpm it is white

Is the white normal after such a short time?

[EuropeanAM]

Yes- especially if you ran it in the 3000-5000 RPM range a decent amount.

[Salmonkiller01]

Thanks for the reply takes concern away. Just going to run it as it goes good just some rpm change at idle. Maybe an injector gummed up , who knows. Hits wide open throttle easily, lots of power.

so all in all my o2 sensor was causing 100rpm fluxuation.

[Salmonkiller01]

The saga continues. My motor still shakes at idle and rpm fluctuates constantly. I did find that where my flush hose connects to the engine block is leaking and the engine harness that runs in that area is covered in salt. Going to pull lower cowlings off and inspect the leak and harness as no one can look at the engine for over a month.
anyone have this issue?