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Dominick
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 1999 Mercury outboard 225 EFI. It will not idle but

Customer Question

I have a 1999 Mercury outboard 225 EFI. It will not idle but runs fine once you give it gas.
Submitted: 11 months ago.
Category: Boat
Expert:  Charles replied 11 months ago.

Hello, my name is***** will assist you.

Do you know what spark plugs are in the engine?

Have you already done any troubleshooting on your own yet?

Does the engine smoke more at idle?

Customer: replied 11 months ago.
I have NGK plugs in it.It smokes more than the other engine.I changed all the fuel filters. It is very distinct working and not working. To start the motor I have to give it a little throttle. I can put it to idle and runs rough and then dies. If I give it gas after starting and get on plane the boat it will run perfect, when I go to idle it idles perfect for about 2 minutes and then runs rough again then dies. It doesn't seem like its loading up. It seems like a sensor is telling it something.I have a vast experience in big blocks and very little on outboards.
Customer: replied 11 months ago.
I was thinking maybe a MAP sensor?
Expert:  Charles replied 11 months ago.

Thanks, ***** ***** have the serial number from one of the engines handy?

Customer: replied 11 months ago.
OG842719
Expert:  Charles replied 11 months ago.

Sorry for all the delays.. It is defiantly a Monday here.

The engine calls for Champion QL77CC spark plugs. It ill not run really well on NGK plugs for some reason.

Can you locate the square pulse pump on the engine, remove the two bolts that hold it to the block, and remove the outermost hose. Use the primer bulb to see if you get any fuel out of the front or rear covers on it.

Can you pull the plugs and do a reading on them? Is any darker or lighter than the others.?

Customer: replied 11 months ago.
I will be able to do this tomorrow and let you know
Expert:  Charles replied 11 months ago.

Sounds good. Talk to you then.

Customer: replied 11 months ago.
I am going to put new plugs in it. What gap would you recommend?
Expert:  Charles replied 11 months ago.

0.035

Customer: replied 11 months ago.
I changed the plugs on both motors. All 12 looked the same. The bad motor had champion and the good motor had NGK. Didnt get any fuel out of the covers. I took it apart and all the rubber was intact. The motor still runs rough. The RPM shows 1400 at idle but its hardly turning. I throttled it up and it ran rough until about 3000 rpm's
Customer: replied 11 months ago.
All the plugs were dark not light colored
Customer: replied 11 months ago.
Should I take a quick video of it running and send to you?
Expert:  Charles replied 11 months ago.

Yes a video would be great. If you can post it to you tube or another file sharing site.

Customer: replied 11 months ago.
You Tube
Bad merc motor 1
Bad Merc Motor2
Expert:  Charles replied 11 months ago.

Can you post the link to those vids. There are literally thousands of Merc vids on YouTube. I cannot locate yours.

Customer: replied 11 months ago.
https://youtu.be/25W5B_Xq8Ckhttps://youtu.be/jUuL3t-mRaI
Expert:  Charles replied 11 months ago.

Can you take the pulse pump from the side of the block, remove the hose from the front plate leave the hoses connected to the center plate. then pump the primer bulb and see if you get any fuel from the elbow on the front or the hole out of the back.

Customer: replied 11 months ago.
You've already asked me to do that and I didnt get any. I'll try again and confirm
Expert:  Charles replied 11 months ago.

Sry, I read back and missed that.

Expert:  Charles replied 11 months ago.

Take the flywheel cover off and make sure that the stater is not staying engaged.

Have you already done a compression test on this engine?

Customer: replied 11 months ago.
took it off and pumped the ball. Nothing out of anywhere. You can hear the fuel going thru the pump
Customer: replied 11 months ago.
Whats next? Thanks for all your help
Expert:  Charles replied 11 months ago.

Did you look at the starter to see if it is staying engaged?

Have you already done a compression test?

Customer: replied 11 months ago.
What about a sensor? Map? Idle? Starter engaged, I don't get why that would make it run like it is No I haven't done a compression check. Top end has maybe 100 hours on it
Customer: replied 11 months ago.
Please advise on next step. Do you want me to do a compression check? Reed valve? It idles perfect after bringing off plane for the exact same amount of time. Compression would have bad idle all the time wouldn't it?
Expert:  Charles replied 11 months ago.

I heard some strange noises from it when it was running. That is why I was asking about the starter and the compression. A failed MAP would also trigger an alarm. You can unplug it and see of the engine runs any differently.

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