Mercury 115 EFI bogging down

This is my first post on this site. I have a 2002 Mercury 115 hp EFI 4 stroke. The engine bogs down when I try to accelerate. It runs good to about 2500 RPMs. Also I can not get the RPM past 5000 even when it does not bog down. Even when it does not bog down it takes a long time to reach 5000 RPM. Lately it will only go to 4000 RPMs. I have replaced the fuel/water separator and the fuel filter in the motor. The bulb is not collapsing. Any help would be appreciated.

Re: Mercury 115 EFI bogging down

There is a fitting on the fuel line to the injectors to attach a pressure gauge. Pressure should remain steady from idle to WOT while under load. If pressure falls of at RPM then you will need further testing and inspection of booth fuel pumps, fittings, and hoses.

If fuel pressure remains steady throughout the testing then you will need to order the OEM Service Manual to begin testing the ignition system. Any weakness of the ignition will limit power and RPM while under load.

Re: Mercury 115 EFI bogging down

Why do people insist on continuing to run motors that arent running correctly?!?!"it wasnt running right,and now,lately its running worse".DO NOT run more than absolutely necessary to diagnose and fix the problem.The EASIEST way to get into the market for a new motor is to run the one you have while having issues.Contrary to popular belief(and i dont know how it ever got started)running issues do not "work themselves out"by running more.Like said,BASICS first.Compression,spark,fuel delivery.

Re: Mercury 115 EFI bogging down

It's a good idea to check your compression to rule that out.
I think that you are having a fuel delivery issue.

One of the first things to check (as already mentioned) is the fuel rail pressure.
There is a fitting on the top of the fuel rail that you can attach a pressure gauge to (I've read of guys using a tire pressure gauge in a pinch)
At idle, you should be getting 38lbs. As the RPM's increase it should increase to 41-44psi.
This test should be performed at the trouble RPM under load.

There's another filter that is on the high pressure fuel pump that is located in the VST (vapor separating tank) that needs to be serviced.
If you are getting low fuel pressure, this filter may need cleaning.
To access the VST you will have to remove the intake assembly.
At this point, I would highly recommend getting the factory service manual to help you out

If fuel pressure is good, the injectors should be sent out for testing and cleaning.
Recently, I sent mine to http://www.brucatosvs.com/fuel_injector.html
They were a pleasure dealing with.
$25 per injector, before and after test results, new filter screens and o-ring.

This motor uses a Yamaha powerhead. Same one as the F115 up to 2006 if not mistaken.
You can do some searching in the Yamaha/Suzuki section archives

One last thing (as already mentioned), if you keep trying to run the motor hard with fuel issues, you can cause major damage because of a lean fuel condition

Hope this helps you out
Scott

Re: Mercury 115 EFI bogging down

I thought I should followup on this post since I believe the motor is fixed. I sent may injectors off to be cleaned. One of the injectors was flowing only 60%. I was able get the boat on the water yesterday for a test run. It ran great! RPM well beyond 5000. MPH went from about 33 to 43. Thanks for the help.

Re: Mercury 115 EFI bogging down

Just to add to this post, I have a 2005 115h.p. four stroke on a pontoon boat.. had a bad bog off of idle and other than that ran great..I bought the boat from back East and only took it out once to know that this wasn't right. I took the injectors off and sent them to Brucato...Out of the four, one was way lean and the other was flooding..Got them back and it runs great...Keep in mind that with Ethanol there will be many issues with injectors. Every boat that I own has a Racor water separator added to at least minimize the water separation issues that occur with Ethanol...I will send my injectors out every couple of years depending on use...A hundred and some change is cheap insurance for this and any motor..Just sent out 6 injectors from my Bridgeport racing engine and again they all flowed differently until they were cleaned..Blame in on our great fuel we have....