Mariner 115 EFI 4 stroke droping revs

Hi all I have a 115 EFI mariner 4 stroke 2002-2005 model. Has any one had any isues with this model mariner that when i run it for abuot 10 to 15 minuts at about 4000 rpm and its runing fine, and suddenly it will drop the rpm to 3500 and loos power like its choking and then pick up again and get a big rush of power as i push the throtel forward just alittle bit, then i have to pull back and it will go well again for abit and repeat the same thing again.I have taken it to outboard mechaniks couple of times but thay say that it is fine and cant find any thing wrong with it. Its pobably some thiong small please HELP !!!

Re: Mariner 115 EFI 4 stroke droping revs

Sounds like a injector or plug, remove injectors and have cleaned as additive/cleaners cannot dissolve the debris in filter. It cant be a coil as same coil fires 2 cylinders or the TPS as it controls ECU not seperate cylinders. Send injectors to Brucatosvs.com...

Re: Mariner 115 EFI 4 stroke droping revs

Did they check the float and valve in the vst tank? The marina where I take my boat said that was a common problem. They say that the valve sticks not allowing fuel into the tank causing the engine to starve for fuel, then suddenly the valve unsticks and the tank fills back up causing the engine to pick back up. They replace it in my 08 115 fourstroke merc saying that the have a newly designed one out that solves this problem.

Re: Mariner 115 EFI 4 stroke droping revs

I agree with Faztbullet, I have a 2004 115 and they were made by Yamaha as and FYI... bought the boat from back east and it would bog off idle...not badly but enough to bother me.. I sent the injectors out to Brucato where they flow them before they clean them and after they clean them and give you all the numbers.. number 3 injector was running rich and number 4 was running way lean...The lean cylinder could have caused some major damage run long enough and hard enough in that state...Injectors are easy to pull out, send it, and put them back on..I think it cost around $125 for all 4 to be done.

Re: Mariner 115 EFI 4 stroke droping revs

the VST chamber contains the high pressure fuel pump..at the bottom of the fuel pump is a little screen that should be cleaned/replaced every couple of years..I just did my 2003 yammy 115.it was very dirty, probably never been cleaned. check your fuel pressure on the rail.

Re: Mariner 115 EFI 4 stroke droping revs

thank you all for your help, just one more thing.what is the VST chamber and where is it on the motor?

Re: Mariner 115 EFI 4 stroke droping revs

reef ranger said:

Hi all I have a 115 EFI mariner 4 stroke 2002-2005 model. Has any one had any isues with this model mariner that when i run it for abuot 10 to 15 minuts at about 4000 rpm and its runing fine, and suddenly it will drop the rpm to 3500 and loos power like its choking and then pick up again and get a big rush of power as i push the throtel forward just alittle bit, then i have to pull back and it will go well again for abit and repeat the same thing again.I have taken it to outboard mechaniks couple of times but thay say that it is fine and cant find any thing wrong with it. Its pobably some thiong small please HELP !!!

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You should take it to another mechanic, these are the classic symptoms of either low oil pressure or high temperature. When the ECM receives signals from either the oil pressure switch or the water temperature sensor that are outside safe operating limits, it both retards the timing and cuts fire to two of your cylinders. Moving the throttle is one of the things that temporarily overrides the ECM but then it will return to the lower rpm operation until the unsafe operating condition has been resolved. You should go to the online operators manual for your motor. It will save you a lot of time and headaches dealing with mechanics who have no clue.