115 efi trouble

[benzico]

hello all,this is my first post,i have gained invaluable info in the past from just searching the forums however i have a problem i cant fix.my engine is a merc 115 efi 2002 ,i believe it has the same powerhead as the yamaha f115.the problem is this-
low rough ilde in nuetral,rpm drops first on acceleration and sometimes stalls,on decelleration in nuetral the engine will also sometimes stall.fuel lines,lp fuel filter,plugs,fuel have been replaced,one section of the old fuel tube had perished and broken down inside.whilst running in nuetral @normal idle and @higher rpm 1200 i removed the injector plugs one at a time,1 &4 caused the engine rpm to drop but injectors 2&3 made no difference.i then pulled the spark plugs,same,all plugs appear to be producing spark.i then listend to the injectors,all sounded the same.i have checked the fuel pressure after the lp pump ,8 psi,and the fuel rail pressure,38 psi @idle,this seemed to fluctuate 2 or 3 psi in sync with the rough idle.
my thoughts are can i swap the injectors around to test ? or does this engine drop cylinders 2&3 for any reason? also should i try and claen the vst, pressure regulator and the idle control valve?
i see that Rodbolt knows his stuff regarding the yamaha hope he doesnt mind helping a merc owner! thankyou for any input

 

[Don S]

Re: 115 efi trouble

I have had this same exact problem on the 4stroke EFI's. Here is a trick I learned from a Merc tech rep a couple of years ago that made them all work. Just a process of cleaning the injectores.
You have to remove the 4 injectors from the motor.
You also have to have a can of Mercury power tuner. PN 858080K01 about 10 bucks.

Nice thing about this powertuner, is the nozzel fits the injector perfectly and I know the stuff works.

You also need a 9V battery and a couple of test leads.

First you have to remove the filters in the end of the injectors.
Hook up the battery with the test leads to the injector. Doesn't matter which is plus and minus. You will here the injector click open. Then spay the powertuner from the engine side of the injector and push everything out of the injector backwards from the fuel flow direction.
I have never left the injector hooked up to the battery for more than 15 seconds, may not hurt it, but I don't know.
Go through this process on all the injectors.
Then repeat the process a couple more times over the next half hour.
Put them back in and start the engine.
Bet it runs smoother and takes throttle.

A couple of things I have noticed. There was always black specs on the fuel pump screen in the VST, and it was cleaned before putting back together.

You will need a new VST sealing ring for the VST, and a manifold gasket, along with seals for the injectors.

I had to re-do one Merc that kept plugging up the injectors until I put the fuel bulb before the water seperating fuel filter. They must just trap crap that will plug the injectors.

This all seems somehow related to the increased use of ethenol gas in this area.

You need (aka MUST HAVE) a 10 mil water seperating fuel filter. If not, you are going to fight this for ever.

It's amazing how small the stuff is that clogs these injectors and causes this problem. I have never seen what caused the problem.

 

[sdsaw]

Re: 115 efi trouble

Don S.,
That's a great tip for the DIYer's out there.

I have a question about the power tuner nozzle and it fitting over the injector tip.
Here's a picture of mine (ignore the torn up seal. That's another story in itself).
The engine side of the injector seems too big to fit the PT nozzle or is it?

Thanks!
Scott

 

[Don S]

Re: 115 efi trouble

Actually, it fits inside the injector nozzle, not outside.
This should help.

Yeah, you need a new seal.

 

[sdsaw]

Re: 115 efi trouble

Thank you Don S.
That's a great explanation!

 

[benzico]

Re: 115 efi trouble

Thanks Don S for the quick reply, will give it a go tomorrow.