I have a 2008 Mercury 150 EFI. Engine has less than 20 hours total. It runs great at low speeds (less than 2000 rpm) but starts to miss badly above that. It never dies just runs very rough and wont increase over 3000rpm. It had been unused for 6 months prior to this time. I had Stabil mixed in with the gas when it was put up before the six months. I have pulled the plugs to check and all appear fine. The fuel filter was new before it was stored. I had the same problem last year and took it to the shop and they said they could not find anything wrong, and it ran fine after I got it back. Any suggestions are appreciated
Make (of engine): outboard
Model (of engine): Mercury
Horsepower: 150 EFI
Checked spark plugs which appear to be ok. no signs of fouling or lean conditions
My name is XXXXX XXXXX X will be helping you today. Most questions will involve troubleshooting, and usually take many posts back and forth. Post back with questions as needed.
Couple of questions back at you.
I do need your engines serial number to identify the engine.
Most of these engines have more than 1 fuel filter, specifically which one did you change?
It is safe to say the fuel is well over 6 months old correct?
Are you getting any alarms?
I do not currently have the serial number with me and it will be tomorrow before Ican get that for you.
I changed the metal spin on filter with the sensor on the bottom.
Some of the fuel was indeed more than 6 months old. I filled the boat up the morning i experienced the problem which added about 15 gallons. The tank of old was approximately 50 gallons.
No alarms or indicators of any type
Just get the serial and we can go from there. Right now I don't know if this is a 150EFI 2 stroke, 150EFI Optimax, or a 150 EFI stroke, or a 150EFI Verado. And I need to know what you have.
The serial number is XXXXX and apparently it is a 2007 engine not an 08 as I was told when I purchased it.
Here is how I would attack this one.
The first thing I would do is swap out the spark plugs for a new set, this could be nothing more than fouled spark plugs from sitting. While the old plugs are out, you want to look at the old ones and make sure none of them come out with rusty electrodes or pure white insulators, either would mean bad head gasket rings. These engines use individual sealing rings for the head gaskets, and they can leak on you.
Next up is to grab a small portable 3 gallon tank with its own primer bulb and fill it with new gas and run the engine on it to rule out your existing fuel in the gas tank as being bad. If the engine is still misfiring on this portable tank squeeze the primer bulb and see if the engine picks up or not. If it does then the engines fuel pumps are bad.
After that, you want to check your fuel pressure with the engine running. Specification is 41 to 44 psi. Fuel pressure regulators can stick open or closed and cause the pressure to be to high or to low.
Finally if still no fix yet I would pull the injectors and send them out for flow testing and cleaning.
With the EFI engines, if you winterize them (or set them up for long term storage, that being defined as the engine not running for 3 months or more).
Part of that process is you have to hook up a small portable tank to the engine. Fill the tank with fuel, stabil, and 2 stroke oil at a 50 to 1 ratio and run the engine on that.
Under normal condition the oil ratio is set by the ECM, and the ECM adds oil as it needs to depending on the RPM. By running this premix batch through it, it forces extra oil through everything. If you fail to do this injectors and fuel pumps will stick if left to sit for to long.
Thats what your looking for
Feel free to post back with questions
Degree in Marine Technology. Gas and diesel marine mechanic.