2001 Yamaha 0X66 200 hp fuel issues

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
Hello everyone I purchased this boat about 2 years ago and the motor has ran like a top until this past weekend. It started with not wanting to crank unless it has almost full throttle. This is a fuel injected motor and never needed more than just pressing the choke to get it started on a cold start. Today I gave it a basic tune up. New Plugs, Impeller, also ran injector cleaner through the motor with a little less than a gallon of gas. While running the cleaner through the system I noticed tons of fuel coming from the prop area. It went through the entire gallon of gas in about 2 minutes. I checked the fuel pressure and it was 35 psi on idle. If I turn the motor off and pump the bulb gas starts leaking from the exhaust,prop area and I have to give it full throttle to get it started. It is almost like something is stuck open and pouring gas into the cylinders. I took the breather off and pumped the bulb and from what I could tell all the throttle bodies looked the same and no injectors were leaking and I could not tell where the gas is coming from. I am leaning towards the lower pressure pump but really not sure what to troubleshoot next. Any help will be greatly appreciated.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
fuel injected motors do not have chokes, .
to much pressure or stuck injector is what I would be looking for.
But if this motor has lift pumps running on crankcase pulses then I would look there too
 

boscoe99

Lieutenant Commander
Joined
Aug 22, 2013
Messages
1,785
If the fuel pump diaphragm has failed then gasoline will be pumped into the motor when the primer ball is squeezed. Gasoline may very well come out of the exhaust.
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
I am about to go out and recheck everything now. It has 2 low pressure pumps that feed the high pressure pump. I am suspecting one of the low pressure pumps is the issue. I had to remove the check valve in the tank fitting at the lake to even get it to pump last weekend.
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
I took off the high pressure pump and split the fuel vapor separator and everything seemed to check out fine. The float is working properly so the only way for I see for the fuel to get into the motor is from a stuck open injector. What the best way to tell which injector is the problem? I also see online where people talk about the 2 low pressure pumps torn diaphragms causing issue with flooding but by looking at the diagram i see no way for it to get into the motor except through the injectors? Any help will be greatly appreciated.

highpressure.JPG lowpressure.JPG fuelrail.JPG
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
the lift pumps work off of crankcase pulses, if they leak the fuel will go direct into the crankcase
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
I hear what your saying but I don't see or understand how. The only vacuum line I am seeing is hooked to the fuel pressure regulator I checked its line and it seemed clean. I must be totally missing something. I know with my old Johnson it had a vacuum line directly connected the the pump that went to the block. I am not seeing that on the Yamahas, Can you explain how these pumps get their pulse? Thanks in advance.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
the pumps are bolted onto the pulse ports(Holes in block), there is a gasket sealing that connection
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
Ok. I see the light now. That has to be my freaking problem. I am going to replace both pumps. I am assuming the new pumps will come with the gaskets and everything I need?
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
Thanks everyone. This weekend I installed 2 new low pressure pumps. The top one was leaking. I also put in new plugs,new impeller,cleaned the 02 sensor, and cleaned high pressure tank filer and she fired up and ran like a champ. Thanks for all the help. I now just need more time to hit the lake.
 

jstatham

Petty Officer 2nd Class
Joined
Apr 3, 2007
Messages
119
Thanks everyone. This weekend I installed 2 new low pressure pumps. The top one was leaking. I also put in new plugs,new impeller,cleaned the 02 sensor, and cleaned high pressure tank filer and she fired up and ran like a champ. Thanks for all the help. I now just need more time to hit the lake.
 
Last edited:
Top