Yamaha OX66 experts help I have a gremlin

[slavis]

It was suggested to me to post on this site and hope a gentleman named rodbolt responds. 2001 250 ox66 pair. Port motor started acting up a week ago. On the way in from a trip the motors had been running for 1.5 hours at 4300 rpm and instantly the port motor dropped to 3000-3400 rpm giving it more gas gave no response.The symptons are erratic but it will always do it within 10 minutes of running sometimes when you are just getting up on plane or after a few miles of being on plane.The motors idle perfect. Either it will bog trying to get on plane around 3000-3400 and surge back and forth until it "catches" and then run fine for a few miles and then drop down to anywhere from 2800-3800 until it "catches" again. The other day it bogged at 3000-3400 for a mile or so and I watched the flow meter and it held steady like the motor was running at 4300(14 gph) Since then I have replaced vst filters-no signs of problems, checked twice the fuel rail pressure both times while it was surging it read 38psi and never fluctuated, checked voltage at high pressure pump it held steady at 12.7 volts, swapped fuel pickup at primer ball, bypassed big racor filters/flow sensor and 3 way fuel valve, replaced all fuel lines except hoses from tanks(including hose inside rigging tube), installed new lp pumps and swapped the entire motor mounted fuel canister/lp pumps and associated hoses up to the vst tank, swapped the vst tanks, swapped rails and installed new fuel lines at the rail, swapped the injectors. Also, checked with the winky blinky(no errors), cleaned/swapped the O2 sensor, swapped crank position sensor,installed new tps(and adjusted-I have test harness) and swapped the tps, swappped the atmospheric pressure sensor, swapped the cdi unit twice(with all coils,wires),installed new spark plugs and swapped the spark plugs, disconnected the intake temp sensor from both motors and they both idled poorly and ran rough(I could not figure out how to remove them to swap), swapped the knock sensor, swapped the high pressure rectifier, swapped neutral cutoff switch, swapped the stator and flywheel, swapped the main engine harness, swapped the wire harness from the injectors to the main harness, swapped the 10 pin plug at the keyswitch, used a short 10 pin plug and a keyswitch to bypass the ignition cable going from the keyswitch to the main engine harness. After numerous test runs this motor defies logic nothing has worked. I bought these motors new and have kept up the maintenence to a high level. Help!!

 

[99yam40]

Re: Yamaha OX66 experts help I have a gremlin

I am not really that knowledgeable on those motors but you have covered most of what is on the motors except for the spark and timing

An inductive timing light will help you see if you have spark problems on certain cylinders and also tell you if the timing is staying steady while problem occurs. A high voltage tester would be better for testing ignition coil outputs but not too many have them.
A peak reading voltmeter made for measuring these ignition systems or a DVA adapter and DVM or DMM will show the pulsar coil and charge coil outputs along with the outputs of the CDI to the coils. Taken while problem is occurring may show something if you are dropping spark to one or more cylinders.

Just my 2 cents

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Forgot to mention I also replaced the t stats, swapped the engine cooling temp sensor and swapped the thermo switches. I also pulled each spark plug boot (twice) while the motor was surging and I could hear the motor run worse each time I did. I am crying UNCLE!

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Also swapped the small check valve just past the engine mounted fuel filter.

 

[cousinabe]

Re: Yamaha OX66 experts help I have a gremlin

Was the winky used while the problem was occuring? The motor does not store any codes.
If no codes, your sensors are fine and time to start chasing fuel, ignition or connections.
Are you batteries and cables all in good shape? Ground wires.
Did you test the O2 sensor while running?

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Thanks for the responses. Cousinabe I only used the winky bklinky while the boat was idleing. If you have a sensor going bad at only higher rpms will the winky blinky catch this? I was only aware of using this at idle. All my batteries/cables are in good shape. How do you test the O2 sensor while running? Today I went back over the motor and swapped the crank position sensor/swapped the O2 sensor with barbell and bracket installed new gaskets/swapped the intake manifold which also included the tps and the high pressure rectifier and swappped the engine mounted oil tank level sensor and nothing has worked. The only strange thing today was when I removed the bracket that the O2 sensor screws into there were 3-4 drops of oil where the barbell goes into this bracket. First time I have ever seen this after cleaning my injectors/ 200 hrs since new. I know I am reaching but is it possible the splits in the piston rings "lined" up and is allowing a little more oil into the O2 sensor tube throwing this sensor off? I did a compression check couple days ago the pressure was 110 on this cylinder the lowest was 107 and the highest was 112. Thanks for the help.

 

[rodbolt]

Re: Yamaha OX66 experts help I have a gremlin

use the winky blinky at the problem RPM. also check your engine knock sensor to insure its tight.
like cousinabe says, that ECU wont store codes but the winky will read it when it occurs.

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Thanks for the tip I will winky it tomorrow. I will also swap(again) and check the tightness of the knock sensor. Why would the barbell area of the O2 sensor have a little oil in the area? Could this be a problem?

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Just got back from test run. Checked the winky blinky at problem rpm and during surging no error codes. Swapped the knock sensor and double checked the tightness no change. I also ran the fuel line directly to the good motor fuel tank installed a clear piece of hose therefore bypassing the filter/flow sensor and 3 way valve. Zero bubbles and problem still present. I checked timing at problem rpm and during surging it held steady with no jumping around. Checked the rail pressure at problem rpm and during surging held steady at 38psi. Swappped and cleaned the engine ground no change. I even made a test harness to operate the knock sensor and oxygen sensor crossing the motors this made no difference. The service manuel under troubleshooting states poor accereration check "power unit seal" What and where is this? I am going to swap lower units tomorrow for grins and giggles. Any other ideas?

 

[lovefish]

Re: Yamaha OX66 experts help I have a gremlin

Please let me know when you find the problem. I have a 2001 250OX66 doing the samething. I changed everything on the fuel system and changed the CDI unit. Also done everything you done cant figure out the problem.Thanks

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Did you check/clean the main ground wire and did you replace the neutral cutoff switch?

 

[lovefish]

Re: Yamaha OX66 experts help I have a gremlin

dont know where is the netrual switch. I had 2 diffrent mech. look at it and cant figure it out.

 

[lovefish]

Re: Yamaha OX66 experts help I have a gremlin

dont know where is the netrual switch. I had 2 diffrent mech. look at it and cant figure it out.

and a 3rd one looking at it now and didnt figure it out yet

 

[boatguy823]

Re: Yamaha OX66 experts help I have a gremlin

six months ago I had a similar problem with one of these engines....idled great, firing all cyls good fuel pressure ,etc etc etc to make a long story short pull the spark plugs and take a look inside the cylinders and check for a spun cylinder sleeve.

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Thanks for the tip. How do you "look" inside and what will I be looking for?

 

[rodbolt]

Re: Yamaha OX66 experts help I have a gremlin

have you removed the injectors,then removed the injector filters, then reinstall them?
each injector has a filter, use a knife and carefully remove and clean or replace them.
Yamaha doesnt offer them but they can be found by a mercruiser dealer looking for about a 2001 7.4 MPI.

 

[lovefish]

Re: Yamaha OX66 experts help I have a gremlin

Rod Bolt the mech. that has it now came ride with me he said it electical but its not the CDI unit he checked all the sensor. Hes just not that used to dealing with this type of problem. Any suggestion on electrical problem. It stalls and will shut down when getting on step wide open. but it will get on step if u get in to it slow and run fine at 4200 rpms. it u try to open it up it starts missing. Thanks for any input

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

Rodbolt thanks for the response. I have swapped the injectors(twice)and the injectors were cleaned/tested 700 hours ago. I swapped the lower units and no change (did not expect it to). What do you think about a spun cylinder sleeve? I was not aware those motors had sleeves. I have tried everything 2-3x. I cannot imagine missing something at this point. It seems logical it could be internal.

 

[rodbolt]

Re: Yamaha OX66 experts help I have a gremlin

a spun sleeve would not come and go. I have only seen 1 engine do it and the symtom was a lack of power but perfect otherwise.
when you checked the timing what was it?
if its surging and the winky blinky is displaying code 1 it sounds like fuel pressure or lack of fuel in the rail or a clogged injector.
but all the systems can be tested with a multimeter.

 

[slavis]

Re: Yamaha OX66 experts help I have a gremlin

I used the winky blinky at idle (a few times) and while it was surging-- never had any error codes. I have swapped the fuel rail and replaced both hp fuel lines. When I did the timing I was mainly looking for a constant reading I was not focusing on the actual number. It was a little unnerving hanging on the back of the boat with my reading glasses. But I think it was around 18-19. Was hoping the answer for the spun seal was a variable condition.Thanks for the help