OX66 tops at 3600 RPMs

[steven 42]

My first post and need help. Motor is a 2001 200 H.P Yamaha OX66. Initial problem was surging at low rpm and not reaching top RPM. Changed the O2 and cleaned the barrel. O2 was un clean able. Low rpm surging corrected.

Changed the low pressure pumps.
Compression 135, 135, 130, 130, 130 126
New fuel bulb, engine mounted fuel filter fuel lines .
Cleaned filter on H.P. pump(pretty new 1 year old)
New spark plugs

Pressure at schrader valve(on VST) steady 52PSI
Vacuum at WOT 6 6hg( low at idle about 2hg)
No air bubbles in fuel line

Any help would be appreciated. Ive put alot of hours with my head in the motor and just trying to help an elderly neighbor.

p.,s. Is 52 psi fuel pressure at schrader high?

 

[rodbolt]

Re: OX66 tops at 3600 RPMs

post the full model number then we can get to nuts and bolts.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

The gentleman who owns the boat tells me the info he has on the motor is
2001 Yamaha saltwater series, 200hp, SX200TXRZ


and he adds #s thata sound like thaey maybe ser# 66X05823



Thanks Rodbolt

 

[rodbolt]

Re: OX66 tops at 3600 RPMs

ok,2.6l ox 66.
52 psi is way to much rail pressure.
remove the fuel pressure regulator and clean the screen ,while your there clean the VST screen again.
make sure the O2 sensor output voltage is correct.
52 PSI will make that mtor run pig rich.
6"Hg vacum at the lift pump intake is WAY to much, 4" is the maximum on that engine.
go find the fuel restriction.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

Purchased a new HP fuel filter today but weather in northeast is rainey.

Is there a way to test the output voltage on the O2 without doing the " Flame Test"? I'm familiar with how to test the resistance(ohm).

Thanks

 

[steven 42]

Re: OX66 tops at 3600 RPMs

O.K Replaced the HP fuel pump filter and the fuel pressure reg filter(both really mucked up). Pressure went from 52 to 35 immediately. Put everything together, started engine and is missing so it won't even sustain an idle. Is this just a major vacuum leak? Got no reading on vacuum gauge but don't know if engine was running long enough to build vacuum. I got a feeling the vacuum lines from VST were incorrectly connected. Will check tomorrow. Any ideas and help is welcomed. Thanks for your help so far. You were right on.....

 

[jp10]

Re: OX66 tops at 3600 RPMs

You missed a fuel filter, the VST. While your at it, add a 10 micron fuel/water seperator filter in your engine well to lengthen the life of those $$ Yamaha filters? What did the high pressure filter cost ya?

-JP

 

[steven 42]

Re: OX66 tops at 3600 RPMs

Which filter are you referring to? I thought theere are two filters in the vst. One on the hp fuel pump and one at the Fuel Pressure Regulator. Am I missing one? Thanks

 

[rodbolt]

Re: OX66 tops at 3600 RPMs

if both VST filters were nasty odds are high the injector filters are nasty.
they can be removed easily.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

I agree, stands to reason that the injector filters are also mucked up. Can I remove the injectors without removing the fuel rail. I assume when I remove the injector I will see the screens.

The engine now fires but won't sustain an idle(dies right out). Could the TPS be outta wack. I see the yellow markings on the TPS where it attaches to the housing but are there any trouble signs I should be looking for. I ordered a Winky Blinky( I don't like to backprobe these connectors) to pull codes but it hasn't arrived yet. Again, thanks....

 

[jeffersondodson561]

Re: OX66 tops at 3600 RPMs

If your pulling 6" hg in your fuel line thats your problem their, any more than 4 is considered high. Check for a fuel restriction from the rail back to the VST. The return fuel pressure line, could be swollen line or kinked. Or if you have a mightyvac pull some vacuum on the regulator and see if it fuel pressure drops at all, if it does not, put pressure on it and see if it increases, if it does not need a new regualtor, vacuum should be about 5"hg pressure should be 6psi. That fuel pump is capable of producing more than 40 psi but take care of that fuel restriction first.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

Restriction eliminated. Both VST and Fuel Pressure Regulator replaced.(VERY dirty) Pressure at rail now, 35.6

Rodbolt brought up a good point. If those two screens were so dirty, fuel injector screens are also probably real dirty too.

My question(see prev post) is can I remove the injectors, individually, from the fuel rail or do I have to remove the rail. It looks like they are just seated in a rubber gromet. Thanks

Meant to say VST and FP SCREENS replaced

 

[rodbolt]

Re: OX66 tops at 3600 RPMs

yes, pull the rail then pull the injectors.
if the rubber seats and the orings are not damaged they can typically be reused, spray a light oil on them for reassembly.
maximum fuel system vacum at the lower lift pump intake is 4"Hg.
the injector screens can be carefully removed and cleaned or replaced.
the early to mid ninties 7.4 MPI mercruiser used the same filter and thats what I use to replace them.
if your try searching this forum I have posted the part number before.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

O.K. so, in the morning the injectors go to the shop.
On a side note, when I removed and opened the VST,, there was a white residue inside./ At first I thought it was salt but the gas doesn't show signs of water contamination. Now thinking it,s oxidation from the ethanol effect in the aluminum gas tank. If this is the case, do you think it would be safe to reinstall the injectors and run the motor, or, remove the gas from the tank and have the tank cleaned or replaced.... Thanks....

 

[steven 42]

Re: OX66 tops at 3600 RPMs

Cleaned injectors are in and motor started right up.
but idled a little high. Adjusted the throttle position sensor at idle(motor off, with test harness attached) to .48V. At WOT though, I only got 3.8 V(book says 5.25 V. Is this a throttle valve ajustment problem? Gettin to know this motor better.

 

[rodbolt]

Re: OX66 tops at 3600 RPMs

5 V is a reference, your TPS output will never achive reference.
3.8 is about right at WOT.
.5V with the shutters fully closed not on the shutter stop screw.

 

[steven 42]

Re: OX66 tops at 3600 RPMs

The boat was pulled and the motor fogged. According to my neighbor(the owner), motor sounded good on the muffs. Will have to wait til spring to see the fruits of my labor. I want to thank rodbolt for all the help he offered. I will post back when the boat is back in the water..... Thanks again