Yamaha OX66 2002 150hp - what is considered low fuel pressure?

DJKaye

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Oct 22, 2013
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Service manual says fuel pressure test should show 35.6 psi. That is when the switch is turned on but the engine not running. Mine read 35psi, close enough. When I am running the pressure drops, at 3300rpm which is my normal cruising speed, the pressure is 28psi. Would this be considered low or within normal range? This is the intermediate pressure, after the electric pump but before the mechanical pump on HPDI engine.

The problem am having is the motor cutting out under load, like getting on plane or hitting a wave. It cuts out for a couple of seconds, then restores full power. Sometimes it will do this several times in quick succession. The engine shut itself off one time after 4 or 5 cycles of this. Restarted without problems. I have changed all the filters, changed the LP pumps, cleaned the oxygen sensor, run on portable tank with new fuel and with ethanol free fuel, using new hose and primer bulb. There is no change in fuel pressure when the engine cuts out.

When it is not cutting out the engine runs fine. Sometimes I can get up on plane without problems and run well in calm conditions.
 

boscoe99

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Aug 22, 2013
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It is normal for fuel pressure to vary.

Highest pressure will be with the motor not running. Say for instance when the key is just turned on.

At idle RPM the fuel pressure will at its lowest. As the throttle is opened and the manifold pressure increases, so too will the fuel pressure. Retard the throttle and the manifold pressure will decrease, so too will the fuel pressure.

This is all being done by the fuel pressure regulator that is plumbed to the intake manifold.
 

DJKaye

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Oct 22, 2013
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Thanks for the reply. Unfortunately my pressure measurements were wrong. There was a fault with my cheap Harbor Freight pressure gauge. The Shrader valve has a small red O-ring that isnt suitable for gas. By taking the Shrader valve out of the system we could see that the fuel pressure is erratic and drops to zero when the motor bogs down. No problem with the pressure regulator, we could control the speed of the boat just by sucking on the vacuum line. Pull a vacuum, boat slows down. So I am going to buy one of the aftermarket fuel pumps. I can’t see spending $700 on a fuel pump for a 19 year old boat, I will hope that the $55 alternative works OK. If anyone has comments on those items please respond. I am going to try one from jet ski plus.com.
 

boscoe99

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Many have reported that the $55 alternatives work just fine. Last a long time. It will more than likely outlast the motor.
 

boscoe99

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Damn my reading skills.

Title of the post is Yamaha OX66. But in the first paragraph you mention HPDI.

Is your model a VX/SX150 or VZ/Z150? Big difference.
 

DJKaye

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Oct 22, 2013
Messages
11
Changing the electric fuel pump fixed the problem. Engine is running well again. You are correct the engine is EFI not HPDI. Hopefully the $55 pump will last a long time.
 
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