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0x66 225 VMAX No Fuel Pressure
I went to the lake last week and right from the start engine idled rough then as I try to run it, it would barely get on plane. It took maybe 100 yards of running it wide open to get on plane. Then it ran ok, not great. It felt like it had half of the power it normally does. I ran it wide open, normally runs upper 60s, it would only run mid 50s. I made the best of it and fished for several hours. Go to head back and it wouldn’t plane off at all. My boat does not have a tachometer by the way. I’m a glutton for punishment so naturally I plan to take this on myself. Get home and try to make sense of it all. Here has been my findings:
1) Immediately check compression just for peace of mind, I’ve had an engine with low compression and had flash backs. All good.
2) Check pressure at the fuel pressure port using a tire gauge, no pressure.(Not the correct tool, I know but it’s what I have and it works). Bulb is tight, no evidence of low pressure fuel issue. Drain vst to verify fuel level. It was full. So I think ok sounds like a high pressure pump.
3) I had a high pressure pump on hand, used but I knew it was good, I pop it in. Check pressure, nothing.
4) I remove vst again to check the regulator, I fasten some air line to it and hook to a wimpy tire inflator to check to see if it will just hold 10 psi or so, just to make sure it’s ok. It did not hold pressure. Air is blowing right out. I think ok, this is getting somewhere. Reconnect vst( less the return line). I plug the return line with a barbed fitting with a gauge, pump builds pressure. I think I have this whooped. Bad regulator. Case closed. Order genuine Yamaha parts from boats.net, regulator and vst gasket for $330.
5) Installed new parts tonight, check pressure and wouldn’t you know it. No pressure. When I turn the key and run back to check while it’s running, It will build 35 psi or so like it should but as soon as the pump cuts off, pressure drops to zero. If I turn the key, run the pump, cut off, wait 30 seconds, let pump run, then check it I still get 0 pressure. I go to Orielly to get a proper fuel pressure tester, get home. Half of the fittings are gone. Can’t make it work with that equipment. I’ll go get another tester tomorrow.
If anyone could shed some light on the matter I would greatly appreciate it.
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You might want to check the 3 mechanical fuel pumps and verify if they are leaking or not. Undo the two bolts that hold each pump to the side of the motor, pump primer bulb and see if any fuel leaks out. If they are leaking its time to replace them.
You should also clean your O2 sensor and housing while your at it.
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If the pump is good it should maintain 35 psi with the key on. Did you change/reinstall the oring at the top of the high pressure pump? It may be leaking down there.
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Other thing is maybe an open injector? I’d lean more toward the pump itself or your reinstall. Check the part diagram to make sure you got it all back together correctly. That oring at the to of the pump can come flying out of there if the pump is hard to remove.
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After removing and checking behind myself I can confirm install was correct. I replaced the o ring on top of the pump for the sake of being thorough. I won’t say that all injectors are tip top condition but surely they couldn’t leak fast enough to immediately drop from 35 to 0. Has anyone had experience with a pump that runs fine but has bad internal check valve?
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If you want a new pump to try that isn't the $700 OEM I used a Quantum when mine went out earlier this year. Other cheap ones are available on Amazon.
Quantum Fuel Systems | OEM & Performance Fuel System Parts (highflowfuel.com)
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Thank you, I ordered a quantum pump. It’s not likely that I have two bad pumps but it is possible. I’ll update with what I find after new pump.
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Update, installed new fuel pump. System is finally building pressure again. I have not been able to lake test since repair due to personal circumstances but as soon as I am able to confirm the success I will update.
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