2003 Yamaha Vmax 150 HPDI bogging down

[Raymond S.]

Hi. I know this is something discussed all over the internet, but I can not find a good answer.

When the problem started, it was running fine on idle, but died almost right away when I pushed the throttle. I could not get on plane.

I connected Yamaha diagnostic YDS system, and got one code: Error 26 injector.

This is when the fun starts: After googling a lot I was thinking let me fix this, and let med do some preventive work to.

So I have now replaced:
- New Hose from tank to engine incl. new bulb.
- New Filter in water separator
- New Low pressure pumps
- New VST pump incl. Filter
- New canister medium pressure filter
- New mystery filters in HP pump
- New Injectors incl. mystery filters
- New Spark Plugs
- New HPDI high pressure sensor
- New realy for injectors
- Cleaned O2 sensor

The result: Bogging down on idle, and Bogging down when throttled 
I can also say I have tried to run it from external tank.

On the diagnostic tool i now have no codes. All normal.
But if I run the engine live on diagnostic, I can see the fuel pressure get red and drop for a second everytime it is bogging. VST pressure 49,8 drops to maybe 20, and at the same time the High pressure 712 drops to around 450. But it get back up and then it runs fine 10-15 seconds before it drops again. And sometimes it stop.

I had multimeter connected to the VST pump, and it get power all the time when running (14V) First 12,8V for about 5 sec.with just ignition on.(You can hear the pump) and then 0V until the engine start. Then it shows 14V. when running.

Latest news is that it now is hard to start also.

Can it be electrical problem??
ECU?

Someone who has some great tips here???

[jdupree]

Have you ever replaced the HP pump?  You did note a drop in fuel pressure.  When my HP pump went out on my OX 66 it gave some of the same symptoms and then quit all together.  If injectors are good as well as the VST tank being clean, I would zero in on the high pressure pump.

[Raymond S.]

I have been thinking of the highpressure pump also, but the VST pressure drop at the same time.

[jdupree]

If I am correct, the HP pump keeps the VST full.  If you are having a drop in pressure that would make sense. 

I went with an aftermarket HP pump on my OX66 and it did just fine.  I would bet that the HP pump is on it's way out.

[Raymond S.]

Hmm.. The two low pressure pumps fill up the VST with about 7 psi, and The VST pump inside the tank push it with about 50 psi to the High pressure pump, and the high pressure pump about 700 psi to the injectors.

Why should the VST drop if the highpressure pump is bad? I dont know. maybe I am wrong her.

[jdupree]

I think you are correct.  Sorry, I haven't had my OX66 for several years now so going off memory.  So you are saying your problem is from the VST tank to the injectors?

[wingtime]

I'm not that familiar with the Yammie HPDI. It sounds like you have a high pressure fuel problem. Could be a pump or a regulator on the HP side.

Does the diagnostics software have the ability to do drop tests while the motor is running? If so just for grins I would do a drop test for each injector and ignition.

[jdupree]

Make sure your LP pumps are OEM.  I am sure that you know how to test them:  unbolt from the motor, pump the bulb while your hand is behind them.  If you feel gas they are bad.  If they are good, I would still concentrate on your HP pump.

BTW, does your VMAX have a 02 sensor like the OX66?

[Raymond S.]

Replaced the High Pressure pum as well this weekend, and now the enging works fine again.  Hopefully it will work for a while, since I have replaced all filters,  all pumps and all injectors.

[wingtime]

Good news.  I suspected something in the high pressure circuit.

I looked at an Etec last year that the high pressure pump wasn't even working and the darn thing still ran!  It had a crazy amount of low RPM hours on it too from being a former marine patrol boat motor.  The owner trying to sell it couldn't figure out why it was overheating while under way.