Engine Trouble

[mason101]

Alright, I've got a '02 Yamaha 150 2 stroke HPDI, and I'm having problems at high RPM's. Everytime I try put her WOT she starts to drop down between 2k and 3k, but will jump around violently. I've read other forums and they have talked about the O2 sensor, but I've also heard that the O2 sensor doesn't affect HPDI models at high rpm's. It could be a fuel pump problem, but I'm not sure how to check pressure at that rpm range without a load on the engine. Don't want to mess her up anymore than she already is. If anyone has any ideas or has dealt with similar problems and can give some advice I would greatly appreciate it.

[Putershark]

If not careful, you could wind up spending a lot more time and effort replacing parts then just taking it to the dealer and pay 1 hour of labor to the have a ECU data dump and code check done...

But in the mean time, one could check some of the more simpler things such as,

1. Battery condition (including water level) to make sure the ECU has enough voltage to operate the engine management system correctly (one of the most simple and forgotten items to inspect) for once voltage drops below 11 to 10.5 volts they get "confused" for a better lack of terms, and cannot make adjustments fast enough to the air / fuel mixture.
2. Check the engine grounds to make sure they are clean and tight (has the same effect as #1) Also check the connections at the Alternator.
3. Pull the plug wires one at at time and with a meter, make sure that any one does not have a lot more resistance than all the others (aboce 10 ohms) thus, breaking down under load. Also look closely at the plug wire boots to make sure your are not grounding out one cylinder to the block as the engine and voltage spins up.
4. Pull the spark plugs and make sure they are not all gummed up with deposits and even not, that does not mean one is not breaking down under load. Pending the number of hours on the engine, it may be wise to just go ahead and install a fresh set of firing pins
5. Check for clean wiring connections to the fuel injectors (pending type of course)
6. Make sure that the engine oil tank is full and the ECU is not shutting down the engine to a limp home mode thinking it is running low on oil
7. Check the fuel lines and filters for blockage or the bulb or fuel line that is cracked and sucking in air.

That is about all I can think of for now, the rest really needs a computer hooked up and talking to the engine ECU to see what is happening in real time.

Let us know how you make out

[mason101]

Thank you for your reply.
I've got a "Winky Blinky" that tells me that everything is running as advertised. I've just replaced the spark plugs, and performed a spark gap test. Which was good. I just replaced the batteries 6 months ago. When it starts to give me problems I can turn the batteries off for a few seconds, and it will go away. I'm not sure if it's advised to keep the "Winky Blinky" hooked up during normal operation, but I think that may be my next step to see if I can get an abnormal ECU code when she starts acting up again.

[Putershark]

Your most welcome,

Just don't make the mistake like I have in the past thinking that something new is good. There is a huge difference between "new" and "known good" when dealing with wear items such as Batteries, Plugs, and Plug wires so double check them again just to make sure

There is also a difference between checking for a code and a laptop hooked up where you can pull a data dump while watching the total engine sensor operation in real time. Things like a plugged fuel injector or intake leak, can crate a false O2 sensor reading since the engine is running so far out of spec, the O2 sensor throws a code since it cannot make an adjustment due to the engine running so rich or lean (whichever the case). So I take any one code reading with a grain of salt and have been burned more than once because of a loose ground or leaking vacuum line

This also reminds me to also check any vacuum lines and loose AFM (Air Flow Sensor) that may develop a gap (leak) past the AFM as the engine warms up can cause a lean out condition. This and any bolts on the intake manifold that may have backed off some...

Very careful use of some Throttle Body cleaner quickly shot around lines and fittings while the engine is running at idle, this to see if it "sniffs" the cleaner and the engine either speeds up or stumbles can help one find such vacuum leaks. Just be careful doing such and only use tiny little blasts of cleaner (will not take much) so you do not start a external fire

[mason101]

I'm going to check all the grounds and nuts and bolts. If I can't figure it out soon, I'm going to take it in. There's ony one authorized Yamaha dealer around here and I haven't been to impressed with them in the past.
Thanks for you help, and hopefully there's just a loose ground.

[Mud Runner]

The first question I would pose is, When was the last time the VST (Vapor Separation Tank) filter was cleaned or changed. The high pressure pump is in the VST tank. At the base of the pump is a screen the size of your pinky nail. If it gets garbage on it, it can give you those symptoms. What you are describing is typical surging attributed to the clogged screen. If you look at Yamaha's website for parts for your motor, you'll see the fuel pump in the drawing for the injector pump. The screen is part # 23 in the drawing below. The Yamaha part # is 66K-13915-00-00. When you service is you must change the O-ring gasket. There a schrader fitting on the fuel rail where you can attach a fuel pressure gauge while you're running to observe the pressure.

[mason101]

I haven't opened the VST up to check the filter, but I did trim the engine and drain fuel to see if there was a lot of junk and sediment in there. It looked good in a mason jar.

[Mud Runner]

The maintenance schedule for all HPDI engines recommends the VST filter be inspected and cleaned every year or 200 hours.

[mason101]

Actually I just ordered the VST gasket, and I intend on inspecting and cleaning the filter as soon as I receive it. Keeping my fingers crossed, and hoping that I can get it fixed. Thanks for all the input.

[Mud Runner]

Good luck. My engines were running perfectly but when I opened the tank, I found the screens were dirty and there were a few droplets of water in the tank. I also run 10 micron Racor filters.