HPDI 175hp Help Please

[Punch953]

OK, you guys have helped me before with my HPDI so please don't fail me now. My buddy's boat-which is also my tuna boat- all of a sudden developed a problem. The boat is powered by twin 175 HPDI's. The boat ran fine, then the next morning things went downhill with the starboard engine. It started out bogging and rapidly degenerated to barely running. YDIS says engine is fine but the idle is terrible and it stalls if you try to open the throttle. If it doesn't stall it just makes a bellowing noise but doesn't go anywhere. Ran it off a seperate tank, changed the vst filter and the one after it. The vst was spotless. Changed the filter on the engine and the o-ring, changed the low pressure pumps and changed the secret filters on the high pressure pump. New plugs, 4 new injectors and the same thing. started swapping parts from the good engine. Changed the injector drivers, the cpu, coils, plugs with no change. Removed every ground and cleaned and re-installed. I rested my arm on the TPS and the engine started running differently. I adjusted the TPS as per the service bulletin and while I was at it adjusted the throttle butterflys. None of them were sticking. If I adjust the TPS by ear I can get the engine to run. Not perfect but it will make almost 5k rpm's. If you move the TPS a thousandth of an inch in either direction the engine will not run. Swapped the TPS and the o2 sensor from the good engine and it is still the same. I need some help here!

[99yam40]

have you compared all of the readings on the YDIS readouts for sensors including the rail pressure, manifold pressure, and TPS to see what is different?

[Agboater93]

I'm having a similar issue. Seems like it's stuck in limp mode. When I remove the cap off the large oil resivoir in the bilge I don't not get an alarm. Is it possible that the sending unit on the tank is bad and putting it in limp mode without the alarm. 2000 ox66 250 saltwater series

[Punch953]

have you compared all of the readings on the YDIS readouts for sensors including the rail pressure, manifold pressure, and TPS to see what is different?

Yes sir, The only thing that was out of spec was the VST pressure-too high. I replaced the screen on the VST pressure regulator and it dropped from 90psi to 55. All components measure in range. To boot I even replaced every piece short of the block itself with the pieces from the port motor and no bueno. Same thing. The motor isn't making horsepower like it did. As I said there is only one exact position on the TPS that the motor will function at all. The port motor is not anywhere near as critical. I lost 200 rpm on the starboard motor and the floscan shows my fuel burn is up 2-3gph on that engine. Also the two throttle handles are not in sync anymore with the starboard engine needing more throttle to maintain the same rpm as the port. As I stated before the TPS sensor is so sensitive that just loosening the adjustment screws will stall the engine as will the slightest adjustment.

[Punch953]

I'm having a similar issue. Seems like it's stuck in limp mode. When I remove the cap off the large oil resivoir in the bilge I don't not get an alarm. Is it possible that the sending unit on the tank is bad and putting it in limp mode without the alarm. 2000 ox66 250 saltwater series

No sir, the tank senders are good. Not a limp home situation which we have had before in the past so I know what it looks like.

[99yam40]

how about the rail pressure on both motors, YDIS should have reading on that.
I had no idea the software gave a VST pressure, or did you measure that with a gauge

how about key on manifold pressure, not started, just key on.
should show atmospheric pressure and agree with weather station close to you.

[Punch953]

The rail pressure is the same on both engines-around 900 psi. The Yamaha software will turn on the VST for you and I also checked it with a pressure gauge and it is correct. The atmospheric pressure transducer I swapped from the other engine and no change. I think the key is the hypersensitivity of the TPS but I don't know the cause.

[99yam40]

The rail pressure is the same on both engines-around 900 psi. The Yamaha software will turn on the VST for you and I also checked it with a pressure gauge and it is correct. The atmospheric pressure transducer I swapped from the other engine and no change. I think the key is the hypersensitivity of the TPS but I don't know the cause.

so apparently you have not checked what the manifold reading is when just turning on the key

[Punch953]

No but I will. Do you have a hunch?

[Punch953]

I used a borescope and I do know that there is enough pressure to fire the injectors if that is a help?

[99yam40]

maybe wiring connection is my only thought.
just trying to find something out of wack

[Punch953]

I don't know. I went through every inch of the wiring. I'm really at a loss. I googled the symptoms and other people seem to have had the same issue but not one resolution!

[99yam40]

if the ECU thinks the motor is at a different altitude it will change the fuel to air ratio

[Punch953]

I swapped ecu's and the pressure sensors. Same thing. I'm lost

[99yam40]

if there is something keeping the ECU from getting the proper info it will be a problem.
I have had enough, I am gone
good luck