Yamah 175 HPDI

Working on a 175 HPDI Yamaha. When I run the diagnostic fuel pressure flashes orange and shows low pressure. Gauge hooked to VST shows 50psi steady at idle and load. Motor does not want to go above 2000 rpms and surges boat will not go on plane but runs great below 2000 rpms like its in slow mode but no alarm sounds. When motor is cold it will sometimes go on plane and pressure will read 4.5 low and around 625 high side. My question is what does the fuel sensor control on this motor? Can it trigger slow mode and what effects does it have on the ECM as far a running goes?

We did take the fuel pressure sensor off in an attempt to clean it and the contacts. Now boat planes all the time but has a miss through all rpms. There appeared to be a green dust substance on the plug contacts. Thinking sensor may be bad, would it cause running problems if it is not working properly?

Also how does the diagnostic program get the low pressure reading as I don't see a low pressure sensor?

Also at idle diagnostic shows NO fuel pressure at idle, it will not show pressure until throttle is applied.

At the H/p pump. Regulator bad (change) Thank's Martin

The low pressure reading you are seeing is the metric conversion of PSI coming out of the HP pump. The is no way to read VST pressure on the computer. It could be as simple as the metal filter that sits on top of the VST needs to be changed or the HP pump is clogged up. I would change that filter first and see what happens, however with just the key on you should see some fuel pressure. If the engine hasnt been run or turned over you will see atleast what the VST is supplying thru the system, once it is running you should see around 700psi at all speeds. You also want to monitor your VST pressure when the engine looses RPMs to make sure the VST is able to keep up with demand. If it cant then there may be an issue in the VST or lack of fuel being delivered to the VST such as lift pumps or possible fuel restriction.

All filters are new including meduim pressure. Pressure never drops at VST steady 50lbs. May check filters at high pressure pump next. Was also told that Yamaha had an issue with a water presure sending unit leaking, causing water to get into harness resulting in corrosion of wires inside the harness. So it may be the harness causing the problem. Also determined that the only two things that will put it in limp mode is loss of oil pressure or an overheat, so that rules out the sensor as it only reads for diagnostics. Also learned that there in to easy way to tap into high pressure side to get a reading.

Sounds like hp pump is clogged,can be rebuilt.The problem with corrision in the harness was due to a bad water pressure sender when you have command link.

Yes, We have command link square plug in back of guage. Going to check filters on HP pump. I there another place that they clog up?

Yes there are about 5 injector size filters in the HP pump,if you have command link with water presure sensor,pull off connecter to sender and inspect,if water got in there it can create some crazy issues.

Where is the water pressure sensor located on the motor? Looks like this one has a tube that feeds water pressure to the gauge.

I know on a 200 hpdi there are 4 screens in the high pressure fuel pump if it is mitssubitshi made, apparently there were different manufacturers of these pumps, the exact same screens that are pressed into the fuel injectors. The "secret filters". They can be easy removed by taking the back plates off of each side of the pump. These pumps generate very high fuel pressures so be careful with all o-rings. The problem is finding a source for the new screens. This week I have been working on this motor and have had the exact same symptoms and this was the problem. The motor you are working on is a 175 but I know the 200 I'm working on is supposed to maintain 900psi +or- 217. I'd be willing to bet this is something check. Again fuel pressures that high are not something to play around with. Only after every filter and screen expecially the high pressure fuel filter has been changed would I attempt this.

Seen a few pics of this being done looks pretty simple. Think we will change them and see what happens since the $1 a piece.

Let me know if this works. Its something that I'm just starting to run into. A lot cheaper than having the pump rebuilt.

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Originally Posted by rickriddle

Where is the water pressure sensor located on the motor? Looks like this one has a tube that feeds water pressure to the gauge.

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If you have a separate water pressure gauge it is not Command Link

Hi.Ditto on the hp pump screens.They are small red screen cone filters.I run a metal screw into the brass end and pry it out with some dykes.Fixed many a sick hpdi this way.

The 2.6 motors make 700 psi,the 3.3 s make a 1000.you are on the right track with the filters,but there are shuttle valves in the pump that need to be cleaned as well to do the job correctly.Pat is correct as usaul about water presure gauge.you may still have command link but someone has rigged it with a mech pressure gauge you should be good.also I don't recommend the removal of filters in the pump without the intention of replacing them.

Replaced the mystery filters and it ran great for 2 days then started acting crazy again. Pulled the injectors and had them cleaned boat ran great again 1st time out. Just have to wait and see if this fixes it. All the little 2 micron filters were trashed up, so hopefully this will take care of it.