High Mid Range Fuel Pressure at the VST Checkpoint on 2003 Z250 HPDI

[Bigtasty]

Last week when I was out one of my HPDI 250s suddenly lost power and dropped from 3800 to 2600 rpm. I've had this happen before so I went right to the Mystery Filters and changed those out. Test run and still only get to 2600 rpm. Diagnostic software shows 6psi on the low pumps and 950-1050psi on the high pressure pump. The number for the high pressure changes quickly between the range. Is that normal? I checked the fuel pressure at the the VST today. It goes to 70 psi for the first five seconds and then drops to 40 with the key on only. Running at idle it shows a constant 62 psi. If I put 15mm of vacuum to the fuel pressure regulator it will drop to 55 psi. I see no change when I pull the vacuum line off the fpr at idle. I've ordered the Mid pressure filter and am waiting for that now. Any other suggestions as to why the electric fuel pump is showing so high?

 

[Bigtasty]

No improvement after changing the Mid filter. Next guess? The screen in the fuel pressure regulator. I wish you didn't have to open it to get out the one screw...

 

[99yam40]

you need to looking at pressures when you problem shows up to see what all falls out of spec

 

[Bigtasty]

No Title

I don't want to take a chance on blowing a powerhead while I know that there is an issue with the mid range fuel pressure running too high. I went after the screen behind the fuel pressure regulator and the regulator itself. Of course, the engineer never had to work on one and put one of the screws behind the mount making it necessary to open the VST. No thanks. A little modification solved that problem.
Pulled the fpr and the screen is clear. Put a little vacuum on the fpr and pressure through it. Only 1mm opens the regulator. No specs on it in the factory manual. Put it back together and now the mid fuel pressure is low at about 30 psi. New fpr ordered, now waiting for UPS...

 

[Bigtasty]

Installed new Fuel Pressure Regulator. Back to 60 PSI coming out of the VST. Took for a test run, no problem. High pressure output remained in the 1020 to 1060 range. Totally perplexed at why the VST output is high...

 

[tommarvin]

Diagnostic software doesn't show you any problems, I've never used it, there's no codes to read,or memory to look back for faults to get you closer to the problem.
Four strokes are so complicated, this mechanic told me he could fix any problem with diagnostic software? Talk is cheap.

 

[Bigtasty]

The software shows that the low pressure and high pressure pumps are in and stay in the proper range at all speeds. The electric pump in the VST of one motor is 15 psi higher than the other motor which is within specs. These are Z250 two strokes also...

 

[Bigtasty]

Where is Rodbolt when you need him???

 

[99yam40]

Rod if not here anymore.
Do a web search for Rodbolt17

 

[tommarvin]

If the software says everything is within specs, are there any problems with both of your two stroke motors?
My crabbing bud has a 90 hp with fuel injectors if your wondering what's going on here.
I thought you had to have fuel injectors for diagnostic software? what software are you looking at?.

 

[Bigtasty]

One motor runs perfectly. The other will run up fine and then drop back to 2600 rpm after a few minutes regardless of throttle position. I have the Yamaha Diagnostic Software. These are HPDI 250 two strokes. The only problem I can find is that the fuel pressure coming out of the VST is about 15 psi higher than the specs call for...