2001 150 Yamaha HPDI, engine surging

[rbgbrig]

My 2001 150 HPDI Yamaha model Z150TXRZ, starts and idles OK, when I bring it up to around 2000 it starts surging violently as if running out of fuel. Here's what I have done so far. I have checked the VST tank and electric motor, all spotless, I put a Gauge on the test port and it shows a constant 50 psi at all times. I removed the filter/strainer between the VST and the mech pump and installed a short piece of clear plastic to observe if any air is flowing. It shows only solid fuel at all times. Using the Yam diag SW, it shows fuel pressure of 750 psi and 5 MPa (I don't know what the MPa is?) when running OK. As it starts breaking up the fuel pressure drops to about 13 psi and the other drops to 1 MPa. Am I facing replacement of the dreaded $1000 mech pump. Is there any thing else I should check. Some mention the 2 vacuum pumps, so I hooked the fuel line directly to a vacuum gauge and it shows about 7 psi of vacuum, which I think should eliminate any diaphram leaks.

[rockangler]

Sounds exactly like the problem I just had fixed except mine waited till you hit 3600 rpm. The same every time. Ran like a top other wise. It turned out to be the fuel pump. The mechanics couldn't figure it out so they called in a yamaha rep and he found the problem. They all said they never say one act like that. They where sure it was electrical as it did it at the exact same rpm every time.The tech said it was because I didn't pump my bulb before I started the engine and the pump had a short period of running dry. Take off your fuel filter, (the expensive one) and look on the inside. On mine you could see the brass color where the gears where slowly shaving away. Good luck, I hope this helps.

[rbgbrig]

Hi thanks
Which pump,the electric one in the vapor tank? or the belt driven mechanical pump. Also which filter, they are all expensive. I have one in the clear plastic side mounted filter between the 2 low pressure pumps and the vapor tank, then one in the vapor tank on the bottom of the electric pump and finally the one between the medium (50 psi) pressure electric pump and the belt griven HP (750 psi) mechanical pump.