Fuel line problem

[Gill7858]

Ok so VST is clean. They even placed a new VST tank on there And it still surges. Ohm'ed all 6 caps and they all read good. Fuel pressure gauge read normal. Bypassed fuel check valve and still surging. They disconnected a yellow wire from the computer and surging stopped. Anyone know what that means?? Rodbolt?

[bajakeith]

surging

OK,,does it surge at all speeds ??? if your tech (& I use the word loosely) has checked the ignition,,,compresion, it can be anything from a bad fuel pressure reg to a bad injector....start motor and raise idle to 1100 and with you hand block off each intake bore to isolate,, if its one cylinder...and also the chamber and pintle for the OX senser can plug and OX senser is very easy to test....need more info on what your motor is doing ??? that motor has like 8/9 little screen filters in the fuel system..and if they replaced the VST tank..I would look somewhere else to get your boat fixed....

[Gill7858]

Took it and dropped it off at the Yamaha dealer. I'm sure ill get the money shaft but at least ill finally know what's wrong. I'll let you guys know.

[Gill7858]

Wtf?

Ok so I took the boat to a Yamaha master mechanic and here what they did:

Check fuel pressure - good
Checked knock sensor - good
Checked o2 sensor - good
Checked fuel pumps (mechanical and electrical) - good
Checked VST - good
Reset TPS - good
Hooked up test lamp - no errors - good
Ohm all spark caps - good

So basically THEY HAVE NO IDEA WHAT'S WEONG WITH IT!!!!!!

mechanic wants me to give him till tomorrow cause he wants to check the exhaust plates. He says they go bad and may cause the engine to choke.

RODBOLT, any suggestions????

Frustration doesn't even begin to describe.

[haines1550]

was there a solution

Did you find the problem.

[Captain Steve]

Ok my mechanic just pulled my VST and the electrical pump filter was clogged. So that's taken care of. He's still diagnosing it because when throttling up it surges from 1700 rpms to 2300 rpms, up and down. Any ideas rodbolt? Btw thanks for the input.

So did cleaning the screen/filter on the back of the VST tank fix your problems? I am having the same problem on a 150 OX 66.

[rodbolt17]

don't thread hop.
a Yamaha is not all yamaha's.
the ox66 2.6L motors did NOT use CCS.
the sx250 DID use CCS.
the VX motors in 3.1L did NOT use CCS.

CCS between cranking and about 600 RPM sparks all 6 cyl.
between about 600 and 800 it drops a cyl.
between about 800-1800 it drops 2 cylinders.

some CCS motors simply wont run correctly between 1700-2300 RPM, it keeps dropping and relighting cylinders.

when you unplug that yellow wire it places the ECU into bypass mode and most all inputs are fixed to a default.
any sensor,other than O2, that gets disconnected the motors locks base timing at 7*BTDC and idle speed is increased to about 1100 RPM.
depending on the sensor ign timing may or may not advance and top speed may or may not be reached.
all sensors can be tested with a digital multimeter.
what your looking for is any (in range) failures.
some years back the owner of another place I used to work at called me about a spark problem on #5, they had trouble shot it for 3 days.
that's when I told him it was supposed to not spark number 5 between about 800-about 1800. .