'03 OX66 250 acceleration issue possible fuel problem

[Fanboatman]

Model number is VX250TLRB. I'll start from the beginning so this may take a bit. I originally posted here a few months ago about it bogging on holeshot. Some suggested lp pumps so I replaced them. Problem slowed but did not go away. Another suggested the exhaust manifold may be broken. I checked and it was, so I replaced it with a hydrotec performance tuner. Problem is still there. I have also replaced ALL filters and screens, all lp pumps, and plugs. I sent the injectors off and had them cleaned, tested, and calibrated. I have checked all plug wires, caps, and coils. So last Sunday I was cruising alone and up came a noise that sounded like the starter was hung in the flywheel but it was coming from the bottom of the powerhead. Turns out the crankshaft balancer completely shelled out, so I had it replaced along with the oil seal while they were there. I was hoping that was throwing everything out of wack but no luck. I had told my shop about the issue and I guess they had some extra time today and another tech stopped by. They showed him and he said he had one do that years ago and had a Yamaha tech come look at it and even he could never find true out exactly what was causing it. But he knew how to make it run better, just not cure the issue. So he takes a pair of pliers and pinches the return line from the fuel rail to the vst and that fixes it. They even did it while it was bogging and it instantly cured the issue. They had a fuel pressure gauge hooked up and said pressure was in spec and never dropped or went above. The other tech said he put a orifice in the other motors return line and never had the problem again, but it did use more fuel and oil after that. I want to fix it right. Does anyone know exactly what is wrong? They think either the fuel pressure regulator or the cdi. I'm leaning toward pressure regulator as I don't think it's a injector control issue but I may be wrong. Heck it could be as simple as a check valve. I'm just lost and confused at this point and just want to get it fixed.

[99yam40]

has any of them ran the boat on the water with the lap top hooked up to see if high pressure was changing?

I believe that if the pressure regulator is bad the pressure will not stay were it should.

If check valve leaks by the VST may run low on fuel and pressure will drop from that .

[Fanboatman]

This is a OX66 so it has no way to hook up a laptop. They did not run it on the water but they did run it in their test tank which is large enough to back the boat in on the trailer and that is how they recreated the issue.

[99yam40]

sorry thought it was a VZ for some reason.
but if pinching the return line helps then there is a problem that needs to be fixed.
Rodbolt or Boscoe should be along soon

[rodbolt17]

by pinching off the return line they are spiking rail pressure.
for the same injector on time they are forcing it rich.
either the injectors are clogged or the rail pressure is low at the failure rpm and load.

[Fanboatman]

Injectors were sent off, cleaned and calibrated and problem did not change at all. Rpms are around 1500. It just bogs intermittently when I hit the throttle to get on plane. Doesn't do it all the time, but probably 75% of the time it does and hasn't gotten any worse in 6 months I've had it. What would be the cause of the lack of fuel rail pressure at that low of rpm if the pressure reading at the Schroeder valve was still in the upper 30's?

[Tucker]

You checked HP pump pressure right? That is, before the guy pinched off the return line? Don't see that mentioned anywhere. If the guy is getting 35-38 PSI after pinching off the return line, then it must be low to begin with.

[rodbolt17]

step back
pat your head and scratch your tush a moment and think.

how does this EFI work?

how does air get in to accelerate?
how does the ECU add fuel for this extra air?

the air is con*****ed by the position of the six air shutters.
the ECU based on TPS voltage adds fuel.

if the TPS voltage rapidly climbs(you jammed the throttle) the ECU reacts by not only sychoneous injection but it also does a group injection.
if rail pressure is already low it will dump when the group injection is done and the motor goes whuuuuuu.
so you can monitor TPS voltage when racking the throttle and monitor rail pressure.
both MUST be done at the failure RPM and load.

I would use an analog meter on the TPS.

if all passed then I would look at the pulser coil ground.

[Tucker]

I think what this is saying is to check/adjust TPS. A critical item that is well outlined in the FSM, not the Clymer knock-offs. And, you need the DVA adapter for a multimeter. Even with that it's still a PIA. In a test barrel that voltage is jumping all over the place and with an old shaky hand holding a phillips on a old shaky 2-stoke, it becomes frustrating. Any tips to make this chore a little easier? By analog meter do you mean something like an old Amprobe with a dial, not digital?

step back
pat your head and scratch your tush a moment and think.

how does this EFI work?

how does air get in to accelerate?
how does the ECU add fuel for this extra air?

the air is con*****ed by the position of the six air shutters.
the ECU based on TPS voltage adds fuel.

if the TPS voltage rapidly climbs(you jammed the throttle) the ECU reacts by not only sychoneous injection but it also does a group injection.
if rail pressure is already low it will dump when the group injection is done and the motor goes whuuuuuu.
so you can monitor TPS voltage when racking the throttle and monitor rail pressure.
both MUST be done at the failure RPM and load.

I would use an analog meter on the TPS.

if all passed then I would look at the pulser coil ground.

[Fanboatman]

I had a full sync and link done which included adjusting the tps. I bought a fuel pressure gauge set but could not find an analog meter. I will try to find one I can borrow and test it as you said. Also, I have a Yamaha manual for this motor not a clymer or knock off. I'm not sure if I will get to test it tomorrow due to bad weather coming. As soon as I find an analog meter and get decent weather again I will test and report back.

[Tucker]

I hope you're not experiencing what I went through. In my area the Yam techs are not trained on these OX66's. Maybe you got lucky and got an old guy (doesn't sound like it), but the young techs don't seem to get the fuel injection system on 2-cycle big blocks. I've had bad experiences with certified Yam techs in my area. I've had to learn on my own. Please keep us posted with developments. Need the Yam test harness to check TPS setting.

[Fanboatman]

Ok, so I made it to the ramp this evening and checked the fuel pressure myself. I left the boat on the trailer and disconnected the throttle cable at the motor(has a hotfoot) so I could work the throttle for the testing. It has 35-36 psi (gauge was jumping slightly) at idle and when you give it throttle. With it in gear the rpms went to 1800 at full throttle. So after checking it multiple times to make sure it was staying the same, I opened it up to full throttle and pinched the return line going from the rail to the vst. When I did this the pressure dropped to 34 psi and the motor would rev up to 2k rpm. I have yet to check all the vaccum lines and check valves, but I wanted to report this so y'all would know the pressures. I couldn't find an analog meter so I am ordering one and the harness for the tps. By the way I had my gauge hooked to the Schroeder valve on top of the vst, if I need the hook it up somewhere else let me know.

[Tucker]

Pressure looks good. You are confident your fuel is good? Maybe a stretch, but have you or the techs run off remote tank to rule out some things.
Cheez, she's been into quite a bit. Had to spit her to replace the crankshaft balancer and had to pull the power head to install the exhaust tuner. (I've never heard of one going bad on a 2-stroke) I wonder if someone screwed something up in reassembly. Bitchin' boat, hope we get you running right soon!

[Fanboatman]

Yes, I have been into it a bit. The factory exhaust tuner/ manifold had some of the end broken off apparently due to the small water ports in the plate under the powerhead being clogged. Got that fixed with a hydrotec tuner. Ran it about 7 hours then the balancer came apart so I fixed that and replaced the oil seal while I was there. It has not been run off of a separate tank, but I bought this boat last September and have run somewhere near 300 gal of gas thru it. That sounds like a lot, but with 2- 28 gal tanks I have filled them up from almost empty about 5-6 times. And I have also gotten fuel from a few different stations, tried different additives, and even ran 89 and 91 octane once each with no change. I called a Yamaha master tech at a dealer in Houston today and he says he is pretty sure it is the fuel pressure regulator that is letting too much fuel go by and not creating the back pressure it needs. I am going to test it with my hand held vaccum pump this weekend and also check all the vaccum lines.

[rodbolt17]

you have been hoodwinked.
bamboozled.
like I said YOU CANNOT test at the dock on the trailer.
ALL tests MUST be done at the failure RPM and load.
at rapid acceleration several things are happening.
1st is the TPS voltage changed rapidly.
this causes the ECU to go to both a synchroneous injection with a group or batch injection.
it also dumps intake vacuum witch causes the regulator to close slightly spiking the rail pressure by about 5 PSI.
now we just spiked rail pressure,increased injector ON time AND we fire the injectors 1,2,3,4,5,6 AND 1-6 for each revolution.
if rail pressure is not there it goes WHUUUUUU.
all that regulator does is maintains a steady rail pressure when the injectors fire.
it is not a magical mystical device.

a loose or faulty knock sensor will mess with you as well.