2001 OX66 250 EFI Cold Start

[yamahaOX66]

My motor has been flawless until now. When I go to start the engine cold it will crank over and start at 750 rpm's but quickly stall on low rpms(2-3 seconds). It doesn't seem to want to go into the high speed idle warm cycle. So in order to start it I have to manually put in high neutral using the throttle until it warms up for a couple of minutes. Then the engine runs fine without stalling at idle.
All normal maintenance for the engine has been performed. i.e clean vst, clean 02 sensor, replace fuel pumps, t-stats, etc.

I'm leaning towards a bad sensor - sw, air, etc, but was wondering if the hp fuel pump or resistor may have something to do with the engine not going into a high idle warmup.

Any suggestions would be greatly appreciated.

[jb123]

what happens to the rail pressure when it falters?

[rodbolt17]

could also be lift pump failure.
trust me its not a sensor,quit hunting that rabbit.

[yamahaOX66]

Thanks Gents,

JB, Haven't measured fuel rail pressure but will. This just started to occur so I haven't done much trouble shooting.

Rodbolt, Could be a lp pump, three new ones were put in this year. Doesn't mean they are good though. I'll check them also.

I haven't had a chance to troubleshoot. When I do I'll report back. Guess I was just hoping someone had a similar issue to point me in a direction.

Thanks.

[rodbolt17]

if a sensor fails it locks base timing at 7*BTDC, normal idle timing is about 7*ATDC.
means if a sensor fails it will idle about 1100 RPM.

however excessive rail pressure or a blown lift pump will cause your symptoms.

[yamahaOX66]

update

ok, measured rail fuel pressure, 45psi!. Cleaned out the regulator screen and pressure dropped back down to steady 36 psi. 2 out of 3 of my (new this year) LP fuel pumps were leaking. They weren't leaking at the crankcase hole but on the side of the pumps. 3 new ones on order plus a new check valve just after the engine fuel filter.

Decided to try and do a throttle plate sync while waiting for the parts. Messed up the throttle sync by mistakenly opening no.4 plate screw (where the idle screw is). Question is starting from scratch, to close all throttle plates (including No. 4). Then adjust the idle screw so the plates are just open and then do the idle rpm procedure to dial it in.

Instead of removing the throttle lever rod, can't you just disconnect the throttle cable link joint. Don't they accomplish the same thing.

I'm having fun troubleshooting, wish I had more time to do it. Really appreciate the help thus far. Once I get the sync back, the throttle position sensor adjustment would be next.

[rodbolt17]

whooooaaaaaaaaaaa
hold on turbo.
slow down.
loosen loosen all 6 shutter screws, back off the shutter stop screw,also mistakenly called an idle screw.
REMEMBER there is NO idle adjustment on EFI.
make sure all 6 shutters are fully closed and the oil pump arm to stopper clearance is .005 to .020".
now tighten 5 of the shutter screws,not the one with the stopper.
now CHECK the TPS voltage.
should be about .5V.
adjust the stopper screw until TPS is about .62V.
start the engine and allow it to warm up.
adjust the stopper until RPM is correct.
tighten the last shutter screw.
have a cool refreshing beverage.

[yamahaOX66]

Thanks,
I'll give an update when I get back on the boat this weekend. I assume I'll still need to pop off the throttle link rod or remove the throttle cable joint.

[yamahaOX66]

Update, It Works

Had to work last weekend but got to work on the boat yesterday. JB123 and Rodbolt17, can't thank you enough as your replies to this thread led me in the correct direction. Thank You

Update,

Replaced blown lift pumps, HP fuel pump high pressure reduced after cleaning pressure regulator screen. Sync the throttle plates, couldn't set idle speed because I Still had a Stall. Replaced fuel check valve past engine filter and cleaned out the check valve on the tank and replaced fuel primer bulb. Still stalled.

Ok, Not sure why I pull the injectors out but I did. I cleaned the screens (strainers) but also found the injector on the bottom to be rusty on the outside body. The inside or past the grommet was clean so it looked like it was just sitting in some water when the engine was tilted up. I pulled the spring clip and looked at the electrical connection and looked ok and it was puckered up with dielectric grease and looked good. Put the injectors back together. After the engine Started right up and I was able to set idle speed. Runs like a champ.

What fixed this? Yes, 2 low pressure fuel pumps were bad. Screen at the fuel pressure regulator was clogged. Both of the issues needed to be and were fixed. But what was the final fix (or error). Was it cleaning the injector strainers or disconnecting the bottom injector and reconnecting it ?. The injector strainers did not look terribly clogged and wouldn't you still see a high fuel rail pressure if they were clogged?

[rodbolt17]

nope, rail pressure is con*****ed by the regulator.
why they put a filter downstream of the regulator? beats me.
sounds like you had multiple issues.