Strange problem with Ox66

[SBSYNCRO]

s250txrx (1999 250 ox66)

Just finished a complete 100 HR service. Also replaces binnacle and cables due to sticking. T-stats and poppet replaced. Lp fuel pumps, vst filter, on board filter, and remote filter all changed about 20 hours ago.

Finally got my hands on the official test harnesses and winky blinky, so as part of the final run-through after the service, I ran around with the winky from cold to hot, idle to WOT, then checked O2 & TPS when engine was warm.

Before/during tests Boat runs well, idle to WOT, and fuel burn rate and performance seem like what I'm used to. 36 mph at 5700 and I get the winky telling me the rev limiter is kicking in (ok, under-propped, I guess?)

Results of tests:

Idle speed seemed determined to stay at 500 or 600 when hot, but not lumpy or rough.

O2 was on the low end of in spec, and climbed slowly (very slowly) while running up the revs, but never got close to upper spec. Check

TPS was perfect (0.5 iirc) but wait... Manual says disconnect throttle. So I do and it now reads something like 0.41. I dial it up to .50 and then fiddle with idle screw. Still can't get idle above 600. I call it good and go home.

Next day I take the boat out and when it hits like 3200 rpm, it bogs badly and simply won't go any faster regardless of throttle position. Below 3200 it seems to run normally.

Aaargh!

Ok, obviously has to do with my TPS adjustment.

What did I do wrong? What am I missing? I'm tempted to just dial the TPS back until it runs correctly, but I'm puzzled by the inability to set the idle up to 700...

Any suggestions?

[rodbolt17]

cause your scatter blasting.
TPS sets at .47V with the throttle shutters completly closed.
means the shutter adjustment screw is not touching the throttle body and all 6 shutters are COMPLEATLY closed.
final setting once the synch and link is done you will see about .6V.
your O2 sensor is failing or dirty.
what is fuel rail pressure AT the problem RPM and load?
what code did the light flash?
there is NO code for the rev limiter.

[SBSYNCRO]

cause your scatter blasting.
TPS sets at .47V with the throttle shutters completly closed.
means the shutter adjustment screw is not touching the throttle body and all 6 shutters are COMPLEATLY closed.
final setting once the synch and link is done you will see about .6V.
your O2 sensor is failing or dirty.
what is fuel rail pressure AT the problem RPM and load?
what code did the light flash?
there is NO code for the rev limiter.

Thanks for chiming in. I honestly thought we were being fairly methodical by following the service manual, but for many of us, this motor seems like it gets demons that are damned hard to exorcise.

Does "synch & link" refer to synchronizing the throttles?

The O2 sensor is showing the correct voltage according to the service manual ("in spec"). But is on the low end of the spec. Is this what makes you say it's failing? (declarative answers like yours are great because of your knowledge, but more helpful if accompanied by some explanation). :-)

I have not checked fuel pressure as I wasn't previously having any problems that I thought were fuel related (engine seemed to be running great after replacing all the lift pumps and servicing the filters and vst). I don't have a fuel pressure tester and my mechanic is out of town for a couple of weeks. (will a "generic" fuel pressure tester work, or does it need to be something special?)

[SBSYNCRO]

what code did the light flash?
there is NO code for the rev limiter.

41. "over revolution control". (I assumed it was a rev limiter as it was kicking in right at 5700 and staying there. )

[rodbolt17]

the O2 sensor voltage should scale between about .3 to about .6V and do it fairly rapidly and constantly at low speeds.
codes 33, and 35-41 are micro processing codes.
where are you getting the code information?
TPS is adjusted to .51V with the shutters closed,then open the shutters about 2.5 turns once the shutter screw contacts the shutter. then adjust the idle from there.
once set the TPA or idle should not have to be touched again until compont replacement is nessasary.

[SBSYNCRO]

Any chance I can just pay you for a telephone consultation?

[SBSYNCRO]

Note, prior to the current problems, the motor was running well and made many trips to our local islands without incidents. On our last trip out there, the throttle cable bound up so badly that we could not make way. I replaced the cables and binnacle (along with changing the LU oil, spark plugs, replacing the t-stats, poppet valve, and replacing (not rebuilding) the entire water pump assembly) and took it for a sea trial. It exhibited bizarre behavior which I finally tracked down to 4 of the throttle plates being disconnected from the throttle linkage. (I must have knocked them loose while I was working on it, or something like that..?). After finding that and resolving it, we ran the boat around with the winky blinky and it gave normal signals. It flashed 33 for about a minute, then flashed one. Then while testing things at WOT it flashed 41 ("Overrevolution Control (during ignition cutoff operation)"). The boat had no problem running through the RPM range and seem to be doing well, if perhaps a bit "lumpy" at lower RPMs.

The mechanic and I then brought her back to the slip and tried to get the idle fixed (he is not an OX66 expert, but a knowledgeable and well-trained marine mechanic). Screwing down the idle screw didn't do anything, so we checked the TPS and it was around 0.4. We set it to the spec in the manual (.50) with the throttle disconnected. (I know realize that this was not the right thing to do).

We then checked the O2 sensor and found it to be in spec with the key on, and so we fired up the engine and watched the number climb VERY slowly. It did not run up and down as some people describe the normal operation being, but according to the manual it was "in spec". (I now know why we got that reading - see below...)

I went back to the boat this morning planning to use the advice here to sync the throttles, double-check the TPS and visually inspect the O2 sensor as follows:

1. Performed "sync & link" (manual refers to as "synchronizing the throttle valves section 3-5)

2. Attempted to adjust idle. Could not get up past 500 rpm using the idle screw.

3. Checked TPS by disconnecting the throttle link and testing across the orange and pink wires. It was slightly off, so I set it to .62 based on another post by you Rodbolt. Then checked across the orange and red wires and it was 5.01 at both idle and WOT. I heard the sensor energize several times while I moved the throttle at the helm. So far so good.

4. RPM was still 500

5. Pulled the Oxygen sensor and found the dip tube completely blocked with carbon. Cleaned it out with a small drill bit and scraped about 1/8" thick layer of carbon from the inside of the housing. I used "Deep Creep" as a cleaning agent and thoroughly cleaned the housing, removing all the carbon deposits by carefully chiseling it with a small tool and a flashlight. I used a paper towel soaked in Deep Creep to wipe off the Oxygen sensor (it did not seem to have lot of crud on it).

I reassembled everything with new gaskets, fired it up, and after a brief run to about 1300 rpm, it settled at 1100 and then when it warmed it came down to 800. I backed out the idle screw until it was 700/750, then adjusted the TPS to 0.62, fired it back up and it idled at 700/750. "Perfect!" I thought.

I then revved the engine up to 1500 (in neutral) and when it came back down it settled at 400 and stayed there. Arrgh!

Dialing the idle screw did nothing to change the idle. I double checked the TPS and it was still at 0.62 at idle (with the throttle link connected) but the engine insisted on idling at 400 to 500 rpms no matter what I did.

Took the boat out to see if it exhibited other problems. It did:

Ran at low range through the harbor very smoothly (more smoothly than it has before). Adding throttle brought her up to 3900 and then she would go no farther. In fact, if you want past this point, it would "roll off" and drop down a bit to 3800 or 3700. Backing off the throttle would bring the RPMs up briefly before dropping back down to "normal".

Now if I didn't know better, I'd be suspecting the low pressure pumps or VST filter. But I JUST replaced them all only about 20 to 40 hours ago. (not long ago), along with a new Racor 10 micron water separator and on-board fuel filter.

Oh, I found one other problem - the high pressure fuel resistor when measured was out of spec - it is supposed to be 0.53 - 0.57v and it measured at something like 0.45 (I have ordered a replacement). Could this be causing the problems? is this a part prone to sudden failure that causes these symptoms?

I'm getting so sick of this engine; I've spent dozens of hours and thousands of dollars replacing parts and paying for mechanics (yes, I'm an idiot, but I'm not an expert on this motor and nor is anyone else within 100 miles of me). I actually paid a mechanic to drive 250 miles to come work on it because even though he's not an expert on this motor, he's a smart and honest guy. Unfortunately there is no source of knowledge for him to tap in to in order to better help me. He feels just a sick about it not working at this point as I do.

Well maybe not; it is starting to ruin my marriage. I'm not kidding.

If I could find some dynamite right now I would probably tape it to the side of the cowl and light it off during the fireworks display on Monday.

[SBSYNCRO]

the O2 sensor voltage should scale between about .3 to about .6V and do it fairly rapidly and constantly at low speeds.
codes 33, and 35-41 are micro processing codes.
where are you getting the code information?
TPS is adjusted to .51V with the shutters closed,then open the shutters about 2.5 turns once the shutter screw contacts the shutter. then adjust the idle from there.
once set the TPA or idle should not have to be touched again until compont replacement is nessasary.

I'm getting the codes from a Winky Blinky (official Yamaha part, not home made) and counting the flashes. I'm interpreting them based on the table on page 9-5 of the yamaha service manual.

I've read every post of yours I can find about the TPS, and the instructions of yours I followed this morning (and the other day) are slightly different from those you posted today. Here's what I was following:

Remove the air silencer--this exposes the throttle body--diasconnect the throttle cable---left side of motor----. Top butterfly is #1. The TPS is located to the right of it (mounted on the throttle body)--wiring harness runs down the side of the throttle body. Red, Pink, Orange wires. Disconnect the wires at the clip and install the test harness.-turn on the ignition switch--- With the meter set on DC Volts contact the Pink and Orange wires--your reading will probably be somewhere between .40 and .55. You want to set it to .58- .62 at idle position ---closer to .62--do this by moving the TPsensor clockwise (loosen the two screws)re-tighten the screws and slowly open the throttle plates to wide open --you will hear a clicking noise--that is the sensor--- move one of the probes to the red wire--at WOT you should be at 5.0+++ not to exceed 5.25. Do this about 3 time to make sure the settings do not change. If your readings are within those numbers, you are finished adjusting. If you have trouble getting the .62 by adjusting the TPS alone--get it as close as you can by adjusting it then try adjusting the idle screw to get it closer. If you are where you need to be--take it to the lake and start it up--let it warm up and check the idle RPM 700 to 760 in neutral---600 to 650 in gear. Assuming the TPS is working properly, you should be enjoying a smoother idle with the added bonus of better performance throughout the throttle range. If none of the adjustments worked or became erratic--the TPS may be bad and will have to be replaced

[rodbolt17]

gotta run back to basics.
its a simple speed denity EFI setup.
the two stroke version doesnt use an ISC(IAC) as airflow at idle is fixed vial the shutters.
so the ecm now uses the TPS value for throttle angle.
the ecu is mapped to adjust fuel and ign timing based on crankposition sensor,pulser coil inputs and TPS feedbacks.
this gives the ecu information on throttle position and engine speed.
the map sensor and intake air sensor gives information on air density.
hence the term speed-density system.
with the shutters fully closed, not at idle position but FULLY closed.
set the TPS to about .51V.
first check the 5V reference.
once the TPS is set adjust the shutter screw until you see about .6V.
then start the engine and adjust the shutter screw until the proper RPM is obtained.
remember the ECU is stupid.
it assumes fuel rail pressure and all its inputs are correct and reacts accordingly.
if you have a fouled plug,bad plug cap resistor or anything else the ECU will attempt to make the engine run.
wont run correctly but it can alter fuel and timing to attempt it.

[SBSYNCRO]

Hey Rodbolt,

Thanks again for your continued advice, and for the service you provide to all of us down-on-our-luck Ox66 owners. Unfortunately, this internet forum method isn't working to get the problem fixed (let's blame it on me just being stupid).

I have given up on this motor (and the boat) and told my partners that my wife is going to leave me if I don't stop spending so much time fruitlessly working on this boat. So they are on their own.

They have a mechanic, but as I said, he is honest, smart, hard-working and knowledgeable, but doesn't know all the bloody undocumented procedure and idiosyncrasies of this motor like you do. Can we engage you for a couple of hours of time to consult with him (professional-to-professional) and help diagnose and fix the problem (and give us a reasonable understanding of whether we should keep pouring money into this motor or replace it)?

I sent a PM to you, but I gather you probably ignore your PMs (I can imagine you get a lot of them).

Thanks, and I hope you can help us out.