2001 150 ox66 Alarm when key on, limp mode

[Yamaholic]

just purchased a 150 ox66. alarm is on when key is turned on and doesn't go off. engine is defaulting to limp mode. Not a temp sensor as I disconnected them and as well the engine was cold. Looked at wiring diagram for 703 controls and the pink wire from the alarm buzzer activates alarm when it goes to ground. Pink wire goes directly to the cdi with no splices. Do the other pink wires to the theremo switches, TPS, and air pressure sensor also act as a ground? ie, are they all on one circuit?
Primer bulb goes tight so I guess the fuel pump diaphragms are good.
I try the engine in neutral and it seems to rev and stay at higher than 2000rpms as long as I hold it but when I put it in forward, it will originally start to increase rpm but probably only reaches 4000 before the engine cuts back about 3 times until it is only at approx. 2000. I don't have an rpm gauge but I think I am pretty close to what I am saying. I haven't cleaned out the VST but would this give an alarm when engine isn't even running???
I can start the engine, unplug the controls, and after a minute or so can plug controls back in and alarm is off, but engine still defaults to limp mode.
How does the throttle position sensor affect this engine? is it only used to meter the fuel? I don't have the remote oil tank or engine mounted tank in use as previous owner mixed gas. right now I will mix gas until I get all the parts to switch back to oil injection. Got a really good deal on engine and figure that I will spend way less over all than cost of a new 4 stroke even with high fuel consumption. Compression is between 110 and 115 on all cylinders as well.

Not sure what else I can add but any help would be appreciated. Thanks.

[rodbolt17]

there are NO sensors that can trigger an audible.
low battery voltage can.
low engine oil tank level can.
overtemp or a shorted wire can.

anytime its in limp mode the audible should be on.

[boscoe99]

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[Yamaholic]

Motor defaults to limp mode. this is know because when I put in forward and give it throttle, it will immediately accelerate, then with throttle held in same position, it will drop rpms in a stepped fashion a couple of times until it is back to maybe double the idle rpms. The motor identity is a 2001 SX150TXRA Salt Water Series II. The purpose of revving in neutral was to see if it would hold rpms above 2000 for anymore than a couple of seconds as it will not do this when in the water.
Primer bulb- read that if it doesn't go tight, diaphragms are leaking. just didn't know if this triggers an alarm or not.

My problem is- I have an alarm as soon as I turn the key on and the fuel pump cuts in. there is about half a second after the key is turned on until the pump cuts. there is no alarm right away, but starts as soon as the relay for the fuel pump clicks. I am not really familiar with outboards but well seasoned as a backyard mechanic on cars, snowmobiles, etc. I am a mechanical engineer and understand small engines fairly well, as well as the protection that goes with the electrical systems. Just hoping someone out there who might have the similar problem could point me to a solution in a time efficient manner. otherwise, the troubleshooting will probably take a while to figure out the problem, but I am confident that I will eventually find it.

If you are certain that the only audible alarm is from the oil tank, battery, overtemp(or shorted wire on temp sensors you mean?), I will focus on that.
I have already unplugged the temp switches, no change in performance. I will rule that out and switches are open under normal idling.
I will check battery voltage but it starts fine and I have 12.5 to 13.0 volts on power wires.

[Yamaholic]

12.7 volts from battery without engine running. 13.3 at idle. The batteries are old and I had to charge them to get the engine to start. Maybe this is the issue?
Also, just had the engine running with muffs on. I turned on key, alarm sounded, started with alarm still sounding, but alarm went off after 40 seconds. stopped engine, started again, same thing. Maybe the voltage is too low just after cranking and takes a while to get up to where it is supposed to be. also may be the case that as I increase throttle, voltage is not enough to maintain the electrical system, causing engine to go into rpm reduction mode(limp mode). Guess I will try some fresh batteries but not expecting any change. hope I am wrong.

Remote oil tank is not connected. Anyone else have this modification? did you have to jump any wires on the engine side connector to turn off any alarm?

[99yam40]

I do not think the fuel pump should be cutting off after 1/2 second.
Monitor voltage to it and fuel pressure

Probably getting low voltage to ecu or other parts at motor bringing in the alarm

[Yamaholic]

sorry, meant to say half a second before the fuel pump cuts in.

[Yamaholic]

update

tried engine again with charger hooked up to batteries and still the same thing. Alarm sounds when fuel pump cuts in(just after I turn key to on) and stays in alarm for approx. 40 secs while engine is running, then alarm goes off. I haven't tried again in water as I have a half hour drive to launch. any other suggestions before I bring to water to test?

[rodbolt17]

if the engine makes 4000 RPM its a fuel issue.
NOT an RPM reduction OR limp mode.
the ECU does NOT monitor fuel.
there are NO sensors that will back off RPM unless its coupled with an audible.

its not a bad sensor.
\its not a bad ECU.
fix the fuel system.

if the audible sets its.
oil tank on the engine low.
loss of 12V at the ECU.
ovetemp.
water in the fuel if equipped.
and that's about all that will set an audible AND rpm reduction.
ANY time you get an RPM reduction you WILL get an audible.

[Yamaholic]

Thanks Rodbolt. I appreciate your help. I have the gone to a portable tank. Fuel filter(cup on port side) seems to be full. I will take out the filter again and check. The alarm does not go off when the limp mode happens that is the weird thing. so if this is a fuel issue, is the ECU involved in the reduction of rpm? or do you just think it is a starvation issue? it really seems like a computer con*****ed stepped reduction. Again, I can't confirm the rpm as I do not have gauges on my boat yet. Anything in the VST that needs to be cleaned?

[rodbolt17]

like I said, ANY alarm that will trigger RPM reduction will also trigger the audible alarm.
yes there is a filter in the vst as well as a filter in each injector.
the ECU does NOT and CANNOT monitor rail pressure.
monitoring rail pressure is YOUR job.

[Yamaholic]

Thanks again.
I will clean out the vst and other filters.
Can you explain why this engine will hold rpm when in neutral? ie, I can rev it up and it will stay at where the throttle is held. when I put in gear and try, it will originally rev and then it cuts back as I explained to what I thought was limp mode, but maybe not as there is no alarm sounding when this happens.

[99yam40]

more fuel is needed to create power, no power is needed in neutral

[Yamaholic]

checked the fuel injectors and vst. there were as clean as a whistle! looked like new.
I would think a fuel pump would be either good or not. I can hear it cut in and cut out when it pressurizes.

[rodbolt17]

dude
your kinda dense.
the ECU nor the fuel pump monitors pressure.
at key on the ECU grounds the pump for about 3 seconds.
once started NOTING. let me reiterate for about the 20 11th time. NOTHING monitors fuel or the pump or the rail pressure.
am I clear on this now?
no fuel alarms, NOTHING.