2001 OX66 Won't go into closed loop?

[Jim Lloyd]

Hello,

First-time poster here.

I have a Yamaha SX250TXRZ. The boat has not been used in a year while undergoing a hull side paint job, rewiring, new electronics, etc., etc. All useable fuel was drained out of the tank prior to the layup.

Last week, I added 20-gallons to the tank and ran the boat on the muffs. The idle speed did not drop down like it normally does and I assume the motor did not go into closed loop operation. I shut it down for about five minutes and restarted it. This time, the engine idled high ~1200 rpm and then dropped down to the normal ~700 rpm range and idled perfectly.

Yesterday, I put 50-gallons in her and launched the boat. Again it idled high and never went into closed loop. It then started to drop cylinders, smoke and stall and became hard to start. I terminated the trip and trailered it back to the house. At home I drained the Racor and found water. I then drained the clear filter under the cowl and the VST and found more water. Once all of the water was out, the motor started quickly and idled normally on the muffs. It transitioned into closed loop this time, unlike the behavior at the ramp. I measured 37-psi of fuel pressure at the VST schrader valve.

I take another trip down to the ramp and she stays in an open loop high idle of ~1200 rpm, despite letting it run for over 10-minutes. However, there was no hard starting, missing, smoke or any of the other symptoms like before?only the fast idle remained. So I haul it back to the house, again. I hook the motor up to the muffs and she high idles for too long. I shut it down for five minutes and restart it and she jumps right into closed loop and runs perfectly. An important note is the hose water temperature is ~72-degrees, whereas the river water temp was 59-degrees.

I?m fairly confident the smoke and rough running was fuel related and it is corrected.
On the other hand, I suspect the thermostats are not fully closing and not allowing the engine to warm up. As a result the temp sensors don?t signal the ECU that the engine is warm and it prevents the engine from going into closed loop operation. I base this on the fact that the engine operates properly (goes into closed loop) on the warmer hose water, but not in the 59-degree river water.

I have new t-stats and gaskets inbound along with a gasket for the O2 sensor, which I intend to clean/test. Am I overlooking anything?

Thanks for any help.

Jim

 

[cousinabe]

Re: 2001 OX66 Won't go into closed loop?

i think you are spot on with new t-stats.

 

[rodbolt]

Re: 2001 OX66 Won't go into closed loop?

I would start with the t-stats if I did not have my diagnostic test lamp.
but its not really going into or out of closed loop.
this system uses a thermosensor,only 1, to signal the ECU the engine temp.
the TPS and pulser coils tell the ECU information for timing and below 113*F the thermosensor can increase timing and fuel as well.
your engine also uses the CCS system which shuts down the spark on *5 until 2000 RPM and *2 from 850 -2000 RPM.
engine temps under 113 will cancel CCS.
so yes its very possible to stick a t-stat open and the ECU will react to it due to the thermosensor signal.
stupid ECU wont realize the engine has been running 10 min and should be warm it simply reacts to a signal.
however if anyother signal is out of range,other than O2 sensor which isnt monitored for codes, the ECU reacts by cancelling CCS and fixing timing at 7* BTDC.

 

[Jim Lloyd]

Re: 2001 OX66 Won't go into closed loop?

So, what I've always interpreted as the open-to-closed-loop transition is actually CCS dropping Cylinders #2 and #5? The service manual is good for testing procedures and specs, but short on description and operation of the engine management system. I appreciate the info, rodbolt.

My entire ?diagnosis? is based the fact that the motor will idle down on a 72-degree garden hose as opposed to 59-degree river water. In any case, the t-stats are due to come out, so I?ll at least be able to rule them out. Should I do the continuity test on the thermosensor?

Without the test harnesses and winky-blinky I?d pretty much be shotgunning any diagnosis and I?m not about to start throwing parts at the thing. There?s a good Yamaha guy in Daytona Beach I?ll probably haul it to if the t-stats don?t remedy it. He?ll not only figure it out, but will take the time to teach my dumb *** a little more about the outboard.

 

[rodbolt]

Re: 2001 OX66 Won't go into closed loop?

loyd
we have complained about Yamaha manuals since 1984 when they hit the US.
at least we get some now with actual color coded wire harness diagrams.
but yes, incredibly shot on descriptions.
a tune-up spec guide part # LIT-18559-84-05 will help you a lot.
covers 1984-2005.
most the sensors can be tested with a service manual or the spec guide and a standard DVM a DVA adapter can be had for about 50 dollars or so for peak output readings.
if your careful you can slide paper clips up the wire on the backside of the connector, radio shack sells alligator clip jumber leads for like 6 for 3 dollars.
for resistance tests you have to uplug the sensor or coil being tested to avoid parallel or series circuits.
have your buddy resaerch a tech bulliten on 3.1L t-stat housings, yours may be old enough to be covered but I cant remember.

if the cooling system was all good your difference in the hose VS lake should not matter.
but t-stats will gather grass and corrosion nice thing is they are easy to check,remove and replace.

but I think your on the right track, just remember what can cause a high idle and loss of top end.
remember if the o2 sensor is bad it can create a lean run above 4000 RPM. if the thermosensor fails it will idle high and run rich but usually will make top speed.

 

[Jim Lloyd]

Re: 2001 OX66 Won't go into closed loop?

Pulled the thermostats out today. Both had some crud built up, but more importantly, I found the equivalent of a smoking gun in the starboard head. Check out the t-stat on the right.

That's the good news. The bad news is boats.net shipped me some POS aftermarket thermostats that won't work. So much for the test run tomorrow.