Yamaha HPDI 200 low idle

[seasick]

I don't troll so that is not a possible cause in my case.My plugs always (so far) look pretty good, grey with a tinge of brown so I don't have reason to suspect too rich a mixture.
I have not been able to understand how the thimble could be an issue. I would think it is either clogged or not and warming up the motor wouldn't make a difference. The Yami motors also will run rich if the O2 is not working correctly. When cold these motors need to run rich. That is another reason I doubt it is the thimble. ( one caveat: If the O2 sensor is an open circuit, the motor will run lean, not a good thing)
I have not ruled out the O2 sensor because that device needs to be warm and pretty warm to work correctly. If you check your sensor you will see 4 wires. Two are the sensor signal and the other two are there to power a built in heater. When you power the engine the heater gets activated and is supposed to heat the sensor tip up a few hundred degrees. I can't say for sure if mine is working and to be honest, since the motor runs fine after a minute or two, I am not going to pull the O2 sensor out. In addition, that part is pretty expensive.

Recently, I have been pondering the possibility that the low idle is an injector issue. Either the ECU is not requesting enough gas ( possible bad sensor signal) or the injectors are not working to spec. Maybe that is more common when oldish injectors are cold. Heavens knows that my 19 year old injectors have not been cleaned EVER! Gotta love those SX motors.

Since this cold start idle has been going on for almost as long ago as I can remember, I just ignore it. I have other boat issues that really need service

 

[ROBERTH]

Injectors were one possibility to consider, but the consensus was if we get full RPM's at WOT, likely no issue with injectors. My issue started at 700 hours so I can't believe it would be the injectors that early with 2 micron filters and additives in the fuel to keep the system clean.

The draw tube if you inspect it has to actually seat like a valve from what I can see in the design. Not an expert in this area, but the o2 Sensors were checked and passed all tests so I don't suspect them to be an issue.

We will see, if the new draw tube and cleaning of the carbon resolves the issue, then I am very happy. So far so good.

 

[ROBERTH]

Adding pic here, cold start now going immediately to 700 rpm's. Before the the cold start was stumbling at 400-500 and as it would warm up would move to 600 and eventually after about 5 min. on it's own would get to 700. If able to rev it in neutral, could get it to 700 quicker, but another interesting behavior now is that before, if you rev in neutral, it would not allow it. It would immediately die out. After the cleaning, I can now rev and it does not bog down.

Definitely, something is much different now.

 

[seasick]

Hmmmm.
Mine does allow me to rev it in neutral. I start it and if the idle starts to drop, i push the throttle (in neutral) forward till I get about 900 revs. I let it run for 2 minutes or so and after that all is well. But to be honest, often the first 20 seconds under power and at speed faster than no wake speed, the motor will often run a bit rough and then clear up. The roughness could be low fuel rate , bad spark or incorrect air/fuel ratio. Also important to mention that my motor runs on 6 cylinders below about 1100 revs so if the roughness issue is related to a specific cylinder, I can eliminate two of the eight!

 

[ROBERTH]

That behavior sounds a bit different than what I have. I never have any signs of issue with roughness or stumbling. They run smooth all the time. Just will bog down in neutral when cold and having the low idle issue. That to me sounds like an issue with the computer not providing enough fuel or too much fuel when cold.

Worth mention, while my mechanic had the boat for a couple of months, he went through extensive wire testing, sensors, etc. He utilized the Yamaha tech support team he has in his network and tried multiple ideas.

I feel really good so far that I am onto something here that might be the cause of my issue. I really hope so as I do like the way these motors run when they are running properly.

One of the problems I have now with the mechanics is they are so focused on the 4 strokes, that the 2 strokes knowledge base is diminishing. He did make some adjustments off the top of his head, but found out later, after reading the 2 stroke service manual, that he was following the 4 stroke settings and not the HPDI 2 stroke settings.

I went back and adjusted to the manual for the HPDI 2 stroke and it did make improvements.

Also found it interesting that the idle rpm's should be 700 and not 600 for this motor. Not a big deal really, but one thing I did notice is at 700, I get a lot more voltage output. They also seem to run better at 700.

I also found it interesting that over the years I had asked the mechanics to check the oil link rod setting and every time they told me it was fine .
When I checked the setting per the manual, they were way off and really pushing way too much oil. Again, not sure their thoughts on this, but if they are trying to be on the safe side and not blow an engine due to lack of oil, I get it. I too was very scared to back off the setting and watched the engine temps like a hawk when running after my adjustments and also monitored the oil usage. Seems so far, I am good on the adjustment and saving a lot of oil as well. This really should help out as well.

 

[ROBERTH]

Seasick, have you tried the Seafoam before? It might help you out as well.

One of the comments on the can: "Helps reduce hesitations, stalls, pings, flat spots and rough idle due to deposit build up."

 

[seasick]

Seasick, have you tried the Seafoam before? It might help you out as well.

One of the comments on the can: "Helps reduce hesitations, stalls, pings, flat spots and rough idle due to deposit build up."

I haven't because I am a bit (!!) of a skeptic about snake oils
Did you add it to your gas or somehow spray it into the motor?

 

[ROBERTH]

Haha, yeah, not so sure this is one of those snake oils as it has proven to me it actually does something....There are some videos on Youtube where folks test these snake oils and see the cleaning affects of the carbon. It actually does remove the carbon. Don't expect is to strip all the carbon off of a piston, but you can see some cleaning on the valves, valve stems and pistons in some of those tests.

One thing you will notice is that when spraying it on the hardened carbon, it starts to dissolve it immediately. It is a lubricant/cleaner and think it is safe to use. But, hardened carbon requires some help with a wire brush. I expect if I let it soak overnight it would help more, but I am very impatient.

I removed the front intake baffle and with motors running, just sprayed in each intake bore per the instructions on the can. Simple process to follow....much easier than Dunk's method to put it in the fuel tank and run the fuel through, however, adding it to a 3 gallon can and running it through would likely remove any varnish and also carbon, but with the Ethanol with Ring Free Plus and Startron, thinking I don't have any varnish issues in the fuel system, thus why I just did the quick/simple method to spray directly into the intake while engine was running.

As I mentioned before, I was also very skeptical...why I have used it as a last resort, but I have to admit, it does work and has made a dramatic improvement to the running of these motors so far.

Just based on the excessive carbon buildup I am finding in the o2 sensor housing says it has/needs to be cleaned.

 

[teaklejr]

Adding pic here, cold start now going immediately to 700 rpm's. Before the the cold start was stumbling at 400-500 and as it would warm up would move to 600 and eventually after about 5 min. on it's own would get to 700. If able to rev it in neutral, could get it to 700 quicker, but another interesting behavior now is that before, if you rev in neutral, it would not allow it. It would immediately die out. After the cleaning, I can now rev and it does not bog down.

DefinitelyView attachment 10362, something is much different now.

Cant wait to uncover boat so I can try cleaning O2 sensor and sea foam motors. Everything you descried is exactly what mine do right donw to bogging out in neutral when trying to rev up. Thanks for the update i will report back but wont be for 3 more long months.

 

[seasick]

Be careful when cleaning the O2 sensor. It can easily be damaged. The Yamaha recommended method is to soak the tip only of the sensor in RingFree for a hour or so. Do not completely submerge the O2 sensor probe, just the tip. You also need to be careful when unscrewing it so as not to break the top where the wires are. You should use an O2 sensor socket but not ll of them will clear the housing and wires. You don't need to take the sensor out of the housing if all you want is to check the thimble.
To test, use a propane torch ( not oxy-acetylene) to heat the tip while measuring the voltage of the sensor leads(grey and black wires). the tip can be heated fairly hot but don't overdo it. As it heats it will generate a small increasing voltage. Voltages range from 0 to 1 volt. As long as the voltage changes as you heat it, the sensor is probably good. Yamaha always recommends replacing gaskets. The other two wires are the heater leads. That should measure 100 ohms.

 

[tilewave]

do you have a long " no wake" ride back to your slip or do you go back to the slip at low rpm's like trolling speed ?

 

[seasick]

The actual run is relatively short about 4 minutes at idle. I forgot to mention that the rough running symptom occurs even if I didn't have the low idle issue. The symptoms are probably related and could be sluggish injectors. Or them again, it could be a spark issue. Since it goes away after a little throttle, I may never find the cause.