Engine Trouble - symptoms familiar?

[Boats Rock]

It sounds like after the time back and fourth with the dealer it will turn out to be a intermittent electrical issue or a fuel issue. Both will not set a light or a code. Codes are for sensor problems not a poor connection to say a coil pack or ECM. And starving for fuel is a back to basics problem.
I always told my mechanics when they would go off in a direction in diagnosing that was going in a area that sounded strange to go back to the basics, follow the diagnosis trouble shooting tree and not jump to the end and just replace a expensive part and find out that it was a vacuum leak or a pin hole in a fuel line.

 

[JUST-IN-TIME]

the YDS shows voltage on all sensors and batteries

 

[jekyl]

I'm having very similar problems with one of my 200hpdi's and there are no alarms going off and yes i will be seeing my Yammie mechanic in the morning.
I have replaced all 10 micron filters twice in the last 3months. In fact replaced new yammie ones with Racors and have had filters on the motors replaced recently also.
Can someone tell me aboutr the VST filter/membrane and other things to ask the mechanic to check.
After coming home on one motor last night the port side one won't even hold idle anymore.
2 days ago we left our harbour here with 4 guys and nearly full fuel and water/ice and we pulled 34 knots at 4800 rpm using 100ltres per hr.It was a shotgun start in a tournament. We then trolled all day and had no problems even came back to port that night with no issues.
I'm sure it's fuel but would like to know about these fuel pump membranes as well.

 

[jekyl]

Well we just spent over an hour trying to get this motor going and after plugging in the laptop and checking the fuel pressure with the gauge we still can't get it to run for more than a few seconds.
I am sure it is a fuel or filter issue as we have had to replace the elements in our 10 micron filters.
The mechanic has also checked the o2 sensor as well as all the plugs etc.

Strange thing is the other one runs very well of the same tank.

 

[Twisted28]

Having a similar issue here. While investigating an 2-stroke oil delivery issue which I can confirm was the small filter in the remote tank, I had swapped the ECU from port to starboard and found the starboard engine was doing the same thing cutting back the RPM's and then kicking in ect. I just switched them back and found the problem to follow the ECU and now the Starboard is strong and the Port is cutting back. At WOT the port (which I susspect is the bad ECU) tops at 4400 and the Starboard at 5000.

Doing a hole shot test with each motor one at a time, there is a difference of 1,000 rpms trying to get up on plane.

My question here is would there be anything other than the ECU which would trigger this when it is following the ECU itself?

I know it may be a dumb question but thought it's worth a post.

 

[wrobinson]

I had the same kind of deal with my old 225s. Took the engines to several mechanics and finally the last one started communicating with yamaha directly. For the record, I was pretty underwhelmed with Yamaha's knowledge of their engines. The mechanic kept telling them he thought it was the ECU (computer) but yamaha said that couldn't be it.

After several frustrating months (no codes generated) it turns out the computer or ECU was going bad. They finally swapped it out and it was fixed.

Here is a lesson learned. If I have ever had work done on one motor, I always do the same thing to the other motor whether it exhibits symptoms or not. Well when I told the mechanic to go ahead and get a new ECU for the other engine, he talked me out of it saying these things rarely go bad. On the trip home the other engine started acting up, I had to turn around in the waterway, go back and get another ECU afterall. Never go against your gut.

I think this happened at about 1600 hours.

Good Luck!!

 

[Twisted28]

I've been having an issue with my port side engine (2000 Yamaha 4 stroke, twin 225's).

We were running at about 4200 yesterday, and I noticed the port side engine kept cutting down to about 3500 on it's own, randomly and abruptly. Once it would return back to 4200, we would try to accelerate and it would actually lose power - dropping back down in the 3k range again. It really felt like the engine was choking on something.

We had a mechanic look at it, and he couldn't find anything. Both engines ran fine at 6k, passed any computer diagnoses, and we couldn't reproduce the problem, yet it was happening all day yesterday.

We've had this same issue 3 weeks ago and even tripped the engine alarm, not being able to get it back up above 1700, so we really feel something is wrong here, but once we shut down it takes hours of running to reproduce again.

Anyone have any thoughts?

If you have not resolved this yet, try switching the ECU's it is not difficult to do or have your mechanic switch them.
If the problem follows the ECU, you know what to do next.

 

[Twisted28]

Follow up to the RPM issues I was having and posted in response to the original post.
Problem on my end was solved when I replaced the ECU this weekend. Apparently the ECU was going bad for a while without notice due to the dropping of RPM in the hight end range which I typically do not push due to the fuel costs.
Boat now runs like NEW! At WOT I now get 38.5 knots @5,000 RMPs with each motor equal in power and performance. @4100 RPMs I got 28.5 knots burning 15 GPH/motor which are numbers I have never seen on this boat.
Even though my fuel burn is not great Changing the ECU fixed the issue.