Engine misfire alarm

[techmitch]

I do have a Bravo III. I think 22.4 is stamped somewhere on them but will have to see if I have any pictures of the prop to tell. I believe the props are stock from whatever came with the boat. So what's the standard that came with 2011 Sea Ray 260 Sundecks? I have a 4 bladed that's just before a 3 bladed prop. That's an option to change the pitch to control RPM perhaps. I'm surprised that the PCM doesn't just limit RPM so WOT is at or just below the limit. I'm getting near 5,000 at WOT with the trim all the way down. I give it a few shots of up trim, RPM increase a 200-300, the bow rises a smidge and I get about 3-5 MPH increase. It hadn't occurred to me that there be an issue hear but I will keep it below 5,000 from here on in based on hwat the shop tells me.

Third chart down.
R-14 1/4 X 22 1/2 SS 1936162 B3 G2 3RH
L-15 3/4 X 22 1/2 SS 1936161 B3 G2 4LH
https://owners-resources.searayweb.com/propeller-charts-files/2011 Sport Boat Sport Cruiser Prop Chart.pdf

 

[Brite Idea]

You could talk to a prop shop about tweaking the props. They could re-pitch to give a little more bite and knock down the rpms a couple of hundred.

 

[Chris Lovlecae]

What performance changes would I see by upping the pitch? I imagine the acceleration initially would suffer with a higher top end? I suppose mine are the 22.5 pitch and I'd go up to the next highest pitch which would be 24.

I'm asking Mercury when the Rev. Limiter kicks in. The shop did say that I hit it but there was no real change in RPM. Just a quick pause in the RPM which happened too quickly to register on the Tach but I heard it.

I'm surprised that the PCM allows the engine to over-rev. I'd assume the throttle passes a throttle position angle to the engine PCM which then sets the appropriate fuel air mixture for that setting. Why would the PCM allow a setting that results in an RPM outside the limits?

This will be the 4 week mark that the shop has had my boat. The management said that my boat is baffling the techs. No one is sure what is causing the misfires. As I posted before, the PCM said the engine was running rich which is apparent by the sulfur sort of smell that was notices plus the O2 sensor errors. They mentioned that it could just be bad gas for that. They pulled the O2 sensors, took pictures of them, and sent them to Mercury who said they looked OK. My question there would be, is the engine running rich because the O2 sensors are bad OR are the O2 sensors bad because the engine is running rich? I'd assume the latter but none of that should be connected to a misfire.

I'm to the point now where I asked the shop to see if the problem can persist to the end of the season with no real damage so I can use my boat. Then the shop will have 6 months to explore the issues and not be on any sort of timeline.

Mercury asked the shop to take it out on one more test drive to get some more data. They had some specific things they wanted the techs to do while underway.

I will say that while this process has been slow, the shop seems to be very thorough and they are in contact with Mercury to determine what try next. They aren't just throwing parts at the problem and wasting needless customer money which I appreciate. I really feel that when they give me my b oat back, the issue will be fixed for good but time will tell.

 

[techmitch]

Can't go back and read the whole thread, but, have we base lined the boat with the stock prop's and can you reach max WOT rpm's or above?

 

[Chris Lovlecae]

The boat gets to 5k RPM with the lower unit all the way down at about 43 MPH. With a few shots of up trim, RPM to 5,300 and speed up to 46 MPH. I have to make sure the trim tabs are up. Pulled a tube with three teenage girls and 9 people in the boat no problem. Holeshot seems fine but I've never really cared about it. I haven't messed with the trim tabs much to see what effect they have. A future upgrade is to go to the electric Bennett tabs where I can get the trim tabs position. Yes, I know everyone does it by feel but I like to see where things are. My trim sensor needs replacing and it bothers me that it doesn't work...seems like an easy, though tedious thing to replace.

 

[Chris Lovlecae]

I want to share this response from Mercury on this thread incase anyone else has the same questions I did so it's in the official Club Sea Ray record. I had asked Mercury to let me know when the Rev Limiter logic is invoked and if I went to the next pitch up propeller what would the results be. Here is what they sent in italics:

The WOT (wide open throttle) RPM is 4800-5200 rpm as shown in the chart below. Your engine is the 350 MAG ECT section below.


The rev limiter is usually set 150 rpm above the WOT range so as chart is shown below your engines rev limit is 5350 rpm.

I would not be too concerned about a couple of faults logged for over rev as this can be caused by several things. However, if you can go onto plane and trim up to the best efficiency, your WOT rpm should be within the specification of 4800-5200. We like to see you WOT rpm at the higher end of this range. If the rpm was within this range, the propellers pitch is the correct selection for this vessel. If you are able to go above this WOT range, you will want to look at going up in pitch. Each pitch size will change rpm 150-200 rpm. Going up in pitch will lower rpm and going down in pitch will increase rpm.

Honestly, I've been very pleased with my interaction with Mercury Marine. Hopefully, others have has the same experience. But for those with DTS engines that wonder where the Rev Limiter lives...here you go!