Nissan 4 stroke idle questions

[Wee Hooker]

Finally got a chance to run the new 30 4 stroke this weekend. Overall, very pleased!. Starts in a heartbeat, purs like a kitten. Sipped 1.5gal of gas over two 3-4 hr fishing trips!. I did notice two minor quirks though. Not sure if this is normal or not.
First, if ideling for a good 10-20 min (in or out of gear) it willperiodiclysurge a just a little for maybe 10 seconds then drop back down. Not much, jst enough to hear and feel. I assume this is something the ECM is telling it to do, but don't know for sure.
Second, at dead low idel (set by dealership @ just under 800 as memory serves) she produces a small vibration, in gear, that radiates through the aluminum hull.. Not real noticable but enough to make the trolling motor mount rattle and fishfinder vibrate at a natural frequency. Is this normal or do I need a readjust of someting.

btw, the motor (with factory 9.9x10 prop) pushed the fully rigged , 900#+/-16' mirrocraft 1615-O between 1.7mph (at idle) and 30mph @ WOT) per the GPS. Very nice match for this boat!

 

[pvanv]

Re: Nissan 4 stroke idle questions

Sounds like you probably have the correct match for the boat.

As for the two idling items you mentioned, we have found that some minor anomalies such as you mentioned tend to go away as the break-in is completed. Minor variations in fuel, humidity and temperature seem to trigger an occasional (and harmless) change in (extended) idle speed as the ECM compensates, learns the result, and stabilizes, which is what it is designed to do. I suspect that changes in barometric pressure would also trigger some compensation. This situation seems to be more pronounced during break-in.

The sympathetic vibration at 800 rpm may be something that will continue. On my own boat, I am able to cause various sympathetic vibrations of different gear by changing rpm of the motor. The precise rpm varies with which motor is installed, but the natural vibration frequencies of the boat and gear is the culprit in my case.

 

[Wee Hooker]

Re: Nissan 4 stroke idle questions

Thanks, PANV, great info as always.
The motor only has 3-6 hours on it tops.
I can live with the vibration as I really don't troll that low/slow other than very early season.

 

[TOHATSU GURU]

Re: Nissan 4 stroke idle questions

What Paul said with one addition. Aluminum hulls tend get a lot more vibration than fiberglass hulls. I would suggest 1/4 rubber matting over the transom to act as a dampner.