DT 140 stuck in Guardian Mode

[Lake Norman]

I have a DT 140 in fresh water. Last fall I had a problem where the engine would sometimes go into Guardian Mode for a period of time (days or a week or so). I've had a Suzuki mechanic examine but no problem was ID'd. The engine was fine for several months but the problem just restarted. Ran great for tow hours, then into Guardian Mode. It came out of Guardian mode after being operated for 15 mins (slowly going back to the dock) and then all was well. One week later same issue but not coming out of Guardian Mode.

Any ideas what could be causing this?

No warning lights, no alarms and recently fueled. Have not tested it unloaded.

Engine is 7 years old, modest use and well maintained. Oil changed 5 months ago.

[Solarman]

OK, not familiar with guardian mode term? If talking about the motor limiting rpms, or limp mode, then I can understand.
What rpms does it do to when it does this. Also, it is important to know if your motor has carbs, or the EFI fuel injection system?

When it went to lower rpms, did you try pumping primer bulb? Was the any difference if you did this?

And when you mention oil changed, I'm guessing you're referring to the lower unit oil/ gear case oil.

Post back a little more info.

[Lake Norman]

Yes, have heard it referred to as "limp mode"

The rpms peak at 3000 every time. Yes, the oil change was the main case not the lower unit. I've not tried pulsing the ball but the issue does not feel fuel related (would have peaked at other / random rps I would think).

Fuel injected.

Idea?

[Moonlighter]

Ok, you must mean a DF 140 4 stroke outboard since you changed the engine oil. Please confirm that for us.

The thread title says DT 140 which is the 2 stroke version. Hence the confusion. It is always best to state upfront the engine model, year, hp and whether its 4 stroke or 2. This has a significant bearing on the advice you might get.

The 4 stroke DF140 can go into safe mode or similar where revs are limited to about 3000rpm for a number of reasons. In some cases, the Suzuki diagnostic system used by the technician will record errors like that and will help diagnose the exact problem.

Did your mechanic connect up the laptop to the engine to check for recorded codes and faults?

One possible reason for revs limited to 3000 is that the neutral throttle switch on the engine may be faulty.

On these engines there are two switches that affect the engine starting and then being put into gear and running.

1. The switch in the throttle binnacle, which prevents the engine from being started if it is not in neutral. So that would likely not be the problem in your case.

2. The switch on the linkages in the engine prevents the engine being revved excessively (more than 3000rpm) if it is in neutral. This switch can become mis-aligned, break or have an intermittent fault.

I would expect that this problem would most likely manifest itself when the engine has been shifted from neutral to forward gear, and then attempted to accelerate, but then refuse to go past 3000. As it reaches 3000rpm you may feel the engine start to misfire as well. Acceleration would also be "doughy" compared to normal. If you shift it in and out of gear a couple of times, it might come good if the switch was loose or misaligned. In this case, it will gradually get worse and worse.

If that is what your engine is doing, then check that switch as it could well be the culprit. They are not, according to my mechanic, expensive to buy (about $50) and fairly quick and easy to replace. If you google you should be able to find video of its location, or a service manual will show it. Your mechanic will know where to find it.

Otherwise, if that is not the case, please describe as fully as you can what the engine is doing and the exact circumstances when it happens. We cannot see your engine running, so we rely on you to tell us as much as possible so members here can offer realistic suggestions to help you out.

[Lake Norman]

The mechanic did connect to the Suzuki diagnostics - NO CODES.

Other comment was that the only things that cause it to go in to Guardian mode is oil pressure and temperature . The other sensor may cause a warning light, but not for it to go in to Guardian.

[Solarman]

OK, if peaking at 3k rpms, then check the neutral safety switch sensor as-sy. Located at the shifting linkage on the motor. The switch limits rpms to 3k, if bad, or not adjusted properly, the motor thinks it is in neutral. It does not throw a code for this. This is what Moonlighter described in his post #2.

Good luck. Post back if you find anything.

[Lake Norman]

Update

The two possible issues were (1) low battery; (2) the switch suggested.

The issue returned when the battery tested 100% - so its likely NOT #1.

We changed the switch - and thus far the issue has not returned after using the boat 3X. Boat will be used this week for spring break - but optimistic.

Will report back.

[Moonlighter]

Thanks for reporting back, sounds like you may have found the issue. Let us know when you are satisfid that the fix is confirmed.