Help? "Limp Home" mode kicking in for no reason... Not sure where to start?

[SoldTheBayliner]

Hi all,
I have a 2000 Super Air with the Apex 5.7liter engine. Just de-winterized, first time out this year today. Brand new impeller in there, temperature and oil pressure were great all day, we were out for a few hours. I wakeboarded, wife wakeboarded, boat ran great. Kids got on the tube, boat ran great. I'm constantly watching the temp gauge first time out... acting totally normal... creeping towards 170/180 and you can see when the thermostat opens up, gauge walks back down to the 160 range... perfect.

So then the littlest kid gets on the tube and we slow things down... we're not idling, but not going fast enough to get the tube up on a plane. So the engine is pulling, but at lower RPMs, like 2000 range probably. It's hanging out at about 3000 for a typical wakeboard run. After maybe 5-7 minutes of cruising like this, the engine cuts out like it's gone into "limp home" mode, which I have had happen when overheating before with a blown up impeller. But the temp is still sitting at 160, no obvious issues. Shut it off for a while, start it back up, and cruise the same way for another 5-7 minutes, and it happens again.

We put the big kids back on the tube and ramped it up to a "normal" tubing speed... 18 or 20 MPH, RPMs at around 3k.... ten, twelve minutes, no problems at all. Not an issue. Everything seems smooth and happy.

No excessive water in the bilge, oil pressure good, temp good....

put the little kiddo on the tube again and slow things down..... 5-7 minutes in, bam, limp home mode.

What the heck? Any ideas?

I've read about the knock sensor maybe triggering that if it's going bad? It's got the knock sensor that is also the drain plug on the engine block, and it was out all winter but wasn't treated any differently than I've treated it in previous years.

What else can trigger that cut-out, limp home mode thing?

thanks in advance...........

[functionoverfashion]

From your description it does sound kind of like a sensor giving bad readings. But it can't hurt to check for water in the FCC (fuel filter housing) by draining some fuel from the bottom into a glass jar or similar.

You'd expect it to get worse and stay worse, if it was water in the fuel. But any time you have a run issue on a "first trip out" fuel is a likely culprit and easy to rule out.

[windsurfnut]

Oil pressure and Temp switches are separate from the gauge senders. Your temp/pressure can be reading ok to the gauges but a bad switch will trigger a fault.

I think you can unplug them to keep the ecu from seeing the fault and see if it stops.

[SoldTheBayliner]

Cool, I will check the fuel, thanks. Stored it with 2/3 of a tank this winter with stabilizer in it, like usual... maybe a little less fuel than I normally leave in there. I shoot for 3/4 tank. The gauge switches... can I just unplug at the sending unit on the motor? I'll give that a shot, but they were sure acting like I was getting good readings. I think I'm going to get a knock sensor and see if that stops it also.....

Another thought... what triggers the knock sensor? I'm wondering if it's just running a little rough at lower RPM's and maybe new spark plugs or something would smooth things out enough to not trip that thing? It sure feels fine sitting in the driver's seat though....

[Bevostein]

Is your water strainer seated properly and on nice and tight. Probably not your issue since you're not overheating but I have a buddy whose 2000 air was giving him fits at the start of the season a few years ago. Sounds similar in that it would overheat at low RPMs but would be fine at running speed. Turns out his water strainer was off threaded and letting air in the system.

[SoldTheBayliner]

Water strainer seems to be sealed good, but I'll check it... it's definitely not overheating at lower RPM's though, sitting between 160 and 175, you can watch the gauge creep up and then see when the thermostat opens up and it creeps back down to 160. No issues with temperature. I was watching the gauge when it kicked into limp home mode once, and the temp was at the lower end of the range, sitting right at 160. It seems to be unrelated to temperature.

[SoldTheBayliner]

Update.... replaced the knock sensor... $60 gamble.... It did the same thing again yesterday, first day on the new knock sensor. Ran great at higher speeds, but 5 or 7 minutes into a slow-speed little kids tube run, so the boat is not up on a plane... lugging along at slower speeds, maybe 2k RPMs, and limp home mode kicked on. It feels like it's running great to me until that moment... I'm stumped. I think I'll put new plugs in it and then bite the bullet and take it to a shop, unless someone has any other great ideas??
Again, it's not overheating. Not even close. Temp seems perfect.

[mpost]

I believe two other things that will put you into limp mode are over temp and low oil pressure. Both of these are not sensed by the same thing that drives your oil pressure and temp gauges. If your gauges are showing OK try disconnecting the other sensors to the computer and run it like that. Just keep a close eye on the gauges. Several threads discussing this on CCF recently.
Here is one. http://correctcraftfan.com/forum/for...ki-nautique-96

[SoldTheBayliner]

OK, update... I finally gave in and took it to the shop a couple weeks ago. They took it out and ran it, had it kick into limp home mode, and decided that low V-Drive oil was the culprit. They topped that off and didn't have it kick into limp home mode any more. Boom $300, thankyouverymuch. I picked it up, took it out on the water, and after an hour or so of playing, it kicked back into limp home mode. Twice. So frustrating. I took it back to the shop, they put it on the computer... it's not throwing any codes, runs perfect in the shop. They took it back out on the water, couldn't get it to kick into limp home mode. They had a theory that maybe someone played with the perfect pass and it was set at a super low speed, so that was kicking it into limp home mode. I told them that has probably been on since 2012, we don't use it. It's never been an issue before.
They topped off the engine oil (oil pressure has been perfect so I doubt that will fix anything.
So I'm going to pick it up today, another $150...and I'm assuming no fix.

So temperature is perfect (they verified the gauge is reading correctly with a thermometer on the motor), oil pressure is perfect, new knock sensor, transmission/V-drive oil and engine oil are perfect, no codes on the computer, and limp home mode kicking on intermittently. The only thing I have to go on is that when we've had it kick on, we've either been going through a fairly tight corner (so boat leaned sideways a bit), or with the nose in the air a bit going slower for small kid tube runs... and they can't duplicate it in the shop, when the boat is sitting flat on the trailer.... so my only potential thought is that it has something to do with some level of some fluid being tossed around....

Someone mentioned water in the fuel filter deal... I haven't messed with that. Does that sound like a likely culprit? Can someone talk me through how to check that? I've never messed with it, I just remember scary warning labels on that thing... haha.

Thanks.........

[NautiqueJeff]

Very simple. Only two things can cause the boat to go into limp mode. One is an overheat condition being sensed, and one is a low oil pressure condition being sensed. If you really are experiencing either of those conditions, you need to figure out why. Sometimes the switches that control the limp mode fail though, and activate limp mode even though there is no real issue. This would cause your gauges to read normal readings, but the switches for the SLOW system are signaling a problem, even though there is none. These switches are SEPARATE from the sensors for the gauges.

My bet is that the oil pressure switch has failed. You can disconnect the wire from that switch, and that should allow you to run the boat normally until you can get a new switch. It may also be the water temperature switch, and same deal with that, just disconnect the wire until you can get a new one and the boat will run fine.

Here's the oil pressure switch:
https://www.nautiqueparts.com/produc...nd-gm-to-2006/

Here's the water temperature switch:
https://www.nautiqueparts.com/produc...-mpi-r020014a/

We're talking about the SLOW system here. See diagram below.

These are the ONLY things that can trigger limp mode. Nothing else can do it.

[nyryan2001]

Very simple. Only two things can cause the boat to go into limp mode. One is an overheat condition being sensed, and one is a low oil pressure condition being sensed. If you really are experiencing either of those conditions, you need to figure out why. Sometimes the switches that control the limp mode fail though, and activate limp mode even though there is no real issue. This would cause your gauges to read normal readings, but the switches for the SLOW system are signaling a problem, even though there is none. These switches are SEPARATE from the sensors for the gauges.

My bet is that the oil pressure switch has failed. You can disconnect the wire from that switch, and that should allow you to run the boat normally until you can get a new switch. It may also be the water temperature switch, and same deal with that, just disconnect the wire until you can get a new one and the boat will run fine.

Here's the oil pressure switch:
https://www.nautiqueparts.com/produc...nd-gm-to-2006/

Here's the water temperature switch:
https://www.nautiqueparts.com/produc...-mpi-r020014a/

We're talking about the SLOW system here. See diagram below.

These are the ONLY things that can trigger limp mode. Nothing else can do it.

Jeff- that’s the only 2 things for his model/year.. or Any Nautique to go into limp mode?

[nyryan2001]

Just saw the exact same behavior he described on a newer boat.

BAD ignition coil.

this engine has ignition coils?

[NautiqueJeff]

For 2000, my info should be correct.

His engine is kind of an oddball though. There weren't too many Apexes sold.

[SoldTheBayliner]

Jeff,
This is gold. You just saved summer. Thank you so much. I have had zero luck finding anything about what triggers the limp mode. My (only option little local) shop obviously knows as much about it as I do.....

Yeah the Apex seems to be hard to find info about... I didn't know how rare it was when I bought the boat used (first Nautique).
Can you tell me where to find the oil pressure and water temp switches on the motor? They are a completely different thing than the sending units for the gauges? Or is the sending unit/switch the same thing with two wires going to it?

Assuming the gauges are reading correctly (shop verified the temp gauge) that pretty much has to be my issue. Unplugging both of these switches in the short term won't cause any other issues?

[NautiqueJeff]

Unplugging either / both of the switches won't hurt anything. You'll just lose the automatic limp mode feature.

The oil pressure switch and sensor (two different things) should be connected very near each other to a T-fitting. Not sure of the exact location on the Apex, but probably on the lower part of the engine near the front. On the GT-40 they are low down on the front right side (when facing the FRONT of the engine). Remember, in a V-drive boat, the engines are mounted backwards!

Look for these two things, mounted to a T-fitting.

The oil pressure sensor (for the gauges) looks like the picture below. It may be silver or it may be black.



The oil pressure switch (for the SLOW/Limp system) looks like the picture below:



Disconnect the wire on the oil pressure SWITCH. See if that fixes your issue. If it does, order a replacement at the link in my earlier post.




If that doesn't fix it, look for the temperature SWITCH, not the sensor for the gauge. It should be near the top of the engine, and will look like the picture below. Disconnect the wire and see if that fixes the issue. If you lose the reading on the gauge after you disconnect the wire, you unhooked the wrong thing, and you should hook it back up and keep looking!



If that's the issue, here's the link for a new one.

https://www.nautiqueparts.com/produc...-mpi-r020014a/