2007 DF140 RPM Restriction

[shallowaterhunter]

About every 1 out 5 times I start the engine and take off the RPMs wont go over 3400. Back in May I had an overheat/over-revving alarm. I have had the boat out about 4 times since then. Could this be a result of that alarm and if so, is there a way to clear the alarm?

[shallowaterhunter]

Follow-up. If i shut the engine off and restart, it runs normal.

[Harper]

Should have cleared that particaular fault code automatically after the problem was fixed. You might have to have it looked at with an SDS program.

[Moonlighter]

Do you have the engine connected to a NMEA2000 network so that engine data can be displayed on digital gauges or sonar/GPS screen?

[shallowaterhunter]

Yes, displayed on digital gauges, not the sonar/GPS.

[Moonlighter]

Ok. I think I know what your problem is ....

There is a known issue with earlier DF90-140 series engines when connected to the NMEA2000 engine interface, which yours is to enbale the digital SMIS gauges to run. If the issue only started AFTER the engine was connected to the NMEA2000 network, then almost certainly, this is your problem.

When the engine is started, there is a voltage drop that on some engines, exceeds normal parameters, and the interface then sends a low voltage signal to the engine’s ecu, and this puts the engine into safe mode where it will not rev above about 3000rpm. Most times, if you turn the engine off, wait a few moments and restart, it then runs fine.

I had this problem when I connected my 2010 DF115 to the NMEA2000 network back in 2011. It took some serious investigations involving Suzuki Japan to figure it out and come up with a solution. It only affects some motors in the DF90-140 series engines made prior to 2012. The root cause seems to be in the ecu wiring or programming.

One way to test if this is the issue in your case, is to disconnect the engine interface cable from the engine, and run it several times without the digital gauges. If the engine always starts and accelerates up to speed fine, then we know that this is the problem. Or, as I said earlier, if this problem has only arisen after the NMEA2000 netwoek was installed, then almost certainly this is the problem.

The interface cable is powered by its connection to the engine’s ecu, thru the SDS plug on the engine where it is connected. The solution is to change the interface cable’s power source to a separate battery, eg from being powered from the start battery thru the SDS connection, to the house battery.

The fix is therefore to disconnect the red (batt+) wire in the plug on the adapter cable that connects to the SDS plug on the engine, and extend that wire to be long enough to connect it to the house battery.

On my engine, I have a long SDS adapter cable that runs all the way to the helm. So here is what I did:

1. At the engine end, I removed the pin connected to the red (batt+) wire from the bcak of the SDS adapter cable plug and taped it up. This effectively removes power from going from the SDS plug to the interface cable.

2. At the other end of the adapter cable, up behind the dash where it plugs into the interface cable, I cut the red wire in the adapter cable just behind the plug and then connected it to wire that I ran to the positve busbar.

The end result is then that the interface cable is powered by the house battery and is thus protected from any voltage drop when the engine is started. Thus eliminating the potential for any low voltage signal that puts the engine into safe mode.

This solution has worked fine for me and others.

[shallowaterhunter]

Thanks Moonlighter. That sounds like it could be the case. The 2007 engine was installed on a new boat in 2011 so i assume that is when the NMEA2000 interface was installed. I bought the boat last July so I dont know what problems it had before that time. A couple of things happened around the time it started doing this. Like I said, I had the overheat/over-revving alarm (my bad) and I installed an amp and stereo speakers that run off the cranking battery. I have 3 batteries for a 36-volt trolling motor and a cranking battery on the boat. I don't have a house battery and prefer not to have one for weight/space reasons. Could this problem be caused in part from running the stereo amp while fishing and then having slightly lower voltage when cranking the engine? It always re-starts and runs fine when i shut it down after the safe mode operation. If that is the problem, then i guess i can live with it as long as i am confident that is the problem.

I will try the test that you suggested and see what happens.

Thanks.

[Moonlighter]

The problem will likely occur regardless of whether the starting battery is new or not. And yes, mine was the same - I could soon tell if it was in safe mode, switch it off, wait a moment, restart and it would run fine nearly every time. I only had a few occasions where it did it twice in a row. My concern was that one day it would happen in a situation where I needed to be able to hit the throttle and for it to GO!

However you could test the theory, as one thing we know is that these engines really need a solid 12 v supply to run properly. Everything you can do to help in that regard is a good thing.

One other thing is to check where the white ecu sub-wire is connected.

You may have heard about the famous Suzuki “white wire”, and there is a sticky thread near the top of this forum that tells you more about it. Anyway, it is a critical wire because it supplies power to the ecu.

It SHOULD be connected directly to the positive terminal on the start battery, but some installers did a shortcut and connected it to the pos lug on the starter motor instead. This is a very bad idea.

So check your battery + terminal (or master battery switch + terminal) to find that wire, if you cant find it there look at the starter motor, and make sure its connectd properly and that the wire itself and the connector is not corroded.

Suzuki Japan issued a service bulletin that outlined the issue and the fix as I have already posted.

I havent played with batteries set up to run 36 volts, but is there not a way that you can run a set of cables from one of those trolling batteries that you can use for this purpose?

[shallowaterhunter]

Use one of the trolling motors for what purpose, to power the amp or to assist with cranking? I can wire one of the batteries to my Perko switch (1+2 position) to assist in starting if needed.

[Moonlighter]

To connect the interface power to as per instructions in post #6.