DF225 won't rev past 4000

[dedzaboy]

Hi. I have a DF225 (2005) on a 23ft Seafox. On a recent trip when attempting to accelerate home in time for happy hour I found that the motor wouldn't rev past 4000rpm. Usually from a standstill it gets up and goes towards 5000 then I back off a bit once I'm planing. On this occasion it took a while to get planing and stubbornly refused to go past 4000. Closing the throttle slightly has no effect, i.e. the top 1/4 of throttle movement isn't doing anything. This was a few weeks ago and I've not used the boat since, until this morning when I went for a quick spin to see if the problem still exists, and it does.
I haven't checked anything at all at this stage, I ran out of time anyway but thought I'd ask if anyone out there has had a similar problem and can point me in the right direction.
Thanks!

[artdf175]

sounds like hitting a rev limiter, don't have a book in front of me at the moment that gives reasons -- off my head I thought most of those had a limit of 3000 rpm.. but will look or someone else may chime in..

has there been any alarms?

and might check the throttle cable to see if there is anything hanging up under the motor cowling

Art..

[dedzaboy]

sounds like hitting a rev limiter, don't have a book in front of me at the moment that gives reasons -- off my head I thought most of those had a limit of 3000 rpm.. but will look or someone else may chime in..

has there been any alarms?

and might check the throttle cable to see if there is anything hanging up under the motor cowling

Art..

No, max rpm is 5200 I think, certainly more than 5000 so it's not a rev limiter problem. Not a throttle cable issue either, seems more like a sensor may be limiting the revs for some reason. I'm going back to the boat tomorrow to see if I have any error beeps / flashes. No audible alarms when running though.

[Moonlighter]

I think Art was referring to a sensor-activated rev limit, not the engine hitting its normal max rpm. Some cut in at 3000 but others at about 4000rpm.

First port of call would be to clean and replace fuel filters, both the water separating filter and those under the cowl. I had a similar problem and it was my water separating filter full of rubbish, must have picked up a dirty load of fuel. New filter element sorted it out immediately.

And then check the anti-syphon valve on the fuel tank. They can be problematic little suckers, and are not actually necessary or required on outboard powered boats. Had a problem on mates boat recently where his DF300 would stall as it came off the plane. Had us stumped for a while until I was told about the anti-syphon valve. We unscrewed it off the tank, took it to the workbench, punched out the ball and spring and seat inside it, so it was then an open barb, and reinstalled in on the tank and reconnected fuel hose. Problem solved.

By the way, you really need to get that engine propped so it will rev out to close to 6000rpm. If your current WOT max rpm is down near 5200, you are lugging the engine and not doing it any long term good. You will get better acceleration, mid range cruise speed and better economy if you prop it into this range.

Have you done anything recently to the engine or associated systems recently? Added anything electronic to the boat?

[dedzaboy]

Thanks for that. No, no changes at all - the only thing that is slightly different is that when this problem first occurred it was after some hours of running which might well point to a fuel problem. I'll change the filters and see what happens.
I just checked the manual and max rpm at WOT is 5000-6000, from memory I get around 5500 so should be good.

[dedzaboy]

Well, new remote filter / separator element, and new low pressure filter fitted, made no difference at all. Both looked clean anyway (except for a bit of corrosion on the outside of the separator element), both are almost a year old but the boat has had little use, I'd be surprised if it's more than 30 hours since those filters installed. I haven't changed the high pressure filter yet (and don't know how old it is) although I do have a spare so maybe I'll try that tomorrow. Expensive though.
Definitely doesn't feel like a rev limiter kicking in; in neutral at the dock there's obviously a limiter which won't let the motor rev beyond around 2500rpm and that's very noticeably a limiter, it makes the motor 'hunt' if you try and open the throttle up in neutral; this current problem doesn't feel like that at all, it's just 'flat' up to 4000 and won't go beyond but there's no hunting or misfire.

[dedzaboy]

Having studied the manual a bit more it seems that there are situations where a rev limiter will kick in, namely over-revving, low oil pressure and overheating, but in each case it limits the engine speed to 3000rpm (by providing an intermittent fuel injection signal). Since I'm running out of steam at 4000rpm and there's no suggestion of misfire / intermittent signal it seems unlikely to be a 'deliberate' fault.

[artdf175]

yes in neutral there is a limiter
however, at the dock .. if you can't get out.. carefully tie the boat down and you can put it in gear and get past that low rpm threshold
you indicated not many hours..
that brings up a question on quality of fuel . .just how old do you think the fuel is?
and you should be getting that engine up to closer to 6000 rpm at wot
in the past has it been able to run at that speed?
as Moonlighter suggested you might want to double check your prop to make sure it fitted correctly for your setup
however let us know results after the high pressure filter change
art

[dedzaboy]

I have been getting out to test and will do so again as soon as I've changed the HP filter, might not be for a few days though. I couldn't remember what rpm I get at WOT so just checked the survey from a year ago and it was 6200rpm - not getting that now of course, only 4000. Fuel is recent - tank was filled approx 1 month ago, boat was used for a two hour trip at 22kts and running fine, then trolling for a few hours, and then having packed up the fishing gear and ready to head for home found 4000 was all I could get. So got home at around 20kts for an hour or more. Tried the boat again maybe three weeks later and the same problem, max 4000.

[Moonlighter]

Look this may be a long shot but...

I had a problem with my DF115 that turned out to be the engine ECU picking up a intermittent low voltage fault signal from the NMEAa2000 interface cable that caused it to put itself into a safe mode that limited it to just below 4000rpm, very very similar to what you are saying. Throttle feeling doughy under acceleration and no matter what I did, would not rev past 4000.

Except mine didnt do it all the time, just an intermittent issue. We eventually sorted it with some help from the Japanese Suzuki gurus who visited us here in Aus. Smart boys!

So i am wondering if you may have a faulty sensor somewhere on the engine, and the one I am thinking of is the neutral throttle switch on the engine. It was one of the potential culprits we were looking closely at on my 115 before we found the NMEA2000 issue.

There are 2 of these switches as I understand it, one is in the throttle control at the helm, it wont be this one because if it was, the engine wouldnt start at all.

The other one is in the engine bay and is where I think you should look. It could be out of adjustment or faulty. I have seen a couple of reports around where they have failed.

My thinking is that if this switch is telling the ECU that the engine is in neutral when it is not, the ECU retards spark advance to zero, restricts revs and also restricts fuel flow thru the injectors, hence the doughy acceleration and rev limit. When mine was suffering this issue, i didnt get the misfiring etc that you normally get when you hit the rev limiter, it was strange and threw us off the track in our diagnosis. Also, there were no fault codes coming opup on the computer either.

So I would look closely at that switch. Worst case I think is that they are only about $30 and I dont think they are hard to replace.

[Wired Up]

Engine Overrev

Posted my problem with DF225 some time ago, I did all sorts of work, bottom line it was my tach as that is where the logic for overrev is, blew my mind.

[dedzaboy]

Latest thinking is that it's being caused by slightly clogged injectors - a friend has had similar problems with a fuel injected Honda outboard and cleaning the injectors cured it. I'm waiting for some parts to arrive to enable me to take things apart and clean the injectors then we'll find out. I don't think it's an over-rev problem as there's no deliberate misfire, just no willingness to rev. The motor's also becoming more 'lumpy' at idle now.

[Solarman]

wot limits at 4k

Could try running a small tank with injector cleaner, otherwise it could be the fuel regulator dropping pressure on the injectors?
Just thoughts, best of luck.

[redlowrey]

Mate the only way is to remove them, ultrasonicly clean them and flow test them.

[dedzaboy]

So, I finally got the time to have a look at the injectors. It's a bit of a work up to get to them but having removed collector boxes etc there they are on two rails, with a flexible hose joining the two rails. The flexible hose is fitted to a bolt-on fitting on the port rail, and this is made of plain old steel which, apparently, is prone to rust! Having taken everything apart the port rail in particular was full of rusty metal, and it's a miracle the thing ran at all. Prior to all this, the engine had begun running noticeably rougher and in fact cylinders #4 & #6 (lower two on port bank) weren't running at all. It was no surprise to find these two injectors clogged. A couple of hours with a 9V battery to open the injectors and plentiful use of carb cleaner seemed to do the trick, after refitting everything all six cylinders were running nicely. I also took the opportunity to renew the high pressure fuel filter & a smaller low pressure fuel filter - I'd already renewed the water separator filter and main low pressure fuel filter. Took the boat out this morning and bam, straight up to WOT at 6000rpm. Excellent.
I wasn't able to renew the rusted fitting since I'm in Grenada and parts are not easily available - it took two weeks just to get the gaskets and o-rings I needed for the injector job - but I cleaned it up with a brass brush on a Dremel and it should be good for a while. I'll look out for a stainless or brass fitting I think, and replace it later.
This is obviously a problem that had been getting steadily worse for a while but since it was a gradual deterioration I hadn't noticed until performance really dropped off - the motor is now running better than it has for a long while. I've learnt that down here in Grenada injector servicing is a regular pastime for many boat owners due to poor quality fuel, although in my case it's a poor quality fitting that screwed it all up.