DF50 Stalling at high revs

[BigNige]

I have a problem with my DF50 (circa 2007). 6 months ago it was lumpy, unreliable and would often choke at about 4500 rpm sometimes getting through it and sometimes cutting out. Been working through things with the local dealer. Replaced a bush in the float chamber (but old one was ok) checked out fuel lines water separator primer bulb (replaced) also spark plugs and injectors were checked but things gradually worsened until it would only run for a couple of minutes at any revs before cutting out and I would have to wait a couple of minutes before I could restart. On reflection I think this latter stage was due to a length of US spec hose that I had put in. This hose has an internal liner (for ethanol resistance?) and I think the dealer had scrunched this up inside the line while swapping primer bulbs separators around causing difficulty filling the float bowl with the primer bulb. Everything I was reading said fuel pump so they put in new one.
The situation now is that the engine starts first time runs at 2-3000 rpm forever and doesn't miss a beat. At about 4500rpm it begins to get lumpy. At 5000 rpm it cuts out after 20 to 30 seconds and the float chamber is empty. I can run it for longer by pumping the primer bulb but much above 5000rpm I just can't pump fast enough. In the good old days WOT was 5800rpm.
The only thing that has changed within the timeframe of this problem is that the original 80L fuel tank that came with the boat had to be replaced. I replaced it with a 25L tank (the same one that came with the engine). Because of the way I use the boat (MacGregor 26) I cannot relate the two issues but the engine was permanently connected to the 80L tank until it wasn't.
Any ideas

[Moonlighter]

I would try a different portable tank and see what happens.

Tank vent is open, yes? (I had to ask!) it still sounds like a fuel starvation issue, doesn't it?! I did hear some bad things about the new EPA tanks being problematic for venting issues.

Maybe try running with the tank cap loosened off so air can get in. Carefully.

[Solarman]

Have you had problems with ethonol fuels recently, "ethonol lined hoses"?

Cleaned/replaced all in-line filters?

Is it possible trash from old pump could be lodged in front of needle-valve seat restricting fuel (slightly) going into bowl?

Just thoughts. Good luck.

[BigNige]

Tks. for your thoughts. I'm going to try paralleling the two tanks if I can get another connector otherwise I'll jury rig a container that I can hoist up the mast to give me a positive head of fuel and see what transpires.

[artdf175]

one more thing you might check is an air leakage from a hose connector
what is the primer bulb doing when it cut out.. deflated ?
if deflated you more than likely have a tank vent issue or plugged fuel line
if it is full shape, then I might suspect a hose leak. along this line, you should be able to pump way more fuel than the engine is consuming which also lends itself to a bad connection and drawing in air
If possible take a look at the inline fuel filter (pre low pressure fuel pump) and see if there is any air inside the filter.. should be none.. and if it is drawing in air someplace you will see a flow of air bubbles.

Art

[BigNige]

Update

Finally got some calm seas to test at WOT. Rigged up a temporary tank with positive head on engine nothing in line just a 5/16" hose. Ran smoothly up to 5200rpm but would go no higher. Bought the necessary parts and connected my two 25L tanks in parallel. Got a clue in the parts numbering of the tank connector which had DT9.9 - 40W so I suspect that the 25L tank may be only suitable up to 40HP??? Anyway tested it on the water and essentially the same as the temporary tank. Now waiting for the dealer to come and have a look. Did replace the engine control cables a couple of months ago. Maybe something needs adjusting there. They had looked at all the connections etc. under the hood previously but I will make sure they check again.

[artdf175]

sounds like you may have partially solved part of the problem
when you were up and running at 5200 rpm .. status of fuel bulb? full .. flat?
before you mention fuel chamber being empty

have you looked into adjusting the float in the high pressure tank?

and yes a new cable, not adjusted correctly, might not allow the throttle to fully open could also be a limiting factor

and being a 2007 engine, did you have a compression/leak down test done and checked the valves for proper adjustment?

art

[Elliot Griffin]

Agree with artdf175 to test compression and cylinder leakdown. See my posts. I has similar symptoms, and chased fuel and electrical for a while. After compression test, I realized it was another issue.

[BigNige]

Latest Update
Dealer checked cables no problem there. Still only runs to 5000 then dies.
Came out a second time intending to do a compression test but didn't, instead checked plugs (OK) and connected diagnostics but nothing obviously wrong there.changed the low pressure diaphragm pump for one from a 110HP engine then went out for a test run. Same as before, 5000 rpm for a while then died. Primer bulb takes about 6 pumps to firm up when running up to 4000 rpm which seems normal but this goes up to about 14 pumps at 4500 and above. This too may be normal as it is much better than earlier when it felt that the entire fuel system was empty. Dealer went away saying he would get a new ECU and try that. Still waiting (this is Malaysia!!).
I took off the prop to see what would happen and it ran up to 6000+ rpm no problem.
So what are we left with?
ECU - What function of the ECU could be causing such a problem? Does it control the voltage to the high pressure pump. If it does why is this value not shown in the diagnostics. Could it be the injectors but again no evidence of this in the diagnostics (unlike Ghannan98 post showing 255 injector failures)
Compression - What was wrong with Elliots engine? Ring failure? Bore wear? I would expect poor starting, loss of power (not evident until the engine dies) excessive oil consumption.
I'll run some fuel injector cleaner through it just to eliminate that possibility but really I (and the dealer) are stumped.