Volvo Penta 4.3 GXI cutting out at 3000 rpm

[Dalen]

Hello! I need help as I am on my last legs with this issue and starting to wish I had bought a new engine originally, but here we are.
I'm not mechanically in the know other than the very basics of engines, though I am capable and willing to learn.

I have a 23ft sealine with a Volvo Penta 4.3 GXI 2006 (I think) and it is cutting out at 3k revs (instantly) no spluttering etc. just like someone has turned the key.
It has been with a local marine engineer in Guernsey for almost a year now and after that time they have had no success in solving the issue stating they have exhausted all options bar replacing the ECU at £1.8k, so are not willing to spend any longer on it. With a bill of almost £6k on a boat only worth 12-13k (with a working engine) I'm also hesitant to spend much more.
A few notes:

• The engine was rebuilt by an engineer when I refurbished the boat in 2023 as it had been semi submerged in rain water. The engine was okay for the first 4-6 months before this issue started to appear more often until it was never able able to go above 3k.
• She did ground out and stall in astern close before all of this started on sand at around 2-3 knots, however everyone I have spoken to says that this cannot be related to this issue.

So far they have done the following:

• Run the engine on an external fuel tank.
• Replace spark plugs
• Replaced idle air control valve
• Replaced the distributer cap and rotor
• Replaced the coil and module
• Replaced the crank sensor
• Replaced both high- and low-pressure fuel pumps
• Replaced the fuel pressure regulator
• 6 sea trials on separate occasions after each part was replaced by elimination.

Any help would be massively appreciated, I can also send any pictures needed.

 

[Grubble]

I don't suppose they've read any fault codes? There is quite a lot of diagnostics you can do before you start replacing parts on the off chance something will fix it. At least you have a lot of spare parts now.

 

[Dalen]

I don't suppose they've read any fault codes? There is quite a lot of diagnostics you can do before you start replacing parts on the off chance something will fix it. At least you have a lot of spare parts now.

They are not a registered Volvo dealer so didn't have a laptop that could plug in as far as I am aware. Is there a high chance that this would show something? Also not sure I've been given any spare parts! I will check the boat.

 

[Grubble]

They are not a registered Volvo dealer so didn't have a laptop that could plug in as far as I am aware. Is there a high chance that this would show something? Also not sure I've been given any spare parts! I will check the boat.

Ask them what codes they found, or what diagnostics they carried out. You might want to research what diagnostics are available for your year of engine (it depends on the type of ECM) - later ones have more data than earlier ones which give very basic information. If however they are just randomly swapping parts that isn't a good sign.

They should definitely give your old parts back - after all there doesn't appear to be anything wrong with them. If you do buy a new ECM it's not entirely a waste of money as you can still sell it afterwards, but I can see why you don't want to put any more money into something that may never work properly again.

 

[spannerman]

Sounds like they don’t know what they are doing so have just thrown parts at it and hope to get lucky.
The first thing to do is connect a timing light and see if the ignition disappears at 3000revs, if so then see if the 12v feed to the coil disappears at this point. If all is ok, run it with a fuel pressure gauge and see what happens to the pressure at this point, if the pressure is good then check the injection system, if its throttle body injection then just look down the venturi and see if the fuel cuts off and is the cause. If its multi point injection then check if the injector pulse at one of the injectors stops at 3000 revs. Its a simple process of elimination to find out if its fuel or ignition that stops at 3000 revs.
Seeing as its been submerged you could also have corrosion somewhere in the engine harness that is affecting a signal at higher rpm and the resistance shuts down the fuel/ignition system, as all the sensors run on 5v so it won’t take much corrosion to stop a signal.
I have a Volvo V8 in the workshop now and the insulation on the wires on the engine injection harness is cracking and falling off causing some wires to short against each other, it needs a complete new harness.