BBB

check the engine grounds coming from the engine harness to the ground studs on the bell housing.

BBB

as mentioned before check the fuel-water seperators, pull them and drain them into a clear container and check for water.

Dave_N

I agree with BBB, could be a fuel contamination issue.

It is not that unusual to find cam and crank faults in the fault code history even when both are fine. I am assuming these are not active faults which would trigger a steady audio alarm. Check the resistance according to specs below.

Camshaft Sensor - A to B 24.04 mohms and B to C 24.05 mohms

Crankshaft Sensor - A to B 23.2 mohms and B to C 23.21 mohms

What is the 5 volt sensor circuit doing when the problem occurs? Is it maintaining 4.9 to 5 volts?

I have also seen secondary voltage leaks near the ECM cause "phantom" problems on the 496. You have ignition coils directly below the ECM. The Electro Magnetic Interferance (EMI) from a 40,000 volt discharge (spark jumping to ground) within a few inches of the ECM will cause the engine to stumble. Sounds unlikely, but I learned that hard way that it can happen.

Dave

Preuni

Thanks very much for the information so far!
Here is todays update:
- no water and no dirt in the water seperator....
- no dirt or debris on the screen of the inlet of the booster pump.....
- no fault codes when engine is at idle
- fault codes of cam and crankshaft sensor when under load, but these fault codes do not stay in the memory when engine is shut off and then is restarted
- all injectors tested ok
- fuel pressure stable at idle and under load, no fluctuation
- Batterie and ground connection of engine checked out ok twice...
- meassuring the resistance of the sensors produced strange readings..about 9 kohms

Ordered both crankshaft and camshaft sensors to replace the current ones. If that doesnt cure the problem I will tear this electronically overengineered piece of s*** out of my boat and put in something simple with a carb and a mechanical fuel pump! Any 540s on sale?


-

mobilecal

MillerLite88

I didnt read all these post but I had a similiar problem. I unplugged the knock sensor and WOW!!!! There was the problem and it ran like a spotted ape!!! I replaced the old one with a new one after that weekend and it was still fine. Bad Knock sensor!!!

-Shoe