Marine TDI 5-Cylinder 140-5 issues

[Zanshin]

I’ve got an engine problem that I just cannot “debug” and I’m looking for suggestions

The engine is a 2.5L VW 140-5 marinized “ANH” that is the same 5-cylinder used in VW Transporters and other vehicles. The differences are in cooling – marine engines use efficient salt-water impeller-driven cooling rather than air, and the ECU has been modified to reduce the output to 140HP but to make the engine more reliable for maritime use. One example is the cut-off valve which is normally open and only shuts off when it gets 12V (you don’t want your marine engine to cut off in a lightning storm).


My problem is that once I advance the throttle beyond 1100RPM then, after a few seconds, the RPMs start fluctuating wildly and sometimes it sound like the engine is almost ready to cut off.

• I’ve got a registered VCDS-Lite version installed and have applied the “hammer mod” to make the idle IQ around 5-6.
• There are no error codes generated by the engine.
• When the engine is cold it will run at 1200 or 1800 RPM with no problem for a couple of minutes. I can hear the turbo kick in. But once the engine warms up it goes back to the fluctuating RPM problem and no power
• I can only run continuously at about 1000-1100 RPM
• I’ve got dual primary 30um filters with a manometer and have replaced the filters and show no back pressure/blockage
• I’ve removed the fuel supply from the secondary filter and when I turn on the ignition, I get about 250ml of fuel from the small 12V pump in less than 30 seconds.
• I’ve replaced the fuel filter between the fuel pump and the injection pump.
• The air supply is unblocked. The filter is clean, but I’ve removed the whole filter assembly just to be sure.
• I’ve removed the cut-off solenoid and cleaned the entrance with Q-Tips (no evidence of any debris) and made sure the spring has enough tension. I’ve tested the solenoid with 12V to make sure it activates.
• I’ve gotten a “cloned” ECU to see if I might have a broken ECU but that made no difference.

I’m at my wit’s end regarding what to try next! I still think it’s a fuel delivery issue but can’t think of what step to take next to locate the cause.

I have an extra small 12V fuel pump, would adding that in series in order to increase the fuel delivery pressure cause undue problems or make a difference?

I should add that I’m currently in wonderful St. Lucia. While a beautiful Caribbean island, the concept of “high tech” means something completely different here to what one would expect in the USA. I can’t get technical assistance and shipping in parts, even something the size of a spark plug, costs at least $200 in shipping. So I’m limited in what tests I can perform.

 

[oilhammer]

Can you look at the engine's data and see if something looks out of the ordinary? Like the air (intake), ambient (if it has it), fuel, and (I assume?) some form of coolant temps?

 

[Zanshin]

I've gone through the VCDS data, but haven't seen anything that jumped out at me as a "cause" rather than an "effect" the IQ fluctuates wildly when the RPMs do, going from 10 to 50+. But I don't know if that is the engine trying to compensate for another problem, or the cause of the issue.

The voltages, the air pressures and fuel temperatures all seem constant and in the ranges expected. All measurements were done with the coolant at 80c or higher.

 

[oilhammer]

Maybe wiggle around on the harness and see if you can induce some sort of change? Sounds like it is temp related from what you are saying.

I assume this engine has a lift sensor on one of the injectors?

 

[Zanshin]

Harness wiggled - no change in behavior.

There is a lift sender, but no error showing. How do I find the lift sensor values using VCDS? The shop manual for this engine is at VW150-Workshop-Manual.pdf

 

[Zanshin]

I've just had to motor in windstill conditions and only made 2.5knots and made it to the next destination a full day later than expected. The problem is really vexing.

The issue begins when the engine comes to temperature. What changes to the engine configuration/settings when that happens?
Also, could this be a problem with the turbo-charger, as I think it starts to whine at about 1200 RPM - in the range where I get the fluctuating RPMs

 

[Zanshin]

Great, the only response after @oilhammer to my TDI problems is a spam mail

(SPAM mail has been removed, so this post might not make sense..)

 

[Frans]

No negative fuel temps? (bad/rusty sensor)

What's the digital vcds throttle input value vs the real life throttle position?

Any exhaust obstructions that can reduce exhaust flow?

What's the exact ecu nr?

 

[Zanshin]

Hello Frans (goedendag),
The fuel temps are good and in range - I went through every single block in the manual and checked all the values to make sure that they were in range (blocks 000, 001, 003, 004, 006, 007, 008, 010, 013, 014, 015, 019 and 125 are documented). Some of the checks I also did by removing the cables and checking the resistance values as well. There were no anomalous readings anywhere.
But I didn't check things under load, and oddly enough last night I thought about the throttle input. This is done by a Bowden cable to the engine, and there the mechanical movement is turned into the digital sensor reading. I only looked at the throttle values at idle and at 1600RPM but never looked at them to see if they were changing along with the fluctuating RPM values - this I'll do once I hook up the VCDS unit again (which is a huge pain to access).

The exhaust is a "wet exhaust", meaning sea water is injected into the exhaust stream to cool it down, and then the mix of gas and water goes through a sump and gets pushed out the side of the boat. It is easy to hear and see the water / exhaust flowing and there is no obstruction there. The exhaust gas is hardly visible, but what can be seen is more white than black.

The ECU Nr. is a bit different, here's the image:

 

[mech644]

I work in a boatyard, no experience with the marinized VW tdi’s but have dealt with a lot of different diesel issues. If your boat were here we would run the engine directly from a jug of diesel. 3 to 5 gallon container with hose running directly to the injector pump or in your case the supply pipe that feeds the injectors, and put the return line into another container.
If you still have the same running problem then you can rule out the fuel supply system.