Engine Won't Start: Troubleshooting & Fixes

Hello,
When I replaced my turbocharger, I disconnected the fuel lines from the diesel filter and removed the lines between the fuel injection pump and the injectors.
After assembling the engine, it now won't start . The transparent hose leading to the fuel injection pump is filled with diesel, but it has an air bubble above it!
I've been letting the engine run for minutes now, but unfortunately, nothing is happening!
Does anyone have any information on what I should do now?

There are no error codes stored, and the diesel filter is only about 3 weeks old!
The engine is an AKN (V6 TDI).

Best regards, Achim.

Hi,

Have you already loosened the injector lines at the nozzles and kept pumping until diesel starts leaking out of the fittings?

Best regards, Rainer.

Hello Rainer,
Thank you for the quick response!
I haven't loosened the connections yet. I'll try that right away tomorrow.

Best regards,
Achim

avoso wrote:

I've been letting the engine run for minutes now, but unfortunately, nothing is happening!

Hi Achim,

Assuming all the connections are properly sealed, it should also work with the starter. The pump didn't run dry just because the lines were disconnected! Just crank it for 30 seconds and then pause (to prevent starter overheating), etc... or even better: put the car in gear on a hill, turn on the ignition, and let it roll down with the accelerator fully pressed.

Best regards, Christian.

Deleted upon request.

Okay, so if it absolutely refuses to start, try this:
Detach the oil drain hose from the pump, insert a piece of U-shaped hose, and use a vacuum pump to extract about 1/2 liter of fuel (this may take some time). Do not pump the diesel through the vacuum pump, as this could damage it; instead, use an intermediate container. Before starting, disconnect the return lines at the fuel filter (clamp both lines on the left and right sides of the preheating valve with suitable clamps to prevent fuel from being drawn back through the return lines).
Please note that the tank should be more than half full, otherwise the tank's overflow pipe will be sucked dry, and you will introduce air into the system.

Then, restore everything to its original state. Loosen the high-pressure lines at the injectors, start the engine until diesel fuel comes out, and then reconnect the lines. It will then start 100% of the time. Let it run for about 5 minutes.

Best regards,
edz

edazer wrote:

Detach the oil drain hose from the pump, insert a piece of U-shaped hose, and use a vacuum pump to extract approximately 1/2 liter of fuel (this may take some time). Do not pump the diesel through the vacuum pump, or it will be damaged; instead, use an intermediate container. Beforehand, clamp the return lines at the fuel filter (both lines on the left and right sides of the preheating valve) with suitable clamps to prevent fuel from being drawn through the return line. Please note that the tank must be more than half full, otherwise the suction cup inside the tank will be pulled empty, and you will end up getting air into the system.

Hi,

Exactly . The fuel tank should be nicely full... I once changed a fuel filter with "only" 10 liters in the tank, and even then, the incline didn't help .

A large syringe can also be used -> suck, clamp the tube, release the vacuum from the syringe, suck... etc.

about the mountain:

Choose the highest possible gear depending on the incline (but not too high), get a good amount of momentum (otherwise the car will stall, especially with a cold engine ), and quickly engage the clutch and give it .

Best regards, Christian.

Hello,
My engine is running again! Rainer's tip was by far the best!
I also received original documents from a kind person on how to bleed the fuel line, but unfortunately, it wasn't possible to do it due to a lack of 'special tools'!

Here's how I proceeded:
Fuel filter filled with diesel.
2. Loosen two of the fuel injector lines (place a cloth around the fuel injectors to absorb any spilled diesel!).
3. Let the engine run for about 4 seconds.
4. Lines reattached, and two others loosened.

After all the lines had been bled, the engine started without any problems. Some air bubbles still passed through the transparent hose to the fuel injection pump, but they did not appear to have any noticeable effect.

Best regards and thank you.
Achim.

@Rainer:

Hi,

I'm curious to know why the presence of air in the fuel injection lines ( ) prevents the build-up of sufficient pressure ( ). What is different in this regard between a six-cylinder engine and a 1.9-liter engine ( )?

Best regards, Christian.

Hello,

Quote:

I'd be interested to know why air in the fuel injection lines ( ) prevents the build-up of sufficient pressure

.
To be honest: I don't know.
My assumption is that with an open circuit, and therefore a 'nozzle opening pressure' of 0 bar, the fuel injection line fills up more quickly because the high-pressure generation in the ESP encounters virtually no resistance to pressure generation.

Perhaps Gustav, as a specialist in injection equipment, can provide a more well-reasoned explanation and correct me.

Quote:

What is different in the six-cylinder engine compared to the 1.9-liter engine

?
"Fuel injection pumps and their surroundings, from VP44 to VP37. According to my information, the fuel injection pump in the V6 TDI is a radial piston pump controlled by solenoid valves, unlike the axial piston pump with an electrically controlled metering unit found in the 1.9L TDIs (excluding current pump-nozzle engines)."
Both injection systems operate at different pressure levels, and the VP44 is capable of generating higher injection pressures.

Best regards, Rainer.

Hi,
In my opinion, the cause lies in the air pockets within the injection lines, which prevent pressure buildup due to their spring action. This prevents the injectors from reaching their specified pressure, and the trapped air cannot escape.

Hello Christian,

However, the check valves on the ESP should allow for pressure buildup, to which the fuel injection lines are connected... or not?

Best regards, Rainer.

Hi Rainer,
There might be something to that. It could depend on whether they are designed for that purpose or just to prevent the lines from draining when the system is off. If they are not fast enough, they might not close quickly enough. However, if they are fast, they might not be 100% airtight, which could allow air to be sucked into the ESP (Electronic Stability Program).
Let's wait for the expert then.