Pre-Pump Pressure: Measurement & Optimization

Hello everyone,
How much fuel does the pre-lift pump deliver in a TDI PD engine?
I suspect that the pump in the tank no longer has sufficient power.
I want to install an external pump between the fuel tank (in my T3 bus) and the fuel filter.
I could still really use some suggestions and advice regarding my planned approach.
Best regards, Hoin.

The PD elements require a pre-pressure of at least 3.5 bar and a maximum of 5.5 bar (gear pump).

Thank you for your reply.
I installed several fuel pumps (gasoline pumps) between the tank and the engine, but they all failed after a relatively short time.
Nowadays, I don't use any pre-lubrication at all, and it works perfectly.
Thank you again.
Best regards, Hoin.

Hoin wrote:

Meanwhile, I'm now shooting without any priming, and it works wonderfully.

Hi,

If the tandem pump at the progressive cavity pump (ZK) provides sufficient suction power "down to the tank," then it is certainly possible. This is because it provides the filling pressure for the positive displacement elements (PD elements), which is a few bar.

As I understand it, the pre-charge pump is essentially just a support for the tandem pump.

Ulf is absolutely right; normally, you don't need a pre-pump.

If I remember correctly, the pre-charge pump has a pressure of 0.5 bar.

It actually only serves to support the tandem pump and is intended to ensure a smooth, bubble-free fuel flow.

CU Gremlin.

*dust off*

Quote:

It actually only serves to support the tandem pump and is intended to ensure a consistent and bubble-free fuel flow.

How loud is it, actually?

"At my car's alarm system, it has always been very noticeable. When you turn the ignition key..."
When you turn the ignition, it starts up briefly and makes a distinct noise.

Now, it has been constantly audible for a week, meaning that if you listen quietly in the...
Idling while rolling, stopped at a traffic light, or – even better – driving through a parking garage.
rollt, meint man ständig ein Hubschrauber kreist über einem... Bat a parked car.
Then the "helicopter noise" can be clearly located in the lower right corner.

This gives rise to three questions:

* How long will this last?
* How much does it cost?
* Can you replace that thing yourself, or - if it's not useful anyway - can you completely remove it without any risk?

Regards,

Peter.

Hmm,

"In my Golf IV, the fuel pump only runs briefly when I turn the ignition on, and only when the fuel tank is half full or less. Otherwise, it remains silent when I turn the ignition, and I've never heard it running at all during normal engine operation."

How long has your fuel filter been installed? It could be contributing to the noise. Otherwise, the pump will need to be replaced.

Mine is just under 2 years old and has (only) 58,000 km on it.
The fuel filter has never been changed; it's only due for replacement at the next service.
Approximately 60,000-mile inspection (WIV).

My pump actually *always* starts, no matter how full the...
"Tank" is (or was) always clearly audible - and it is especially noticeable now, for example.
"The tank is completely full, but it still doesn't run. Of course, that could be..."
...have now contributed to premature wear and tear.

How is this thing controlled? I have VAG-COM, and it shows...
but without any errors.

Regards,

Peter.

pschaefer wrote:

How is that thing supposed to be controlled?

Via relay, through the engine control unit.
Error messages only appear if the monitoring of the relay coil circuit detects any deviations. Whether the pump is running or not is not monitored.

My pump is also running constantly (I observed this for a while using an LED).

How is that thing supposed to be controlled?
Via relay, through the engine control unit.
Error messages only appear if the monitoring of the relay coil circuit detects any deviations. Whether the pump is running or not is not monitored.

My pump is also running constantly (I observed this for a while using an LED).

Could it be that in my AJM Bora, which also has a diesel-powered auxiliary heater connected via a T-piece before the engine, the fuel supply is only truly sufficient when the pre-pump is running?

'I've noticed for a while now that I always feel like the engine runs a bit better when the fuel gauge is just slightly above half full, even though the engine's power should theoretically improve continuously as the weight decreases.'

However, there are no jolts or significant potholes – it's hard to describe the feeling, but it's as if the car is 'more willing' to accelerate.

If applicable: Can I switch the pump to 'continuous operation' mode?
VAG-COM is available - knowledge is rather limited .

best regards
herwig

herwigw wrote:

I've noticed for quite some time that I always feel like the engine pulls a little better when the fuel gauge is just slightly above half-full, even though the engine's power should theoretically improve continuously with decreasing weight.

I would also recommend monitoring that with temporary LED indicators for now, if I were in your position.

Tap into the pump relay or the pump itself and check if it actually starts running only when the fuel level is below ~0.5.

If that's the case, you would need to rewire the relay, for example.

For some time now, I've noticed that I always feel like the engine pulls a little better when the fuel gauge is just slightly above half-full, even though the engine's power should actually improve continuously as the weight decreases.
I would also recommend monitoring that with temporary LED indicators for now, if I were in your position.

Tap into the pump relay or the pump itself and check if it actually starts running only when the fuel level is below ~0.5.

If so, you would need to, for example, rewire the relay.

aha - using VAG-COM would have been too easy .

For starters, it will probably involve occasional testing with the electrical tester.


Thank you, Ulf!

For quite some time, I've noticed that I always feel like the engine pulls better when the fuel gauge is just slightly above half-full, even though the engine's power should theoretically improve continuously as the weight decreases.
I would also recommend monitoring that with temporary LED indicators for now, if I were in your position.

Tap into the pump relay or the pump itself and check if it actually starts running only when the fuel level is below ~0.5.

If so, you would need to, for example, rewire the relay.

aha - using VAG-COM would have been too easy .

For starters, it will probably involve occasional testing with the electrical tester.


Thank you, Ulf!

My question was probably nonsense - sorry!

Apparently, I don't have a pre-lift pump at all: Besides the supply and return lines at the tank, there's only a two-pin connector, and according to a VW master technician, this means I don't have a pre-lift pump because those two pins are only for the fuel level sensor. Cars with a pre-lift pump would have a four-pin connector for the fuel level sensor.

Either I'm imagining things, or the improved acceleration when the fuel tank is only half full has a different cause.

The expert also mentioned that if I had a pre-pump, my auxiliary heating installation using a T-piece in the fuel line (instead of a dedicated fuel line from the tank) would be inadmissible, and he would expect major problems because the fuel might not flow easily enough through the pump when the pump is stationary (heater on, engine off).


best regards
herwig

Hi,

For PD engines, a separate fuel sensor is always required for the auxiliary heater. (There's even a special pre-assembled part from VW where this sensor is already integrated). For non-PD engines, the diesel can be tapped from the fuel line using a T-piece.
For no engine, the fuel pump must not be located without a T-connector *within* the supply or return line.

Regards,
Sure, here is the translation of the text from German to English:

'Micha'