VW TDI Pumpe-Düse with extended holding current

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VW TDI Pumpe-Düse with extended holding current

Postby KimAndersen » Thu Jul 16, 2015 8:14 pm

For those who likes diesel engines from Volkswagen which are equipped with a 2.0 Pumpe-Düse engine (engine code BMM) are here something that I would like to share with you.

As I´m a curious to know how things works and sometimes not, wanted I to find out the relationship between fuel temperature and the injection time on a VW Pumpe-Düse engine were.

This image is showing the electrical current ramp on pumpe duse injector number 2 together with a reference waveform in the background. As noted is there a difference between those waveforms, where the reference waveform have a slightly longer holding current - precisely 234 microseconds.

PD_EXTENDED_HOLDING_CURRENT.jpg
VW Pumpe Düse - extended holding current


The long holding current is something I made by putting a 330 ohm resistor inside the fuel temperature sensor (G81) connector and thereby simulating a fuel temperature in the return hose at 101 degrees celsius which of course is a very high fuel temperature compared with the normal reading at around 70 degrees celsius.

A question for you readers - is the longer holding current equal with a longer injection time and thereby more fuel is being injected into the engine.

I know, I could just have connected my VCDS tester and I would have the answer, but I forgot to make that test.

These are my thoughts whether or not this can be used in a diagnostic context will the time show, I just wanted to show that this can be seen in the electrical current ramp with a Picoscope.

VW_TDI_2.0_PD_CURRENT_RAMP_EXTENDED.psdata
VW Pumpe Düse - extended holding current
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Regards
Kim :wink:
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Re: VW TDI Pumpe-Düse with extended holding current

Postby Robski » Thu Jul 16, 2015 9:41 pm

did you take into account smooth running values ?
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Re: VW TDI Pumpe-Düse with extended holding current

Postby KimAndersen » Fri Jul 17, 2015 3:05 pm

Robski wrote:did you take into account smooth running values ?


No, I didn't.

My theory or conclusion regarding the extended holding current may not be the whole true. Today
was I trying to replicate the same test as yesterday, but this time with a warm engine and this
time I couldn't extend the electrical holding current by the 330 ohm resistor in circuit.

The test today was conducted with a 5K ohm potentiometer in circuit with the fuel temperature
sensor (G81) and the objective with this test was to simulate different fuel temperature from as
low as 0 to 140 degrees celsius and at the same observe the holding current ramp.

This is not easy task with a potentiometer in circuit you can easily make to big adjustment and
hit the upper threshold at 140 degrees and when this happens, it slowly descends to the default
value at 40 degrees celsius and a DTC are present in memory together with some valuable freeze
frame data.

There is no doubt that it has a big influence on engine behaviour when you listen to it. A simulated high fuel temperature will make the engine run more smoothly or softer, but this is because it retards the injection point.

I believe that my observations with a cold engine still is true or at least to someone else have some more vital information regarding PD injector holding current and the fuel temperature.

Regards
Kim :wink:
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Re: VW TDI Pumpe-Düse with extended holding current

Postby clt » Wed Jul 22, 2015 12:13 pm

Hey Kim
I do not now if you can use this, but this is what seat writes about the fuel temperatur sensor.

SIGNAL APPLICATION
This signal is used by the control unit to
determine corrections in the volume of fuel to be
injected. To determine this value, it first makes
an internal calculation based on the sender
signal, in order to determine the fuel density.
The fuel density has an influence on the mass
of fuel being injected, since for the same
injection time, the lower the fuel density, the
lesser the fuel mass injected and vice versa.

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Re: VW TDI Pumpe-Düse with extended holding current

Postby KimAndersen » Thu Jul 23, 2015 11:00 am

Hi Claus

Thanks for the information but I already knew this.

The manufacturers in the automotive industry ain't that informative in telling about how the
calculations are done inside the ecu - I wonder why !!!.

One thing I know about the fuel temperature sensor (G81) which mainly are used in PD are that
it's used as substitute values for the coolant temperature sensor in terms of a fault or a diagnostic trouble code are present in the ECU memory and that goes the other way around too.

But, what I discovered when I was trying find some information about the fuel temperature sensor
(G81) is that the resistance table over the fuel temperature (G81) is identical with engine
coolant temperature sensor and that I didn't know before this investigation.

I´m not finished with my investigation of the fuel temperature sensor yet, so time will show
what I can find out about this sensor.

Regards
Kim :wink:
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