What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

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KimAndersen
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What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by KimAndersen »

According to the information I have from the Erwin Technical service system, there are two ways
to test the low pressure system in a 1.6 TDI engine - namely before and after the fuel filter.

A regular fuel pressure gauge (VAS 6551) is placed in series with the filter and the fuel pump is activated
by EOBD tests under "Actuator test" - in my case I used the VCDS software from Ross Tech.

During this test, the fuel pump must deliver at least a pressure of 4.5 Bar - this is theirway of specifying
the correct fuel pressure.

So far so good.

I then decided to do this test, but first with a regular fuel pressure gauge just to see if the fuel pump
could meet the specifications - before I connected my WPS500 pressure transducer and my picoscope software.

This test showed a fuel pressure of about 5 Bar the first 2 seconds of this actuator test and then drops
to a pressure of about 4.5 bar - so I would think that the pump has passed this test !.

The next test was with the WPS500 pressure transducer located in the same place as the regular fuel pressure gauge - so my expectations were the same in terms of the correct fuel pressure of around 4.5 to 5.0 Bar.

I am of course well aware that the WPS500 pressure transducer is far more precise and sensitive to pressure fluctuations in the fuel hose.

The next thing I saw on my Picoscope, I did not expect to see when I started the actuator test of the fuel pump.I noticed that the fuel pressure increased vertically above my 13.8 bar scale and then dropped to about 0.4 bar pressure - it looked very strange !!!.
FUEL PUMP ACTUATOR TEST VCDS
FUEL PUMP ACTUATOR TEST VCDS
This just raised a new question as to which of these two tests is showing the correct picture of the fuel pressure !.

I'm most likely the WPS500 pressure transducer shows the correct pressure, but I have to admit I'm a little confused in terms of the result of this test !.

The fuel pressure with the engine idling is around 0.5 bar with the WPS500 pressure transducer mounted in series with the fuel supply line before the fuel filter.
LOW FUEL PRESSURE BEFORE FILTER
LOW FUEL PRESSURE BEFORE FILTER

FUEL PUMP ACTUATOR TEST VCDS VACUUM
FUEL PUMP ACTUATOR TEST VCDS VACUUM

In the end I just want to say the car starts and runs well and there are no trouble codes in the engine management.

But I have experienced three times where the engine has gone into emergency mode and where the car would not really take some RPM.

In one case, I got a strange DTC regarding something with the fuel pump (unfortunately I do not remember the code).

Occasionally there may be a long start time, but no DTC is reported in the engine management, so it is not a persistent problem.

Why is there a difference between a regular fuel pressure gauge and then a WPS500 pressure transducer in terms of different pressure measurements and which are based on the same test?

Is the fuel in-tank pump defective. ?

I do not really seem to have found an answer to my two tests !!!.

Skoda_Octavia_2014_1.6TDI_Low_Fuel _Pressure_System_Test.psdata
Skoda_Octavia_2014_1.6TDI_Low_Fuel _Pressure_System_Tes
(24.25 MiB) Downloaded 231 times

Regards
Kim

victor2k
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by victor2k »

Hello,
According to the Bernoulli's equation the sum of the static pressure and dynamic pressure will be constant:if the WPS 500 adapter introduces a restriction, the static pressure will be a lower one,in some cases even negative.Also the value -1.5 Bar is a nonsense,you can't have a value lower than -1(at sea level),maybe you need to check the sensor accuracy.
Best regards
Attachments
IMG_20220505_100451.jpg
IMG_20220505_100509.jpg

Steve Smith
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by Steve Smith »

Hello and thank you for the post, sorry for the later reply

My first thoughts are "measurement error" where I suspect the AC coupling feature may have been active.

Looking at the psdata file, this is not the case

My next thought is the zoom feature of the WPS500 pressure transducer, could this have been accidentally activated?

Just looking through the Owners Guide for WPS 500 and the zoom feature:

Zoom modes 1 to 3

The zoom feature is used to show small signal details within a larger signal, such as
pulses from intake vacuum, or to amplify pressure pulses from the exhaust. It operates
by removing all of the voltage from the signal within the selected range below 100 Hz
and then magnifying the remaining signal.

Select the zoom using the zoom button shown in Section 5: “Front-panel controls”.
Continued pressing of the zoom button will step the level of amplification through the
three zoom modes. Press one of the range buttons to turn off the zoom


This does sound similar to AC coupling (Removing the voltage from the signal)

Food for thought at this stage as I would have expected to WPS to display static and dynamic pressure values as per the gauge but with the advantages of monitoring pressure change against time

I hope this helps, take care.....Steve

KimAndersen
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by KimAndersen »

Steve - I think you are right about my "measurement error". Somehow I must have enabled my zoom feature without being aware of this.

I have made some new measurements of the fuel pressure before the fuel filter and they now show the correct pressure during the "Fuel pump actuator test" and start up of the engine.

Everything is as it should be in terms of the right fuel pressure. It's nice to know that your equipment is working properly.


FUEL_PRESSURE_IDLE_SPEED_BEFORE_FUEL_FILTER.jpg

FUEL_PUMP_ACTUATOR_TEST_VCDS.jpg

Thanks for your help Steve and Victor2k - it's much appreciated




Best regards
Kim

Steve Smith
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by Steve Smith »

Thank you for the feedback Kim, this is all teamwork.

Take care.....Steve

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leonardorj
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by leonardorj »

Mesmo usando um transdutor de pressão. Eu sempre testo a vazão. Certamente existe um módulo de bomba de baixa e seu pwm

KimAndersen
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by KimAndersen »

Just to round off the problems I've had with the fuel pump in the Skoda.

I ended up changing the fuel pump, as it has driven 227,000 km and there had been a few times when the car had gone into emergency mode - so it was time for a new pump.

Regarding the previously mentioned DTCs which I could not remember - then I found a VCDS log file where the most known DTCs ( P308D 00 [101] - RPM too low ) were present together with the DTC ( P3043 00 [100] - Mechanical failure ).

So the old fuel pump from Continental was replaced with one from Stark with part number ( SKFU-0410207 ).

As a frequent user of the Picoscope, there is no better opportunity to measure a brushless three-phase fuel pump than now. But how can you test this BLDC pump and to that I can only say that Steve Smith has made a fantastic case study " Maths is cool " regarding three phase BLDC motors, which is a great help when you have to test this fuel pump.

A thing or two that I have thought about the previously mentioned DTC P308D and P3043 and what criteria are needed - before the engine management sets these DTCs.

A test I had thought of doing was to put a variable 1 ohm resistor between one of the phase windings
that goes from the pump module (J538) and to the pump itself (G6) - this test is also called an " Unbalanced Resistance Test ".

New Fuel Pump Unbalanced Resistance Test
New Fuel Pump Unbalanced Resistance Test

The next thing I did was to put an amp clamp around the phase winding where I had placed my variable resistor and then slowly turn up the resistor to then observe my picoscope amp measurements.

I recorded the amp reading on the one phase winding, but I didn't save my reading (sadly) - but what I saw on the picoscope was a very distorted amp reading as I would expect when inserting a resistor into the circuit.

When the resistance reaches 0.4 ohms, the glow plug lamp starts flashing, which means there is one or more DTC errors in the fuel system and at the same time the pump starts making some noise as if there is air in the system.

The next step I took was to connect my VCDS diagnostic tool and see which DTCs the engine management had set and sure enough - there were two DTCs present in the ECU - namely (P308D) and (P3043) which are the most common DTCs regarding the problems you can get from the fuel pump into the tank.

I also tried disconnecting a phase winding completely, just to see what DTC comes up and if the car can be started.
No - it cannot be started with only two phase windings and it sets the following DTC ( P3044 00 [100] - Short Circuit ) which means that the current in the phase winding is greater than 25 amps.

I think these DTCs could just as well be from a bad fuel pump module ( J538 ) as from the fuel pump.
After all, there are 6 mosfet transistors built into the pump module - so just a small amount of resistance
in one of these mosfet's (let's just say 0.4 ohms) could create the same DTCs in the motor control as the pump itself.

When I look at this waveform which shows the phase current on a single phase winding and then the phase voltage on the three phases and subsequently compare this with Steve Smidt's case study, I see some differences between them.

My question is then.
Is my waveform a known good capture of an engine running at idle (770 RPM) and with a fuel pump at 3582 RPM correct?

I have used a multiplication factor of 2 - i.e. the same as in Steve Smidt's case study.

New Fuel Pump Brushless 3 Phase RPM Measurement
New Fuel Pump Brushless 3 Phase RPM Measurement

I'm a bit unsure about the rpm on the fuel pump, whether I've put the rulers in the right places on my waveform - it looks a bit low, but when I look at the specifications on a Continental fuel pump for a diesel engine, it's stated at 5800 RPM.

I am well aware that it depends on the load on the engine and thus also the reference signal (PWM) from the engine control - can anyone tell me what the fuel pump RPM should be when the engine is idling !!!.

There are so many ways to test this brushless motor and here it is always good to have a known good waveform when you are facing a diagnostic problem.

I think we might as well get used to testing these brushless motors now - they have been here for a few years and there will probably be more of this type in the cars today.

I'll stop with my waffle now or it won't end. :wink:

Best regards
Kim

NEW_FUEL_PUMP_3_PHASE_BRUSHLESS.psdata
New Fuel Pump Brushless Style
(650.42 KiB) Downloaded 184 times
NEW_FUEL_PUMP_PHASE_TO_PHASE_VOLTAGE_DIFF_PROBE_TA057.psdata
New_Fuel_Pump_Phase_To_Phase_Voltage_Diff_Probe_TA057
(421.73 KiB) Downloaded 170 times

tintoverano
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by tintoverano »

I've always wanted to try this method form picoben: https://www.picoauto.com/library/traini ... _xXlEuXHZk, but never got to it

KimAndersen
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by KimAndersen »

I'm just a little unsure if "Martin's Method" can be used on this type of brushless motor. This motor uses 120° Square-Wave Commutation and not sinusoidal (sine-wave) commutation as I believe was used in Ben's case.

But I'm sure Ben can answer this question ?.

Steve Smith
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Re: What is the correct way to test the fuel low pressure system on a Skoda Octavia 1.6 TDI - CHLA engine type?

Post by Steve Smith »

Hello and thank you for the posts and the reminder about this forum post viewtopic.php?p=100521#p100521 looking at BLDC motors

Regarding pump speed Kim, assuming your motor incorporates a 4-pole rotor, then the number of electrical cycles per one revolution of the pump/rotor is 2

In the forum post link above, we to were handling a VAG pump (Audi SQ5) where our pump speed (after fix) at idle was 3206 rpm with 5.439 A consumption (3 phases) which is not too far away from your 3582 rpm
The SQ5 pump speed (after fix) increased to 7767 rpm under load.

I agree with you Kim, these are figures based on our theories and it would be good to define a typical BLDC pump speed at idle. Does VCDS incorporate a pump speed value for verification?

Assuming our math’s is correct, prior to replacement of the SQ5 pump, the pump speed appears to max out at 10,000 rpm with 7.6 A consumption (3 phases) which potentially serves as an indicator of delivery failure (Remember this pump could not generate sufficient flow to achieve the required pressure)

Just looking at the frequency of the current in your capture "NEW_FUEL_PUMP_3_PHASE_BRUSHLESS" we have 119.3 Hz, which again is similar to the value recorded in Image 8 A in the above forum post (109.1 Hz)

At this stage we can surmise with the engine at idle speed:
Pumps speed approx. 3200 – 3600 rpm
Pump current frequency approx. 108 – 120 Hz
Average current consumption (single phase) approx. 1.8 – 2.2 A

In order to compare current values in a single phase I have used the math channel LowPass(abs(A)*0.333,50) for capture "NEW_FUEL_PUMP_3_PHASE_BRUSHLESS" (see below)
Image 1A
Image 1A
and LowPass(abs(D)*0.333,50) for our capture used in the BLDC Math’s is cool forum post
Image 8 A from BLDC Maths is cool forum post
Image 8 A from BLDC Maths is cool forum post
It is worth noting that these comparisons are for differing fuel systems (one gasoline and the other diesel) Therefore we should make allowances for the differences in pumping medium and the design of the fuel systems with regards to recirculation etc.

Looking at this from another angle, I do remember studying my own fuel pump from a BMW 320d (F31) here viewtopic.php?p=99974#p99974 using NVH due to a noise generated during the low delivery rate setting of 60 l/h
Image 3A
Image 3A
In this forum post we identified excessive noise at a frequency of approx.48.9 Hz (x 60) = 2934 rpm during the lower delivery rate setting. It would be foolish to assume this is an accurate representation of pump speed; I do however find this coincidental we are around the 3000-rpm mark once again (could this be our fundamental frequency assuming the pump is generating one disturbance per revolution?)

Regarding the Martins Method, most certainly YES. We will however need another phase current (ideally all 3) in order to plot each against one another

We could take advantage of our Low pass filter option when plotting X&Y at time frames faster than 200 ms/div (Block mode)

Using a 200 Hz low pass filter for all phases will support the formation of the desired perfect circle
Image 4A
Image 4A
I hope this helps and food for thought as ever, take care……. Steve

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