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

KimAndersen · Post by **KimAndersen** » Tue May 03, 2022 7:29 pm

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

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

: 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 27 times

Regards
Kim

victor2k · Post by **victor2k** » Thu May 05, 2022 7:43 am

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

Post by **Steve Smith** » Thu May 05, 2022 3:08 pm

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 · Post by **KimAndersen** » Sat May 07, 2022 6:31 pm

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.

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

SKODA_OCTAVIA_2014_1.6_TDI_FUEL_PRESSURE_ACTUATOR_TEST_BEFORE_FILTER.psdata: (8.68 MiB) Downloaded 18 times

Skoda_Octavia_2014_1.6TDI_FUEL_PRIMING_FUEL_PRESSURE_STARTUP_ENGINE.psdata: (8.6 MiB) Downloaded 14 times

Best regards
Kim

Post by **Steve Smith** » Mon May 09, 2022 8:14 am

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

Take care.....Steve

leonardorj · Post by **leonardorj** » Mon May 16, 2022 12:51 am

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

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