Relative Compression/First Look Advice VAG PD105

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philreed52
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Joined: Sun Sep 19, 2021 1:25 pm

Relative Compression/First Look Advice VAG PD105

Post by philreed52 »

Good Afternoon,

Please excuse me if there is something obvious that I am missing (I am very new!) but here goes. This is my first unsupervised test using the Pico (see my intro) and my "practice" vehicle is a VW Passat PD 1.9 BXE with rough running and over fuelling when cold. I began my diagnosis by conducting relative compression finding that 1 cylinder is very slightly lower than the others although within 10% difference.



I then used a FirstLook sensor to check the crankcase, inlet (fitted to the airbox lid at the vacuum pipe connection) and exhaust.

Crankcase pulses uniformed.

Inlet manifold uniformed noting a drop where the inlet valve opens
Exhaust- now this is where i came unstuck. You will see that the cylinder that looks lower than the other 3 coincides with a drop in exhaust pulses. I would have thought this drop would appear at the following peak when the suspect cylinder was on its exhaust stroke?



I hope my waveforms attach properly!
Any advice will be greatly appreciated

Thank You
Phil
Attachments
VO09 DZE Cranking and Crankcase Pressure.psdata
(1.67 MiB) Downloaded 38 times
Volkswagen_Passat_2009_Diesel_20210919-0001.psdata
(911.09 KiB) Downloaded 29 times
VO09 DZE Cranking and Inlet Manifold Pressure.psdata
(1.49 MiB) Downloaded 24 times
VO09 DZE Cranking and exhaust pressure.psdata
(1.57 MiB) Downloaded 21 times
VO09 DZE Cranking and Crankcase Pressure.psdata
(1.67 MiB) Downloaded 24 times

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