Relative Compression/First Look Advice VAG PD105

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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
VO09 DZE Cranking and Crankcase Pressure.psdata
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VO09 DZE Cranking and Inlet Manifold Pressure.psdata
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VO09 DZE Cranking and exhaust pressure.psdata
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VO09 DZE Cranking and Crankcase Pressure.psdata
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Posts: 1
Joined: Thu Feb 17, 2022 9:49 pm

Re: Relative Compression/First Look Advice VAG PD105

Post by Oliwaa »

Did you find the fault?

If not, is there any weird sounds from intake like popping or backfire?

These engines have a common issue where customer doesnt change oil often enugh and the cam lobes start to wear on the hydraulic valvelifters, so tha cam becomes round and the lifter is punctured and preventing oil pressure in it.
It often ends in one or more cylinders not opening intake or exhaust valve.

Taking off the valve cover is about 10 to 30 minute job and easily to look at the lobes and lifters.
And if you open the airbox it often smells exhaus while idling and you feel the backblow.

It is one of my first tings to look at after checking fault codes 😅

Also common with injectors rattling and destroying the seals on them, always change those as well when changing camshaft and lifters.

Oh and 10% on relative compression seems a lot

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