Audi A5 TFSI rough idle, misfires

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rudolf
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Joined: Wed Sep 07, 2016 1:35 pm

Audi A5 TFSI rough idle, misfires

Post by rudolf »

Hello,

I have a problem with my personal car, an Audi A5 1.8 TFSI, MY 2008, CABD engine.
Bought the car in August 2018, took out the engine and rebuilt it. I wasn't the one doing the job, only assisted when I had time.
At first it had a hardly noticeable misfire, but we just accepted it as it was running smoothly.
* For reference, I used 5W30 VW oil (G 052167M4), but I have oil coming out everywhere, so the next step will be using 5W40 Motul X-clean. I've read about cases where the oil change helped. *
Once the cold weather arrived, the idle got worse. Sometimes not even starting on the first key. Once the engine warmed up, it ran smoother, but still not okay. The backfires while warming up are awful, hence I haven't driven the car for almost 2 months now, just checking this and that on weekends.
Since I ran out of ideas, I checked the compression with a gauge. I got values of 9-5-8-9 for cyl 1-2-3-4. Seemed too low, so I hooked up my Picoscope 4423 and the WPS500x to check it properly.
I have attached my findings for both cold and warm engine. The test was done with the fuel pump fuse removed, all coils disconnected, all plugs removed and full throttle pedal pressed while cranking.
I then started reading up on this on the pico website, training section.
If I understood correctly, my intake valves are retarded, which means that the timing is off. Assuming nothing has broken or got worn out in the 2.000 kms I've driven the car since rebuilding.
Hopefully this weekend, I will double check and do an idle measurement both cold and warm using the Pico guided tests.
Please share your thoughts on these findings.
Thank you in advance!
Attachments
Audi_A5_2008_cyl 4 warm.psdata
(966.6 KiB) Downloaded 505 times
Audi_A5_2008_cyl 4 cold.psdata
(1.44 MiB) Downloaded 425 times
Audi_A5_2008_cyl 3 warm.psdata
(1.02 MiB) Downloaded 434 times
Audi_A5_2008_cyl 3 cold.psdata
(997.1 KiB) Downloaded 418 times
Audi_A5_2008_cyl 2 warm.psdata
(1.03 MiB) Downloaded 431 times
Audi_A5_2008_cyl 2 cold.psdata
(2.94 MiB) Downloaded 444 times
Audi_A5_2008_cyl 1 warm.psdata
(964.49 KiB) Downloaded 420 times
Audi_A5_2008_cyl 1 cold.psdata
(902.68 KiB) Downloaded 436 times

ben.martins
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Posts: 539
Joined: Tue May 16, 2017 1:02 pm

Re: Audi A5 TFSI rough idle, misfires

Post by ben.martins »

Hello Rudolf,

Thank you for your post and taking the time to upload your captures. I've created references for the warm and cold captures you have created and attached them here for you to view so we can see all 4 cylinders compared to each other.

One thing that stand out on both is that cylinder 2 appears to have a much lower compression than the others. This isn't as much once warm but I think it is significant and something you might want to look further into. If the timing was off then I would have expected all cylinders to be the same as they'd all be affected equally.

I think timing is still important to verify though and to continuing checking with WPS500 whilst cranking, it will help if you can restrict the intake slightly as this will help reveal some detail with exhaust and inlet valve opening times but we can't now take the peak values as correct. As you have a 4 channel scope it would be great to see in-cylinder compression, crankshaft position and cam position sensors all on one screen to get a further detail.

If you need assistance with setting this up then please don't hesitate to get in touch.

Kind regards

Ben
Attachments
Audi compression warm with references from 2 3 and 4.psdata
(3.03 MiB) Downloaded 484 times
Audi compression cold with references from 2 3 and 4.psdata
(3.99 MiB) Downloaded 453 times

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