850 T5R momentary cut out under hard acceleration

[PSJVTHEBEST]

A quick update. I have just taken her out again and with the fault codes cleared and TRACS off, there is no change, the quite violent hesitation occurs around 4500-5000 rpm in sport mode and seemingly just as it wants to change up a gear. No issue when stationary - she winds up to 6k without an issue. When cooled down I will check the wastegate actuator - it does seem a little stiff.*Dancake, I will definitely be interested in your TCV!

[Dancake]

I'll see if I can retrieve it tonight or tomorrow.

[PSJVTHEBEST]

I forgot to mention that immediately after switching on the engine the ABS warning light came on and when I got back after the test drive and checked the codes the 424 ('Pressure switch for TRACS, faulty or short circuit') was back!

[Baffler]

Originally Posted by PSJVTHEBEST

I forgot to mention that immediately after switching on the engine the ABS warning light came on and when I got back after the test drive and checked the codes the 424 ('Pressure switch for TRACS, faulty or short circuit') was back!

Interesting...this is the fellow located on the brake master cylinder? Perhaps this is linked to the brake lamp switch (did you mention a previous repair?) or an early indication of solder joints failing on the ABS module?

In the meantime try clean your existing TCV with some carb cleaner and, once dry, spray some dry PTFE through it, if you have some to hand, or a couple of drops of 3in1 oil and shake out any excess.

[PSJVTHEBEST]

Thanks Liam. I also forgot to mention that the ABS warning light went out after about a quarter mile on braking.
From what I have read, the TRACS pressure switch is integrated into the ABS module (haven't looked for that yet!) but you are right that the brake pedal switch did play up and I cleaned it and now the brake lights work. But I believe it does have something to do with TACS - I need to research that!
Thanks for the advice on the TCV.

[Shinsplintz 101]

You can by a new oem tcv for about £40. Made by PIERBURG. Just Google it.

[Luxobarge]

Originally Posted by Shinsplintz 101

You can by a new oem tcv for about £40. Made by PIERBURG. Just Google it.

Correct, exactly what I did, and it's still working fine.

[PSJVTHEBEST]

Thanks Shinsplintz and Luxobarge. Dancake is kindly sending his TCV for me to try first. I still wonder if the (recurring) 424 (TRACS) code is signalling a cause or contributory cause of the problem though!

[Baffler]

Originally Posted by Dancake

I replaced the original Pierburg TCV (part number 7.21681.01 12) with a new Pierburg TCV (part number 7.28197.16.0)

Amazingly, a Google search of said replacement TCV actually brought up above posting from Dancake in: What did you do to your 850/X70 today???

Originally Posted by PSJVTHEBEST

I still wonder if the (recurring) 424 (TRACS) code is signalling a cause or contributory cause of the problem though!

It may very well be contributing to the issue and will certainly need addressing...especially before the next MOT.

A new TCV would help confirm whether your existing TCV is doing it's job, or not, and would be £40 well spent if nothing only to have it in your spares bin. You can then focus your attention on the TRACS fault.

I would hate to see you throwing more parts at it so there are some great and recent ABS fault finding threads from Duke1, Luxobarge and El Padrino which may help to effectively identify and diagnose the issue.

[PSJVTHEBEST]

Thanks Liam, great advice.