2014 A6 split-second power loss

[Toby73]

I have a 2014 A6 Avant and I'm getting a really strange power loss when driving that lasts for less than a second.... I could be in any gear and it's not just when accelerating, but if I am accelerating hard the power loss is much more noticeable - really jolts the car and throws you forward in your seat. To passengers it feels like I have dabbed the brakes. If it happens when I'm pulling away it feels like I have stalled but then the power comes back. It's like some kind of extreme mis-fire. This happens on average once a day.  

Another issue I have which might help diagnose the first problem (if they are related) is that I'm losing coolant but it's been into the garage and they say there is no apparent leak from the tests they've done and they have checked the oil for any milky-ness. I'm thinking maybe head-gasket but wouldn't I be seeing more regular symptoms and milky oil? Starting it seems a little rough and sluggish and very occasionally it doesn't turn over first time but have replaced the battery. Seems to run fine once started. I'm not sure what checks you do for a head gasket but pretty sure the garage looked into that.

I'm really hoping all these mystery problems are somehow related but have a feeling it is going to be expensive. If anyone can help with advice I would appreciate it. It's going back into the garage next week for another look but they seem to be scratching their heads too. 

[Steve Q]

Have you had a diagnostic check to see if any fault codes flag up? 

Could it be the turbo? 

If you're loosing coolant then it's got to be going somewhere. Could be a failing expansion tank cap. 

[Stevey Y]

On 4/21/2023 at 9:23 AM, Toby73 said:

I have a 2014 A6 Avant and I'm getting a really strange power loss when driving that lasts for less than a second.... I could be in any gear and it's not just when accelerating, but if I am accelerating hard the power loss is much more noticeable - really jolts the car and throws you forward in your seat. To passengers it feels like I have dabbed the brakes. If it happens when I'm pulling away it feels like I have stalled but then the power comes back. It's like some kind of extreme mis-fire. This happens on average once a day.  

Another issue I have which might help diagnose the first problem (if they are related) is that I'm losing coolant but it's been into the garage and they say there is no apparent leak from the tests they've done and they have checked the oil for any milky-ness. I'm thinking maybe head-gasket but wouldn't I be seeing more regular symptoms and milky oil? Starting it seems a little rough and sluggish and very occasionally it doesn't turn over first time but have replaced the battery. Seems to run fine once started. I'm not sure what checks you do for a head gasket but pretty sure the garage looked into that.

I'm really hoping all these mystery problems are somehow related but have a feeling it is going to be expensive. If anyone can help with advice I would appreciate it. It's going back into the garage next week for another look but they seem to be scratching their heads too. 

Hi head gaskets do not always put water in to the oil it is more the other way where gas is introduced in to the cooling system and via the exhaust gas escape water can get back the other way in to a cylinder, ask the garage to do a sniff test on the header tank, this involves !Removed! an adapter with a reservoir of the testing fluid to the expansion tank then run idle for 20 mins, the fluid will change colour if it detects exhaust gas, I agree with Steve a full scan is your best route.

Steve.

[Toby73]

Many thanks Steve 1 and Steve 2! Sorry I have only just seen these responses - it's in the garage today so I forwarded your comments in case it helps them. Waiting for the dreaded phone call! Will post an update if there is anything interesting to report

[Magnet]

Hello Toby,

How much coolant is it losing over say 200 miles or per week? 
Kind regards,

Gareth.