Pin-point performance issue on TFSI quattro

[prel2000]

Desperately trying to identify a common denominator which links performance of engine, exhaust sound, smoothness of power steering, braking performance.

I get varying levels of performance from my TFSI quattro (BWE engine). At times it feels quite lethargic where the engine struggles to breath, exhaust note is louder, power steering is heavy and braking performance lacks. At other times I get fantastic performance from all the above and it feels like car completely different car to drive.

The performance seems to improve after the car is driven and then left idle for 5 or so mins or if switched off and left standing and then re-started.

A lot has been spent on the car as I plan to keep hold of it for a while - please see signature for mods etc.

Just wondering if the issue is related to a sensor i.e. map sensor or 02 sensor etc. Would a fault display in the dash if these were on the way out etc?

Any help or some pointers in the right direction will be appreciated.

Thanks

 

[joinerman]

Try loosening the fuel filler cap when it's feeling gutless, listen for a whoosh of air entering the tank & try driving it with the cap loose.

 

[gary_a4_quattro]

Interesting question raised @prel2000 ( and a nice list of mods on ur car too ! )

I'll piggy back on this thread with interest if that's ok - I'm guessing mine isn't as pronounced as yours suggests to be, however the 'variable' performance effects mine , though it's not as dramatic I would say as the OP's. Haven't noticed any variance in braking performance , but there is a subtle change in exhaust note, smoothness and performance.
When it's good, it's seems the turbo spools up more immediately, lower down the rpm range and power delivery more linear. On a not so good day, I'd describe it as more turbo lag, coupled with a coarser engine note.

Interesting you should mention the fuel cap @joinerman , I'll certainly try that to see if there a correlation. Does this relate to the N90 valve ?

I'm sure there will be some positive suggestions to try , fingers crossed

 

[joinerman]

If the air vent in the filler cap is blocked or partially blocked you will be getting a vacuum in the tank causing fuel starvation, warmer days you will notice it more

 

[Charlie Farley]

I don't think there is a connection between the brakes not being consistant to be honest, I think that may just be a brake issue that is coincidental to the other issues you are having.
as gary says really aswell, he's also got the 220 special eds avant so we're all in the same boat really.
If I were you rather than take random guesswork at what maybe going on , try running vcds thoroughly and see what info is returned also any other data not just errors or fault logs issues, vcds does do a very good job at showing up problems and possible faultly components.
Another thing that maybe something to look into , during warmer weather and deffo humid wether the performance from the tfsi engine can vary a fair bit, I did notice numerous times that on warm and warm humid days the performance was effected a fair bit, the engine was just lacking that cooler charged air which is so important to the turbo engine, on cooler days it is brill but get some hot or clagy wether and you'll notice the effects.
have a look at your intercooler and make sure the ducts are nice and clear also the coolers themselves, I found a shed load of debris in both sides of mine including mouse nest and paper mixed with leaves that were all nestling well and truly into the ducts and blocking the air flow, it doesn't take a big restricition to cause an even bigger effect on the engine performance.
on the exhaust side of things mine has allways sounded a bit deeper on start up for a minute or so, sounding like a wet fart to be honest, had it checked and no leaks , so not sure why , anyway after changing the tips it sounds deeper all the time which I like, it used to sound a bit tinny when going through tunnels or under long brigdes etc but not now, sounds rather nice actually, just need to get time to fit the milltek .
DV valve is allways a prime suspect for erratic turbo performance aswell, when was your replaced if it has been that is.

 

[gary_a4_quattro]

My only thought of common denominator on @prel2000 's car was one of a vacuum issue, tho' that's doesn't really explain the power steering feel. Would a faulty pcv present those issues together ( tho again how the power steering is effected I can't think )

My next step was to do some logging in vcds see if that hi lights any boost issue, mine has a rev D diverted valve which I have read conflicting opinions about ( I know RTech favour the 'old' rev G diaphragm type and see it as a service part )

Be good to hear of any thoughts on logging, is it just requested vs actually boost or are there any parameters that should be recorded - hope this helps out the OP too

If the air vent in the filler cap is blocked or partially blocked you will be getting a vacuum in the tank causing fuel starvation, warmer days you will notice it more

Did I read something somewhere that the tank vapour is drawn into the inlet or pcv system somehow ???

 

[prel2000]

Have updated signature with all recent mods...reading through it again I've surprised myself on how much I've had done to it....

The car has always been run on super unleaded (95% v-power) and maintained regardless of cost. In the last year and half I've had chain and tensioner done, revised oil pickup, cam follower, cambelt, waterpump, clutch, flywheel, fuel filter, BR7 NGK plugs, 10-40 Mobil1, gearbox and diff oils changed, new thermostat, CTS, N75, N80 valves, brake pads all round, front bushes, links, suspension arms + mods in signature, - so I don't think symptoms are maintenance related.

From what I can remember the car has been doing this since I purchased it back in 2010 (2nd owner). One thing I can say is when its performing its SERIOUSLY PERFORMING....and a real pleasure to drive, which is why i'd like it to behave that way every time..... Or maybe its a bit like the Mrs who gives me a treat once in a while...

Anyhow as per all your suggestions;

VCDS is definitely something I have been meaning to have done. Need to find one locally to NE London.
Fuel /air mixture - def will try this out next time its feeling laggy
Intercooler - Ill get down there and give this a good clear out
PCV was changed to latest revision about 3 years ago - will it likely have failed again so soon? - I remember error on dash when it failed.
DV valve - I swapped out for Rev D soon after purchasing the car in 2010 and only recently upgraded to a GFB DV+ valve

Also I know it seems strange with regards to the power steering and braking performance but its def noticeable on how better these feel when its in one of its good moods....

Anwyay, appreciate all the help gents. Will keep you posted on progress and welcome any further suggestions.

 

[prel2000]

Just a quick update here all....
I had an issue whereby the connector on the vacuum pump was starting to wear and so causing a leak at the joint with the vacuum hose. A fix was applied by the very competent mechanic at a mates garage and now the car is feeling much livelier then has been for several months in-between.
Definitely an area of investigation that I would advise you to look at it if you've exhausted all other avenues to fix a similar issue.

 

[Darren1983]

Hi mate.

How did you discover that's where the leak is? I noticed mine seemed to have some movement in it the other month but assumed it was normal.


Thanks
Darren

 

[prel2000]

Mine was doing exactly as per this clip...


Sent from my SM-G935F using Tapatalk

 

[Darren1983]

Thanks chap. Il check mine when it's running.

Do you know how the mechanic fixed it.

 

[prel2000]

Superglued the plastic down and then applied strong bonding over the top to keep it that way. TBH I was happy to replace the pump but he convinced me his fix will work and it did for less then half for what it would have cost for a new one...wohooo..!

 

[Darren1983]

Weirdly I had the car running today and her a slight knocking/tapping coming from the back of the engine and it looks like it is the pipe going to the vacuum pump. I held it and it stopped tapping.

 

[Dani_B19]

Weirdly I had the car running today and her a slight knocking/tapping coming from the back of the engine and it looks like it is the pipe going to the vacuum pump. I held it and it stopped tapping.

I wonder if this is the cause of your issues Darren?

 

[Darren1983]

It's certainly possibility. I'm going to look into it and see if I can repair it or change the hose.

 

[prel2000]

Darren, I don't think it will be the hose and I certainly wont recommend you start there as its not a cheap item.
Get the hose disconnected from the plastic connector and see how much play there is between that and the housing of the pump. If there's play there and I been told there shouldn't be any, then that is most certainly where you problem lies. You will then need to get the pump off and apply the same fix as described above and see how you go. Couple of hours of labour and a few pounds (superglue and bonding). Def worth a bash at this before you start replacing bits.
FYI....A good check is to take the hose of from the other end whilst one side is still connected to the pump and check if there is some sort of vacuum. If yes then you know the pump is doing its job and the hose itself is most likely good too. Just the leak where the two connect to fix.

 

[Darren1983]

Thanks for the info. Without even taking the hose off I can see a lot of play in the connecter. When I wiggle the hose the connecter moves with it and when the engine is running there is a distinct tapping/knocking noise which stops when I hold the hose firm.

 

[Donfero]

Mine was doing exactly as per this clip...


Sent from my SM-G935F using Tapatalk

Had this issue, i got hold of a pump from an A5 just changed the nipple and the problem was gone!!

 

[Donfero]

Mine was doing exactly as per this clip...


Sent from my SM-G935F using Tapatalk

Had this issue, i got hold of a pump from an A5 just changed the nipple and the problem was gone!!

 

[Donfero]

Do you check your intercooler pipes for oil?

 

[Dani_B19]

What do you mean you just changed the Nipple?

 

[Donfero]

What do you mean you just changed the Nipple?

The black thing that the hose is attached to.

 

[Donfero]

What do you mean you just changed the Nipple?

The black thing that the hose is attached to.

 

[Darren1983]

been looking at this and thinking about it and I may be totally wrong but im not sure how it would affect the performance of the car?

on other tfsi engines the vacuum pipe tee's off and another pipe going to the inlet manifold but on the a4's it doesn't do this, it goes directly to the bulk head and the nipple on the manifold is capped.

I may be completely wrong but I cant see how it would affect performance if it isn't connected to the vacuum on inlet?

 

[prel2000]

Fix it and see....worked for me!

 

[Darren1983]

ive ordered so bonding glue so going to give this a try this week at some point.

 

[prel2000]

Thats it..should def notice a difference once connector is held down firmly.

Unfortunately my joy was short lived as the pump finally gave up and started to leak oil from the casing. £350 later and now on a new pump. Car is behaving the same as after the connector was fixed on the previous one.

 

[Darren1983]

Rubbish luck there bud. Least you've got it rectified now.

 

[Darren1983]

sorry just another quick one on the back of this, obviously when I remove the vacuum pump il need to replace the gasket. does anyone know the part number for this?