Sluggish/Limp/No boost - 8p a3 2.0tfsi quattro

[abstract97]

Hi,

I've recently bought an a3 and it's suffering from a huge performance drop, it struggles to go above 40-50mph depending on the road and the revs don't budge when going up a hill, it's incredibly sluggish. I can hear the turbo spool and upon deceleration i can hear pressure being released and there is a slight tinny rattle. I've scoured these forums and the rest of the web for potential causes but each one has been a dead end.

The car has only done 60K and is still all OEM, apart from an induction kit that the previous owner fitted.

These are the following things I've checked and done.

- No smoke from exhaust
- No EML

- Scanned with VCDS, only fault shown is relating to the haldex pump, don't think this would cause performance drop/no boost.

- Smoke tested, with no leaks found
- Checked all Intercooler pipework
- Checked vacuum lines, found a small crack so replaced them, these run between the manifold and vac pump.
- Replaced brake booster line
- Checked PCV system, no leaks
- Replaced diverter valve for a G generation
- Checked and cleaned MAF, obd data logs indicate this is operating normally
- N80/Evap has been checked and is operating normally
- O2 sensors removed to check Catalytic Converter flow and made no difference.

I've just taken off the downpipe as a final option today to check the condition of the turbo wastegate and it looks great. No play in either the turbine or the wastegate. The turbine spins freely and the wastegate is absolutely solid and doesn't move.

I've turned the car over with the downpipe off and the wastegate stays shut and doesn't open either. The actuator rod behind is in good condition and hasn't sheared off.

I'm out of ideas on what could be causing this now and i can't find any other potential causes.

Can anyone help?

 

[kudi009]

Not too familiar with the TFSI engines but if you can hear the turbo spool normally, and the boost / intercooler piping is all connected & in good condition, I'd think it would either be a faulty actuator or a broken shaft (so the exhaust side is spooling but not the intake, but I think this would be very loud)

 

[abstract97]

Not too familiar with the TFSI engines but if you can hear the turbo spool normally, and the boost / intercooler piping is all connected & in good condition, I'd think it would either be a faulty actuator or a broken shaft (so the exhaust side is spooling but not the intake, but I think this would be very loud)

I've had an endoscope into the intake side/compressor housing and the compressor wheel spins freely when I turn the exhaust turbine.

I originally thought the actuator/wastegate had failed as there was a loud tinny rattle upon letting off/deceleration. I've inspected both - the actuator rod is solid attached at both ends and doesn't move. The wastegate penny washer is also fully sealed to the turbine housing.

Could the N75 that supplies vacuum to the actuator cause an underboost if it failed, despite no errors being thrown/CEL? I've only heard of overboosting with the N75.

 

[kudi009]

I originally thought the actuator/wastegate had failed as there was a loud tinny rattle upon letting off/deceleration. I've inspected both - the actuator rod is solid attached at both ends and doesn't move. The wastegate penny washer is also fully sealed to the turbine housing.

Could the N75 that supplies vacuum to the actuator cause an underboost if it failed, despite no errors being thrown/CEL? I've only heard of overboosting with the N75.

I know that for some petrol engine codes, there was an infamous issue with the wastegate arm rattling with a similar noise to what you describe, fixed with a little clip, though you probably know about that.

I'm not sure if the actuator / N75 could fail without a CEL but at this point you seem to have ruled out pretty much everything. A simple test would be to apply vacuum directly to the actuator using a bleed kit and see if the arm moves freely - that could point you at either the actuator or the N75

 

[abstract97]

I know that for some petrol engine codes, there was an infamous issue with the wastegate arm rattling with a similar noise to what you describe, fixed with a little clip, though you probably know about that.

I'm not sure if the actuator / N75 could fail without a CEL but at this point you seem to have ruled out pretty much everything. A simple test would be to apply vacuum directly to the actuator using a bleed kit and see if the arm moves freely - that could point you at either the actuator or the N75

Tested the N75 this morning and it seems like it's working.

Absolutely no idea how to proceed.

 

[kudi009]

This guy has similar symptoms as yours and it turned out to be the ECU

Audi 2.0 TFSI no boost , major headache

Hi .. new to here, been lurking for some time now.. Could do with some help .. Have brought a 2005 A4 2.0 TSFI which has had a light bump to front. All repaired now and itching to drive it, but cant :frown: Car doesn't rev over 4k and turbo doesn't 'kick' Ive had every possible reader scanner...

www.audi-sport.net

I'd do another check over of all sensor values with a fine-toothed comb as well
Don't think anybody would blame you for taking it into a professional at this point!

 

[abstract97]

This guy has similar symptoms as yours and it turned out to be the ECU

Audi 2.0 TFSI no boost , major headache

Hi .. new to here, been lurking for some time now.. Could do with some help .. Have brought a 2005 A4 2.0 TSFI which has had a light bump to front. All repaired now and itching to drive it, but cant :frown: Car doesn't rev over 4k and turbo doesn't 'kick' Ive had every possible reader scanner...

www.audi-sport.net

I'd do another check over of all sensor values with a fine-toothed comb as well
Don't think anybody would blame you for taking it into a professional at this point!

I'm reluctant to taking it to the stealers as they misdiagnosed previous issues on my previous cars. Hard to find an honest independent these days as well.

I'm going to go over everything again I think, potentially might have missed something. Had the ECU benched so I can rule that out.

 

[abstract97]

Did some more data-logging with VCDS.

I put the car into 2nd gear and stamped my foot. The green line indicates the N75 duty cycle. Goes up to 94% which (I believe, If I understand correctly) closes the wastegate as the ECU requests boost.

The turbo slowly, does indeed start to provide the requested boost as per the actual pressure shown by the blue line. (pink line being requested/specified).

The WGDC / N75 then drops to 30% just shy of 1900 RPM.

Peak MAP (during this log) @ 4,800 RPM measures 1480 millibar, takeaway atmospheric pressure (around 1010 millibar) gives me 470 millibar aka 6.8 PSI of boost pressure being made by the turbo.

If I've done my research correctly, at 2,000 RPM the KO3 should roughly produce 700 millibar (or 10 PSI) of boost, but during my log, the requested boost pressure at 2,000 RPM was only 410 millibar (5.9 PSI) and the actual boost was 250 millibar (3.6 PSI).

At this point could there be an issue with another part of the engine, perhaps the fueling system? Why would the ECU only request such a low air pressure - or am I interpreting these logs wrong?

I did another logging session for the fuel rail pressure, and that seems to be in normal operating values, between 30 and 120 bar.

Anyone else shed any light onto my situation?

 

[abstract97]

Here's the base log for more info.

Engine Speed - (G28)​	Boost Pressure - Control (N75)​	Boost Pressure - (specified)​	Boost Pressure - (actual)​
/min​	%​	mbar​	mbar​
800​	0​	330​	1010​
840​	0​	330​	1010​
840​	0​	330​	1010​
800​	0​	330​	1010​
800​	0​	330​	1010​
800​	0​	330​	1010​
800​	0​	330​	1010​
800​	0​	360​	1010​
800​	0​	360​	1010​
800​	0​	360​	1010​
800​	0​	360​	1010​
800​	0​	360​	1010​
800​	0​	360​	1010​
840​	0​	360​	1010​
800​	0​	360​	1010​
840​	0​	360​	1010​
840​	0​	360​	1010​
840​	0​	350​	1010​
920​	0​	650​	1020​
1120​	63.9​	1200​	1020​
1200​	69.4​	1220​	1060​
1120​	94.9​	1310​	1080​
1280​	94.9​	1380​	1100​
1400​	94.9​	1490​	1130​
1640​	94.9​	1540​	1160​
1840​	94.9​	1490​	1210​
2000​	52.9​	1420​	1260​
2200​	38.8​	1350​	1300​
2400​	29.4​	1340​	1330​
2600​	29​	1330​	1350​
2840​	26.7​	1370​	1370​
3040​	27.5​	1390​	1370​
3240​	29​	1390​	1390​
3480​	29​	1400​	1390​
3680​	29.4​	1420​	1400​
3920​	31.8​	1440​	1410​
4120​	33.7​	1440​	1430​
4280​	34.9​	1450​	1450​
4520​	36.5​	1460​	1450​
4680​	37.6​	1480​	1460​
4680​	39.6​	1310​	1480​
4800​	0​	540​	1280​
4280​	0​	310​	1130​
3640​	0​	310​	1070​
3040​	0​	320​	1060​
2520​	0​	310​	1050​
1960​	0​	290​	1040​
1520​	0​	270​	1040​
1240​	0​	270​	1030​
1040​	0​	280​	1020​
920​	0​	290​	1020​
840​	0​	310​	1020​
840​	0​	310​	1010​
840​	0​	310​	1010​
840​	0​	310​	1010​
840​	0​	300​	1010​
840​	0​	300​	1010​
840​	0​	290​	1010​
840​	0​	290​	1010​

 

[kudi009]

I'm well out of my depth now..! I don't suppose there's a metric in VCDS for actuator sensor, in case the vaccuum from the N75 isn't being translated fast enough into actuator movement?

 

[abstract97]

I'm well out of my depth now..! I don't suppose there's a metric in VCDS for actuator sensor, in case the vaccuum from the N75 isn't being translated fast enough into actuator movement?

Nah there's nothing of the sort. The WGDC indicates the n75 is working and the actuator is doing it's job, as the boost immediately starts climbing.

My concern is why the ECU is only REQUESTING such a low boost amount, it should be much higher which leads me to believe there's something else within the engine ecosystem causing the problem.

 

[abstract97]

So, for those interested I figured it out. TLDR - It was the timing belt. 4 teeth out on the exhaust camshaft sprocket to be exact. I'm surprised the engine was still running and hadn't bent any valves.

One of my other friends who had VCDS checked a few other measuring blocks I missed, found out the engine was misfiring in each cylinder, despite sounding and idling OK and having brand new coil packs and spark plugs. We then checked measuring blocks 091, 093, and 094. The timing was being pulled to the limit at -8 degrees, compared to the specified value of 28, which made us check the belt. Turns out it had never been changed, it was frayed, and had bits missing. I replaced the belt over the weekend and now the engine is running wonderfully.

Find attached a few photos of the belt, and timing retardation before/after. If anyone else has similar issues, make sure you check the timing retardation.

Shoutout to @kudi009 for your quick responses and for attempting to help diagnose my issues.

My final concerns - the Phase Position Bank 1 (If I'm correct) is to do with the timing chain? I've taken the car out for a drive and done some final logs and the Specified vs Actual cam adjustment values are perfect now, always less than a degree of difference, which would indicate the cam adjuster is working fine, but the phase position is staying at -10. I was going to change the timing chain anyway and have a new VVT solenoid on the way, I'm uncertain on why this is at -10. Shouldn't it be close to 0??

 

[kudi009]

Wow! That's totally unexpected.. I would have never considered the timing to be at fault here because, as you say, it's normally very obvious.
Kind of silly as well that despite being so far out there was no CEL..
Very well done on figuring it out basically by yourself, I'd have sent it to the garage long ago..

 

[abstract97]

Wow! That's totally unexpected.. I would have never considered the timing to be at fault here because, as you say, it's normally very obvious.
Kind of silly as well that despite being so far out there was no CEL..
Very well done on figuring it out basically by yourself, I'd have sent it to the garage long ago..

Yeah! I never expected it either! The engine didn't sound like it was misfiring and it was driving fine, just no boost.. Honestly never would have thought to check timing.

I made a vow to never take it to a garage again unless absolutely necessary. Saved myself £1200 from my local audi/vag specialist and over £4000 from the main dealer, plus it only took a few hours out of my weekend to change.

The belt kit was around £150 from TPS.

Just placed an order for the chain, cam follower, vvt solenoid and a full service kit (Oil, filters etc) which I'll be doing this weekend. Hopefully the phase position will return to zero (or close enough) afterwards.

Then onto the haldex pump.