V50 General : Performance issues - illusion or real?

[Xariez]

Hey,

So much like the title says, I'm currently having something funky going on with my V50. It's a T5 automatic from 2004, and I'm not sure if something IS going on, or if it's simply a placebo-effect.

Previously, after making a turn (so gearbox probably sitting in first-second gear), I could more or less floor it and it would shoot away. Right now it's still building speed, but I feel like it's not revving as "quick" as previously (perhaps just the gearbox learning/adapting more and more to my own driving style?).

Another thing I noticed, was that this issue seemed to be gone after I had the battery disconnected for a few hours while installing some extra lights in the grille of the vehicle. This is probably what's throwing me off the most. Is this just a placebo-effect, or could something be going on that a ECU reset fixes?

Oil change interval is at 20kkm and has been driven with roughly 10kkm right now. Engine air filter also looks decent. Any ideas are welcome!

[FunkyMelon]

When was your turbo control value last replaced?

These are pretty much consumables and should be replaced every other year (IMO).

When they begin to fail you start to see intermittent boost.

[Xariez]

Originally Posted by FunkyMelon

When was your turbo control value last replaced?

These are pretty much consumables and should be replaced every other year (IMO).

When they begin to fail you start to see intermittent boost.

No idea. I got the car a year ago or so, and I'm having some kind of doubt it was replaced within the year they had the vehicle either.

Is there a way to diagnose this, apart from getting "intermittent boost"?

EDIT: Will go get a OBD2 reader tomorrow/Tuesday and come back with some numbers. Need one anyways and should perhaps give me/us some kind of idea what's going on.

EDIT 2: Should also be mentioned this only happens when going from a standstill. While overtaking, for example, I got 0 issues.

[Welton]

Some fairly common areas to check:

Boost Pressure Sensor (at the Intercooler - mine went bad and really slowed the car down).

Turbo Control Valve.

Turbo 'Check' Valve (one-way ball valve/flap built into the turbo housing).

Fuel Pressure Sensor on fuel rail (this would be my first call).

Mass Airflow Sensor.

Air Conditioning Load (the compressor saps a fair bit of engine power).

[LizardOfBodom]

Originally Posted by Xariez

...

Another thing I noticed, was that this issue seemed to be gone after I had the battery disconnected for a few hours while installing some extra lights in the grille of the vehicle. This is probably what's throwing me off the most. Is this just a placebo-effect, or could something be going on that a ECU reset fixes?

...

When battery is disconnected ECU looses all learned data and starts the adaptation process from the scratch. It is advised to do a throttle body calibration after every battery reconnection (just start up the car and let it idle for 10mins or so), and then also do a TCV adaptive learning by doing some WOT accelerations, that allows the ECU to learn the min-max values, and adapt to your driving style.
Regardless - there might be a problem as FM and Welton said, check all those and replace if not sure. Boost readout trough ECU will give you some info if TCV is knackered or not, but as mentioned - this thing just fails ever so often so replacing it as maintenance item is recommended.

[Xariez]

Originally Posted by Welton

Some fairly common areas to check:

Boost Pressure Sensor (at the Intercooler - mine went bad and really slowed the car down).

Turbo Control Valve.

Turbo 'Check' Valve (one-way ball valve/flap built into the turbo housing).

Fuel Pressure Sensor on fuel rail (this would be my first call).

Mass Airflow Sensor.

Air Conditioning Load (the compressor saps a fair bit of engine power).

Will try to get most of these checked. But two follow-up questions:

1) If the fuel pressure sensor is going, shouldn't the OBD-reader read bad (or erratic) fuel pressures as well? Any ideas what kind of pressure I should expect at idle/under load/etc?

2) In a similar fashion, if the TCV is going, shouldn't the vacuum/boost-gauge be reading quite incorrectly as well? I believe I've read somewhere T5's should generate around 0.6-0.7psi of boost, though not sure how much vacuum should be produced at idle?

EDIT: If it matters, the reported average fuel consumption has been lower for some time right now. Granted, it's been warmer outside as well and cold starts haven't been as cold, but while I previously had 10.0-11.0L/100km, it has barely moved from 9.0L/100km currently?

[LizardOfBodom]

FPS that is going out would trigger engine management light, in most cases, but if you can check the values - from what I remember it oscillates between 400 on idle to 500 on WOT on mine.

if its any help to you - here is a datalog file that I recorded 2y ago, bear in mind my car is s1 tuned so turbo pressure values will be higher, but fuel pressure or TCV behaviour would be similar.

EDIT - ref the vacuum, a value of 23.5 rings a bell, I think thats what I have reported by Torque when driving with obd2 adapter active.

[FunkyMelon]

Originally Posted by LizardOfBodom

EDIT - ref the vacuum, a value of 23.5 rings a bell, I think thats what I have reported by Torque when driving with obd2 adapter active.

Definitely not 23.5psi engine would be in bits lol!

0.7psi is standard boost (IIRC).

[LizardOfBodom]

Originally Posted by FunkyMelon

Definitely not 23.5psi engine would be in bits lol!

0.7psi is standard boost (IIRC).

It was a think-shortcut, meant negative in/hG or whatever the value is

[Xariez]

Originally Posted by LizardOfBodom

It was a think-shortcut, meant negative in/hG or whatever the value is

Vacuum is looking identical to my readings, and boost was around 0.5 (though I could have pressed it harder). Fuel pressure is reading everything between 291-300KPA.

The annoying part is that it seems to have gotten slightly (but noticably) different. So perhaps just a "placebo" effect in the end, or just a ECU with reset values that hadn't quite reached it's "learned" state?