VAG-COM Log - Spot the issue?

AlexGSi2000 · Feb 20, 2012

Hi,

Just wondering if anyone could help me out with this log - I think I may have an issue with the MAF or N75 - just need some advice really.

The car is an Audi A4 2.5 V6TDi - The issue is with the boost.

When I put my foot down, the turbo spools, boosts for a short while and then drops it again, it will do this about 3 times when my foot is down in 4th, 5th or 6th gear.

Im not too good reading VAG-COM logs so was wondering if someone could help me read the information?;

Many thanks!

Bondiblu · Feb 20, 2012

Has the car been remapped for starters, doesn't look like it? Spec boost versus Actual, doesn't look too bad at all, it seems to have a little lag to begin with but seems to hover around requested ok.

You're MAF doesn't look too happy though, and seems to be restricting IQ. Generally the IQ RPM(torque limiter) should be the limiting factor, but as you can see the IQ MAF (smoke limiter) seems to be doing most of the limiting.

AlexGSi2000 · Feb 21, 2012

Many thanks! - The car is not remapped - How can you tell that the MAF is restricting from the log?

I spent a few hours going over the car yesterday, all vac and boost pipes are ok with no leaks.

I was thinking it could have possibly been something to do with the vanes on the VNT sticking - but since you reckon its the MAF I will probably swap that over first.

Bondiblu · Feb 21, 2012

AlexGSi2000 said:
Many thanks! - The car is not remapped - How can you tell that the MAF is restricting from the log?

I spent a few hours going over the car yesterday, all vac and boost pipes are ok with no leaks.

I was thinking it could have possibly been something to do with the vanes on the VNT sticking - but since you reckon its the MAF I will probably swap that over first.

Well looking at channel 8 (I think it is) last 3 columns on the right of your image, You have
Drivers IQ request (throttle pedal), IQ RPM(torq) and IQ MAF. Throttle pedal request will always be the highest value at any given RPM (only at 100% throttle) as it's a request for injection. The torque limiter is preset in the ECU in a table, the MAF regulates injection dependant on airflow, but generally should sit above RPM IQ at WOT. The only time IQ MAF should be the limit is on spool up (ie if you suddenly boot it, the MAF restricts IQ until airflow has caught up with IQ request to minimise smoke, basically maintains Air Fuel Ratio). General hierarchy of the Injection Quantity Limiters (at 100% throttle) is from the bottom IQ RPM(torque) -->IQ MAF(smoke) --> IQ Driver request.

So either somethings affecting airflow (possibly EGR) etc or your MAF not reading correctly if everything else is working that is.

Taking into consideration that there could be many factors affecting the figures in your logs.

AlexGSi2000 · Feb 21, 2012

Think I got that! New to the world of these logs - I know what they mean, just dont know how they correlate! I unplugged the MAF before and it seemed more responsive - not sure if it was placebo or not. I will pick up a MAF towards the end of the week and report back! Thanks again.

Bondiblu · Feb 21, 2012

AlexGSi2000 said:
Think I got that! New to the world of these logs - I know what they mean, just dont know how they correlate! I unplugged the MAF before and it seemed more responsive - not sure if it was placebo or not. I will pick up a MAF towards the end of the week and report back! Thanks again.

The fact that it seemed more responsive is a good indication. Yes, please keep us posted

AlexGSi2000 · Feb 24, 2012

Thanks again Bondiblu - The new MAF arrived this-morning.
(Purchased from euro car parts as an OEM quality equivalent - but was actually a new genuine VAG item which was £78 cheaper than the dealers)

Fitted before I left for work (work is 10 minutes away) although I haven't had the chance to drive the car properly yet, the car feels much more responsive - I held my foot down in 4th on the motorway slip road and it didn't seem to drop boost once.

I think that's pretty much sorted it! - the car still feels slow, but I think that's because its only 180bhp which is pushed through an AWD system on an estate car.
Now iv got the boost issue sorted I can now look towards a few mods - unfortunately there isn't much scope with the 2.5 V6 TDi engine - on the cards so far is a remap and turbo-back exhaust which should see me to around 215bhp.
Next option would be a hybrid turbo which would see around 225 - 230bhp after that its big money to get more power out of these. - so I think I will be content with 215/230bhp.

I guess I just miss the unrefined acceleration / boost from my Ibiza Cupra.

Bondiblu · Feb 24, 2012

AlexGSi2000 said:
Thanks again Bondiblu - The new MAF arrived this-morning.
(Purchased from euro car parts as an OEM quality equivalent - but was actually a new genuine VAG item which was £78 cheaper than the dealers)

Fitted before I left for work (work is 10 minutes away) although I haven't had the chance to drive the car properly yet, the car feels much more responsive - I held my foot down in 4th on the motorway slip road and it didn't seem to drop boost once.

I think that's pretty much sorted it! - the car still feels slow, but I think that's because its only 180bhp which is pushed through an AWD system on an estate car.
Now iv got the boost issue sorted I can now look towards a few mods - unfortunately there isn't much scope with the 2.5 V6 TDi engine - on the cards so far is a remap and turbo-back exhaust which should see me to around 215bhp.
Next option would be a hybrid turbo which would see around 225 - 230bhp after that its big money to get more power out of these. - so I think I will be content with 215/230bhp.

I guess I just miss the unrefined acceleration / boost from my Ibiza Cupra.

Thanks for posting up, and I'm glad it's sorted. You could do some more logs to prove the point.

Yes, a remap should liven things up a bit

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VAG-COM Log - Spot the issue?

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