Boost issue?

[S4_dan]

Hi guys,

Me again! This time I've got a query about the boost behaviour. Been like it since since fitting a known working MAF.

If I drive up to 1600 rpm and change up a gear, the acceleration remains fine/normal.

However, anything over 1600 rpm and you can feel the boost kicking in etc, then change up a gear, I get a dead spot for a second or two before it picks up boost and goes like the clappers.

Nothing directly to any boosting issue or diverter valve is showing up in VCDS (about the only DTC that isn't showing at the moment!!).

Where is the DV located on the 2.5?

My theory is that the turbo is stalling during changes and hence the dead spot in acceleration. There is no strange noises that I'm aware of either.

Where do I start looking?!

Cheers,

Dan

 

[AudiLeon]

How many miles has your car done, when did you last have the turbo vanes cleaned?

 

[boardy1987]

Hi I just bought an 03 a4 2.5 quattro and am new to this. I have experienced the same problem in mine and have also that sometimes if im going in 5th or 6th gear near 100mph it cuts down to 80 or so. When I slow down and go up the gears again its fine. My mate is a mechanic and hes going to change my diesel filter to see if that helps before going into turbos etc. Hes said that that was a problem in quite a few cars hes delt wiv in the past. il post up on sat how it goes. Hope this helps.

 

[S4_dan]

How many miles has your car done, when did you last have the turbo vanes cleaned?

160k and last saturday. The actuator rod was nice and free with about an inch in travel. I gave it two doses an hour apart. No change in performance.+

Hi I just bought an 03 a4 2.5 quattro and am new to this. I have experienced the same problem in mine and have also that sometimes if im going in 5th or 6th gear near 100mph it cuts down to 80 or so. When I slow down and go up the gears again its fine. My mate is a mechanic and hes going to change my diesel filter to see if that helps before going into turbos etc. Hes said that that was a problem in quite a few cars hes delt wiv in the past. il post up on sat how it goes. Hope this helps.

I don't believe its the fuel filter, although never say never! The car drives and pulls great. And if I'm trashing it (only done twice) it doesn't have the issue as the revs are much higher on the up change. The car is FSH and it due at the end of the year. Only covered 8k since last year.

Keep me posted if you will please as it's something to look at.

Cheers,

Dan

 

[abyrne153]

You can check if the vanes are sticking by undoing the 2 10mm studs that bolt the turbo actuator to the turbo. Careful and dont drop any into the V of the engine. Once removed you can move the vanes by moving the actuator up and down by hand. The operation should be completely smooth. Even slight notchiness can cause the problems described. Scan for fault codes that suggest overboost as this can also signal sticky vanes. A proper clean means stripping down the exhaust side of the turbo but you can use the Mr Muscle oven cleaner technique described elsewhere in this forum. It does work as I have tried it before.

 

[S4_dan]

You can check if the vanes are sticking by undoing the 2 10mm studs that bolt the turbo actuator to the turbo. Careful and dont drop any into the V of the engine. Once removed you can move the vanes by moving the actuator up and down by hand. The operation should be completely smooth. Even slight notchiness can cause the problems described. Scan for fault codes that suggest overboost as this can also signal sticky vanes. A proper clean means stripping down the exhaust side of the turbo but you can use the Mr Muscle oven cleaner technique described elsewhere in this forum. It does work as I have tried it before.

Did the mr muscle clean last saturday. The actuator rod does move freely with about in inch in travel. Whether that is moving the actual vanes or not though.....Do the vanes not move from the HOT/exhaust side of the turbo? I just know what i'm like when it comes to dropping nuts!!!

Dan

 

[abyrne153]

Yes the vanes are on the exhaust side. Go onto youtube and do a search for VNT or VVT turbos and you see various videos that will give you an idea of the workings. If the actuator arm moved freely and I mean really free with no notchiness at all then the vanes are not sticking. You really need to unbolt the actuator though to feel what is going on as there is too much resistance in the diaphragm spring to tell whilst it is still attached to the turbo. Check the pipes to the N75 boost valve that controls the actuator as well for splits or leaks. Check all boost pipes and intercoolers for signs of leaks. Intercooler leaks show up as oil stains on the intercooler rads. Oh also the egr valve could be sticking. Mines blanked off with a home made blanking plate but these can cause problems too. There are so many things that could cause your symptoms but you have to start somewhere.

 

[Andie0]

Are you running an aftermarket dv

 

[S4_dan]

Are you running an aftermarket dv

No. I can't even find the DV! lol

 

[Andie0]

The dv could be faulty and not holding your boost correctly.

 

[Andie0]

Hate to say this But i have heard of similar problems and the problem eneded up being the turbo