Over boost fault

[GTI_69]

Has anyone experienced their 2.5L T5 over boosting then cutting power and going into limp home mode? Turn the ignition off then goes back to normal untill over boost is picked up again? Any help much appreciated.

[h100vw]

The best thing to do would be log the boost with VAG-COM, I am pretty sure thats possible.

There may be fault codes in the ECU which give you more idea as to waht's going wrong.

Gavin

[gregozedobe]

One common cause is sticking variable vanes in the turbo. Typically happens in a TDI that is driven very gently all the time at lowish revs, then when the driver puts their foot down and the revs come up to 2,000 or so the boost increases but the vanes don't move so there is too much boost.

If the van is covered by warranty VW usually jusy whack a new turbo in, but if you have to pay for it you can free the vanes up yourself (if you are mechanically adept and don't mind getting your hands dirty), or pay someone else to free them up (it will be much cheaper than a complete new turbo).

Another possibility is a faulty actuator (the thing that moves the vanes).

As h100vw says, looking at the fault codes recorded by the ECU using vagcom/vcds or the delaer software tool should give you more info.

Please let us know how you get on, it all adds to the corprorate knowledge on here.

[Jmac]

Got this one going on with the Mk5 Golfs, will under boost then overboost, this will put the system inot limp and exactly like you say its ok after a key cycle. I have a Golf coming back for checks im gonna take the 2 bolts off the actuator and give it a workout. If all fails it will be turbo off and a strip down, like previously mentioned variable vanes sticking.
Good luck , ill post up how i go with the Golf.
Just on the codes expect to see P0234 Over boost condition, boost regulation exceeded.
This code should prompt you to check piping and the above mentioned. They seem to be bad for sticking. Had 2 Golfs now so its time to get the fix. Car is coming back in a couple of weeks, actuator jiggle 1st then strip the turbolader
Cheers
Jmac

[gregozedobe]

Yes, it is a known problem with VAG TDIs.

My "preventative maintence" is to make sure I give it a good burst of full accelerator at least once every drive, usually in 3rd gear. I do mostly highway cruising, so my TDI is driven fairly gently nearly all the time, hence the need to "exercise the vanes" at regular intervals.

[Jmac]

I totally agree with that one mate 100%. The Golfs in question have been driven like miss daisy and is the main cause so yeah keep that up and you should be right.
Jmac

[Preen59]

Dad had a Caddy a couple of months ago in the W/S with the same problem. It was under warranty so he told them to take it to VW and they, as you say, stripped the turbo and gave it a good clean apparently.

A mechanic down the road also had an issue with a 1.9 TDI golf that turned out to be the boost reference line going to the vane actuator had a pin hole in it and was pumping too much boost all the time.


I've never had any of these issues (haven't had any engine issues at all.. Even uses bugger all oil.. If any) with my Caddy, but i give it a good squirt quite regularly.

[Jmac]

Yes Preen thats what i intend to do with the MK5 , give it a good clean out mate, sure thats whats going on. A good squirt keeps it at bay im sure.
Cheers
Jmac

[Ivo]

Mine goes into limp as well. 99% of the time its within a few minutes of starting the engine and accelerating heavily. I am very easy on the engine when its cold and warming up.

I can be driving for 1 hour,stop for 2 or 3 minutes and turn the engine off then start up and pull out into traffic with my foot down hard and the motor ( sounds like mechanical injectors) will rattle loudly and then it goes into to limp mode.

The mechanic found a fault code and thought it wasa faulty hose clamp that was allowing a pipe to partly separate and that was causing some other component to trip. We changed the clip but its still doing it unfortunately. Next service is due soon will get it checked again.

[Preen59]

Mine goes into limp as well. 99% of the time its within a few minutes of starting the engine and accelerating heavily. I am very easy on the engine when its cold and warming up.

I can be driving for 1 hour,stop for 2 or 3 minutes and turn the engine off then start up and pull out into traffic with my foot down hard and the motor ( sounds like mechanical injectors) will rattle loudly and then it goes into to limp mode.

The mechanic found a fault code and thought it wasa faulty hose clamp that was allowing a pipe to partly separate and that was causing some other component to trip. We changed the clip but its still doing it unfortunately. Next service is due soon will get it checked again.

When things cool down (your inlet), the engine creates boost more easily. That "rattling" noise you can hear is the wastegate fluttering like mad trying to dump exhaust pressure to alleviate the boost spike.