TDI power loss

[davetherave]

Have a 110 TDI with 42k on clock, anyone out there had problems with power loss when under load? Its peeing me off, I'll be giving it some welly and all of a sudden the power drops off from about 4,500 down to about 2,000 rpm. Then the power is crap until I turn off and turn back on again, anyone no the reason?

Had MAF changed but still happening, any ideas?

Cheers

Dave

 

[sssstew]

sounds like its going into limp mode. you could get someone with vag com on a laptop to see what fault codes are logged. Could be a boost leak somewhere, tis common when under load which leads to a positive deviation error being logged. But vag com will tell all.

 

[jonjay]

Boost leak was my first thought...is the car quite smokey?

 

[cheshire cat]

dirty fuel filter? p.s. how mutch power do you expect above 4500rpm

 

[Nathanio]

Boost leak I would say. Had something similar before on last tolly TDI and the boost vacuum pipe (to the n75?) came off and the car kept going into limp mode.

 

[Cubix]

check to make sure that the air filter is fitted properly. I have experienced in the past on my 110 Passat TDi that if I suddenly boot it, i get the same problem and it turned out to be the air filter being slightly out of position when it was fited.

 

[davetherave]

Thanks all. No the car is'nt smokey, and the fuel filter was changed at the back end of last year. Will check the air filter and vacuum pipe though. Failing that I'll get hold of someone with vag com for further diagnostics.

Cheers.

 

[dmjw01]

Interesting that everyone says it sounds like a boost leak, because in my opinion it's equally likely that it's kinda the opposite problem: an overboost caused by a sticky VNT mechanism.

As the revs rise, the VNT should first "open up" to increase the boost up to its maximum, but as the revs rise further it should then start to "close down" in order to keep that boost under control. If it didn't do that then the boost would rise too far.

It could be that your VNT mechanism is opening up successfully but then failing to close down fast enough to prevent an overboost as the revs get higher. The ECU will detect the overboost and go into limp mode to protect the engine.

If you have VAG-COM, you can try exercising the VNT mechanism. I think it's Group 11 you need, and click on the "Basic Settings" button. The engine will go into a fast idle at about 1400 rpm and start cycling the VNT backwards and forwards every 10 seconds. Leave it doing this for 10 minutes or so, and it often frees up the mechanism.

 

[ChrisUK]

power drops off from about 4,500 down to about 2,000 rpm

It's not as simple as a major clutch slip is it ?

 

[sssstew]

Interesting that everyone says it sounds like a boost leak, because in my opinion it's equally likely that it's kinda the opposite problem: an overboost caused by a sticky VNT mechanism.

As the revs rise, the VNT should first "open up" to increase the boost up to its maximum, but as the revs rise further it should then start to "close down" in order to keep that boost under control. If it didn't do that then the boost would rise too far.

It could be that your VNT mechanism is opening up successfully but then failing to close down fast enough to prevent an overboost as the revs get higher. The ECU will detect the overboost and go into limp mode to protect the engine.

If you have VAG-COM, you can try exercising the VNT mechanism. I think it's Group 11 you need, and click on the "Basic Settings" button. The engine will go into a fast idle at about 1400 rpm and start cycling the VNT backwards and forwards every 10 seconds. Leave it doing this for 10 minutes or so, and it often frees up the mechanism.

yes yes very good point david. worth looking into. not sure if you can exercise the VNT on the non PDs.

 

[TornadoRed]

I agree that this sounds like an overboost situation, and the engine control module is putting it in to limp mode to protect the turbo. I'd suggest checking the turbo control valve (N75) first.

I'd be very, very surprised if it was a MAF problem or a fuel filter problem.