OK, morning all.

Firstly, I'm new to 2 things here, I've never had a Diesel, and I've never had a turbocharged car(10 previous years with an MX5), so this is a bit of a learning curve. Anyway, I've had a problem now with my Fabia VRs since Monday, dropped all boost and I limped turbo-lessly home the remaining 3 miles. (Didn't know the ignition off and on trick, I work in I.T so it sounds very familiar ). Anyway, various things pointed to it being the MAF sensor, so this was replaced. The car did drop boost once more whilst accelerating, but that was it, I took it for a thrash along the A14 last night for about 50 miles at 70mph(+/- 20mph ) and it didn't miss a beat! Pulled fine, didn't hurl out loads of black smoke or anything!

Anyway. what I've noticed since the first time it dropped boost is a woooooo noise (best way to describe it is it sounds like an ambulance siren in the distance) at certain times during boost. If I remove the vacuum pipe to the VNT actuator on the turbo it doesn't seem to do it (revving it on the drive, haven't driven it with it removed as I wasn't sure whether I've knacker anything). I've checked all the boost pipes and they seem fine, no holes etc. Has anyone got any ideas? Could it be the pipe seals that may be giving way under load, hence the woooooooooo(I do actually quite like the noise )???? Or could the black vlave block on the inner wing have gone faulty??

Additionally, how come they dont have a wastegate? What happens to any excess boost?

Sorry for all the questions, all info/help gratefully recieved.

Cheers

ps, forgot to say, I have removed the VNT actuator and the mechanism all moves freely and smoothly.

Edited 22 May, 201016 yr by jacko2111

it sounds like you have a small split in one of the pipes from the turbo which is opening up under max boost which (if so) willl just get worse, it's hard to generate much boost stood still , so not much use, I would remove the undertray and check everything out down there-- also good chance to drain the oil out of the pipe and intercooler and clean up, cheers Nic

Boost leak, or VNT sticking.

Boost leak, or VNT sticking.

whats VNT?

whats VNT?

Variable Vane Turbo. Reduces turbo lag by using variable vanes to control the gas flow through the turbo. Vanes are moved by an actuator mounted on the turbo, and controlled by the vacuum from the N75 valve in the vacuum control box. The vanes can get clogged up with soot and stick.

I've checked the pipes and cleaned them out but can't find any splits/holes/etc, had the intercooler of and cleaned that, seemed ok too. Must admit, haven't replaced the pipe seals yet, but will do that next week. Have checked the VNT and it seems to move smoothly enough, so I don't 'think' it's that. The Turbo was replaced about 19000 miles ago under warranty (before I had it), so I'm hoping it's good for a few more miles yet! Can the N75 valve go faulty???

Thanks for the reponses anyway. And Raddish, here's a good video that shows what VNT is:-

http://youtube.com/watch?v=J8tW_4n6lx0&feature=related

Cheers

Edited 22 May, 201016 yr by jacko2111

A scan may point to a faulty N75 valve!