My VAG TDI being an arse

[jonathan_dyane]

I should have known better than buying a VAG product, but tempted by excellent potential fuel economy and cheapness I got sucked in...

 

The car: Audi 80 1.9 TDI.

 

The problem: Flat as fuck over 3000 rpm, feels like you hit a wall when you hit about 82 (just like a speed limiter). Below this point goes pretty well. Does not drop into limp mode when this happens.

 

Intake hoses and vacuum hoses appear intact, replaced a couple of dodgy ones.

CEL is not illuminated (and it comes on as it should when you start engine so not had bulb removed).

Does not have a variable geometery turbo so it's not that.

 

I don't think a coked up inlet manifold would make it lose power so violently at a specific point whilst being fine below this rpm. Is this a reasonable assumption?

 

I currently suspect the N75 valve, and am considering hooking the vacuum pipe from the turbo pipe directly to the wastegate to bypass it; will this make the engine/turbo blow up? I noted when I replaced some vacuum pipe the n75 is full of oil, is this bad?

 

Advices much appreciated. Never had this problem with the Merc!

[Ian Nexus]

any codes coming up on a Vagcom (or VCDS lite) scan?, you can check boost using the VS scan facility

[michael1703]

How old is the fuel filter?

 

Always the first thing I change with this sort of problem and a fresh tank of fuel with injector cleaner, has a good success rate

[Guest]

Maf sensor was a common problem on the early galaxy's so i'm guessing your audi would have the same engine.

[Morgan84]

Agreed with the previous of fuel filter

 

Also,if the car does have a MAF,try disconnecting it and see if that makes a difference to the car;air flow meters can be dead,but not show up on a fault code reader.Another place to check is the intercooler pipes are all ok

[jonathan_dyane]

Thanks guys!

 

Runs worse with MAF disconnected.

 

Intercooler pipes also intact.

 

New fuel filter.

 

Tried to interrogate it with vag-com (cheap ebay lead) earlier today, but yet was unable to access car despite lead being installed and car seemingly realising it was plugged in (CEL flashing). Apparently I need HEX-USB lead not KII-USB which doesn't work; I guess my lead is either KII or a load of shit.

 

Don't suppose anyone in Merseyside has hex-usb vagcom/vcds?

 

Cheers!

[Cavcraft]

I should have known better than buying a VAG product, but tempted by excellent potential fuel economy and cheapness I got sucked in...

 

The car: Audi 80 1.9 TDI.

 

The problem: Flat as fuck over 3000 rpm, feels like you hit a wall when you hit about 82 (just like a speed limiter). Below this point goes pretty well. Does not drop into limp mode when this happens.

 

Intake hoses and vacuum hoses appear intact, replaced a couple of dodgy ones.

CEL is not illuminated (and it comes on as it should when you start engine so not had bulb removed).

Does not have a variable geometery turbo so it's not that.

 

I don't think a coked up inlet manifold would make it lose power so violently at a specific point whilst being fine below this rpm. Is this a reasonable assumption?

 

I currently suspect the N75 valve, and am considering hooking the vacuum pipe from the turbo pipe directly to the wastegate to bypass it; will this make the engine/turbo blow up? I noted when I replaced some vacuum pipe the n75 is full of oil, is this bad?

 

Advices much appreciated. Never had this problem with the Merc!

 

N75 fo sho, my Pisshat did the same. It's not a long or expensive job the excellent http://www.centralvwaudi.com/aboutus.htm did mine for about £60 inc. fitting iirc.

 

One way of 'testing' it (if it isn't too far gone) is to knock the engine off for a about 10-15 minutes then trying again. In the early stages of N75nessthe turbo will spool up again and performance is restored. In the later stages it will just keep being shit.

 

*Edit: almost certain the Galaxy/Alhembra/Sharan had the 130 engine, these 80TDis are all 85-ish bhp I think.