Loss of acceleration in 3rd gear @50mph

[RoscoLabri]

Hello all,

The last couple of weeks I've been having troubles with my Seat Leon 1.9 TDi. It seems to have lost alot of it's pace at higher speeds. The acceleration will slow right down when I'm in 3rd gear and reach 50mph and continue even if I change gear to 4th/5th. I tried bypassing the 3rd gear before it gets to 50mph but it then does the exact same thing in 4th gear at 60mph.

The diagnosis/Excess of pollution light comes on once in a while, though it's not very consistant, where as the gear/acceleration problem is always a dead cert.


I struggled to catch up an old Ford Fiesta the other day in 4th gear on a straight, flat road

I should just mention that the car has had it's MOT a couple of days ago and passed, and the garage also cleared the dashboard light yet the same problem still exists.

The car is still at the garage, and from the sounds of it the guys down there aren't too sure what the problem is at the moment, so I thought I'd ask around here to see if anyone else has had the same problem.

Thanks in advance.

 

[sssstew]

hmm, does it reset when you turn off then on? I reckon it might be going into overboost due to sticky turbo vanes.....

Either that or a boost leak which isnt enough to trigger limp mode....

 

[PaulieB]

excess pollution came on when the vw polo blew its head gasket, and also came on when my ibiza coil pack went if thats any help.

both symptoms involved bugger all acceleration

 

[sssstew]

TDIs dont have coil packs so rule that one out.

 

[Muttley]

TDI 90, 110, 130, 150? What year? What mileage?

Likely causes include sticky turbo vanes and sticking EGR valve. Most TDI 90's dont have a VNT turbo.

 

[RoscoLabri]

Sorry for the late reply.

It's a Seat Leon 1.9 TDi S (90), 05 plate and 59k miles.

I have been told that the Turbo needs replacing, at a cost of around £1100

The thing is, some days the turbo will work like a dream, no matter what gear I'm in or speed I'm going at, yet other days it won't and I get the same problem as before.

I'll quickly copy out the what the garage typed up...

Vehicle suffering loss of power under acceleration. Please check and report - 3rd gear 50mp.

Carried out checks and confirmed fault.

Checked and found on road test at 3000rpm in 3rd gear turbo is overboosting by 0.5 bar.

Carried out checks for leaks in intake system/ boost system/ exhaust system and vacuum system, all ok.

Pressure/ solenoid valve (N75) function tests ok.

Checked boost pressure sensor reading ok.

Checked function of wastegate acctuator rod using vacuum pump tested and moves freely.

Also releases pressure ok when ignition switched off.

Turbo overboosting requires replacement of turbo. Cost to replace turbo, including parts and lab and vat £1118.11p.



Is it definitely the turbo that's broken here? Surely it wouldn't work at all would it?

If it is, I guess I'll start looking for a recon unit or something

 

[S3 AKR]

Not sure if the diagnostic conclusion is correct or not, but look at it as an opportunity to start mod'ing!

 

[Muttley]

RoscoLabri wrote

It's a Seat Leon 1.9 TDi S (90), 05 plate and 59k miles.

You have a late model TDI, and almost certainly have the ALH engine. ALH is effectively a 90 BHP version of the ASV, and has a VNT turbo. Can you check you data sticker (under the carpet in the boot) or the service book and find out?

I'll quickly copy out the what the garage typed up...

Vehicle suffering loss of power under acceleration. Please check and report - 3rd gear 50mp.

Carried out checks and confirmed fault.

Checked and found on road test at 3000rpm in 3rd gear turbo is overboosting by 0.5 bar.

That's a symptom most commonly associated with sticky turbo vanes. The VNT technology uses vanes to vary the turbine inlet cross-section and increase the gas flow speed at lower revs, instead of a wastegate to dump excess pressure at high revs. The vanes sometimes stick and don't open as they should, resulting in higher gas flow speeds at mid-revs, which leads to overboosting. This is detected by the Manifold Absolute Pressure sensor (the MAP, not the MAF) in the inlet duct after the intercooler, which puts the engine into limp mode to avoid damage.

Carried out checks for leaks in intake system/ boost system/ exhaust system and vacuum system, all ok.

Pressure/ solenoid valve (N75) function tests ok.

Checked boost pressure sensor reading ok.

Leaks would lose boost, not result in overboost

Checked function of wastegate acctuator rod using vacuum pump tested and moves freely.

That line makes me suspect they don't know the engine, assuming it is ALH, and at '05 I'd doubt it's anything else. If I'm right and this is an ALH engine, it has a VNT turbo and doesn't have a wastegate. The actuator controls the vane position. They say it moves freely, but testing as a wastegate would not necessarily be adequate.

Also releases pressure ok when ignition switched off.

Turbo overboosting requires replacement of turbo. Cost to replace turbo, including parts and lab and vat £1118.11p.

But no explanation of what is wrong with the turbo to cause the overboosting? They aren't being straight with you.

Is this a SEAT dealer, an idependent VAG specialist or a general-purpose service center?

My guess is it's an ALH engine with a VNT (variable geometry) turbo,and that you have sticky vanes, usually caused by carbon build up in the exhaust turbine. They can be cleaned, but dismantling turbos is not for the faint-hearted: I haven't done it, but there are people here who have.

Replacing the turbo will fix the problem, but may not be necessary.

Does the car spend most of its time at low power settings, for instance urban commuting, and rarely get a chance to run on full throttle? Sooting up is accelerated if the exhaust turbine doesn't get hot enough to burn off the soot.

This is one time when the Italian Tune-up, going for a run at sustained high speed, can help. You need a decent stretch of motorway free of traffic jams, preferably with a hill. The idea is to put sufficient load on the engine to burn off the carbon.

 

[muddyboots]

Way be worth trying the Innotec cleaner stuff first - not used it myself but it's to try and cure this sort of problem isn't it ?

Got to be worth a try before shelling out £1100 on a new turbo...

 

[Andrewcupra TDI]

surely a new turbo is less than 1100 notes , contact the companies who rebuild turbos / hybrid them etc

worth a look around

also worth a look at the other brand turbos on the net , ie ebay , for example skoda vw audi etc as they all share the same engines

 

[Husbandofstinky]

This is one time when the Italian Tune-up, going for a run at sustained high speed, can help. You need a decent stretch of motorway free of traffic jams, preferably with a hill. The idea is to put sufficient load on the engine to burn off the carbon.

+1 and keep at it.

Have always given all cars when fully warm 'a damn good thrashing' once a week.

All cars of all ages need it.

Hopefully getting it nice and hot will free some of the carbon and keep at it until you've had enough weeks or months later (depends on how much a PITA it is, your tolerance and cash situation) or that the symptoms have gone.

Next route would be the cleaner part, its been done on here before and am sure you could find a thread with it on. It is a big job though still.

Last resort - hybid

 

[LewisLeon]

Had a very, very similar problem with my TDi 110.
What seems to have worked for me (touch wood...) was to give it a damn good service with quality parts, wait for it to be properly warmed up and find a nice long hill and boot the arse out of it, basically.

 

[Husbandofstinky]

There ya go.

Just don't go mad - 'sorry h'officer just cleaning the soot of me turbo'