Drop in power

spartacus 68 · Oct 3, 2015

On route to pick up my daughter from work and my trusty V6 seemed to go give up the ghost on a slight incline when I floored it.

This has happened a couple of times before when hauling a trailer. Is it going into limp mode? Thing is, on the run back the turbo kicks in and she whistles as the revs increase. Power on tap.

Car is 2.5TDI quattro V6 avant (AKN) with 168k miles.

Please tell me it's not the turbo. Split vacuum hose possibly? May or may not related but it's struggles on warm start. Plenty juice on battery, and starts from cold. Probably on original glow plugs as I'm scared the damn things shear if I try and replace them.

aragorn · Oct 3, 2015

Sounds like the turbo, but not necessarily terminal.

Usually the cause is the VNT mechanism sticking. The car will then either over or under boost depending on how it sticks, then ECU will decide its not happy with the boost control and shut the engine back to limp mode with 0 boost. Power cycling the ignition resets the ECU and it will give you the boost back until it detects the fault again.

It could also be a split vacuum hose or similar, causing the same loss of boost control.

Towing a trailer puts the car into a different range of load sites than driving normally, your typically using larger throttle angles and the cars under far more load, not pulling up thru the rev range as normal, so means a turbo thats slightly sticking might scrape by in normal driving, but will trip the limits when the trailers on. Same thing with an incline etc. It'll likely continue getting worse.

First step is to check all the boost control pipework and vacuum pipework for splits or tears.

Then you can physically check the VNT mechanism to see if its able to smoothly move thru its range of operation.

If its sticking, you can read the thread on using "Mr Muscle" to clean the VNT vanes.

spartacus68 · Oct 4, 2015

Cheers Aragorn. Will check it out tomorrow.

PAULF · Oct 4, 2015

+1 to Kevs' diagnosis.
Try to move the actuator lever through full range - you'll probably want a screwdriver or something(it should go up to the stop)
Unbolt the exhaust and with a bit of tube squirt the Mr Muscle in past the turbine blades until it comes back out.
Bit of cardboard (prepared earlier) to stop spillage, leave for an age, operate the actuator again and repeat until free.

Check the N75 by having somebody start the engine and watching the actuator lever move up.

There are tests with VCDS if you have it.
(I have a KII genuine going if you haven't and are interested)

If anything is ******** and you need bits, let me know before I get rid of the Avant

aragorn · Oct 4, 2015

Are you breaking the Avant Paul?

spartacus68 · Oct 4, 2015

Spent the day on the Amtrak today. Beautiful day for it. Exhaust section out, actuator levered up and down and Mr Muscle a plenty. Should have stopped there, but I'd always wondered what the intake manifolds were like, so whipped of the driver's side. Passenger side looked okay. Filthy job. Used Mr Muscle, then Gunk remover, plenty hot water, etc. Had to stop because the light was going plus I need a gasket where it connects to the EGR valve. Tight as a gnat's chaff to work around fuel pipes and electrics.

PAULF · Oct 5, 2015

aragorn said:
Are you breaking the Avant Paul?

Sort of - if somebody wants it as is.
If not I was just going to bin it
I doubt 'd take stuff apart too much so the bilstiens are wasted, - but the engine is on a pallet from when I bought it and I suppose I could remove the pump and injectors as Diesel Bob did them not too long ago. Dunno about anything else - you needing something?

PAULF · Oct 5, 2015

spartacus68 said:
Spent the day on the Amtrak today. Beautiful day for it. Exhaust section out, actuator levered up and down and Mr Muscle a plenty. Should have stopped there, but I'd always wondered what the intake manifolds were like, so whipped of the driver's side. Passenger side looked okay. Filthy job. Used Mr Muscle, then Gunk remover, plenty hot water, etc. Had to stop because the light was going plus I need a gasket where it connects to the EGR valve. Tight as a gnat's chaff to work around fuel pipes and electrics.

Good job well done mate!
Was the actuator sticky at the start?
You might want to blank the egr too - it'll reduce the chances of it gunking up.
(Just blank it with a bit of plate, no need for any coding on our engines I got mine off the bay of E for about £5)

aragorn · Oct 5, 2015

Was thinking about the rear top mounts. What bilsteins are on it?

PAULF · Oct 6, 2015

I didn't think the Quattro rears have top mounts - the shocks go inside a housing and bolt through (IIRC), the Bilsteins are B6s

Anyway, more to the point - how's the Amtrak Loco Spartacus?

spartacus68 · Oct 6, 2015

PAULF said:
I didn't think the Quattro rears have top mounts - the shocks go inside a housing and bolt through (IIRC), the Bilsteins are B6s

Anyway, more to the point - how's the Amtrak Loco Spartacus?

No idea PAULF. The turbo still has Mr Muscle in it from Sunday! It's probably eaten it's way through the vanes!

Called Audi on Monday as I need a card gasket where the EGR valve connects to the air intake manifold and new Allan key bolts. Surprise suprise they need to be ordered. Had to go to Dundee today with work, and literally just in the door, so didn't pick up the part. I'll swing by tomorrow and pick it up and fit come hell or high water. Been pi$$ing down since Monday.

I'm keeping the EGR as standard. It's covered 168k miles from rolling out of the plant in Ingolstadt, so that must say something.

On a different topic, I resprayed the wings again, and the bottoms of the front doors. Had to drill out the securing Phillips screws on the door trims which hide all matters of sin. Wouldn't mind but it's exactly a year since I did this job.

aragorn · Oct 7, 2015

You complained about the grot in the manifold, which is caused by the EGR, and yet dont see the merit in fixing it?

jbh · Oct 7, 2015

I personally would blank of the EGR also.
Ive done this in my 1.9tdi quattro and have noticed a slight increase in mpg and throttle response and that was before I cleaned the crud out the inlet manifold.
I think every tdi ive had has had the EGR blank fitted

spartacus68 · Oct 7, 2015

Calm down lads. EGR blanking plates now ordered. Anything for a quiet life.

Fitted the other bits back on the engine, but it failed to start. I suspect I'll have to bleed the fuel pipes at start-up? Battery gave up so now on charge. I take it I can just do one side of the engine as the fuel pipes on the passenger side weren't removed to shift the air intake manifold.

PAULF · Oct 8, 2015

I don't recall bleeding mine for that - are you getting air in the clear pipe?
If so the fuel has syphoned back and you'll ned to do a full bleed.

spartacus68 · Oct 8, 2015

It's a strange one Paul. I've put the battery on trickle charge so will attempt again tonight. When I disconnected the metal fuel pipes on the driver's side (only way to remove that section of the air intake manifold), there was no loss of fuel. I'll check the plastic fuel pipes on top of the engine to see it hasn't drained back. If it has, does that mean turning the engine over and removing each fuel pipe in turn to bleed, including the bank on the passenger side?

aragorn · Oct 8, 2015

The pump should bleed the high pressure lines by itself.

spartacus 68 · Oct 8, 2015

Quick update. Had the battery on charge last night, so reconnected everything back up. Also refitted the new gasket to the EGR valve which ironically I'm going to blank in the next week or so. Fired up the Amtrak and after a few tense seconds it spluttered into life. Seems there's plenty power on tap. Thanks for the tips guys.

Saturday beckons and my Meyle lower wishbones have arrived from Ireland for my wife's A2. It's like working for Phil Mitchell.

PAULF · Oct 8, 2015

I always used a hose clamp on the fuel feed whenever I disconnected any fuel component in the engine bay as these can be a little fickle.
I'd clamp it before the filter, that way there will be no drainage back to the tank.

Drop in power

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