A4 TDI 2.5 V6 - underpowered / lack of boost

[Griswald]

Hi All

I have recently bought an A4 2.5 V6. It seemed to be underpowered from day one. It does smoke quite a bit when starting from cold only, within a few mins it clears and runs normal. Also when starting from cold its a little lumpy, like its not running on all 6. Once its warmed up its smooth and seems to run on 6 cylinders. It has had a new Air Mass Meter fitted but the problem lack of power remains - It will accelarate, but at its own pace, she wont be hurried !

It has been into a Local Audi dealer for attention on other items(service/brake discs/pads/engine stripped to remove a damaged glow plug etc) nothing else was reported, all the fault codes are clear. They did confirm it was underpowered but didnt offer anything up as to why and just handed me over the bill !

If anyone has some advice to point me in the right direction I will be grateful - Thanks in anticipation
:zx11:

[Niall76]

How did the glow plug become damaged? Just wondering if the problems are related to that?

[Griswald]

Hi thanks for your reply....
I am not sure how the glow plug became damaged. It has a full ASH up to 80k I bought it on 99, and was not aware it was damaged at the time, I was told it was a bit smokey due to the glow plugs needing changing, I found out otherwise. I also bought it knowing it was a bit underpowered and told it was the air mass meter. Audi confirmed there was a faulty meter and replaced it (but the underpower situation still exists) I suspect the glow plug was damaged by someone trying to replace the glow plugs, as all 3 on that bank were jammed up tight according to the Audi dealer who repared it. It has been suggested that the waste gate may be stuck open, preventing the turbo building up pressure, but am not sure if this turbo model has a waste gate (I am not mechanically minded, hense my search for help)

[adamss24]

Hi, i suggest you remove the rocker cover and check for abnormal wear on the camshafts lobes. Also i would replace the coolant temp sensor as it will make the engine run lumpy when defective. Also have a good garage do a pressure test on all the cylindres and post the results on the forum. What year is the car and was the diesel filter replaced recently ?

[Griswald]

As well as the other work stated, both rocker covers were replaced as they were leaking oil. Will look at the temp sensor. The Audi garage did report back and said it had full/normal compression, is that the same thing as a pressure test on the cylinders ? The car is 1999, pre facelift model. Diesel filter replaced as part of the service

[Griswald]

:zx11: :aargh4:
I have been told there is no abnormal wear on the lobes, so im still at a loss as where to look to sort this out.

One thing I have noticed is the oil temp gauge, it sits at just over 60 'c and below 80'c is this normal or should it be higher ? and could this be part of my problem ?

[nicfw]

OK, so the compression test is fine, cam wear is alright and presumably no fault codes. So what else can be limiting the gas flow through the engine? Check all inlet and exhaust pipework for obstructions, such as gunge build up from crankcase breather system on the inlet side. There have been some gruesome pictures on car forum sites of this problem.

[Niall76]

This problem sounds like a right thorn in your side. I'm not overly familiar with diesels but it's still basically a pump. So, one other thing that may be worth checking could be the injectors? I'd stick a bottle of injector cleaner in with your next tank of diesel. Hey, it's only a fiver so not too much to lose on this one. Other than that, I'm not sure? What's the exhuast like? The baffles haven't collapsed have they (probably clutching at straws here).

I take it the turbo has been looked at to make sure all is well with it? Wear and tear in that will give reduced power. Could be worth checking it out?

Hope you get it sorted soon, let us know how it goes.

[Niall76]

Could also be worth having a read of this http://www.vwaudiforum.co.uk/forum/showthread.php?t=6366

[Griswald]

Thanks for the tips, will check all the pipes on the weekend to make sure they are not blocked. Will also get some injector cleaner for the tank and let you know how I get on with that.

[adamss24]

Another thing to consider could be blocked cats on the turbo side increasing the back pressure and limiting the gas flow to the turbo. Another thing to consider is the anti shudder valve-if stuck will limit the air flow to the inlet manifold-causing the said symptoms. Take the car to a good audi specialist for few more testing and post watever fault codes are logged in the memory. Regards.

[Griswald]

I had a peep under the bonnet tonight, found 2 splash back hoses off and a wire (a bit worrying given its just come out of a Audi main dealer who had stripped the engine to rapair the damaged glow plug) not sure what the wire is but I have attached 2 photos in the hope that someone with a bit more knowledge than me can identify it for me.
Anyway, when I connected it the car became more responsive and the performance has perked up a bit, but still not getting boost from the turbo. I am arranging for it to go and have a diagnostic test and will post findings in due course.

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[Griswald]

Hi - does anyone know what the loose wire is I found in the engine bay ?
Pictures above
Thanks

[adamss24]

That's the oil temp sensor wire. It fits on the sensor that has the round prod on the oil feed pipe that goes to the turbocharger. Hope this helps.

[Griswald]

Thanks Adamss24 for the info.

When I found that wire off and a splash back hose off I have been looking under the bonnet almost on a daily basis, namely to see if the splash back hose was staying on - and it wasn't. I kept pushing it back on and next day one of them would be off again.

This am i decided to take a closer look and found that one of the splash back hoses (the last one at the front cylider) had been mistakenly 'clamped' under what looks like an exhaust mainfold joint ( im sure its not that but being dull etc) its part of the silver metal thing just to the right of my hand in the photo that seems to feed both banks and is at the front/top of the engine. I also noticed that where this splash back hose was trapped there was black scorching marks on the fuel feeder metal pipe (hot air escaping as it could not fit snug on the gasgit)

So off to the Audi garage that had it last when they stripped it to do the faulty glow plug, in fairness they took it straight in the workshop to get it sorted. Once I had it back it was like a new car !!! i was now getting boost from the turbo. So this leak from that mainfold was letting all the pressure out of the system and hense my lask of go go.

Still having a mate do a diagnostic next week to make sure all is well
Thanks to all for trying to help - much appreciated