Limp mode at 62mph

mk1_nutter

mk1_nutter

Member
Hi guys at the garage i work at the weekends, we are having trouble with an 1.4tdi 75bhp

If the car is driven hard through the gears, as soon as it hit around 62mph it goes into limp mode.

The Turbo and the 3 valves have been replaced from a working A2.


Any suggestions?
 
Are there any error codes?
Either way, it'll be a boost leak for sure - either a split / leaky intercooler causing underboost failure (the bottom of the intercooler seems prone to failure), or one of the three boost control lines (tiny bore flexible rubber hoses) that go round the back of the engine into the N75 valve causing overboost failure.


Incidentally, why was the turbo replaced?
 
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I beleive its showing positive deviation. I think the turbo has been replaced as they boys thought that was the problem. Back to the garage tomorrow so i will see how they have come along. How can the intercooler be check on the car? will it make a loud noise at high rpm?
 
Hi all,
i hope i'm not butting in here and don't wish to detract from the original question but this is my first post and i have a similar problem with my beautiful 90 bhp TDI that i recently bought and would be ever so greatful if someone could help.

After buying the car and travelling just 8 miles of the long 200 mile drive home in the dark, the car lost all power whilst overtaking a lorry on a slight up hill stretch of the motorway travelling at around 70mph. I lost all ability to accelerate even when i changed down through the gears and the car gradually lost speed to the point where it wouldn't go any faster than about 55mph and the revs at around 2,000 ish, i presume this would also be limp mode?
I just managed to get past the lorry and pulled over, turned the engine off and phoned the seller who ignored my repeated calls, presumably only too aware of a problem with the car. So stuck as to what to do started the engine again and all seemed ok.
I drove a further 20 miles or so only for it to happen again and this time the engine management light also came on. This happened a further 4 times on my journey home with the car running and pulling perfectly between these incidents.

I have had a scan carried out which gave 4 fault codes, these were;

Cylinder 1 Glow Plug Circuit (Q10) Electrical Fault: P0671 static-no indication on display
Cylinder 2 Glow Plug Circuit (Q11) Electrical Fault: P0672 static-no indication on display
Cylinder 3 Glow Plug Circuit (Q12) Electrical Fault: P0673 static-no indication on display

Incidentally even on a very cold morning when i turn the ignition on before i start the car the glow plug warming light only illuminates for a second or so and when i start the engine it idles rough for a little while but then goes fine.

I had a mechanic look at the car and checked the wiring harness to the glow plugs which he said was fine but apparently 2 of the glow plugs were bad so all 3 of them were replaced with genuine new one's from Audi.
As a result he car now starts a bit better but the glow plug warming light still only stays on for a second or so where as i have a friend who also has an A2 diesel and their light illuminates for maybe 5 or more seconds?

The fourth fault code was;
Charge Pressure Control: Positive Deviation: P1557 static-no define

This is the one i presume is causing the limpo mode but i have no idea what it is?

Although a terrible start to A2 ownership, i love the car and would be immensely greatful if someone could offer a little advise to avoid it being a too costly problemand hopefully a simple fix as having paid good money for the car could really do without the additional expense.

Sorry for such an epic first post and many thanks in advance to anyone who might be able to help,

Dolly.
 
Also forgot to add that as i press the accelerator and rev the engine i am getting a sort of whoooing sound rather like a police siren. Could this be connected to the above problem?
 
Welcome! With the 90 it is likely to be the split intercooler as above, or possibly sticking turbo vanes - the 90 has a clever variable geometry turbo but they can coke up over time. As you can hear a whoosing sound under acceleration that suggests leaking pressurized air... Open the bonnet and look for signs of oily discharge from the bottom of the intercooler as per the above...
 
Thanks very much for the reply.
I did check the bottom of the intercooler for oil leaks as i read that could be a problem but all seems good in that area with no leaks.
 
Thank you for that link Spike.
I will get it looked at again and ask the garage to check the turbo.
It does make sense what Dan b also suggested regarding leaking pressurized air as i'm getting the whoooing sound when i rev the engine, would the sticking turbo vanes cause this sound as it's most of the time now but only goes into limp mode at high motorway speeds?

Dolly
 
There could be other causes for boost leaks other than the split intercooler, it's just that that's the most common one.
When you say whoosh noises, is that when you're actually driving the car and accelerating? Is it at the same time as the revs build, or is it when you take your foot off and it whooshes afterward?
As you're in the Midlands,you might be worth taking it to someone like Stealth, who could give you a proper diagnostic.
 
My boost problems (very similar to these) were due to two pipes going to the N75 valve had been swapped over so the N75 valve was ineffective and couldn't control the boost

My code always came up as a boost deviation.

Was fixed when i had my car remapped at Stealth.

J
 
Could i ask where the 3 and 5mm pipes are to be found on the TDI 90?
I am getting the whoosing sound whenever i press the accelerator and rev the car now and it went into limp mode again yesterday on the motorway when i accelerated to 80mph (was testing to try to make it happen when the coast was clear with no other cars around).
Really want to get this problem sorted and i am hoping and praying that it could be something simple sounding like these split hoses?
Are they easy to get at to replace?

Thanks, Dolly.
 
Hi Dolly

The small bore pipes snake around the engine bay quite a lot. On the top right of the engine bay, you will see an assemblage of small hoses going into a valve (the N75). There will then be several pipes which go around the back of the block (behind the air scoop) and then down the back towards the wastgate regulator (on the turbo) and the manifold, with the third one going to the ECU. They're tricky to see and check when they disappear off down the back. They do have a nasty habit of splitting with age and cause all manner of turbo-boost-related problems.

However, as you say you have a "whooshing" sound, is that when you are on the accelerator? It is possible that that is the noise of compressed air escaping somewhere - possibly a split intercooler which is again common on our cars. You can visually inspect the bottom of the intercooler (the small vertically-mounted radiator on the left at the front of the engine) for signs of oil discolouration and/ or obvious splits/ cracks. It should be a nice clean silvery colour all the way down, but if it's dirty and black and foul at the bottom, it's likely it's leaking oily intake air and could be the cause of your problem...
 
Thanks very much for that Dan, will do some more investigating and check the intercooler for leaks again too although when i looked before it all seemed clean.
Do you think that my problem could be similar to that of Hooley's regarding the pipes being connected wrong? The reason i ask is that when i bought the car and took it to a mechanic the engine cover was missing so he thought someone had been messing, or again would that not cause the whoooo-ing sound (which really does sound like a subdued police siren) which by the way seems to happen when i accelerate or rev the engine.
I'm really hoping its not the turbo itself as its 800 and something pounds on an exchange basis for the part only without fitting which i could seriously do without.
 
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