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octavia mk1 boost problem


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#1 Biged

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Posted 04 August 2010 - 20:43

Has anyone has similar fault.
Start veihcle up drive as normal full boost no engine managment light on, then after approx 6 mile there isnt any boost, switch engine off restart back to normal full boost again.
Did notice there is a slight hesitation when lightly accelerating. not a misfire as just replaced coil packs and plugs as they went down.
Vehicle has been remapped so have replaced the divertor valve, ws thinking the n75 valve might be on way out ??? Is it worth getting the n75 j valve as this may run better with the car being remapped???
Have checked the fault think it said boost fault between turbo and throttle!!

Any would be great

#2 pauldazzle

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Posted 04 August 2010 - 21:14

It was 17705 code then? If it was I very much doubt replacing the N75 valve will solve it. Have you just had it remapped by any chance ?

#3 Biged

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Posted 04 August 2010 - 21:16

It was 17705 code then? If it was I very much doubt replacing the N75 valve will solve it. Have you just had it remapped by any chance ?


Yes spot on m8, that does look like the code i had, what are you thinking?

#4 pauldazzle

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Posted 04 August 2010 - 21:16

You better read this. http://uk-mkivs.net/...s/t/170257.aspx

#5 chicken_eyebrow

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Posted 04 August 2010 - 21:17

From your description of the fault code it is indeed the 17705 code

"pressure drop between turbocharger and throttle body"

You'll need to check all your boost hoses, that's the big diameter ones between the turbo, intercooler and throttle, but also the small diameter vac hoses around the engine and valves like the N75 valve.

#6 Biged

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Posted 04 August 2010 - 21:19

From your description of the fault code it is indeed the 17705 code

"pressure drop between turbocharger and throttle body"

You'll need to check all your boost hoses, that's the big diameter ones between the turbo, intercooler and throttle, but also the small diameter vac hoses around the engine and valves like the N75 valve.


Will do but it does seem like an electrical fault as when switching engine off the back on it returns to normal, cant hear any leaks, boost pipes being split etc, as far as i can remember it was fine before the remap

#7 chicken_eyebrow

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Posted 04 August 2010 - 21:29

If as you say it feels like there is no boost at all then it sounds like it's going into limp mode where it runs at only 5psi

You'll find when you turn it off and back on again it comes out of limp mode but then as soon as you use the turbo again and it detects the boost leak again it'll go into limp mode.

To go into limp mode it usually has to be a pretty big boost leak so the first candidates I would be looking at are the large diameter hoses between turbo and intercooler (in the wheel arch) and intercooler to throttle body (behind the headlight)

Remaps can cause this as you are going from a fairly tame 10psi max boost to 15psi or more and some of these hoses and hose clips might have been on the car for the best part of 8 years

Edited by chicken_eyebrow, 04 August 2010 - 21:31.


#8 Biged

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Posted 04 August 2010 - 21:33

If as you say it feels like there is no boost at all then it sounds like it's going into limp mode where it runs at only 5psi

You'll find when you turn it off and back on again it comes out of limp mode but then as soon as you use the turbo again and it detects the boost leak again it'll go into limp mode.

To go into limp mode it usually has to be a pretty big boost leak so the first candidates I would be looking at are the large diameter hoses between turbo and intercooler (in the wheel arch) and intercooler to throttle body (behind the headlight)


Thanks for that will check tomorrow, ps i drove the car 5 miles from switching it off and restarting and it drove fine even under hard acceleration, if the pipes were split etc surely i would hear this clearly when boosting as the pressure would be escaping ?

#9 pauldazzle

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Posted 04 August 2010 - 21:34

I hate to tell you this, but solving the 17705 code can turn into a nightmare. There are several pipes on the boost system that are prone to splitting that can cause this. When I had this on my Golf Mkiv Anniversary it turned out to be a problem with the remap. Custom Code maps have a known issue with this particular fault. & there are definitely generic maps out there that have an incorrect value written into them that cause this code. If it's down to the map it normally throws the code on cold start.
If you actually have a split pipe I would start by replacing the 2 small braided pipes on the fuel pressure regulator, & the one connecting to the pipework under the inlet manifold. They are prone to splitting & because they're covered by the braiding it's difficult to tell if they've split. The pipe to the top of the DV is also known to split. There's also a pipe under the inlet manifold that splits too. The pipe that goes from the top the turbo pipework to the N75 again often splits, & can be hard to spot without taking the pipe off. The pipe from the pancake pipe to the intercooler can become unseated, but this is normally accompanied by a loud whooshing sound under boost

#10 Biged

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Posted 04 August 2010 - 21:38

I hate to tell you this, but solving the 17705 code can turn into a nightmare. There are several pipes on the boost system that are prone to splitting that can cause this. When I had this on my Golf Mkiv Anniversary it turned out to be a problem with the remap. Custom Code maps have a known issue with this particular fault. & there are definitely generic maps out there that have an incorrect value written into them that cause this code. If it's down to the map it normally throws the code on cold start.
If you actually have a split pipe I would start by replacing the 2 small braided pipes on the fuel pressure regulator, & the one connecting to the pipework under the inlet manifold. They are prone to splitting & because they're covered by the braiding it's difficult to tell if they've split. The pipe to the top of the DV is also known to split. There's also a pipe under the inlet manifold that splits too. The pipe that goes from the top the turbo pipework to the N75 again often splits, & can be hard to spot without taking the pipe off. The pipe from the pancake pipe to the intercooler can become unseated, but this is normally accompanied by a loud whooshing sound under boost



Yes it does seem a bit of a nightmate lol, might put the original map back on and run it see what happens, this will be easier to start with rather than looking for a needle ina haystack, thanks for the tips will update the progress i make or dont make lol.

#11 chicken_eyebrow

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Posted 04 August 2010 - 21:43

Thanks for that will check tomorrow, ps i drove the car 5 miles from switching it off and restarting and it drove fine even under hard acceleration, if the pipes were split etc surely i would hear this clearly when boosting as the pressure would be escaping ?


If its one of the big hoses then usually you would hear a noise, the turbo to pancake pipe hose popped off on mine once after I didn't tighten the hoseclip and it sounded like a spitfire and went straight into limp mode. As pauldazzle said it could be one of the smaller hoses if you can't hear an obvious noise. 17705 is a ******* to fix, there are members on here that have replaced pretty much everything including buying new throttle bodies etc and still not cured it :doh:

#12 Biged

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Posted 04 August 2010 - 21:50

If its one of the big hoses then usually you would hear a noise, the turbo to pancake pipe hose popped off on mine once after I didn't tighten the hoseclip and it sounded like a spitfire and went straight into limp mode. As pauldazzle said it could be one of the smaller hoses if you can't hear an obvious noise. 17705 is a ******* to fix, there are members on here that have replaced pretty much everything including buying new throttle bodies etc and still not cured it :doh:


I will just need to dig my magic wond out lol, it will be getting sold if i cant :) cure it

#13 pauldazzle

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Posted 04 August 2010 - 22:10

Yes it does seem a bit of a nightmate lol, might put the original map back on and run it see what happens, this will be easier to start with rather than looking for a needle ina haystack, thanks for the tips will update the progress i make or dont make lol.


When this happened to my Anniversary I spent 2 weeks replacing virtually every pipe on the boost & vacuum systems to no avail. The tuner was convinced it wasn't the map, but after chasing my tail for 2 weeks looking for a non existent boost leak, in desperation I got the Revo trial loaded in & the code stopped. :rofl: Got the car Revo'd a month later & never saw the code again.
In saying that the most common cause of 17705 is a split or loose pipe.

#14 Biged

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Posted 04 August 2010 - 22:14

When this happened to my Anniversary I spent 2 weeks replacing virtually every pipe on the boost & vacuum systems to no avail. The tuner was convinced it wasn't the map, but after chasing my tail for 2 weeks looking for a non existent boost leak, in desperation I got the Revo trial loaded in & the code stopped. :rofl: Got the car Revo'd a month later & never saw the code again.
In saying that the most common cause of 17705 is a split or loose pipe.


I think it will go for the original map on first as it was fine until it was mapped, could be the remap runing slighty more boost causing an old pipe to split but hope not as it seem a nightmare trying to trace which pipe is split and leaking, have ordered new boost/vac pipes anyway graet fun :D

#15 pauldazzle

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Posted 04 August 2010 - 22:27

Like I stated earlier usually when it's the map it does it on cold start. I once plugged up Vagcom & every time I started the engine it would throw the code I'd clear it start it & the code would appear. Once the engine had warmed up it was fine.

Edited by pauldazzle, 04 August 2010 - 22:27.


#16 Biged

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Posted 04 August 2010 - 22:31

Like I stated earlier usually when it's the map it does it on cold start. I once plugged up Vagcom & every time I started the engine it would throw the code I'd clear it start it & the code would appear. Once the engine had warmed up it was fine.


Going to get the logs with vagcom on way to work will let me see whats going on, will start to get bothered when i run out of things to check lol, got loads to check before i get to the stage of letting it go on fire :D

#17 borris

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Posted 04 August 2010 - 23:09

Like I stated earlier usually when it's the map it does it on cold start. I once plugged up Vagcom & every time I started the engine it would throw the code I'd clear it start it & the code would appear. Once the engine had warmed up it was fine.

i get this too on a cold start up never did it before remap hhhhhmmmmmmmmmmm

#18 Osku_P

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Posted 05 August 2010 - 06:18

From your description of the fault code it is indeed the 17705 code

"pressure drop between turbocharger and throttle body"

You'll need to check all your boost hoses, that's the big diameter ones between the turbo, intercooler and throttle, but also the small diameter vac hoses around the engine and valves like the N75 valve.


Is there by any change any full set of silocone hoses like this http://www.siliconho...=0030&cat=00230 on sale for AUQ engine? Would be great to have that kind of set ready when I will have boost/vac leak :'(

#19 westallc

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Posted 05 August 2010 - 08:02

they do a boost set for the vrs not cheap

most issues are with vac lines and by fitting a catch can wich is a must with this engine you can remove most and throw them in the bin

#20 Bodge

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Posted 05 August 2010 - 08:28

they do a boost set for the vrs not cheap

most issues are with vac lines and by fitting a catch can wich is a must with this engine you can remove most and throw them in the bin


Agreed. Buy a catch can and start the breather/vacuum hoses from scratch. My money is on a vacuum hose under the inlet manifold.

I've had the exact same symptoms before.

First time it was the Y-shaped breather hose on the rocker cover and the S-shaped vacuum hose for the breather system under the inlet manifold.
Then it was a dirty throttle body and intake air temperature sender.
Then it was a leaking vacuum hose that I hadn't done up properly. You'd be surprised how much a small leak can screw up the running! The car was a complete dog.
Then it was a perished vacuum hose in the suction pump system, so I ripped the entire system out.

The 17705 is never anything major, it's just annoying! If it does turn out to be a bug in the map, don't give up, get the guys who wrote the map to remove the code.

Have you had the other resultant error code up yet? Should say something like Bank 1 running lean/rich. Don't freak out when you do, just means you have an air leak.

#21 Biged

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Posted 05 August 2010 - 08:30

they do a boost set for the vrs not cheap

most issues are with vac lines and by fitting a catch can wich is a must with this engine you can remove most and throw them in the bin


Have just flashed the original map back on to the car, now running fin all be it slower lol
No fault codes stored great.
Poss the remap is causing the n75 to operate out of tollerence causing the limp mode?
Almost certain no pipes can be at fault as they would show up when im driving it with the original map on it.
Might get the boost pressure turned down slightly on the remap and try it from there, could also be the n75 valve needing replaced if i am running higher boost?
Was looking at the n75 j version not the original n75?

#22 Biged

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Posted 05 August 2010 - 08:44

Agreed. Buy a catch can and start the breather/vacuum hoses from scratch. My money is on a vacuum hose under the inlet manifold.

I've had the exact same symptoms before.

First time it was the Y-shaped breather hose on the rocker cover and the S-shaped vacuum hose for the breather system under the inlet manifold.
Then it was a dirty throttle body and intake air temperature sender.
Then it was a leaking vacuum hose that I hadn't done up properly. You'd be surprised how much a small leak can screw up the running! The car was a complete dog.
Then it was a perished vacuum hose in the suction pump system, so I ripped the entire system out.

The 17705 is never anything major, it's just annoying! If it does turn out to be a bug in the map, don't give up, get the guys who wrote the map to remove the code.

Have you had the other resultant error code up yet? Should say something like Bank 1 running lean/rich. Don't freak out when you do, just means you have an air leak.


Where did you get the diagram so you could remove most of the vac pipes from? Where did you get the catch tank from any pictures of the install

#23 Bodge

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Posted 05 August 2010 - 08:46

Don't fall into the normal trick of blaming the N75. Everyone does it, and they normally end up out of pocket and dissapointed! People love changing it because it's easy!

There is no upgrade for the standard N75, so you don't need to change it when mapping.

The J version N75 is just a really really old design, with a slow response, so it can't react fast enough to the rising boost levels and causes a momentary spike in boost pressure. It's a downgrade, and a shady way to get a couple of extra psi out of the turbo without remapping. It definately won't help you here, if you're worried about having too much boost.

The reason you don't have the error code on the standard map may be due to the fact that the leak isn't leaking enough. Either that or it's the map. Who did the map? Do you have a boost gauge?

#24 chicken_eyebrow

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Posted 05 August 2010 - 08:49

Almost certain no pipes can be at fault as they would show up when im driving it with the original map on it.


The original map peaks at about 10psi boost whereas a remap will peak at something like 18-20+ psi

So if it's only a small leak or crack in a pipe it might not show up under lower pressure

#25 Biged

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Posted 05 August 2010 - 08:55

Don't fall into the normal trick of blaming the N75. Everyone does it, and they normally end up out of pocket and dissapointed! People love changing it because it's easy!

There is no upgrade for the standard N75, so you don't need to change it when mapping.

The J version N75 is just a really really old design, with a slow response, so it can't react fast enough to the rising boost levels and causes a momentary spike in boost pressure. It's a downgrade, and a shady way to get a couple of extra psi out of the turbo without remapping. It definately won't help you here, if you're worried about having too much boost.

The reason you don't have the error code on the standard map may be due to the fact that the leak isn't leaking enough. Either that or it's the map. Who did the map? Do you have a boost gauge?


The y shaped breather pipe on mine from the cam cover was split, have resealed it, was like this when i got the car last week and was driving fine then with original map on it. I thought this was just a oil breather pipe and not a vac pipe?? Any ideas for price or part number of this pipe as it may be the cause when putting more boost through the pipe work?? The map was a slight increase in boost approx 10% as didnt want to push the car too much as its getting old lol

#26 SNH

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Posted 05 August 2010 - 08:59

theres an uprated y pipe for sale here http://briskoda.net/...breather-pipes/
a worthwhile upgrade as the standard one is a weak point :thumbup:

#27 Biged

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Posted 05 August 2010 - 09:13

theres an uprated y pipe for sale here http://briskoda.net/...breather-pipes/
a worthwhile upgrade as the standard one is a weak point :thumbup:


Thanks for that, have just sent him a pm

#28 pauldazzle

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Posted 05 August 2010 - 10:12

When I bought my Anni the y piece was completely shot, but it wasn't throwing a code. You still need to replace it though. I would get the free Revo trial loaded in & see if it throws the code. i believe there are Revo dealers in Edinburgh & Dundee. Isn't going to cost anything & could save you a whole lot of grief.