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Occasional low boost pressure - VRS


YellowCar

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Hi, on about 3 occasions in as many months now my car has run with low boost pressure.  I don't have a gauge so it's just by feel.  It's not coming in and out, it just doesn't appear to be there.  There is no warning light and no code appeared when I had it remapped, when I leave the car and restart it's fine and takes off again.  It has had a stage 1 remap and I use a pipercross panel filter, when I had it remapped I replaced the MAF and cleaned out the throttle body, 99% of the time it's fine with good mpg, but I'm just starting to get concerned about this issue.  The car has done 68,000 miles and is in pretty good nick all round.  It was also Terracleaned but this had occured before I had this done.  This is the first turbo I've owned and only had the car since July, so any help/advice would be greatly appreciated.  Also, is it normal to hear the waste leaving the car?  People ask me if I have a dump valve fitted, and I don't, it's not as loud as a dump valve at all, but it is audible from inside the car with no radio on.

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  • 3 weeks later...

Sit rep:

 

Sorted the noise on cold start, apparently a hose had popped off the secondary air pump.  Alongwith that the scan picked up code 17705 (I think), pressure drop - check DV.  Garage checked over the hoses for leaks and all looked sound as I thought, so we went for a DV swap, they had a used Forge one with the correct spring so had that fitted.  Cleared codes, test drive, scanned again and fine.  Ran it for a few days after (was running very nicely), then limp mode again, all smooth, not drastic loss of power but no (or very little) turbo.  I stopped for 5 mins and when I started it up again it was fine.  Took it back to the garage for a scan and same code popped up.  He suspected the ECU was 'learning' the new DV, especially if pressure had been down for a while before.  Cleared codes, few days later has done it again today on the way back, driven for about an hour this morning and ran sweet, but limp mode home.

 

It's starting to do my head in now, garage is cool they're willing to persevere and help me out, but does anyone have any ideas what it could be?  I would have thought if it is a split pipe it would be a more consistent, persistent problem?  If it was n75 it wouldn't be running so smooth (there are no misfires or uneven acceleration).  I think they checked air flow and all is good, but every now and again there may be a little lump on idle, but that is every now and again, like 2 or 3 times.

 

Cheers

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If it was a split pipe wouldn't it be a more persistent, consistent issue? When it was scanned after the DV was done there was nothing for lean fuel. It only seems to happen once every dozen trips or so. Anyway it may be worth a test, is it the kind of thing most garages can commonly do?

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If you fancy ago yourself. Get a cheapo tin of carb cleaner for the £1 shop (blue and white tin) remove all the plastic covers and with the engine running spray all the pipes with carb cleaner. If theres any splits the carb cleaner will get sucked into the cylinders and the engine will struggle for a moment. Then you'll know roughly where, if any pipes are split

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The ECU can be pulled out of limp mode by recycling the ignition so no need to wait 5 mins.

17705 can be a real pita to pin down. As stated check all the pipework around the inlet manifold especially the S pipe under the manifold which is notorious for splitting. Clean the throttle body too as if it's gunked up that can cause 17705.

This pretty much covers it. http://uk-mkivs.net/topic/10891-17705-the-saga-is-over-well-for-me-anyway/

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Yeah I cleaned the TB a while back (without disconnecting it), a job well worth doing and the guide on here was great. I think the garage focused on the pipes at the back, don't think they looked under manifold too much.

Ok, plan of attack

1) More thorough check of pipe work/smoke test

If still no joy

2) Get post-map software checked out

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When I had 17705 on my mkiv Anniversary I replaced pretty much all the rubber boost/vacuum pipework, & the DV, but it turned out to be the map at fault :wall:

Edited by pauldazzle
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I'm glad I read the sticky thread here as I'd probably do the same. A bit gutted I went for a DV, at least it can be ruled out I suppose and it is worth having, holds boost better (when its running right!). At least I can badger the garage a bit because I paid out for having that done, they've got to see it through now.

What's making me think as well is the guy who did the map scanned it to check its health beforehand and this code was nowhere to be seen. Think its only happened since, so I reckon its the map software, or the increased pressure has split something slightly. Don't think he did a bad map, power delivery is nice and progressive and mpg is great, cant complain and I'd be surprised if he's messed up. Also if I take it back to him, if he wrote the problem into it he may not see it. There's a guy at the garage who did the DV is a mapper which could be handy, may be able to talk him into assessing the map as part of the next diagnostics step.

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Smoke test done, no split pipe. Was a very very slight leak (that they needed UV to see) where a pipe connected to the turbo. They reckon they'd be very surprised if that was throwing the code. So it looks like getting the software looked at and potentially remapping the remap. Not sure if that's good news or not, can't see it being anything else now really. They made the pipe in question more snug. The guy that does remapping there is a vee dub enthusiast so it will probably be worth a shot.

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Sorry for jacking this tread. Hello to all. I haven't yet introduced myself. I'm from Slovenia and own octavia octavia 2002 1.8T 4x4 arx engine (custom remap to 195hp-long story). I'we done alot of reading on this forum regardin 17705 code. Had this code before remap. I tried just about everthing there is to try and still have this code. I throws me in limp mode almost every day when starting car, quick restart after warm up and its ok. No other codes for more than 3 months.

Vag com looks ok, boost ok, currently trying n249 bypass problem stays. So yesterday I've electricaly disconected n112(got code) and had almost 2 psi higher boost, actualy even specified boost was higher than usualy. So is there a possibility my combi valve isnt working properly? Please help

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Hello again. Today i got a vaccum pump and tested combi valve and all conections between intake mani and combi valve. All ok, combi valve not leaking, opening and closing nicely, tested n112 and n249 thru vagcom and vacuum pump everything working, sai pump blows alot of air. Connected all together and then tried readiness test and sai wont pass. Still got 17705 code.

Oh fuel trim are 0,6 and -3,9. Any clue annyone?

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Replace your N75 valve. This can play up and cause limp mode to protect engine/turbo from unwanted conditions as it is acting as a boost controller between ECU and Turbo. Limp mode is approx 5psi Max.

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Yp that's correct only 5 psi. So had some time thru weekend when my daughter was sleeping. Did another pressure and vacuum test. On both ocassions only 1 psi lost in 30 second and no audible hissing. Did a long trip over 120 miles everything ok. Then yesterday morning again limp. Checked when came home and found readiness test for sai is ok. Funny though last time i deleted fault code on Thursday and only experieced limp yesterday. Fuel trim sit now on 0,8 and -5,5. Aint that bad. So i guess it has to be some hardware problem that ecu doesnt detect so it could throw a code.

Another thing - when i start car sitting for a few hours - so it cools, my revs go very high (almost 2000 rpm only when it cranks) and then immediately go to 1200 rpm until sai stops and then slowly decrease when engine gets warmer.

Since i have no one around to test another n75, i might buy a new one and give a go.

 

Thanks  

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Hello again. Finally something new. Didn't clear fault codes for a week now. On thursday my car stalled after start, tried to start again it would crank but no start, tried again and it did start. Didn't have time to check what it was, so yesterday morning leaving to work car wouldnt start until it cranked fo almost 10sec. And got a code. P0343 camshaft position sensor signal too high. of course 17705 is still there. Tried cleaning sensor but no succes, ordered a new one. So now VVT not working and also litttle les boost down on the revs. About 12 psi on 3000 rpm.

I think its posible this sensor (camshaft) might be the reason for 17705 code in the first place. I remember when car was mapped boost was holding 17 psi from 3000 to 5000 rpm, but now it was 17 psi from 3000 to 3500 rpm then dropped to 15psi and again 17 psi from 4000 to 5000 rpm. I guess it was bad for a few months now, but not enough to throw a code? Has anyone had same problem? Will report when i change the sensor (its a two minute job).

Edited by robek85
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