Hi all,

 

I have recently purchased a 2003 Octavia VRs thats had some interesting 'modifications' done to it which Im working through.

 

I am stuck with it surging under boost quite noticably. It drives fine other than that. I have read up on a few things so have a good idea where im going but would like some advice.

 

It had a cheap aftermarket cone filter fitted which has now been replaced with a standard airbox and new filter. It has an aftermarket BOV of dubious quality. Its missing the N249 valve, so im guessing its been bypassed, how well im not sure.

 

First thing I did was a global scan and found that the knock sensor for cylinders 1 & 2 was not responding, that turned out to be wiring and was easily rectified and is no longer coming up as a fault and in live data seems to be reading correctly, this made it run a bit better. The only recurring code is for the missing N249 valve, would this cause running issues? I also found the vacuum pipe from the boost pipe too the N75 valve had a split in it, I replaced this and again surging has improved but its still there.

 

MAF readings look ok in live data, but as I had a spare MAF I swapped it out, no difference so its back to the original one.

 

Comparing desired boost against actual boost in live data the the actual is in line with desired but keeps dropping out and then back to desired.

 

I can't see anything obviously wrong, but am now running out of ideas. When I get a chance I will put a smoke machine on the boost pipes and check for leaks on the intercooler pipework, although I can't hear the usual whistling of a boost leak.

 

Any advice greatly appreciated. Im not new to turbo motors, and have worked on more cars than I Care to imagine, but the 1.8t VAG lumps are new too me and previous owner bodges are confusing matters. 

 

Has it been remapped?, if so, do you know if it was by a known good company, or could the map be suspect.

 

Plenty of info on the n249 deletes here -

 

Could well have been remapped. Im going to order a boost gauge to see whats going on.. There was a gauge cluster screwed into the dash top with wood screws when I got it.. so that got ripped out straight away as it was offending me. God knows if it worked, unlikely. 

 

Ifit has been remapped if i get a second hand ECU is it plug and play or does it need to be coded to the car? I would prefer this car standard. 

If it's been remapped by a reputable company, they should be able to flash it back to stock, no new EMS needed.

I have no history on this car so wouldn't have a clue who has mapped it if it has been.

10 hours ago, Jux said:

Could well have been remapped. Im going to order a boost gauge to see whats going on.. There was a gauge cluster screwed into the dash top with wood screws when I got it.. so that got ripped out straight away as it was offending me. God knows if it worked, unlikely. 

 

Ifit has been remapped if i get a second hand ECU is it plug and play or does it need to be coded to the car? I would prefer this car standard. 

The ECU is not really plug and play apart from physically, it will need coding to the car, as will the immobiliser that is built into the ecu circuitry.

Okay I wont be looking for another EC then

Shoud be getting a boost gauge tomorrow. What is standard boost? 0.7 bar? And what would indicate a typical map? It has no supporting mods so i would very much doubt its anything more than a mild tune if it has been mapped

 

So I had a poke about for an hour today and found some more horrible bodges at repairing intake pipework which would have been drawing in air after the MAF, so I have repaired this and again the surging is reduced and only really noticeable on hard acceleration in the higher gears.

 

The N249 solenoid is still present and ticks away merrily  when activated via diagnostic equipment, but after a run it still comes up with 

P2100 - static - no indication on display (17608)

 

I'd rather not bypass it, my question is what problems does this cause if its failed? 

As a side note with the N75 disconnected it drives fine and holds (reduced) boost perfectly. 

Boost spikes p to about 0.9 bar and then fluctuates between 0.4 & 0.6bar If I disconnect the N75 it holds 0.5 bar perfectly. 

 

Ill take it too work on the weekend and smoke it and see if I can find any intercooler/vacuum leaks. 

Have you tested the dump valve to see if it holds pressure?. What brand is it?.

I was told it was a forge 007.. But looking at it fairly sure its a generic ebay clone.. I have ordered a standard recirc valve and pipework so I can just get it back too standard as trying to fault find with so many unknown quantities is a PITA. 

Looks like this http://www.ebay.co.uk/itm/25mm-Atmospheric-Turbo-Twin-Piston-VTA-Universal-Blow-Off-Bov-Dump-Valve-/112073897301?fits=Car+Make%3ASkoda|Model%3AOctavia|Cars+Type%3ARS+1.8+T&hash=item1a181ff555:g:61gAAOSwaB5XmWSJ

I bough it as a dealer trade in so didn't really pay big money, so am expecting to spend a few pennies on it. Front calipers were toast s new calipers, discs and pads.

I would not do too much more until you get a known good dump valve on there as that could well be your issue, especially if it is a clone with the wrong rate internal spring.

Edited 10 March, 20179 yr by kentphil1

Good advice. Previous owners aye, I removed some tuperware from pollen filter housing

has somebody put the tupperware on because the oem water deflector is missing from the n/s scuttle panel?.

Strange thing is that the deflector is still in place., pollen filter was as dry as a bone but the footwells are wet. Used to do a lot of A4's with scuttles full of water. Suspect its got another leak but PO focused on the scuttle area. Going to keep me busy this car, I can tell lol

So successful day today.

 

Fitted standard recirc dump valve and still spiked to 0.9 the hovered around 0.5 bar

Bypassed the N249 running the dump valve straight to the intake and plugging original pipe. Boost all over the place swinging wildly from 0.5 - 1.0 bar

Threw an old manual boost controller I had knocking around, and adjusted it after an initial run and it hold 0.7 perfectly

 

I still have the 249 bypassed but presume my real issue is a dead/lazy n75, it ticks away merrily through diagnostics software s nothing wrong with wiring. 

 

I also smoked it while it was in work, no leaks so thats all good. 

 

New N75 and I should be away? 

So new N75 fitted and all pipework returned to standard, pulls like a train and no more recurring fault codes for the N249 valve (P2100 - static - no indication on display (17608))

 

Requested and actual boost levels are matching and no boost cut/limping/EML

 

The only weird thing is that boost gauge reads around 0.5 bar...unplug the n75 and it drops too 0.3. Duff gauge? it was an ebay cheapy for testing?

So the only boost leak I cold find was air bypassing from the intake pipe out of the body of the new n75 valve... Pretty sure it shouldnt do this and the old one is completely sealed. That said I cant see that causing it not to hit 0.7 bar of boost.. Just sits at 0.5, and if I unplug the electrical connection it it it only boosts too 0.3 bar. 

 

Any further suggestions? Do these carslimit boost until the car has warmed up? as I have an intermitent coolant temp fault code