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N75 and boost oddities.


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Hi ive run into a strange problem with boosting on my auq it appears to not like n75 valves.it started doing only 5psi a couple months ago from cold but since it only happened a couple times i wasnt concerned since then i had a stage 1 map on it and now wont achieve over spring pressure at all. Ive checked it can achieve boost using a cheap mbc and im using that as a bandaid at 10psi while i sort this out. Tried several n75s all f type valves a couple out of used but previously proper boosting auqs and a brand new one albeit a non oem copy valve. Result was none of them produced more than limp pressures done a check on vagcom and sure enough with the new stage 1 map its requesting 2085mbar which i think equates to around 16psi or so, i also checked the n75 dc in vagcom and the numbers seem to be ramping up to high 90s.im not sure of any other way to go about testing n75s. Also after the map i constantly get a 17704 cooling system fault even after changing cts and stat for oem items i get this code right away at startup and it only allows me to clear after 10mins of running.on vagcom temp reports fine holding at between 85-90 constant.then the next day there it is again code pops up right on power up. I know my turbo is producing boost ok as the manual valve allows me to set boost as i please but i dont want to run with this forever as its got bad drivability also i done a diy pump test for boost leaks and none apparent (i replaced a lot of pvc stuff last year along with coils and plugs) actual boost also seems to be reporting identical to guage in vagcom and maf readings as far a max goes seem in line at 142gs when i use 10psi.i would have expected some response even if its surging from the valves ive tried but its just constant 5psi from them all. Any help and guidence would be great if anyone knows whats going on here thanks

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Have you checked all the vacuum/boost pipes for leaks? Very common problem on Golf mk4 derived cars.

The 17704 problem sounds like there could be a bad value in the stage 1 map. Had a similar start up problem caused by a bad map a few years ago. Suggest you get the Tuner to flash the ECU back to a standard map, & see if it stops.

Edited by pauldazzle
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I made myself a little diy pressure testing setup with a small compressor to check for leaks none found.i do still have a pssssst sound when im under heavy load from left side but im at a loss where its from as no leaks and holds boost with a manual valve.

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Standard DV always worked best for me. You really shouldn't be getting a psssst sound, which makes me think something is leaking somewhere.

Sounds like the ECU is stuck in Limp mode, but 17704 as far as i know doesn't cause Limp. From the symptoms you describe I would of expect the dreaded 17705 code which does cause limp to be present not 17704!

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Funny you say as i have had 17705 (pressure loss between turbo and tb if i remember) but its only been a couple of times, nothing specific apart from its only showing up when im using the mbc as a bandaid to acheive at least stock boost.another curious thing is my sai pump doesnt run at all now but i never get any sai incorrect flow faults.

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