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Hi Rich
Sorry haven't looked here for a while. In my picture the round plate with the holes around the edge is the actual valve. Which is normally held shut under spring pressure. So putting power on the n75 won't give you a clicking sound. If it does there is something wrong with the valve. It is turbo pressure which opens the valve against the spring. When you start the engine the n75 is energised assisting the spring in keeping the valve closed preventing turbo pressure from reaching the waste gate. As turbo pressure increases the ecu switches the n75 valve on and off quickly which the ecu can vary this gives a varying pressure to control the opening of the waste gate. If the system fails, pipe burst valve jammed shut, strainer blocked the waste gate fails shut which would over pressure the engine causing damage which is why the ecu has a safe or limp mode. Have you cleaned the small black disc in the picture as this is a fine strainer which if blocked prevents turbo pressure getting to the waste gate causing the ecu to change to limp mode at approx 25000rpm on the 2.5 tdi.
 

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The mesh disc is clean, I thought there would be a moving part in the valve that moves to open/close the disc when powered up, I took an N18 valve to bits which has moving parts and these valves are used on other years/models of engine to do the same job.
Thanks for reply.
 

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New genuine N75 valve fitted it runs a lot better but when the turbo kicks in (about 2500rpm) it picks up well but there is a bit of `surging` to the turbo boost as it accelerating, ONLY when the EGR n18 valve electrics are unplugged, if the n18 is plugged in it runs rough at 2500rpm and sounds rattily. All pipes are ok.
 

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After weeks of changing solenoids and pipes etc. etc. and run out of things to check I got round to cleaning and greasing the multi blocks in front of the sump and now it runs like a dream.
Google `VW 17660 N108 `
 

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Hi all, can anyone clarify what the o.p. has said in the additional notes above? My van is a 2.5 ajt 88, I have fitted an Allard egr delete and changed all vac hoses. The n75 started mooing soon after on switch off, has now started mooing when driving. Runs and pulls fine though. Does it mean that with an egr delete the n18 becomes redundant and can be used to replace the n75? Any help appreciated, Thank you.
Iain.
 

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After weeks of changing solenoids and pipes etc. etc. and run out of things to check I got round to cleaning and greasing the multi blocks in front of the sump and now it runs like a dream.
Google `VW 17660 N108 `
Can you be more specified mate?
Explanation will help me and many others.
 

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Hi all, can anyone clarify what the o.p. has said in the additional notes above? My van is a 2.5 ajt 88, I have fitted an Allard egr delete and changed all vac hoses. The n75 started mooing soon after on switch off, has now started mooing when driving. Runs and pulls fine though. Does it mean that with an egr delete the n18 becomes redundant and can be used to replace the n75? Any help appreciated, Thank you.
Iain.
yesterday found the source of the problem..not the n75 valve,it was the n18 egr control solenoid, when I fitted the Allard delete pipe, I blanked the now redundant vacuum outlet from the n18, guess it was sucking and trying to implode itself, if you get what I mean. Removed the blanking bolt from the hose, and hey presto! the milking parlour has cleared off!! Cheers,
Iain.
 

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After many hours/money chasing every N75 N18 solution to the running problem a hookup to the computer brought up a code 17660 which is the `cold start` solenoid N108 on the pump which is about £130, but a google to see were it was brings up some stuff on the wiring plugs (which are below the altanator) which may be the problem. After a clean of the multi plugs the van ran great again!
Also make sure the thermostat is OK and the temp quickly as it will be running on `choke` for a good while,
 

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yesterday found the source of the problem..not the n75 valve,it was the n18 egr control solenoid, when I fitted the Allard delete pipe, I blanked the now redundant vacuum outlet from the n18, guess it was sucking and trying to implode itself, if you get what I mean. Removed the blanking bolt from the hose, and hey presto! the milking parlour has cleared off!! Cheers,
Iain.
Hi Enduroclarky,
Sounds like we have the same set up as you - I've got the EGR delete kit from Allard on mine and have both redundant hoses blanked off with bolts stuck in the ends - Has leaving the hose now open made a difference - if so did you unblock both hoses, or just the one - I spoke to Allard and they didn't think either would now do anything so could actually be removed completely?
We have issues of power loss up hills mainly, especially when cold. The hose to the wastegate actuator on the turbo looks iffy, so I'm going to swap that out too. I've got an intercooler to fit, but want to try and resolve any existing niggles before I do!
Cheers!
 

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Hello, I am new to posting on the forum so please forgive any mistakes etc., I will eventually get it right T: . I am the proud owner of a 2001 88 hp AJT 2.5 TDi, with about 165 k. on the clock. My query is about the possibility of the vacuum pump being faulty and hence not supplying enough suction, and this having an effect on the operation of the EGR and turbo wastegate; the reason for my question is that I have noticed a decrease in performance and general engine smoothness, exactly at the same time my brake assistance is almost gone (servo is OK, vacuum pump has been checked and provides very little suction-I am waiting for the replacement to arrive). Hoses and electrical connectors seem to be ok, so before I get into checking all that it would be great to know if there is a link there.
Thanks for the interest, and congratulations for a great forum.
Keep rolling
:D
 

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Hi guys i have a 2011 sportline bi turbo it has always done the mooing sound between 2/3rd gear but now does it for a few minutes after i switch the van off, im pretty sure someone said a biturbo will have two n75's is this right? does anyone recommend where to get the silicone pipes from?

cheers
 

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Hi Gents, hope you are well!

It seems that all the N75 valves available online look like the EGR one and not like the OEM AVC 2.5TDI one. Does anyone have a vacuum line diagram that shows how it must be connected?
 
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