mk4 tdi 150 arl - what is this connection on my mk4 tdi 150?

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Fri 14 Jun 2013 15:31
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

on my 2003 mk4 tdi arl golf, just above the oil filler cap, there is an unused plastic connector coming out of a short pipe between head and the manifold, what is this for?

also i seem to have an issue with low boost! no smoke whatsoever but had it remapped few months back, yet recently a dyno showed 145 bhp! it has just had a new n75 valve. It struggles to go beyond 3000rpm when on the move, when it does, nothing really happens! I can't really see any leaks in the boost pipes, normally they would be dripping oil if there was! my intercooler is probably the original but i dont want to spend the time/money changing it if its not the cause! my turbo does seem to spool by itself after short journeys, as if i was revving the engine when im not. Almost sounds like the fans are kicking in but its coming from turbo, car has 165k. 'economy' remap few months back should mean i see 170+ bhp, not 145. also i struggle to get more than 50 mpg on motorway, what could this be?

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Fri 14 Jun 2013 15:52
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - unthrottled

yet recently a dyno showed 145 bhp!

A rolling road test will yield whatever flywheel horsepower the operator thinks you want to hear. They often use ludicrous 'correction' factors to give optimistic estimates of engine power.

If you had a boost leak, it would manifest itself as being slow to come on song rather than running out of breath.

Sounds like you still have a problem with vane actuation-might not have been the N75 valve after all!

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Fri 14 Jun 2013 22:47
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

n75 only changed (was original) after lots of black smoke (LOTS) AT 4K PLUS, PRE N75 CHANGE, DYNO SHOWED 140, THEN, 110, 110, 105 BHP, I SAW THE SCREEN, graph etc. it never felt like 150 bhp before hand, any ideas on the open connection above oil cap? this bothers me a little

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Fri 14 Jun 2013 22:49
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

i should add that when i start from cold theres a fair bit of lag, yet starting from warm, no lag, i thought maybe if theres a slow boost leak, air pressure has time to release when car is left parked up?

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Mon 17 Jun 2013 16:44
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - BenG

Would need a photo of the connector you mention. However, on my car (Seat Leon Mk 1 with ARL engine) there's a tube which runs from the LHS of the cam cover (i.e; opposite end to oil filler cap) to the large-diameter black plastic air pipe which runs across the back of the engine. I assume this is a breather of some sort.

I guess any open pipe into the inlet pipework would affect air metering if it is after the MAF and so could affect engine power. If after the turbo, then you'd have a boost leak.

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Mon 17 Jun 2013 22:55
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

http://s431.photobucket.com/user/carnut1980/media/20130606_144147_zps8ebb8566.jpg.html

heres the pic of the connector

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Sun 23 Jun 2013 11:12
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

does anyone know what this connector is for? its just above the oil filler cap on my mk4 golf tdi arl!

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Mon 24 Jun 2013 08:49
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - craig-pd130

This is just a guess, but as the connector is on a pipe linking the engine breather system to the intake pipe to the turbo (well, I think it's the intake pipe, anyway), it is probably something to do with crankcase pressure monitoring or venting.

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Fri 28 Jun 2013 18:07
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - BenG

My ARL does not have that light grey plastic plug attached to the breather pipe so I don't know what it's for I'm afraid.

I guess you'd want to make sure its not leaking pressurised air from the turbo though.

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Tue 2 Jul 2013 20:55
mk4 tdi 150 arl - what is this connection on my mk4 tdi 150? - carnut1980

what would be the easiest way to do a boost leak test? smoke? cant see anything near IC, though its probably the original, the turbo area looks oily, though not on the pipes going in and out of it

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