My s4 surgery

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Matt82

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well things have started in earnest

i got the s4 into the s4 surgery secure compound (basically a shack out the back built by a previous tennent, has three walls made of fencing boards, the garden fence is the forth wall. the "roof" is corrugated steel and leaks quite extensively. my attempted to get the electricity going lead to a shower of sparks...) it has no doors, you just remove to panels and drive in

the other night i put vagcom on the car and found it was in limp due to "positive boost deviation". it had one code F DV as well.

i now have two new 710n valves and an n75 on order. the y pipe is off.

i stripped things back and decided to make a play for the tbb too as i could tell that didnt look right. sure enough it has a ruddy great split

then i had a play with the n75 and had a suck on the three pipes. one is clearly going to the wastegates but tbh i couldnt get it to hold pressure and cant remember if they actuate on pressure or vacuum. can anyone remind me?

one hose clearly goes to the breather system (the vacume part?) and then one i expect is the pressure part going to the compressor housings. no idea how ill test to see if those are connected or even air tight.

sadly the engine looks like its been worked on by monkeys in the past and its really not feeling like a good buy at the moment.

the rubber hose coming off the PAS pump looks shady but im going to rock on :rock:

next stop, silicon boost hose kit and work out how to pressure test it all properly
 
An N75 thats off will allow all the boost pressure thru to the actuator.

It will have one Feed line from the inlet manifold, one output to the turbo actuators, and a bleed line to bleed the boost off to hide it from the actuators.

I recently was under the bonnet of craigs trying to fit a silicone hose kit and its horrible horrible job. the biggest issue was the TBB didnt quite fit right meaning the nearside boost duct wedged itself firmly into the fan. Ended up having to remove the nearside intercooler to boost duct pipe and replace the rubber one to give the duct enough movement to clear the fan.

I suspect hes going to have to get either a different Silicone TBB or an OE one.

Plus, half the hoses from the turbos to the intercoolers are buried up under the motor in a rats nest of pipes, and tbh we just couldnt see the point changing them so left them be.
 
nope? with the valve off, its open, so ALL the boost pressure is fed to the actuator and the engine runs actuator pressure (4psi).

To control the boost, the valve bleeds off some of the boost coming from the inlet, so while the engine is at 8psi the actuator is only seeing 4psi (for example)

It wont have any sort of 1 way valve inside it, its just a streight forwards electronic bleed valve.
 
sorry, i meant the air line to the wastegates themselves, are they supposed to be air tight?
 
yup, in built bleed valve

are wastegates actuated on positive pressure or vacuum?

im so tempted to get it running right again, save up some pennies, try and diagnose the rattle on the off side bank and then put it back in the garage and do an engine pull.

i can do the belts, rollers, water pump all at the same time. when it goes back in (famous last words) it should be perfect.
 
Positive pressure.

Boost gets applied to the actuator and at ~4psi it opens.

N75 just bleeds off the amount of boost the actuators see.
 
hi there mate

yeah, i decided i was sick of working on logically/sensible engine bays and needed to work on something layed out by window licking crack head Masochists
 
thats coming from a guy doing a restoration on a porsche 928!

on the s4 im terrified of dropping any tools or parts under the bonnet because they would never ever be seen again.

after a while i know its lay out by the back of my hand but until then its a scary place to spend your evenings
 
Matt82 said:
thats coming from a guy doing a restoration on a porsche 928!

on the s4 im terrified of dropping any tools or parts under the bonnet because they would never ever be seen again.

after a while i know its lay out by the back of my hand but until then its a scary place to spend your evenings
Click to expand...

Things I've lost in the engine bay:

- 13mm spanner
- 2x large washers from top of suspension mounting
- 1x airbox clip
 
ah, so you found it then :p

pedro, you haz an s4 too?
 
lowly? you bought the sensible car, we all know how good the 20vt is.

ive got an s4 sat in my lock up, which after ive got sorted, could very well have a dead turbo. turbo change on a 20vt is pretty simple bar manifold bolts being rounded to nothing. ive got that to face (twice), after the engine is removed

lowly? i dont think so
 
Indeed Matt, she will be all good again soon, its moe hard work than physical parts i bet.

Most of the work done on S4s is labour, parts cost the same as on anything else tbh.except often there are two of them,lol
 
No matter how hard you try though you'll never get the sound of a twin turbo V6 from tiny 4 cylinder!

Except for BYZAN A4s Quattro which does sound just like an S4!
 
Last edited:
i managed to spend another couple hours in "the compound" under the bonnet of the audi tonight and came out feeling positive.

fhose is off and sure enough its dead as a dodo. im waiting for this silicon hose set to arrive now

i had the cam belt covers off, no evils to report in there

i had a light pressure line on the on the wastegate line and sure enough it holds pressure so now i just need to wait for the silicon kit

there is a rubber hose from the pas pump that looks a bit dodge and might explain the leak/lack of pas fluid

fhose is off, its dead. one hose leads off under the manifold, and leads back to the bulkhead. how do i know thats not been compromised? whats its function?

most of the front bushes look new. my dampers are red, whats that about?

brake fluid looks almost new and ive got an engine oil leak that looks like it comes from the oil cooler area. i had the under tray off, both of the bottom IC hoses look fine too

so im pretty happy
 
Theres a useful F-Hose delete thread on audisrs or rs246 (i forget which), i would go read and do it. Kill the N249 while your there. Its probably also worth replacing the two green 1 way valves just to make sure they're ok, as they're not expensive. the black 1 way is more pricey, but gets deleted with the N249.

Craig has the RS4 front manifold pipe and 1.8T rear hose you need to complete the F-Hose delete using mostly OE parts, so if your interested, drop him a PM and i'm sure you can have them for some beer tokens.

OE dampers are red. Thats normal.
 
im still trying to figure out what i gain from deleting the fhose. in laymans terms, the fhose is where the breather system links back to the manifold

this is a weak point on any engine due to the way the oil vapour kills the rubber

when i put the silicon set in, its sorted, i might even consider a catch tank

i think it would be well worth changing the non return valve there too as that'll be a major boost leak
 
Your just rerouting the breather and removing a weakness.

There is another breather inlet on the back of the manifold anyway. I'm not sure what purpose the F-Hose even provides.

Audi themselves got rid of it on the RS4 and 2001 S4.
 
i dont think it removes a weakness, it just moves the weakness elsewhere

breather systems are prone to failure due to the oil vapour and the fumes, it just kills rubber. if a made a t section on the back of the inlet manifold it would be more joins to leak and the rubber will still get damaged

im not keen on the breather hose that goes from the back to the front and joins the f hose.
 
;) i wont do it just because everyone else does it. i might see otherwise in the future but ill just put the silicon set on

all i need now is a crate of quality jubilee clips
 
cable tie them, probably still better than it was......LMAO

It sounds to me like sh was still a bargain mate, just needed some much needed TLC
 
Matt82 said:
im not keen on the breather hose that goes from the back to the front and joins the f hose.
Click to expand...

That gets shortened right back to the spider and T'ed into the manifold back there with the delete. Its hard plastic anyway though, not rubber
 
ill be making up a boost leak tester soon too because it doesnt look like the silicon hoses will be arriving as soon as i hoped

im planning to remove the big y pipe and pressure test from the intercooler on wards on each bank, obviously blanking the other side off too.
 
This was discused on AudiSRS the other day, but I can't access it from work.

78mm seems familiar. Think the RS4 Y-pipe was slightly bigger at 84mm. Might be a few mm out, but pretty certain they are right.

Defo agree with Aragorn in respect of pressurising from the Y-pipe as at least you are then testing the seals around the DV's and all the turbo pipes. I've had leaks in both of those places in the past. If you just tested from the intercoolers you would effectively be missing out the majority of the intake. Appreciate that any leak from the Y-pipe down as far as the turbos would result in a vacuum leak rather than a boost leak, but those would still cause you problems as your MAF wouldn't be measuring everything going into the intake and you'd run the risk of sucking in unfiltered air.
 
turns out the start of the Y is 3inch exactly, 76mm. ive got some of that laying around from another car

just need a plug and a tyre valve for it..
 
boost hose set arrived today, ive done the tbb, fhose, post IC and DV hoses. two new DVs too

i also started the engine and had a listen around with my stethescope. the heads sound good, pas pump is a bit noisy, but the off side exhaust manifold sounds like a cement mixer. once the car has run for about a minute it goes quiet though

i have 5L of 5w40 fully synth diesel engine oil and 1L of auto gearbox fluid, this is going in tomorrow, this ought to be a very good cleaning product

im itching to get it out on the road and see how it feels powerwise, but its too windy to take the side off my SECURE COMPOUND and im due to be at a mates leaving thing soon.

i want to mod the airbox to RS4 spec tomorrow too. i will find out tomoorow!!
 
my shed is a scary place. when i got out there with the tools i was raring to go, once i realised how bad the wind was and that the roof was shaking, it started to get plain scary!

ive still not made up a boost leak kit, but ive been so anal with getting things on properly that i highly doubt there will be any leaks

ive had a good look over the cars dyno plot.... it makes 350lbft from 2.2krpm to 5krpm, then tails off, making 320bhp... honestly one of the best "remap" s4 dyno plots ive seen.

im hoping the offside turbo is noisy due to oil flow issues, so hopefully the cleaner should do the trick
 
it's a cleaner for the engine.

Just bung a litre in and run gently for a few hundred miles as championed by TSC on CGTI forums.
 
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