No boost problem (really; NO boost - 3psi)

[tacq]

Im starting to run out of ideas on a S2 ABY where boost is completly absent. The engine runs fine under all conditions but the maximum boost that I come up to is approx 3psi; and this is with a (approx) 0.7bar spring in the wastegate...
Engine has a K26/27 and 3" dp+exhaust; custom exhm, custom i/c, 3bar map with other program+rs2 injectors, and now 7A cams.
The following have been checked/tried without any difference:
Fuel pump
Turbo
Wastegate in different configuration; even without controlhose ...
Stock ECU+injectors
Tried without exhaust; only running with dp
Pressure tested for leaks
MAF
new timing belt+changed to 7A cams.
TPS with tb
no errorcodes are noted
no exsessive black (fuel) smoke
no missfires
adjustable fuel pressure regulator

I unplugged the MAF connector and then i was able to get it to 4psi at one occasion before it hesitated like lack of fuel (with lots of throttle). If I remember correct; doesnt just the ECU run on emergency mode with MAF failing? it usually results in exsessive fuel consumption but it still runs fine (with 0.4bar boost).

So what is the obvious Ive missed ?

[Audi_CQ]

WG stuck open?

[Knight Rider S4]

Thinking the same thing.......did the problem start when you had stuck the 0.7 bar spring in the WG

[tacq]

Wastegate stuck?

Sorry guys; wastegate valve are not stuck; Ive tried with another wastegate and different spring aswell

[alg]

WGFV either 'gummed up' or wiring/connections broken ? Sounds like you are only getting failsafe mechanical boost.
If that is not the answer it is worth sitting down and searching the forum. This topic has been covered many times.
My RS2 last reverted to mechanical/failsafe boost due to a breaking wire to the WGFV that MRC resolved after a pressure test revealed no boost leaks. But it was difficult to spot until vag com showed it worked occasionally and we had a closer look !

[tacq]

Not limp-mode

Its not even having limp-mode boos pressure; and with a 0.7bar spring thats where it should be at then but pressure is not more than 0.2bar (max ive seen). This is not the frequently covered low boost issue; its more no boost issue.

[DJones]

Try re setting your crank to TDC and checking your cam timing together with the actual position of the cams make sure you have not broken a woodruf key and spun the pully on the cam.

[Chris M]

Would be worth re-checking all of the above. What DV have you got? I'd make sure thats ok, mine sticks once every blue moon and i only get 0.5bar boost

Cheers,
Chris

[s2dude]

Try re setting your crank to TDC and checking your cam timing together with the actual position of the cams make sure you have not broken a woodruf key and spun the pully on the cam.

Good Plan

[ian_jemo]

tacq did you every resolve this issue, I'm having exactly the same problem

Ian

[220bhp]

As D Jones said its worth checking the woodruf key on the crank pulley, I know its a pain undoing so much to see but it fits your symtoms . I had the same problem,until I changed the cam belt and found the woodruf key hanging on buy a thread ,also its not unknown for the pulley its self to fail one or two posts on here I think.

[ian_jemo]

Whats the wood ruf key?? How can this cause low boost? And where is it hiding I don't even know what it looks like

Cheers

Ian

[220bhp]

Its at the front end of the car ,it holds the front damper on the end of the crank or to be more precise stops it from moving on, its apart of the cambelt pully which fits into a keyway on the end of the crankshaft, if the crankbolt has not been tightend enough, for exsample on the cars last cambelt change, for which you need a special crank locking tool,plus some 400nm of torque to tighten the crank bolt, which should be put in with locktight, it can come loose and allow all the torque from the engine to go through about 6mm of metal, a very weak point IMOA on iI5 .

[UrS4boy]

I presume the ABY is similar to my AAN (93 UrS4) with the exception of the intake manifold, etc. With the AAN, you can drop down to just wastegate spring "boost" (about 6 psi gauge) when the boost signal hose to the ECU comes off the moisture trap. The moisture trap in an UrS4 is under a black plastic cover (that also covers the POSs and a whole connector bar) and looks like a little black film cannister. The OEM hose clamps get weak and the hose comes off. As a result, the ECU doesn't get a boost signal to feed back on and all you get is the WG spring boost. The solution is buying the smallest gear clamps you can find and replacing the OEM clamps on the moisture trap.

Instant 60 hp about 50p.

Dave F.

[ian_jemo]

Cheers for that,

One thing I did try was to drive the car with the WGFV disconnected and it drove exactly the same. Do you think my WGFV isn't working?

Its only about 3 months old.

Ian