no boost

[DEREKCO]

Hi guys need your help I posted recently about no boost ,I have done a boost leak test and no leaks even using soapy water ,I have taken all the hose,s off from MAF sensor right through to the throttle body ,inspected for any splits none, I have tested from MAF to the hose out of the intercooler no leaks, the engine runs sweet ,one thing I did notice is I have a vacuum/boost gauge and I have massive vacuum when you drive up to 2000 rpm anything above that it's guttless, I have no missfire it starts first time ,it ticks over fine just no DAMM boost

[RoadKill]

tried unplugging the multi function temp sender on the water manifold?

[macspring]

http://www.s2forum.com/forum/showthread.php?t=79611

Check this out incase it is relevant.

Post the cause in due course.

Good luck.

[DEREKCO]

No boost

Well I have done all the checks,the boost test ,renewed 3 vacuum hoses, and disconnected the MFTS, all to no avail still no boost what next?

[newsh]

Massive vacuum?? That's not possible.. the only time you should get vacuum is tickover, overrun and cruising, as soon as you open the throttle to accellerate it should go to zero Bar (or 0 psi) and then almost straight away into boost. If you have no boost at all on the gauge, even at WOT then the turbo is not working, either seized or shaft broken. (Or you have a boost pipe missing entirely, in which case the car would probably not start..)

[dbojar]

Well I have done all the checks,the boost test ,renewed 3 vacuum hoses, and disconnected the MFTS, all to no avail still no boost what next?

Check n75, DV, WG, ex manifold, turbo..

[DEREKCO]

No boost

Could a broken wastegate cause no boost as I have said I overtook 1 car eased off then went for a second overtake as I pulled out I felt the car come off boost no smoke ,nothing no misfire no lumpy tickover starts first time ontick over I get about 8_10 vacuum pulling away the gauge goes to zero the goes no further today I took the whole front of the car off sprayed everything in soapy water did another boost test as per form links NO LEAKS ?

[newsh]

As per PM, could be wastegate stuck open, if wastegate and turbo are working ok you should get at least 0.4 Bar boost even without ECU control.

[newsh]

Have you looked both sides of the turbo? Cold side and Hotside?

[Kieron20V]

Throttle cable or bracket snapped? Or cam on throttle broken?

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[UrS4boy]

Moisture Trap 101:

Have you checked the boost/vacuum signal hose to the MAP sensor in the ECU via the moisture trap yet? No connection = mechanical boost only (about 0.4 bar relative).

Moisture Trap 101:

http://forums.quattroworld.com/s4s6/msgs/20401.phtml

Like electricity, you need confirm pressure flow between the intake manifold and the ECU.

[newsh]

Dave, he's saying no boost = zero .. ie. nothing above atmospheric.

[newsh]

Throttle cable or bracket snapped? Or cam on throttle broken?

Sent from apollo 13 using tapatalk

That's a good point, maybe the throttle isn't opening... wouldn't the pedal feel weird though?

[UrS4boy]

Dave, he's saying no boost = zero .. ie. nothing above atmospheric.

I think the only way that that can happen is a massive tear in the wastegate diaphragm. Otherwise, there should at least be spring pressure boost.

Testing the diaphragm: http://www.sjmautotechnik.com/parts_...inst.html#test

[Pirvu Eugen]

With diaphragm broken....you will have boost. Only if the turbo is not spinning or the wastegate stuck open you have no boost..