No boost under hard acceleration 98 TT BG

[gats13]

The car was working fine til the primary turbo blew, had it replaced with a primary turbo from a b4 and i can get it up to 15 psi if i slowly put my foot down but if i put my foot more than a quarter down on the accelerator the boost just drops to zero instantly and if i keep my foot down the boost jumps up and then drops to zero repeatedly (surges) and i cant feel the second kick in or any kind of vod ??? ??? i understand how troublesome these motors can be but any help would be much appreciated, its a 1998 bg auto.

Cheers

[Rosssub]

Is your CEL-check engine light on when it\'s playing up? Or on at all?

Edit: Welcome to Clubsub by the way. ;D

[gats13]

yes it will come on if i dont let off the accelerator and go into limp mode, turn off the car and its gone.

 Rosssub said:

Welcome to Clubsub by the way. ;D

thanks ;D

[Rosssub]

Sweet, I think you have a couple of Vac hoses backwards. Specifically hoses 21 & 22, that go to the Differential Pressure Sensor.

Check your Fault Code/CEL:

http://www.scoobypedia.co.uk/index.php/Knowledge/ReadingECUCodes

Guessing it will give code 65 or 66.

[gats13]

Thanks, will have a look tomorrow. Where abouts is the differential pressure sensor located?

and i will have a go at reading the code too

[Rosssub]

 gats13 said:

Thanks, will have a look tomorrow. Where abouts is the differential pressure sensor located?

and i will have a go at reading the code too

Differential pressure sensor. Also note hose 21 off left side of pic:

Hose 21, goes from the TMIC to this firewall hard line. Then to the left side, of the differential pressure sensor (drivers side).

Hose 22 goes from the secondary relief valve, to the other firewall hard line. Then to the right side of the differential pressure sensor (passenger side).

Differential sensor is labelled both sides, 21 & 22.

[les666]

On a BG the differential pressure sensor is mounted behind the drivers side strut tower in the space between it and the firewall.

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[lachlan]

what model is that with the differential pressure sensor over there ? all ive ever seen is when its next to brake booster

[Rosssub]

 lachlan said:

what model is that with the differential pressure sensor over there ? all ive ever seen is when its next to brake booster

BH5B

[czar loc]

 czar loc']

On a BG the differential pressure sensor is mounted behind the drivers side strut tower in the space between it and the firewall.

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[quote name='lachlan said:

what model is that with the differential pressure sensor over there ? all ive ever seen is when its next to brake booster

/quote]

On all the legacys ive owned its were les666 says

[Rosssub]

Changes to passengers side BE/BH?

I\'m wondering if the longer hoses/hard lines, are to slow the response of the sensor on the later TT\'s?

[czar loc]

Mine have all been BD/BG various aus/jdm, so must move later in the BE/BH

[gats13]

21 and 22 aren\'t backwards and seem to go to the right places one under the intercooler and one to the thing (?) on top of the secondary dump valve. If I feather the throttle it gets up to 15psi but that\'s only at 2500 rpm it used to only just start kicking in around there. I floored it to see what would happen and it surged, then wouldn\'t go above 4psi at higher rpm and over 100 kph. I\'m thinking of taking it in to a garage because I just can\'t solve it

[Rosssub]

Is your waste gate connected correctly?

The Restrictor Pill might be on the wrong side of the T junction.

Hose 23 to the T. Pink dot on the Turbo side of Junction. Pink dot shows where the restrictor pill is.

[Rosssub]

The Paint dot:

If the Dot/0.8mm restrictor pill is on the wrong side, then you will be boost cutting and hitting limp mode. Your waste gate isn\'t opening fast enough.

[Rosssub]

You should be able to see the paint dot on the hose, looking in with a torch.

If the paint is gone you can feel the Restrictor Pill inside the hose.

[gats13]

23 looks okay I squeezed the line on the turbo side of the T and it felt like the pill is there will double check tomorrow. 23 goes into the passenger side guard, is there a solenoid in there or something? Also as the turbo has been replaced with a primary from a later model b4 would that cause any problems going into a bg

[Rosssub]

Hose 23 goes to the Boost Solenoid, inside the guard. Then hose 10 is the recirc/bleed back to the intake.

Going from a VF18 to a VF26 primary could cause boost issues, you might need a boost controller (mbc/ebc).

Until you get one, try fitting a straight hose from your turbo to the waste gate. So your running WGSP-waste gate spring pressure (7psi). If that fixes it then you know it\'s a boost control issue.

[gats13]

I had a go at that and only got 7psi as you said but with all the same symptoms as before

[Rosssub]

Do this:

 Rosssub said:

Check your Fault Code/CEL:

http://www.scoobypedia.co.uk/index.php/Knowledge/ReadingECUCodes

Guessing it will give code 65 or 66.