Only gettnig 0.6 bar (9 psi) on secondary

[nobby]

Hi all,

Having a problem with my BG5 Twin turbo, I can feel the secondary coming in but it's not boosting all the way to 1 bar like it used to, in fact boost is only climbing to ~0.6 bar and staying there. Any ideas?

Thanks
Dave

[Sarra]

Factory stock boost is 1 bar?

Can you check to see what your ignition advance multiplier is?

[nobby]

Yes factory boost should be close to 1 bar, it used to achieve this.

Don't know what the ignition advance multiplier is, or to how to check it..?

[Sarra]

Scan tool.

My first thought was the secondary turbo isn't working, or there is a restriction in the secondary turbo's downpipe. Difficult to know. Could also be the ECU reducing boost due to knock.

[Robbks]

sooo many issues it could be.
best peiec of advice ANY time you have issues with the TT system
-systematically remove every vacuum line from the engine to the solenoid box and clean it out (they fill up with gunk) with upper engine cleaner or carbie cleaner
-Next is to clean out every vac line inside the box
-then flush each solenoid, including removing the vent cap on the top of each of them and clean that too
-re-set the ECU with the check connectors under the dash and see if it fixes it.

replace any cracked vacuum hoses with new ones, and take note of line#2 near the solenoid box as it has a restrictor in it. keep the restrictors in place

also is yours running the twin waste-gated turbo's? or only the single waste-gate on the primary?
if it's the first option.
un-plug the lines for the secondary wastegate and just let the primary wastegate do the job

[nobby]

Thanks for the replies guys, so far I have I cleaned all the solenoids with carb cleaner in daignostic mode, checked boost control solenoid (working fine) and corresponding van lines. Also I've reset the ECU. I have no fault codes anyway.

It sounds like I need to replace/clean all the vac lines (there are loads!) - I honestly don't understand each vac line's function which makes diagnosis more tricky... Is there any way of narrowing it down?

It feels like the secondary is still proudcing boost - at ~5k you can feel the engine characteristics change, but boost will only hit 0.6-0.7 bar.

Not sure if it has one or two wastegates - will check later.

Thanks for your help

[Robbks]

If you haven't read this already
http://www.veloce.pwp.blueyonder.co.uk/ ... opprt2.htm (http://www.veloce.pwp.blueyonder.co.uk/Twin%20Turbo%20Operation/ttopprt2.htm)

Also, if it is a, Early BG5 GT Legacy it will have a secondary wastegate.
this can be unplugged and not used as the Later models and GT-B's only had the wastegate on teh primary turbo anyway

also my car had a simlilar issue with the previous owner.
it would bog down when going into sequential staging

here was the fix

One of the hoses had a build up of oil sludge in it. That particular line was # 10 which bleeds pressure back to the intake prior to the primary turbo. This pressure comes from the exhaust actuator duty solenoid which works in conjunction with the exhaust actuator-positive pressure solenoid.

The duty solenoid controls how much preesure is delivered to the upper chamber of the exhaust actuator during preparatory rotation.

Now because mine was pretty much blocked, all the pressure was fed to the exhaust actuator and caused it to open up to much to early.

But after cleaning, my problem persisted and was actually worse than before.

After lots of head scratching, pulling stuff off, putting it back on - I was just about to give up. I decided to have one final look at the original solenoid box.

I pulled off line #2 inside the box (pressure supply for the exhaust actuator and duty solenoid) and blew through it.... hang on - why is hardly any air coming out?..... ohhhhhh - you muther f#$ka, god damn piece of shiz - bloody restrictor. Ensure that this restrictor is in place

So all is well again. We all know about the restictor for the primary wastegate - but now there is another.

So my advice to TT owners (apart from checking for restrictors) is:

1. Run line #2 from the manifold, not from under the intercooler because the secondary turbo has a habit of losing a bit of oil and this ends up in the hoses. It only seems to happen to lines that bleed pressure to atmosphere

2. Clean out line #10 from the solenoid box to the metal piping and back into the intake

3. Take off the solenoid box and flush the solenoids and clean the round vents on the top of them (they come off) because I believe these allow pressure to be released when the solenoids are turned off during operation.

4. Once all this is done, join the two green connectors under the dash and listen to the test phase. You should here a 'taptaptaptaptap' coming from the solenoid box. This is the duty solenoid for the exhaust actuator working correctly. If you don't hear that noise it is either bunged with gunk or dead.

One of the reasons why the VOD becomes bigger with age is because of these build-ups, leaks and of course a tired engine. The first two are easy to fix.