14 replies to this topic

[peteslag]

After a lot of forum searching I finaly fixed my recirc issue, it was a leaky vac box.  The turbo no longer stalls and gives the turkey noise which is good but now I have a new problem.

 

With a leaky vac box it used to over boost to about 1.25 bar and settle at about 1 bar in third gear and above.  Now it over boosts to 1.4 bar and settles at 1.1.  My plan was to give the car 3 runs and hope the ECU would re-learn and the boost would settle down.  On the first run all was OK until I planted the accelerator in third gear at low revs.  The boost level built up slowly then whipped round to 1.5 bar, the boost immediately dropped off to 0.8 bar then settled at 1.1. 

 

My questions are:

 

how many times can I boost this high without damaging then engine?

 

is the ECU likely to re-learn and return to the original boost levels or should I just reset it?

 

Thanks in advance, Pete.

[siztenboots]

to reset ECU , pull fuse 8

 

engine will be fine, there is loads of safety in the maps and ecu will protect itself

[peteslag]

Quick recap, my VXT has an LEH turbo and I've just fixed a recirc problem by replacing the boost solenoids and vac box.  I reset  the ECU and after a few runs the turbo system performed exactly as it it should, except third gear still doesn't seem right.

 

In 3rd gear, when I accelerate from 3,000 RPM or higher it over boosts to 17.5 PSI and settles at 14.5.  I think this is about right for a stage 2 car.  When I accelerate from low revs in third gear the over boost seems really high.  It hits nearly 22 PSI (1.5 bar) on over boost then hunts for a few seconds then settles at 14.5 PSI.  Here is a quick vid;

 

 

Do I need to worry or is this normal?

[JohnTurbo]

I'd not be too concerned Pete - the stg4s spike to 30psi in some cases, same internals.

 

Its an EDS map too which is known to be reletively savage for stg2.

[peteslag]

Cheers John, thought as much.  I'll need to take you out for a spin in your old car some time, it is going like a dream at the mo.  

[JohnTurbo]

- Which is to say that looks like a spike rather than deliberate overboost. ie the control loop for the solenoid doesn't have quite enough gain to handle fast spoolup.

 

 

Edit....that would be good!

Edited by JohnTurbo, 22 July 2013 - 07:54 PM.

[JohnTurbo]

Just had a thought, you could reduce spiking by adjusting the wastegate actuator rod.....less preload.

[peteslag]

- Which is to say that looks like a spike rather than deliberate overboost. ie the control loop for the solenoid doesn't have quite enough gain to handle fast spoolup.

 

 

Edit....that would be good!

 

I think you're right, I'll just try not to boot it at low revs in third gear, it is the only time it does it.

 

Big thumbs up for the PAX, so long as I get one in yours lol.  I still haven't been in an SC'd vx 

[peteslag]

Just had a thought, you could reduce spiking by adjusting the wastegate actuator rod.....less preload.

 

 

Would I need to wind it out? Maybe a turn at a time?

[JohnTurbo]

Yes indeed. Preload controls spoolup. - Without the solenoid it would also set the boost.

 

But of course!

[peteslag]

Yes indeed. Preload controls spoolup. - Without the solenoid it would also set the boost.

 

But of course!

 

Cheers again John, font of knowledge as always.

[Nev]

the stg4s spike to 30psi in some cases

I've not heard of this myself, whos car was doing this please?

[siztenboots]

mine spiked > 30 when the actuator had totally died

 

I would slacken off one full turn of the bottom nut , then adjust the top nut to take up the slack around the wastegate. Its not a bad idea to fix a second nut on the bottom to stop it coming loose.

[peteslag]

I backed the actuator off one turn, the turbo now runs smoother than a Kashmir cod piece (and still pulls like a train).  Thanks all for your help.

[JohnTurbo]

Good news :-)