Funny one this. Went to the garage today to investigate the turbo overboosting issue (it had been winding around to 3 bar on "testing" then throwing into limp mode where it was still pushing 0.9 bar then.... )

Mate happened to mention he'd seen a split vacuum hose, and had cut it off and reattached it securely, Nice enough you'd think but this is when the turbo started doing all it's weird stuff. The hose to the actuator was checked - all fine - and the VNT mechanism was uber smooth in action. However, as a test we thought we'd take off the repaired vacuum hose (it's the one going to the airbox) and give her a run!

TOTALLY perfect! In fact it boosted up and held boost at peak 1.8 bar better than I'd felt for a couple of months. Drives very nicely now with smooth boost. Question is.... WHY!? I'm now running without the hose to the airbox, and I'm curious why. I don't think the fact I've changed from a stock box to a BMC CDA one has any bearing as it had been doing this "thing" for a while before I went to the BMC.

Any thoughts?

? perhaps the new hose was collapsing under negative pressure?

You do have some weird probs sometimes matey!

Bas

I might try retrofitting some proper vacuum hose, as I'm using this blue stuff, which might be a bit weak.

Happy enough for now though.

Could the car have been mapped while the hose was split?

Chris

If I understand correctly, you're running without the air filter?

If that's the case, I wouldn't recommend that at all.

If I understand correctly, you're running without the air filter?

If that's the case, I wouldn't recommend that at all.

No - the air filter is still cleaning all the air taken in - It's only the vacuum hose which has been taken off the vacuum box.

I love following the threads of your "journey" with the mongrel Jason, its like an evolution!

i doubt it'll be a collapsing hose as being connected or not shouldn't make any difference as the air would still be being pulled through it and if anything removing the hose would make it worse if that was the case as there would be less resistance.

I'd speak to your mapper and turbo supplier jason

I'd speak to your mapper and turbo supplier jason

Spoke to the Jedi master at Allard this morning once the reason had been found. He'd honestly never heard of that happening before and was going to chat to the other chap there to see if he'd heard of it happening

I'm not fussed as the car's going to have the new head & injectors fitted soon anyway, so will be retuned with those mods in mind, and a replacement vacuum hose too.