Z20NET Boost Control Valves - POLL

[Rebellion]

A bit confused here. The Siggy has gone into limp home mode several times now when booting it, but no spanner symbol showing on the dash yet.

I decided that the most likely cause could be one of the two boost control valves being fubared, so I've replaced both of them, but no difference. I'm talking about the ones that look like a black plastic version of Thomas the Tank Engine - one to the left of the turbo and one to the left of the throttle body.

BUT - the ones I took off the engine were both the same part number, which I am sure is incorrect. One of them should be number 55354158 and the other is 12787706. Jezzy's spec sheet says 55354158 is the one near the turbo and Deztroyer's post in that thread says 12787706 is the one near the TB. On mine, 12787706 was used in both positions (and it's run fine for years).

I fitted the two, different, new ones as per Jezzy's and Deztroyer's suggestions, but searching the net shows lots of cars with 7706 fitted near the turbo. Vauxhall and Saab's EPCs aren't any help either, as they both mention the parts but don't show where they fit.

So, which way around are these valves on YOUR Z20NET? Votes and comments welcome.

[John LE]

I'm not an expert on the Z20NET but I gave signumboy a hand with his and the valves were different on his. The replacements he got from VX (due to boosting issues) both had the same part number and when fitted both work perfectly but originally he had the one with the slightly larger pipe bore (the metal pipe) nearest the turbo.

Couldn't tell you the part numbers although Phil probably could

[Ian-Highlander]

Honestly can't remember which is which, although can tell you when I had my problems, I bought one of each of the two different part numbers and I tried them both ways round and it made sod all difference, I ended up fitting them on the way the car had them fitted originally (which I can check for you tonight if need be).

To be honest though fella, unless you've already replaced it I'd be looking at the wastegate actuator diaphram as the cause, it's the most common thing to go on these old girls as it's just a thin piece of rubber and a very loose tension spring.

Fingers crossed it's not what happened to mine (and Duncans in the past), where the wastegate falls off the actuator arm. Mine hadn't actually come right off (Duncans had) but it was flapping around like a goodun and not actually covering the outlet when closed as a result causing my limp home mode and lack of boost. It seems to be a weak point on the Garret 2052 turbos. If it comes down to it being that, it's cheaper and easier to just fit a new turbo (Neo's do the TD04L14T for a great price).

[Caveman_nige]

as voted, 55 by the turbo and 12 by the TB

[Rebellion]

Thanks for the responses fellas. I'm hoping it's something simple before I resort to replacing turbo bits - it might be dodgy fuel; I use Tesco 99 RON petrol and my new job 40 miles away means I've been using a different Tescos to fill up at, and maybe they've been doing what some branches do and letting their tanks run too low and pushing the crap through the pumps into customers cars.

If going back to using my local Tescos for a few tanks doesn't sort it, I'll try replacing the MAP sensor, and if that doesn't work then I'll look at the diaphragm - and if anyone has any advice on changing that, especially without removing the turbo, it would be much appreciated.

As the engine is mapped, bolting on the Misti upgrade turbo and driving to a remappers isn't on - the non-standard boost combined with the bigger turbo will make the car undriveable.