Turbo losing boost at around 4000 rpm

Question

I have a 2005 Opel Astra Turbo Coupe. I would imagine most of you guys are more familiar with the Vauxhall or Holden badge, but it's the same car with the same Z20LET Turbo Ecotec engine.

Anyways, when driving, the turbo kicks in at 2500 rpm, as usual, but when I reach 3500 rpm, I hear what sounds like the wastegate opening, accompanied by a slight loss in power. When I reach 4000 rpm, I hear the wastegate sound again and I lose a lot of power. When this happens, the check engine light comes on. It always happens at exactly the same RPM and if I release and re-engage the accelerator, I get a momentary surge of boost, before the wastegate (or what sounds like a wastegate) opens and I lose power again.

I have had the problem since I bought the car a month ago. Any thoughts or suggestions would be appreciated.

Answer 1

Sounds to me like the car is suffering from a boost leak - either the plumbing has a leak somewhere or the wastegate doesn't hold pressure properly. Does the car have a boost gauge and if it does, can you see if you're losing boost at the same time you get the noise?

Normally you'll have a hard time hearing the wastegate if it's an OEM one as they all normally vent into the inlet tract rather than the athmosphere, so the first thing I'd check is if it has an aftermarket wastegate (and possibly boost controller). If it doesn't, I'd check the various hoses and pipes first to see if there's any boost leaks (you might have to pressurize the intake side for that) and fix those leaks.

If the car has an aftermarket wastegate, I'd check if it's a decent quality one as the cheap ones are mostly good for weighing down a trash can. If it is a decent quality one, you need to check how it's actuated - there is a chance that you have boost spikes that trigger the wastegate.

Edit: Thinking about this a bit more, I would start looking at the wastegate side of things first. If it was a boost leak in the piping, you'd normally just lose pressure gradually rather than having the boost build up and then get the "wastegate sneeze". My checklist would be:

• Check if it's got an aftermarket wastegate and if it does, check that it's (a) a good quality one and (b) that it's working OK.
• Check how the wastegate is actuated and if there's a boost controller somewhere in the mix
• Probably install a boost gauge if the first two steps don't lead you to a fix. What you need to verify is that you're not getting into an overboosting situation or get boost spikes that trigger this behaviour. If you do, you need to address what is causing these problems first.

Answer 2

Turns out the previous owner of the car adjusted the wastegate actuator in an attempt to increase boost pressure. The sudden loss of boost came about because the ECU forced the wastegate open in an attempt to keep the manifold attached to the engine ;) Kudos to whomever wrote the software for the Bosch Motronics unit.

Answer 3

I drive a gtc turbo and had the same problem. Check all the rear and front boost pressure/solenoids and their connecting rubber hoses and pipes....I spent lots on replacing parts, until I found a perished hose connector on the rear boost solenoid... never had a problem again... in fact I'm pushing 166kw on the wheels with no mods :)