Vauxhall Astra SRI 150bhp Diesel losing power

Sounds like turbo lag.

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I take it you're trying to highlight the fact it's a 150bhp engine, which means that full boost is probably running at around 1.5bar above atmospheric pressure (maybe a bit more). Couple that with all the volume in the piping/intercooler/inlet manifold, from a low throttle opening/engine load opening, or just after changing gear, the turbo isn't instantly going to spin up and deliver full boost to the engine.

It's not like slightly older diesels, where boost only typically went to

1bar, and the turbo wasn't relied on just quite as much. *** Posted via a free Usenet account from ***

Err, no. Sorry, like most ASCII art, of which this was a degenerate form, it requires the post to be viewed in fixed width font. I was highlighting 'started'. Implying that it's begun doing this. Turbo lag does not generally change.

Ah. It's more likely been there from new, but chances are the driver has just started to notice it. It certainly doesn't sound unusual to me, and considering it's smaller sibling (the 1.3) exhibits the exact same characteristics (much to the dismay of my boss who keeps thinking he's going to die whenever he goes up north with one - he keeps complaining about no power when pulling out to overtake), I wouldn't say there's anything wrong.

Another factor is if the driver previously had a petrol (or has driven one recently). Initially they drive the diesel like a petrol, keeping the revs up abit, but as they get used to the low down power of the diesel and don't rev it quite as high, they start to notice turbo lag more. And as we all know, once you start to notice something, you keep on noticing it.

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Warning lights are back today, the engin management light. Once this is on there is no power there, when it go's off the power is back. You can hear the turbo but the car is not accelerating. I have it booked in again today for the garage to have another look at it. I have had the car a year and have only just noticed this prob in the last few weeks. I have always had a TDI car so cant remember the last time i drove a petrol. Thanks for your comments but I dont think its my driving technique.

Maybe I'm behind on things but from what ive read and was aware, almost all turbo Ds use fairly low boost

Wonder if youre over-boosting (split actuator hose or similar) and the engine management is somehow taming the engine to save damage?

Wouldn't that cause a torque spike as the turbo spooled up and generated boost, then for it to drop away sharply as it hits maximum? Sort of like a rev limiter set too low.

Depends how and when it spikes. Mines normal profile spools to 0.8bar starting at 2000rpm, max at 2800rpm but if I've been driving 'spiritedly' right before and the turbo is still flying I can hit 1 bar as low as 2200rpm and hit fuel cut without feeling any real oomph beforehand. Its very suprising when that happens lol. But it depends how the ECU handles it, modern turbocharged engines use electronic solenoid control of boost and if the leak is only small it may counter-act the spike for as long as it can then realise it wont cope and soft-cut (limiting fuel on a diesel, instead of a hard ignition cut on a petrol car).

Its entirely speculation on my part but far from the realms of fantasy so i thought it worth offering up.

J

I've not seen any turbo-d engines that only boost to 0.5bar recently. All electronically controller turbo-d's I've worked on usually boost to 1 bar, but modern ones are boosting far higher (how do you think they manage to squeeze 80bhp out a 1.3, or 150 out a 1.9 for that matter).

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Even with ECU controlled boost, even if the turbo goes into a state of overboost for some reason, the ECU won't inject anymore fuel than the maximum programmed amount, so no extra power is gained (unlike a conventional injection pump where it would be possible for more fuel to be injected, although the over fuelling valve should shut down the fuel on overboost). And if the over boost continues for a period of time, the ECU will shut down fuelling and enter limp home mode.

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Probably not you then. Provided the engine management light has come on, the fault codes will be stored, so finding the fault should be reasonably easy. It's most likely a faulty sensor, but without knowing what the fault codes are, I can only speculate.

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Sounds like a de-laminating intercooler hose, restricting air flow.. Have you noticed any smoke from exhaust on acceleration?

Nigel

That actually killed someone who put a car engine in their plane. First time they ran the engine up to full power for takeoff, the hose rapidly crumpled, and a little afterwards the engine shut off.

Finally know the problem, it waz the mass airflow filter and a swirl valve, they are going to be replaced within the next few days so cross fingers everything will be ok after that. Only took the garage 4 go's to find the fault!!!