Astra 1.7 low pressure turbo problems

Could be related to the EGR system on the engine. This is a vacuum controlled system, operated by thermo-switch and a switch on the throttle lever, which is on the injection pump. You should not get vacuum at the EGR actuator (capsule connected to the inlet manifold by a corrugated metal tube) when the engine is cold, or the throttle is slightly open.

HTH

Anthony Remove eight from email to reply.

Most likely the EGR valve stuck open. Blank off the feed pipe and test drive.(you must leave the electrical connections as they are)

If that fixes it, leave it blanked off and enjoy better mpg and performance.

Tim..

performance.

Sounds like the valve is stuck shut rather than open. The symptoms are that there is a problem at partial throttle settings, when the EGR system is designed to replace some of the intake air with inert gas (recirculated exhaust) to reduce NO2 formation due to very lean mixture - if the valve isn't opening, there is insufficient air/fuel mix to ignite properly under compression, hence the kangarooing. EGR has no effect on performance or economy, at full throttle it is shut off so the intake is just air/fuel as normal.

Sorry, should have said no negative effects - a properly working EGR will have a beneficial effect on economy, usually around 10%, and no performance effects.

performance

You are making reference to air/fuel mix, even though the OP has a diesel engine!

EGR on diesels is used to reduce NOx emissions as per SI engines. An excess of EGR will dilute the incoming charge air, but will not result in a 'lean' mixture, as the injection pump will still inject the same amount of diesel. This results in a rich mixture, and a corresponding increase in particulate emissions.

HTH

Anthony Remove eight from email to reply.

(recirculated

Last I heard, diesels ran on air and fuel :-)

particulate

You are right that EGR reduced NOx emissions, both on petrol and diesel engines. On petrol, the inert gas is used to reduce 'pumping' and this can improve efficiency (effictively the inert gas fills some of the vacuum caused at partial throttle settings.) The additional mass of the inert gas lowers the combustion temperature, decreasing NOx production. The situation with diesels is slightly different, as the engine requires a fairy full charge at all throttle settings, otherwise the compression cycle will not be sufficient to ignite the mixture. Without EGR, this results in a very lean mixture with relatively high NOx production. EGR effectively richens the mixture at partial throttle settings (as you say above) but I wouldn't call it a 'rich' mix.

What I wrote before is badly worded, I did not mean to say that EGR causes a lean mix but rather the opposite.

Whatever, the main disadvantage with all EGR systems is the recerculation of particulates, with consequent fouling problems to valves etc.

performance

You are mostly right when you apply this to a petrol engine.- EGR is shut off under full throttle and is only used at cruise.

With a diesel EGR is nil at idle and at maximum at max revs / load since this *is* when you most need to reduce combustion temperature and hence NOx production. I suggst you go read up on this.

The Diesel engine, by its very nature i.e. un throttled runs very "lean" all the time, especially if it is a turbo. Unlike a petrol engine, combustion will result at almost any mixture ratio.

EGR in terms of perfomance then yes it does make a difference. Go drive a Perkins Prima or Ford DE with and without the EGR enabled and you can feel the difference- and see the reduction in smoke without the EGR.

Tim..

Thanks Tim, I've just re-read my reference material, which is from a reliable source, and noted the phrase 'some vehicles shut off the valve at full power' - I'd not remembered the implications of the words 'some vehicles', so I stand corrected as it obviously varies with different manufacturers implementations. Live and learn!

Thanks for the suggestions guys - I will go and try that tonight (sorry, been away for a few days!). A strange thing I noticed was that when I changed the fuel return pipes from all 4 injectors a few days ago (they were perishing), the problem went away completely for maybe