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[Andy B]

When is it supposed to opperate? I've posted under general rather than Omega help as this is a question related to my 1.7 low blow Astra. My EML keeps coming on when I get on the motorway. It used to come on more frequently around town but since I cleared out the gauze infront of the air flow meter and cleared some of the sh1te out of the EGR valve itself it's just coming on at motor way speeds. If I boot it on the slip road & keep my foot planted into the carpet (it won't go much faster than the limit anyway ) it usually stays off, however as I settle down to a cruising speed of about 70 - honest!! - the EML will come on. Some times if you accelerate gently it'' go off but come back on again. When you get into town again, it'll go back off as you pull away for the 1st or 2nd time & stay off.
Fault code via my cheapo TechII is P400 ie EGR fault, but the EGR on it is purely mechanical -- a solenoid opens up vacuum from the brake servo's vacuum pump to the other side of a diaphragm & lifts a valve up from its seat opening up to the exhaust. The air flow meter is a new one but was a cheap replacement from eBay rather than over £100 from Vx.

All ideas greatfully received.  

[CaptainZok]

Solenoid sticking maybe?
Would have thought it would have to be electrical rather than mechanical for the ECU to spot it and light the EML.

[Andy B]

Solenoid sticking maybe?
Would have thought it would have to be electrical rather than mechanical for the ECU to spot it and light the EML.

Mmmm? Maybe I suppose, but solenoids tends to either work or don't work .....I'll see how much a new one is before I commit to getting another (I've yet to find a low blow car still with its engine in the scrap yard ) I've been told by a couple of people that when the air flow meter fails, that can cause what the car thinks is an EGR fault hence my comment re replacement but I do know where there is a Cavalier/Vectra? with a similar looking EGR    I might get that to try.

[CaptainZok]

Solenoid sticking maybe?
Would have thought it would have to be electrical rather than mechanical for the ECU to spot it and light the EML.

Mmmm? Maybe I suppose, but solenoids tends to either work or don't work .....I'll see how much a new one is before I commit to getting another (I've yet to find a low blow car still with its engine in the scrap yard ) I've been told by a couple of people that when the air flow meter fails, that can cause what the car thinks is an EGR fault hence my comment re replacement but I do know where there is a Cavalier/Vectra? with a similar looking EGR    I might get that to try.

Just guessing really but would crud in the EGR cause it and the solenoid to stick and the ECU flag up faulty?

[Andy B]

Solenoid sticking maybe?
Would have thought it would have to be electrical rather than mechanical for the ECU to spot it and light the EML.

Mmmm? Maybe I suppose, but solenoids tends to either work or don't work .....I'll see how much a new one is before I commit to getting another (I've yet to find a low blow car still with its engine in the scrap yard ) I've been told by a couple of people that when the air flow meter fails, that can cause what the car thinks is an EGR fault hence my comment re replacement but I do know where there is a Cavalier/Vectra? with a similar looking EGR    I might get that to try.

Just guessing really but would crud in the EGR cause it and the solenoid to stick and the ECU flag up faulty?

No cos the solenoid just opens up vac to the diaphragm. The diaphragm is connected to the EGR valve & lifts it from its seat.

[x25xe]

The EGR valve opens under engine cruseing conditions.  The idea is that it lets a small amount of exhaust gas back into the inlet manifold which in turn enters the combustion chamber and lowers the temperature.  The reduces levels of Nitrox emissions (I think it is Nitrox anyway).

That is why the light is coming on only with light throttle applications.  It sounds like the valve is sticking.  Cleaning although sometimes effective, will not last long so a new valve is the only answer really .

Hope this helps

[Andy B]

The EGR valve opens under engine cruseing conditions.  The idea is that it lets a small amount of exhaust gas back into the inlet manifold which in turn enters the combustion chamber and lowers the temperature.  The reduces levels of Nitrox emissions (I think it is Nitrox anyway).

That is why the light is coming on only with light throttle applications.  It sounds like the valve is sticking.  Cleaning although sometimes effective, will not last long so a new valve is the only answer really .

Hope this helps

Thanks. That does seem to fit the symptoms. So if the valve is sticking .... what's teling the light to come on? As I say it's not electrical like an Omega's so once the ECU? has told the solenoid to open up vacuum to the EGR's diaphragm, there's no electrical feed back to tell it whether the valve has done as it's been told or not.
 As far as cleaning the valve, there's not really much in there to not work & I have a suspicion that it's only available at geat expense as part of the inlet manifold. I have to say though that under very hard acceleration cars in the rear view mirror soon disappear ..... not as a dot like in the Omega but in a big black cloud of exhaust  
I'll keep my eyes peeled at the scrap yard for a 'new' one to test it.

[x25xe]

No worries.

TBH, I've no idea how the ECU "knows" whether the valve is doing it's job or not.  Maybe there is a sensor in the vacuum pipe which monitors the load on it?  i.e. if the valve is stuck then the load on the vacuum pipe will be high - like sucking on a straw with the other end blocked.

Other than that, i've no idea unless it monitors the lambda, but being a diesel I am not sure if it has a lambda anyway.

Sorry I can't be more specific.  The scrapper option sounds like a plan.  Hope you can find one!

[TheBoy]

egr comes on at cruise. Diesel EGRs are a PITA.

[Andy B]

egr comes on at cruise. Diesel EGRs are a PITA.

When I put a new air flow meter on it a good few months back I had no problems at all with EML for anything. I just have a niggling thought that it's failed already because I've heard that they do. I think I might have to call on a mate of mine - his wife has the same car - we might be able to diagnose bu substitution ..... if she lets us me    

[Omegatoy]

as far as i understand it the diesel egr not opening causes to much airflow past the airflow sensor for any given engine speed hence it flags the light up as it thinks the egr is not opening!!! that make sense??

[Andy B]

as far as i understand it the diesel egr not opening causes to much airflow past the airflow sensor for any given engine speed hence it flags the light up as it thinks the egr is not opening!!! that make sense??

Thanks Graeme/Graham. It does. With the amount of oil in the vacuum pump I'm surprised it pulls enough vacuum to do anything.

[Marks DTM Calib]

Yep, on the later units (petrol AND diesel), the ECU can detect EGR operation by checking MAF.....I suspect the MAF is ok or it would be showing faults under other conditions to.

When you cleaned the EGR, what did you use becasue if it was carb cleaner it doesn;t realy touch carbon.....you need paint stripper to do it fully.

[Andy B]

Yep, on the later units (petrol AND diesel), the ECU can detect EGR operation by checking MAF.....I suspect the MAF is ok or it would be showing faults under other conditions to.

When you cleaned the EGR, what did you use becasue if it was carb cleaner it doesn;t realy touch carbon.....you need paint stripper to do it fully.

Acetone and a [size=9]blowlamp[/size] I only gave it a quick blast with it  ..... honest. I can move the valve by sucking on the diaphragm by mouth.

[Andy B]

I've just fitted another new MAF and taken ithe car for a quick(ish - it is a diseasal Astra   ) blast for a junction on the motor way. No EML .... fingers crossed it's sorted, for the time being at least! :-?