Diesels, EGR, and cack

I had the engine management warning light come on a few times recently in the Astra during urban driving. I guessed from the pattern of it's coming and going that there was a problem with the EGR. I removed the EGR valve and found it was covered in a combination of hard carbon and some softer sludge. I cleaned it thoroughly, so it operates freely again, but was very disturbed by the thick buildup of sludgey cack in the intake manifold, as well as on the valve itself.

I also removed the manifold pressure sensor and found it too was full of sludge. I'm amazed it could even detect the boost pressure properly!

This mess is unboubtedly the result of oily diesel fumes entering the intake manifold via the EGR valve. I also hate EGR on because it increases turbo lag. [1].

On the escort I disabled EGR by disconnecting the electrical connector from teh EGR vacuum control valve. This causes the valve to remain shut. Unfortunatly on the Astra this casues the EMS light to come on and it goes very gutless. Similarly, if I disconnect and plug the vacuum pipe to the EGR valve, the same thing happens! How on earth can the dammed ECU tell that I've dissed and plugged the vauccum pipe!?

Does this mean that I've got to leave the crappy EGR system working and filling my manifold with crud, or is there some clever way to out-wit the ECU?

[1] I noticed reduced lag on the escort after disabling the EGR. My theory regarding this is as follows; The EGR recirculates exhaust gas before it reaches the turbocharger, under part load conditions. This means less gas to spin the turbine, so at part load the turbines are spinning at a much lower speed. This in turn means that when more throttle is applied, it takes longer for the turbines to reach the optimum velocity.
Reply to
DervBoy
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ask that saab turbo dude......

Reply to
Theo

The best and only way to disable the EGR is to cut a gasket sized plate out of some 15 or 18 gauge tin only leaving the central hole where the exhaust gas would pass though un-cut-out. You must leave the vacuum and electrical connections hooked up as you have discocvered.

Tim..

Reply to
Tim..

Unfortunately, due to the EGR system employed on this engine, it is not possible to blank off the EGR valve, or disconnect any vacuum lines or electrical connection without the ECU knowing about it. When the EGR valve opens, the air mass meter can detect the difference in flow. If this change isnt picked-up, then the EML will be illuminated.

Here are some common causes of the EML coming on due to EGR faults:-

1). Filters in the bottom of the EGR/Boost/Swirl vacuum solenoids become blocked or waterlogged. This prevents the quick release of vacuum when requested by the ECU.

2). Low engine oil level means a reduced lubricating supply to the vacuum pump, which as a result produces less vacuum, and the wastgate/EGR opens too slowly.

3). Contamination of the hot film in the mass flow meter. This can often be cured for a while by cleaning with a mild solvent such as brake cleaner.

4). Miscellaneous leaks on the vacuum control system, such as split or loose pipes, punctured EGR diaphragm.

It is also possible that a build-up of carbon/soot is restricting the flow of exhaust gases past the valve into the intake manifold. I havent seen one that bad yet though....

HTH

Anthony Remove eight from email to reply.

PS Picking up my Astra DTi on Monday!

Reply to
Anthony Britt

I may have misunderstood, but I think that statement is incorrect. There is nothing attached to the EGR valve except a single vacuum pipe.

Some of the petrol engine ones are electrically operated and incorporate a lift sensor, maybe you are thinking of these?

The Dervboy

Reply to
DervBoy

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