Xantia 1.9td EGR system?

simoncanfer · Unread post by **simoncanfer** » 26 May 2007, 18:25

Isn't there a switch on the fuel pump that is involved in the EGR system - if I'm right then then another way to disable EGR might be to disconnect the switch or wire it closed - however I don't know which way it works!

Simon

AndersDK · Unread post by **AndersDK** » 26 May 2007, 18:52

No the fuel pump is not involved in this system.

EGR = Exhaust Gas Recycling.
Which simply means that part of the exhaust gas is lead back to the inlet to bring down emission levels.
The system only works at idle and thereabouts. There is no sense in trying to reduce or limit the engine power for the sake of emissions, WHEN the engine must produce power and consequently also produces lots of emissions.

Thats BTW also the basic function of the Lambda sonde and the ECU. This too is only there to bring down emissions at idle and low engine power. It will gradually faint out completely as the engine produces power. Again because here is no sense not allowing the engine to produce power for the sake of emissions.

Might be the fumes reducing system you had on mind ? This system uses a charcoal canister to hold the fumes escaping through tank ventilation. When engine is running at certain power producing levels (i.e. NOT idle) the charcoal canister is vented by way of a controlled electrovalve - into the inlet.
However this system I've never heard of utilising a switch on the fuel pump.

The only purpose of a switch on the fuel pump I could think of, would be a protective safety switch against thermal overload on the pump. For obvious reasons (boom !)

Many cars have a safety impact switch which cuts the power feed to the fuel pump on impacts. In some cases its a mechanical device that blocks the fuel line to the engine.

fastandfurryous · Unread post by **fastandfurryous** » 27 May 2007, 00:14

AndersDK wrote:No the fuel pump is not involved in this system.

Sorry to contradict you Anders, but on some EGR systems, there is indeed a relevant switch on the injection pump.

These are, however, rare systems. Most EGR valves are controlled by the timing ECU. It takes information about engine speed and injector duration (from the TDC and injector sensors) and only opens the EGR valve at times when the engine's need for oxygen is low. (light load, over-run, idle, etc.)

Pre-Lucas-EPIC injection systems (IE fully mechanical ones) that have EGR DO have a switch on the injection pump, which operates the EGR valve directly when the engine is under light load (as detected by "when the accelerator isn't pressed very much")

These systems are rare, as EGR was introduced just before Lucas-EPIC injection.

The Charcoal-canister vapor pipework switch won't ever be found on a Diesel injection pump, as this system was only ever used on petrol-engined cars (but would indeed be very similar in that it detects "light" use of the accelerator, rather than just idle)

AndersDK · Unread post by **AndersDK** » 27 May 2007, 15:23

Thanks F&F. Dont ever hesitate to correct me if & when I'm wrong. Its a pain to bring on false information uncorrected

I know a lot, in fact my knowledge is now that deep, that I know for certain there is even more I dont know about

simoncanfer · Unread post by **simoncanfer** » 27 May 2007, 16:31

Well mine must be a late XUD from 1997, it certainly has a microswitch on the lucas injection pump so maybe it is involved th EGR after all.

Will simply clamping the vacuum pipe off between the vacuum pump and solenoid disable the EGR?

Simon

KP · Unread post by KP » 27 May 2007, 19:26

You have an XUD xantia 1.9td that has a lucas pump fitted??

Thats a rarity that i have heard of but never seen, are you sure you have the right pump?

simoncanfer · Unread post by **simoncanfer** » 28 May 2007, 09:29

Sorry - not a Xantia but a ZX.

fastandfurryous · Unread post by **fastandfurryous** » 30 May 2007, 21:45

simoncanfer wrote:Well mine must be a late XUD from 1997, it certainly has a microswitch on the lucas injection pump so maybe it is involved th EGR after all.

Just to throw yet another spanner in the works, just because there's a microswitch on the injection pump doesn't mean it's related to the EGR. I've seen some pre-EGR engines with a microswitch on the pump, but I've no idea what it's for!

Unread post by **CitroJim** » 31 May 2007, 07:05

fastandfurryous wrote:I've seen some pre-EGR engines with a microswitch on the pump, but I've no idea what it's for!

My 1993 TD has one of these and curiosity got the better of me one day.

As far as I can determine, the switch is to cut off the cold start advance above a certain throttle opening when the engine is cold. Cold start advance is cancelled at all throttle openings as soon as the coolant temperature rises above 60 degrees C.

fastandfurryous · Unread post by **fastandfurryous** » 31 May 2007, 07:25

Ahhh yes.. Electronic cold start advance.. of course.

While I remember... it may also be linked with the glowplug post-heat system, which is cancelled as soon as you press the accelerator more than a couple of mm.