Anyone know how to disable the EGR valve. It has a small capillary tube going to what looks like a diaphagm chamber on the top, and a multi-pin plug connector on the side. Is the wiring for the temperature sensor and the tube used to sense the load/rpm? - Should I disconnect the tube or the wiring or both? -
Is it normal for the air intake duct to get blethered in oil downstream of the valve too?
any help appreciated
Regards Jim
- (#3487) J Adgo, 23 Jun 02
The wires go to a solenoid valve. all you have to do is unplug them. To make doubly sure(incase the valve is stuck open) make a blanking plate to put between the intake manifold and valve body (or make another plate for the exhaust manifold side and remove the whole gubbins...
Oil is normal, most of it comes from the breather...
- (#3489) david miller, 24 Jun 02
There is mystery surrounding the Exhaust Gas Recirculation [EGR] valve. What does it do? Why? Does it affect emissions and MOT, power, economy, cooling?
I have been driving around for a few days watching a bulb that I temporarily connected on the EGR control wiring (instead of the vacuum valve that supplies the EGR itself).
I'll stick my neck out and hope for valuable discussion...
It (only fitted to autos - David Miller, 12 Jul 01) sits on the back end of the inlet manifold. A metal pipe provides a supply of exhaust gas round the back of the engine. When it opens it lets some exhaust gas into the inlet manifold. It is vacuum-powered via a vacuum valve near the EGR, under the big air hose from the air filter. That vacuum valve has its own (thin, hard plastic) vacuum supply pipe coming over the engine and a 2 pin electrical connector. (Its often an oily area "there could be some oil weeping from the inlet manifold, there's a joint in it, behind the EGR valve. Check also the breather pipe from the top of the engine to the air intake. - David Miller, 13 Jul 01" but that that is irrelevant apart from adding to the mystery - who wants to delve in there?!)
I assume the EGR passes exhaust gases when the vac valve is energised and vacuum reaches the EGR itself, not the other way round. (If I'm wrong it affects what I say below) It would be interesting also to know why it has its own vacuum supply pipe (does it on all Auto 'Aces?) and if this comes from the vac pump on the alternator the same as the rest of the vacuum system, or if the variability of the vacuum source is part of the EGR control. Then there is a small cylinder in the vac pipe, what's that for? - probably trivial.
It has been said the EGR "only works at light throttle settings, engine warm". Watching my lamp confirms this. It blips on for a second or so as you lift your right foot. Under power its never on except it blips on for some reason for a fraction of a second during (auto) up-gearchanges under power. It is not on while idling. Notably it is on continuously when you rev up without load, as in the MOT test.
It has also been said the EGR is to "suck in excess fuel and recycle it", it "sends some exhaust gas back to the inlet to reduce NOx levels". Care here. It can't be right to think of it as reducing emissions by simply sucking them from the exhaust flow.
One reference (below) explains "Nitrogen oxides [NOx] are one of the main pollutants emitted by vehicle engines. Oxygen is required for fuel to be burnt in an engine. This is usually supplied by taking in air from the atmosphere. However, the air that surrounds us also contains a large quantity of nitrogen. The high temperatures found within the engine cause nitrogen to react with any unused oxygen to form nitrogen oxides [NOx]." So simply sending normal air, no fuel, through a hot engine, will produce NOx pollutants.
It goes on "The most effective means of tackling nitrogen oxides is to use Exhaust Gas Recirculation [EGR]. This technique directs some of the exhaust gases back into the intake of the engine. These gases have already been used by the engine and no longer contain much oxygen. By mixing the exhaust gases with fresh air, the amount of oxygen entering the engine is reduced. Since there is less oxygen to react with, fewer nitrogen oxides are formed. This can greatly reduce the amount of nitrogen oxides that a vehicle releases into the atmosphere."
This appears to confirm that the EGR tries to help, not by sucking nasties out of the exhaust, but by puffing in low-oxygen "air" at times when the engine is hot and there would otherwise be a surplus of oxygen. This matches the behaviour that I observed.
Is it really worth all that to stop NOx emission just during those rare moments? Is there possibly some "memory" in the EGR valve which keeps it open for some time after it is actuated? Is it about the MOT test? - although I'm told that the only way to get some Rover diesels (with no fuel adjustment) through their first MOT test is to disable the EGR!
Or is there even more to it? Other soures refer to the EGR actually causing cooling. Might it be that, despite the heat in the EGR gas, its low oxygen content not only directly inhibits NOx production during the brief EGR "puff" but also indirectly and more importantly in another way. By killing off the reaction, with either fuel or nitrogen, it removes a heat source leaving the combustion chamber cooler and reducing NOx production long after the EGR has closed - until power is demanded again. So the real benefit is not while the EGR is open but during all "light throttle settings, engine warm" periods.
So, jammed open (ever happens?) or during the UK MOT test might take an engine way outside the way it's intended to run continuously.
More to the point, jammed shut, or disabled might do more than remove an emissions-control finesse. It might affect heat build up in the combustion chambers during "light throttle settings" periods. So, might disabling the EGR be a significant factor in head and head gasket damage which appears to occur before, rather than after, loss of water?
- (#3553) Dave Mason, 28 Jun 02
Dave, your description of EGR is 100%. Paradoxically, the EGR improves emmissions by decreasing efficiency...
EGR will have little if no effect on chamber temps. And, the engine is built to absorb the heat produced at full power anyway...
Mine is removed, has been since about a month after purchase. My fear is always of the valve failing/ sticking open, with the attendant loss of power. Never mind that if you increase fuelling to try and get the power back, then you WILL overheat.
Soot buildup in the inlet tract is a definite issue, look at tdiclub.com for what happens to VW diesels with EGR.
- (#3556) david miller, 28 Jun 02
hi guys,back on the road again,god how good it feels driving the townie about again.
i got a prob with the black smoke,i spoke to the guy at allcar services at st george bristol,he said if have the erg valve blanked off it will cure most of the smoke problem.ive also been told it might be the injectors cuaseing the problem too,so im not to sure which to get done first as its getting worse,its really thick, sooty smoke when i put my foot down.any advice would be most welcome.by the way ive changed the filters recently.cheers.dave
- (#9791) dave, 22 Jul 03 14:39
EGR only operates at light throttle settings, so I'd look at injectors and timing first... If that doesn't do it, then a blocked inlet manifold (caused by the EGR) would be the next check.
Always assuming that no-one has fiddled with the pump settings and the turbo is OK...
- (#9792) david miller, 23 Jul 03 1:27
Hi Dave's.
I have a smoke problem myself, although by the sound of it, its not as bad as yours. I was quoted around £130 each for new injectors, whilst a local diesel specialist can recondition the old ones for £28 each.
You may want to try a diesel additive first though. I used Millers Diesel additive, and the smoke reduction was almost instant. This is because low Sulphur diesel is the norm these days, and to remove the Sulphur, the diesel is treated with Nitrogen. This not only removes the Sulphur but removes lubricants as well. Now depending on where in the world the diesel was mined, depends on the level of Sulphur. More Sulphur = more Nitrogen treating = less lubricants = poor burning = more smoke. On a surfing session one day, I found that BP are the only company that claim to add lubricants to their diesel, to replace what has been lost during the Sulphur reduction process.
Hope that helps
dave Bright
- (#9793) dave Bright, 23 Jul 03 2:22
Dave. Don't underestimate the effect of the EGR valve on the inlet manifold (as David has pointed out). I blanked mine off some time ago and was very surprised re the amount of gunge restricting the air flow. Renovated, or new, injectors do make a difference, especially on fuel consumption. I think I recovered the cost of this with much fuel saving over the following few months. The injectors do wear and the resulting irregular spray pattern does allow a lot of unburnt fuel to come out of the exhaust pipe as black smoke.
- (#9794) John Davis, 23 Jul 03 3:04
Thanks for that John.
Am I right in thinking then that for our driving environment, the EGR valve is a pretty useless bit of mechanics that soot's up the inlet manifold, causing poor MPG and smoke at high revs? Is it also right that the simplest solution is to unplug the EGR and or, bung a ball bearing up the vacuum tube?
Would there be any point to periodically cleaning out the inlet manifold, assuming that its not too difficult?
I'm planning on getting my injectors reconditioned next week, so I'm guessing that it would be a good time to attend to the EGR.
dave Bright.
- (#9795) dave Bright, 23 Jul 03 5:21
Dave. In my opinion yes, most certainly, cleaning the inlet tract and the manifold, is of great benefit. The EGR port can be blanked off with a plate and/or, a ball bearing in the vacuum pipe to prevent the valve from operating. I think you are right, the EGR has dubious benefits and, it's intention, to re-circulate and clean up the exhaust emissions at low revs is not as beneficial as one might suppose. If you are taking the injectors out, it is a good time to take the manifold off because this will give better access to the injectors anyway, a fiddly job at the best of times. If you have not removed the injectors before, be a bit careful with the "spill" tube assembly. It is easily broken but, if a joint does come adrift, a soft solder repair is adequate.
A good wash in paraffin seems to get rid of the gunge in the manifold/inlet tract.
- (#9796) John Davis, 23 Jul 03 7:02
Thank you John.
No I have never removed an injector before, and I have no idea what the spill tube is. I may need some help there. How easy is it to remove the inlet manifold, and will I need to have a new gasket for refitting it?
dave Bright
- (#9797) dave Bright, 23 Jul 03 7:26