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whilst waiting for my EGR valve replacement, I was thinking of blocking the EGR completely

Can it cause any harm to the engine? I know it can make the engine run lean.... I heard the Japanese roadster(mx5) runs without EGR valve..

EGR valve is the one that comes out of the rocker cover yeah?
If so, then it is not a crucial part, so yes you can \"block\" it off.
I have a filter attached to it, and blocked off the hole in the intake.
I wouldn't block off the part that comes out of the engine completely as it is used to vent pressure.

Exhaust Gas Recirculation valve goes from the exhaust manifold to the inlet manifold. You can plug it up and it should still run OK.

When I cleaned out my intake manifold I found the EGR had blocked itself at the intake manifold...car only has 40,000k's on it too

Should be fine. Its quite common when you have after-market header fitted.

You will need to replace the gasket between the valve and the inlet manifold with a block off plate if you want to totally isolate the EGR valve. I bodged up a piece of metal from a coffee can when I blocked mine off to check to see if that was causing my idle problems. Apart from fixing the idle dip my car drove much better with it blocked off but I think that was probably because of the compromise tune used on the SP. It may be different on a non-molested car. As long as you keep the electrical connector plugged into the valve then you wont get any error codes.

However by blocking it off you will have an increase in nitros oxide emissions and higher combustion temperatures under light throttle/cruise conditions and be contributing to the smog problem in the city. You shouldn't notice any increase in performance though because the valve is closed under heavy throttle conditions anyway.

Garry wrote:However by blocking it off you will have an increase in nitros oxide emissions and higher combustion temperatures under light throttle/cruise conditions and be contributing to the smog problem in the city. You shouldn't notice any increase in performance though because the valve is closed under heavy throttle conditions anyway.

QFT.

Garry wrote:However by blocking it off you will have an increase in nitros oxide emissions and higher combustion temperatures under light throttle/cruise conditions and be contributing to the smog problem in the city. You shouldn't notice any increase in performance though because the valve is closed under heavy throttle conditions anyway.

call me simple.. but isnt the EGR pipe only connected to one cylinder?... whats that one cylinder do so much worse than the others? or am i missing something?

Garry wrote:you will have an increase in nitros oxide

Be careful with that, might blow the welds on the manifold, happened to a guy I know in a tricked up Eclipse

Mazda used number four exhaust port for convenience because it was easiest to run the EGR pipe around the back of the head and into the inlet manifold, they could have scavenged the exhaust from anywhere. On the SP it comes out of the exhaust just before the cat.

The scavenged exhaust is then metered by the EGR valve then pases through a port cast into the inlet manifold and is then added to the incoming air just after the throttle plate so that it gets distrubuted evenly to all of the cylinders. Some engines run it through a port cast into the head. Some companies, like Honda, dont have an EGR valve but use the VVT control to get the exhaust gas into the cylinders.

Garry wrote:Mazda used number four exhaust port for convenience because it was easiest to run the EGR pipe around the back of the head and into the inlet manifold, they could have scavenged the exhaust from anywhere. On the SP it comes out of the exhaust just before the cat.

The scavenged exhaust is then metered by the EGR valve then pases through a port cast into the inlet manifold and is then added to the incoming air just after the throttle plate so that it gets distrubuted evenly to all of the cylinders. Some engines run it through a port cast into the head. Some companies, like Honda, dont have an EGR valve but use the VVT control to get the exhaust gas into the cylinders.

but whats it reburning it for? is there something in the exhaust gas that actually helps it burn the next charge of fuel air better?? or is it just reburning the previous charge to ensure its more completely burnt? if so.. isnt that forgetting 3 other cylinders that are making the same gasses?

It has nothing to do with Mazda deciding to use number 4 cylinder exhaust port to scavenge the exhaust. They could have got it from any cylinder or further down the exhaust like in the SP.

Introducing some exhaust gas into the charge air reduces the combustion temperature in all the cylinders which in turn lowers nitrous oxide emissions.

Garry wrote:Introducing some exhaust gas into the charge air reduces the combustion temperature in all the cylinders which in turn lowers nitrous oxide emissions.

Garry, can you explain this more for me.

I assumed the air entering the engine via the intake is as close to ambient temperature (well that's what CAIs try and achieve). So how does hot exhaust gas cool the intake charge?

I should have googled first ..

The exhaust gas reduces the amount of oxygen and thus reduces the combustion thus lowering the temperature.

Yes.