Does an EGR valve matter?
 

I just noticed that along with my VTEC-E swap into my '95 Civic CX they put a cover over the EGR valve, (blanked it off), and there is no box with the solenoid and vacuum control valve, does it matter? I've also got a P08 ECU, non-stock exhaust manifold (4 into 2), with 4 wire 02 sensor. Power seems good, idle is 750 rpm (a little fluctuation), but mpg is terrible, definitely worse than the original 16 valve Canadian CX engine. I just got a P07 ECU and I'm going to get a 5 wire 02 sensor, hopefully with the stock manifold, does the EGR valve matter?:confused:

for operation? NO for fuel economy and maybe emissions YES.

Actually Yes for both....if the ecu is designed to be using EGR, it should be displaying a CEL as the EGR valve is missing (along with the DPFE sensor that controls the flow to the EGR valve). If your ecu is running in a CEL For an emissions issue it then defaults to a generic setup to run the vehicle as the ecu is getting the required metering. And it is designed to reduce emissions (are prolong life of catalytic converter) by recycling exhaust gas back through the intake.

+1 on what Zero said.
old..

briogio,
Don't know in your case.

I acquired a '96 Nissan hardbody pickup XE 4 cylinder. The check engine light was on when I got it. It ran pretty good but I knew it wouldn't pass emissions with the CEL on.

After parting with a 100 dollar bill at one of the parts jobbers I see why the old EGR had never been changed. The previous owner (a relative) said the light came on ten years ago and his friend/mechanic said not to worry about it. The EGR valve is back near the firewall and changing it must be similar to what childbirth is like. The old EGR was jammed up with exhaust debris (I can't remember what position the valve was in), I tried cleaning it but would take a great deal of work to get it up and running again.

The new EGR did seem to help how well the engine runs, and unhooking the battery straightened out the CEL light. I changed it as soon as I got the truck, so no MPG comparison could be made before/after.

Where did the motor come from? If it was from Japan, their emissions laws don't require the low NOx levels that we have in the US so most of their intake manifolds don't have the ports for EGR.
Having said that, I believe that many VTEC motors don't require external EGR as the variable valve timing allows the exhaust valve to be held open longer when needed in order to draw the needed exhaust gasses back into the cylinder.

Honda may be slightly different, but, many auto makers today have totally done away with EGR valves on variable cam engines. They do this by altering the exhast valve lift and duration to keep some spent gasses in the combustion chamber, basically a built in EGR system without extra parts to break. This is good and bad. Bad because EGR always , always hurts power and fuel use, always. It is also good because EGR gasses are introduced after the MAF sensors, which means that there is unaccounted for and non combustable gasses in the combustion chamber, which hurts power and since the ex gasses dont burn on compression and ignition they dont add to engine power.
Quite a few of the performance chips for VCT engines correct the valve timing to cancel out the egr effect, usually resulting in more power and decreased fuel use.

In a properly designed system the EGR allows higher compression and more advanced timing, while still passing emissions.

regards
Mech

EGR is good - EGR does NOT reduce power
 

...This is good and bad. Bad because EGR always , always hurts power and fuel use, always. "...
EGR is good -
in a system that is functioning as designed
EGR does not reduce power output and EGR does improve fuel economy by recucing suction throttling loss .

the ECM does not allow EGR operation when power is needed or when the system is at idle .

so
those who defeat their EGR systems are
DECREASING THEIR FUEL ECONOMY and INCREASING NOX EMISSIONS
while
doing nothing to improve power output

Anyone disabled their EGR and seen what happens in testing, ie with a scangauge?

EGR probably has very little effect on most engines. Most systems disengage at something like 3000rpm (I know mine does) for max power from there up.

Could EGR point be tweaked for economy versus emissions?

For a good article on what an EGR valve does and how to modify it try here: Browser Warning
Autospeed is an excellent source for good info on mods. They are great for testing theories and separating the true from the crap.

it's true and I did the test on my own car for reasons of modification of the intake manifold, I had to remove my egr, immediately noticed the car's onboard computer a fuel consumption increase.
This increase is specially noticeable in winter, cold or city driving at low speed(when egr is working, at full throttle egr is closed).
But there is two sides of egr, some people has clogged egr's, when this happens, the fuel conumption increases more than if you dont have any agr, and ther's a(big in some cases) performance loss, it's not noticeable because its progressive whit the years, only noticeable when you clean the egr.

There is some examples os cars that i have cleaned and worked the egr and intake manifold:

http://img87.imageshack.us/img87/6504/p1020980.jpg
By mario_marques at 2009-04-08

http://img50.imageshack.us/img50/8793/p1020978.jpg
By mario_marques at 2009-04-08

http://img50.imageshack.us/img50/2660/imagem470.jpg
By mario_marques at 2009-04-08

Cleaned:
http://img87.imageshack.us/img87/5757/imagem947.jpg
By mario_marques at 2009-04-08

http://img87.imageshack.us/img87/6583/imagem473.jpg
By mario_marques at 2009-04-08

http://img87.imageshack.us/img87/375/imagem999.jpg
By mario_marques at 2009-04-08

Well, after i cleaned it my clients claim a very nice gain of power and less fuel consumption, the exhaust smoke also reduced for no smoke at all(diesel cars...), i also cleaned all intake pipes(and in those cases the intercooler because was dirty and has a lot of oil inside) and replaced the ccv filter.
This systems, egr, katalitic converter, dpf, etc are very nice but they need to be inspected and cleaned, if you dont clean it, you will spend on fuel a lot more than you pay for cleening them.
I also polished the egr(to prevent for get dirt again), i polished the intake manifold ducts and thermo coated whit ceramic tint(tho prevent them for eat and i've worked the air ducts(oversize them to match the engine head port, gains a little performance to, with more performance at low speed your fuel mileage will increase too :thumbup:)

On engines that come with it you definitely want it to be functioning. I know that on the Nissan KA that if you do not clean out the EGR jet ports on the intake manifold every so often the engine will miss and run rough at idle. Fortunately though there are clean out plugs for them on the intake manifold and all you have to do is unscrew them and run a long, sharp awl through them to clean them out.

On the Suzuki G10 in the Metro/Swift/Firefly/Barina/Cultus, a poorly functioning EGR system (when used) will cause the engine to burn the exhaust valves because they will run too hot. Not only that, but it will negatively impact fuel economy as well. The computer is programmed with the EGR in mind and removing it can cause engine damage.

i have a 1997 jeep grand cherokee that has what looks like a egr delete but i'm not sure the manual says that it's supposed to have one but there's no hole in the exhaust manifold(i think the owner before me got a header upgrade that had no egr port so he got a delete but not sure???) and i'm getting the same fuel economy as listed on the epa website stock???? any ideas???(and i'm not getting any ecu trouble codes so i think it's supposed to be vacuum operated)

EPA emissions system tag under the hood
 

The problem removing the EGR is due to the stock ECM flashing error codes and running on a different injection map like the engine had a malfunction. I've already seen some EGR disabling plates mounted between the EGT sensor and the EGR valve which actually led to increase the fuel-efficiency, and even the turbo had more boost from lower RPMs.

In some cars you dont experience that kind of problem, i already try this in a lot of european cars and no lights on dash, not even dtc when you check up the ecu.
But removing the egr is not the best solution has i told before, the best choice is to keep it, and service it to keep it clean and work perfect.
I didnt notice any performance gain in cars with good egr removed, i only feel difference when i romeved damage or cloged egr, in this cases you can feel a gain, but this gain is not in fact a gain, you're only getting the performance you did lost before.

That's strange. But the 5% average fuel-economy increasement is more noticeable than performance gains :D