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Old 09-23-2010, 02:07 PM   #1 (permalink)
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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?

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Old 10-20-2010, 07:33 PM   #2 (permalink)
Grrr :-)
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for operation? NO for fuel economy and maybe emissions YES.
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Old 11-11-2010, 08:15 PM   #3 (permalink)
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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.
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Old 11-14-2010, 10:36 AM   #4 (permalink)
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+1 on what Zero said.
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Old 11-14-2010, 09:34 PM   #5 (permalink)
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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.
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Old 12-04-2010, 11:29 AM   #6 (permalink)
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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.
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Old 12-20-2010, 10:06 PM   #7 (permalink)
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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.
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Old 12-20-2010, 10:20 PM   #8 (permalink)
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In a properly designed system the EGR allows higher compression and more advanced timing, while still passing emissions.

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Old 12-22-2010, 01:41 PM   #9 (permalink)
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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 .

those who defeat their EGR systems are
doing nothing to improve power output
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Old 12-22-2010, 09:58 PM   #10 (permalink)
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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?

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