I have a 2002 Honda Accord 3.0L V6 with 293,000 miles. 4 speed automatic. I've had very little issues with it over the years, but I had the EGR valve go bad on it. I drove it that way for probably 3 years even though I probably shouldn't have. It would sometimes stall out at warm startups. I finally fixed it a few weeks ago, but the other day it started doing the same thing again, but not as bad. The EGR valve that I put on seemed to be fine. Can driving with a bad EGR valve for as long as I did cause other issues?
yup. intake could be full of soot and carbon
EGR valves are crucial for proper operation of the engine. An EGR valve (Exhaust Gas Recirculation Valve) opens and closes as the computer detects that the engine temperature is running too hot (separate from overheating, running too hot creates excess NOx emissions). This forces the catalytic converter to work harder. The catalytic converter is designed with a properly functioning EGR system, so pollutants will escape into the atmosphere. When the computer detects that the engine is running too hot, the EGR valve opens and allows a metered amount of exhaust gas to be allowed back into the intake, along with fuel and fresh air to lessen the temperature of the exhaust. The carbon dioxide is inert and cools down the engine, reducing NOx emissions. Your car isn't always doing this.
maybe "reburn" isn't the right word. Like you said it's inert so it passes through unchanged. It's behaves almost like reducing cylinder displacement which can help save fuel during cruise or coast.
True, I'll edit it.
maybe "reburn" isn't the right word. Like you said it's inert so it passes through unchanged. It's behaves almost like reducing cylinder displacement which can help save fuel during cruise or coast.
The intent of EGR when it was introduced in the U.S. in 1973, even before catalytic converters, was to reduce the production of NOx emissions which is a major contributor to smog formation. (Look at old photos of Los Angeles!)
EGR works by introducing inert exhaust gas in a controlled manner into the intake, thus lowering combustion chamber temperatures and NOx formation. Back in those days before computer engine controls that also meant a noticeable drop in power and fuel efficiency compared to earlier vehicles.
Not all engines have EGR valves, some accomplish the same effect using valve overlap.
https://www.cambustion.com/applications/egr-nox-development
I didn't know that. I knew it was for controlling emissions, but I didn't know modern computers are so fast, not every car needs an EGR valve anymore, lol.
Valve overlap instead of an EGR valve doesn't require variable valve timing. My daily driver has no EGR valve and is equipped with an old-school (relatively speaking) 16-valve dual OHC engine with no cam phasers or any means of dynamically controlling valve timing.
Interesting, learn something new everyday.
Yes that was the primary purpose originally but it has other effects as well. I imagine that by closing the exhaust valve a little earlier it could trap some exhaust gases in the cylinder for the next cycle and achieve the same result egr, except you have less control over it, unless you employed vvt.