SOHCMAN

Greetings!

I was just reading hondadudes(?) write up for cleaning the EGR ports in the FAQ, and he noted that the clogged ports were causing "Totally plugged up!! Gagged with carbon soot!! This is why there was a lean burn stumble under acceleration"...

Would no EGR flow really cause a lean condition? It would seem it would be better for normal combustion since the intake charge would be cooler air instead of hotter mostly burnt gases mixed in???
Are the gases considered inert, and therefore replace some of the otherwise consumable oxygen, making the mixture not as lean? or is that just speculation?

thanks!
SOHC

Chiovnidca

The inert egr gasses dilute the air/fuel mixture causing it to burn slower. Normally the egr gasses are equally divided between all cylinders, that changes when the ports start getting plugged up. If three of the ports are plugged up, all the egr gasses go through the one that isn't, causing a missfire, the stumble you feel. If they were all plugged up that wouldn't happen.

SOHCMAN

Interesting...

So you either want all of them to be flowing, or all plugged if pluged at all...

I was considering blocking off my EGR, but if its actually a good thing for the engine I will make sure its clean. I was under the impression that it was just for emission reasons and not necesarily good for power or engine longevity.

Should I just clean the ports then? I was primarily going to do it to help keep my intake runners clean.

Chiovnidca

The egr systems only purpose is to reduce nox emissions during low throttle and cruise conditions. It wont affect power output at all.

SOHCMAN

So it doesn't help prevent detonation by slowing combustion? Will blocking it change the AFR or change gas mileage at all??

thanks again...
sohc

Duane_in_Japan

Its been debated if this is a true lean condition, as mentioned the gasses are inert. But with all 4 EGR ports being sucked into one slightly clogged port, the cylinder intake stroke can only intake so much air / fuel mixture and some of that air is now inert EGR gas so that would make less air, same fuel and some EGR inert gas, that makes the cylinder rich. This EGR inert gas also stirs things up a bit in there where this much turbulance is not designed into this type of chamber, the extra turbulance also helps to kill a good flame front. It is a misfire non the less. All very debatable, this little bit of theory is just off of the top of my head and I admit to having a bad memory, oldtimers.

NOX is created from a too lean condition, the leaner you get, the hotter the cylinder gets, the more NOX is produced. A ECU controlled PGMFI cylinder is designed to burn the best at a certain temperature, hence the need for EGR, its built into the ECU map for best performance, clean the damn ports, procedures are all over the FAQ and archives.

SOHCMAN

Cleaned the ports and passage ways, completely jam packed full of 180K miles worth of dry carbon that came out like black snow with the help of a screwdriver.

Wish I could say it was a night and day difference. While it did seem to run better (stock engine) time will tell if not blocking it off was a smart move. I am worried that ample carbon deposits further upstream in the EGR system will quickly take their place in the shiny clean passages...

thanks for the timely replies!
sohc