EGR issues

There is a lot more build up of deposits in my SOHC upper intake manifold than in the main intake tube. At first I thought that the deposits were coming from the PCV port on the passenger side valve cover. Then I learned that the port is an inlet instead of an outlet and the flow would only be reversed if the PCV valve was blocked. I checked the PCV valve and even though it was dirty it was still functional. Now I suspect that the difference in build up is due to the exhaust gas recirculation (EGR) tube that is located just downstream of the upper intake inlet. The photo below shows the EGR tube in the upper intake manifold after the throttle body was removed.

The primary purpose of the EGR is to reduce nitrous oxide emissions. This is also done by the catalytic converter.

Another stated purpose is to reduce combustion chamber temperatures which prevents detonation during hard acceleration or heavy engine loading. My SOHC has a knock sensor that causes the PCM to retard the ignition timing if detonation is detected so I doubt that I need EGR for that.

The PCM controls how much exhaust gas is recirculated into the combustion chambers. EGR is turned off during idle to prevent the engine from running rough or stalling.

It seems to me that EGR may reduce pollution of the atmosphere but increases pollution of my engine intake system with exhaust deposits. I also suspect that my horsepower and fuel economy are degraded by EGR. It seems what is best for my engine is to rely on the catalytic converter to reduce nitrous oxide emissions.

EGR's a good thing

I've read more about EGR and decided that it's a good thing for several reasons. First of all, being somewhat of an environmentalist I'm in favor of reducing nitrous oxides in the atmosphere. And it is more efficient to prevent the generation of nitrous oxides than to reduce them after the fact with a catalytic converter. The way EGR prevents nitrous oxide generation is by introducing noncombustable exhaust into the combustion chamber via the intake manifold. Nitrous oxide is generated when combustion temperatures exceed 2,500 degrees. Adding exhaust gas reduces combustion temperatures and if enough is added the temperatures can be kept below 2,500 degrees.

Before EGR and fuel injection exhaust temperature extremes could be avoided by running a rich mixture. In those days it was common to require exhaust valve replacement at 75,000 miles due to heat deterioration. Increasing the carburetor jet size (richens the mixture) would extend the life of the exhaust valves at the expense of burning more fuel. Today engines with 200,000 miles still have decent compression and I suspect we have EGR to thank for that.

The problem with EGR is that it has numerous mechanical and electrical components that operate in a stressful environment (exhaust). That makes them prone to failure which reduces performance and fuel economy.

However, even when the EGR system is working as designed it results in carbon buildup in the intake system. I noticed when cleaning the crud out of my intake system that certain sides of a chamber or port have more deposits than the opposite side. I'm speculating that this may be due to airflow directional change. Particles in the exhaust have more mass than air and would seek a larger radius (if possible) in a turn. I'm wondering if some type of velocity separator (particle filter) could be built to reduce the particles in the exhaust prior to entering the intake system - or even the EGR components.

I have to agree with the polluting the engine part. This is the intake on my sons Oldsmobile I took apart yesterday. That black pile of tar like goop in the bottom center of the intake manifold should be an opening about the size of a dime. Its the passage from the egr valve to the intake, plugged solid at 75k miles, error 401 low flow, 6 hours latter, problem fixed.