Saturday, October 10, 2015

Formula Vs. Smog Check: EGR sadness

Last time I pretty much laid out my dilemma.   20 year old car, Emissions testing Nazis, questioning my life choices...

So I won't rehash it here.  It's a problem anyone with a car roughly the same vintage as their parent's high school diploma knows well.

This time we're going to attack the root cause of our NOx failure at the emissions testing station.  If you recall, the standard for a 95 Formula in Arizona is 2.00 and I managed to crush the scales at 5.99.

There are two primary emissions systems that contribute to this failure.  The first is the EGR or Exhaust Gas Recirculation valve and the second is the Catalytic Converter.

As I see it, the Catalytic converter is a secondary emissions component.  Meant to clean up whatever the other primary systems left behind.  There are exceptions such as certain vehicles that eliminate the EGR altogether and incorporate similar functionality within the intake system of the engine itself. 

But most of us with older cars will still have to deal with the tried and true EGR valve.  Considering it's exposed to constant exhaust heat, depends on a seal made of rubber and failure of said seal negates its function you're going to have to deal with it at some point.

The good news is that at least on mid 90's GM F Body cars ( 93-97 Firebird/Camaro) with an LT1 V8 the diagnosis and replacement is straightforward.

I should clarify here.  Diagnosis is easy, replacement would be easy if you could somehow wrest the engine out of the car in under 5 minutes.

That's not going to happen in a 4th generation F Body.

But enough of that...

The EGR's function is to circulate exhaust gases back into the combustion chamber to cool it down.  

Combustion temperatures above 2500F cause NOx, a noxious gas that creates excess ozone and irritates respiratory ailments among other things.

So the emissions Nazis are gunning for you if your car exceeds their standards.

On the 4th Gen F body LT1 (V8) cars the EGR is located on the back of the intake manifold in pretty much the most inaccessible location GM could come up with. 

Now if Camaros or Firebirds had hoods that tilted forward ( like the same vintage Corvettes do) it would be no big deal.  Thing is, these cars are cursed with about a foot of bodywork hanging over the engine.  Thank that 60 degree windshield for that one.

Still, you can deal with the EGR and the Fuel pressure regulator as well ( since it's in the same location) so long as you're willing to lay across the front of the car to get to them.

Which is what I had to do to replace mine. 
But we're jumping ahead here. 

Before we start turning wrenches we need to figure out if we need to.

Assuming the rest of your emissions components are working within specification, high NOx generally only comes from the aforementioned high combustion temperatures caused by a bad CAT or EGR valve.

The simplest test for a bad EGR is to stick a vacuum pump on the vacuum port on top of the EGR and give a few pumps.  If it doesn't hold vacuum it's junk, no exceptions.  The EGR relies on a flexible diaphragm that moves in and out as vacuum is applied to it. 

That diaphragm operates a rod ( pintle ) that allows a measured amount of exhaust gas to recirculate in the combustion chamber which helps cool it down and decrease NOx emissions.

If that pintle doesn't move then NOx can run rampant.

The other reason the EGR system can fail is if the EGR passages in the manifold become clogged up.   If the exhaust gas can't get to the combustion chamber it can't cool it down.

It can also cause the engine to run too lean ( too much air not enough fuel ) which can increase HC emissions as well.

Vacuum leaks can contribute to high HC and NOx as well and a torn diaphragm in a 3 inch disk is a pretty big leak.

So now we know the problem, the solution is pretty simple. 

Replace the valve...

While you're at it, check out the EGR passages and clean them out if they're full of crud( as best you can considering where the EGR is.)

Removal is easy, 2 (1/2 inch) nuts on a couple of studs.  Of course getting to them requires draping yourself across the front of the car but once you get positioned, it's not so bad.  I'd also recommend the use of an offset boxed end wrench since the bolts are partially shrouded by the EGR "disc."

Pop it off, remove the gasket, clean up the mating surfaces ( there's likely to be a sticky film left by the old gasket) and clean out the EGR passage of any carbon build up.  Then just bolt the new one on, torque the bolts down and reconnect the EGR vacuum line and you're done!

Really not much more to it. 

Below is a video that outlines the diagnosis and testing procedures.

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