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.
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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