Air Care News
April 1997
NOx standard a
new challenge for technicians
by Vic Cooper
Beginning Jan. 2, 1998 vehicles exceeding limits for oxides
of nitrogen (NOx) during an I/M 240 enhanced emissions inspection area will
fail the test. This is a planned program revision that also includes tighter carbon monoxide
limits for most vehicles.
NOx emissions are formed when enough heat and pressure exist in a vehicle's combustion chamber to combine
oxygen with nitrogen. In the 1970s, vehicle manufacturers attempted to control
NOx emissions by preventing their formation. They lowered compression ratios
(compared to 1960s levels), retarded ignition and cam timing, and installed exhaust gas
re-circulation components to lower combustion temperature.
Nitrogen oxides
are a precursor to ozone -- a contributor to the Denver metro area
"Brown Cloud." The photo at right was taken Jan. 17, 1997, when
readings on the visibility scale reached 213, in the "extremely poor" category.
During the 1980s, a new reduction style catalyst was developed
to strip oxygen off of nitrogen. The new catalyst required a chemically-correct air/fuel mixture
to function, creating the need for oxygen sensors and computer controls. What does all this mean to you?
When a vehicle fails for excessive carbon monoxide, NOx emissions will be low because the excess fuel
cools combustion temperatures. This rich mixture will also cause carbon to build up in the combustion
chamber, thereby raising compression ratios.
After correcting a carbon monoxide problem, the leaner mixture will
raise the combustion chamber temperatures, and may increase NOx emissions.
How do you protect yourself? Plan on performing NOx repairs as
part of carbon monoxide repairs. This would include a verification of EGR operation
as well as ignition timing and timing controls. You also may want to consider using
an engine cleaning product to remove carbon in the combustion chamber. This lowers
compression ratios and removes potential hot spots that may be igniting the mixture
already.
Failing vehicles for excessive NOx emissions creates a new
challenge for Colorado technicians. Take additional precautions to increase the odds of a
successful repair.
Vic Cooper is an environmental technician for
the Colorado Department of Public Health & Environment, Air Pollution Control Division, in Denver.
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Misdiagnoses
and improper repairs main culprits in waiver
denials
by Tom Myrsiades
About 58 percent of
all waiver requests made to the Colorado Department of Revenue (CDOR) by vehicle owners are
denied for a variety of reasons. Perhaps the number one reason is improper repairs
to the vehicle that have little or no effect on emissions results. In some cases,
the vehicle has failed with higher readings than the initial test.
According to Bob Bentley and Tim Barnett,
CDOR compliance inspectors responsible for issuing waivers, some technicians ignore basic
symptoms and recommend that their customers spend hundreds of dollars on what turn out to
be unnecessary repairs. Following are a few examples of what we see over and over.
Case #1:
A 1986 Mitsubishi failed its initial test with a carbon
monoxide (CO) reading of 133 grams per mile (gpm). The customer spent $499 in
repairs -- including a remanufactured carburetor, new jet valves and a new oxygen
sensor. The vehicle was subsequently tested eight more times with failures
ranging from 112 gpm to 201 gpm.
Tim Barnett received a waiver request and, in turn, requested that the
Colorado Department of Public Health and Environment's Emissions Technical Center perform
an evaluation. The problem turned out to be a defective coolant sensor that
prevented the vehicle's computer system from controlling the fuel. After a minor
repair was completed the vehicle passed with a CO reading of 29 gpm.
Case #2:
A 1983 2.8L Ford Ranger failed its initial test with a CO
reading of more than 60 gpm. The customer spent more than $450 in repairs --
including a carburetor overhaul, oxygen sensor replacement, tune up and oil change.
The owner requested a waiver from Bob Bentley because his vehicle continued to fail for
excessive CO emissions.
Bentley asked the Emissions Technical Center to perform an evaluation
which showed that no vacuum was supplied to the newly-overhauled carburetor power valve,
thereby causing high CO readings. The vacuum hose was reconnected and the vehicle
passed at 10 gpm.
Case #3:
A 1986 Oldsmobile failed its initial test with a CO reading of 60 gpm.
The customer spent $783 in repairs -- including a remanufactured carburetor,
purge valve and oil change. This vehicle was tested nine more times with
failures ranging from 31 gpm to 125 gpm.
Acting on a waiver request, Tim Barnett reviewed repairs and
discovered a broken purge vacuum switch. Although the waiver was denied, a minor repair resulted
in a passing test at 18 gpm.
We can achieve cleaner air quality for Coloradans by properly repairing
vehicles. The repair industry within the Colorado emissions program area faces an added
challenge of repairing more transient-tested vehicles than anyplace in the country.
Hundreds of technicians have taken their abilities to the next level and
made the transition required to meet customer needs under enhanced inspection and
maintenance.
If you are a technician who has had difficulty diagnosing and repairing
I/M 240 failures, you need to increase your technical expertise. Training is
available from a variety of sources. For more information call the Colorado
Department of Public Health and Environment at 744-2442.
For waiver requirements and information, call the Colorado
Department of Revenue at 303-205-5603.
Tom Myrsiades is an emissions compliance
supervisor with the Colorado Department of Revenue, Division of Motor Vehicles, Emissions Section.
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Restricted
exhaust: diagnosing the problem
by Lonnie Shrewsbury
Many technicians and motorists have
come to the Emissions Technical Centers for diagnosis of plugged catalytic
converters. This is a problem that is easily diagnosed.
A common procedure to determine exhaust restriction begins with
the use of a vacuum gauge to measure the engine intake manifold vacuum. The drawback
to using this procedure is that it may indicate a number of other engine, mechanical or
fuel-related problems.
Proper diagnosis for a restricted exhaust system is essential
before any components are replaced. Either of the following may be used for diagnosis:
 a
simple vacuum-pressure gauge
a low pressure fuel pump tester
The procedure may be performed at either the Air Injection
Reaction (AIR) pipe or the Oxygen (O2) sensor.
To check at the AIR pipe (See Figure 1):
1.
Remove the rubber hose at the exhaust manifold AIR pipe check valve.
2.
Remove check valve.
3.
Connect fuel pressure gauge to a rubber compression adapter in place of the check valve.
4.
Insert the adapter into the AIR rail pipe.
To check at the O2 sensor (See Figure 2):
1.
Carefully remove 02 sensor.
2.
Connect pressure tester using a rubber compression plug adapter in place of the O
2 sensor (remember to be sure to coat the threads of the O2
sensor with anti-seize compound before replacing after procedure).
Once you are connected, complete the following diagnostic steps:
1.
Observe the exhaust back pressure on the gauge with engine idling at normal operating temperature
(reading should not exceed 1.25 psi).
2.
Accelerate engine to 2000 rpm and observe gauge (reading should not exceed 3.0 psi). A restricted
exhaust is indicated if back pressure exceeds specifications at either rpm.
3. Inspect the entire exhaust
system for collapsed pipe, heat distress or possible muffler failure. If no obvious reasons
for excessive back pressure are evident, a restricted catalytic converter may be the
culprit. If replaced, do so using the manufacturer's recommended procedures.
Occasionally, the above procedure may be performed at the EGR valve.
However, the EGR valve may be more difficult to access and vacuum ports will be
exposed. I recommend performing the procedure at the EGR valve only if the vehicle
does not have an AIR system or an O2 sensor.
Finally, drilling holes in the exhaust is not advised. This could
void warranty coverage.
Lonnie Shrewsbury is an
automotive environmental systems technician for the Colorado Department of Public Health & Environment,
Air Pollution Control Division, in Colorado Springs.
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The Emissions Technician's Night series continues to be an
overwhelming success. Three Tech Night sessions were held during the past quarter, with another
planned for April.
Lincoln-Mercury-Mazda of Boulder hosted Tech Night on Jan. 22,
with 33 Boulder-area technicians in attendance. As always, discussion was lively. A variety of
diagnostic tips were covered, from the recent standards change and NOx diagnosis/repair to the ever-popular
"Top Ten Dirty Cars."
Dave Moreau, Automotive Program Director at the Denver Institute of
Technology, shared his extensive knowledge of NOx repairs and intake/combustion chamber cleaning technology.
Jim Speck, drivability expert for Lincoln-Mercury-Mazda of Boulder,
took the honors as "Top Tech" for the quarter. Jim did a hands-on session on the Ford Variable
Venturi carburetor. He discussed its strengths and weaknesses and potential problem areas, while offering
repair tips to help demystify this unique and often misunderstood fuel system.
Two shorter Tech Night sessions were held at the Mountain States
Automotive Trade Show and Expo '97 on March 8 and 9. These hour-long sessions focused on diagnostic case
studies and a reformatted Top Ten. More than 40 technicians attended.
The Tech Night format and content continue to evolve based on feedback
received from the technicians in attendance. If you haven't been to a Tech Night yet, come to one. It will
save you and your customers diagnostic time and headaches -- just ask someone who's been there. Look for an
announcement of April's Tech Night in the REI report card mailing in early April, or call the Air Care Colorado
hotline at (303) 456-7090. Tech Nights are free, but seating in limited so call to reserve a spot.
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