EPA-AA-SDSB  79-02
                             Technical Report
                Emission-Related Maintenance Intervals  for
                Light-Duty Trucks and Heavy-Duty Engines
                                    by
                            Richard A.  Rykowski
                              January, 1979
                                  NOTICE

Technical Reports do not necessarily represent final EPA decisions or
positions.  They are intended to present technical analysis of issues
using data which are currently available.   The purpose in  the release
of such reports is to facilitate the exchange of  technical information
and to inform the public of technical developments which may form the
basis for a final EPA decision, positon or regulatory action.
               Standards Development and Support  Branch
                 Emission Control Technology Division
             Office of Mobile Source Air Pollution Control
                  Office of Mr, Noise and Radiation
                 U.S. Environmental Protection Agency

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Emission-Related Maintenance Intervals for Light-Duty Trucks and Heavy-
Duty Engines

I.   Background

     The EPA will soon issue two Notices of Proposed Rulemaking (NPRM)
concerned with gaseous emission standards for: 1)  light-duty trucks and
2) heavy-duty engines.  The NPRM concerned with light-duty trucks will
propose more stringent emission standards for hydrocarbons, carbon mon-
oxide and nitrogen oxides.  The NPRM concerned with heavy-duty engines
will propose a new transient test procedure for gaseous emission testing
of heavyr-duty engines and more stringent standards for hydrocarbon and
carbon monoxide emissions.  A new definition of the useful life of an
engine coupled with a new durability test procedure will also be pro-
posed in both packages.  These last two changes necessitate a revision
in the current provisions governing the maintenance of durability-data
engines.  Useful lives determined under the regulations to be proposed
will likely exceed the limits of the current maintenance provisions.

     Both NPRMs will- also, propose new definitions  for emission-related
maintenance and non-emission related maintenance.   The new definitions
are:

     "Emission-related maintenance" means that maintenance which does
substantially affect emissions or which is likely  to have a lasting
effect on the deterioration of the vehicle or engine with respect to
emissions even if the maintenance is performed at  some time other than
that which is recommended;

     "Non-emission-related maintenance" means that maintenance which
does not substantially affect emissions and which  does not have a las-
ting effect on the deterioration of the vehicle or engine with respect
to emissions once the maintenance is performed at  any particular date.

Under these new definitions maintenance restrictions would be limited to
fewer maintenance items than are currently restricted (only those which
are emission-related).  Non-emission related maintenance could be per-
formed at the manufacturer's recommended intervals.  Only those mainte-
nance items which qualify as emission-related under the new definitions
will be addressed in this report.

     A replacement of the air cleaner would be an  example of non-emission
related maintenance.  A dirty air cleaner may affect emissions to some
extent by richening the fuel-air mixture, but the  effect would not be
expected to be a large one.  The effect of a dirty air cleaner could
also be completely reversed by replacement with a  clean air cleaner. A
dirty air cleaner should not cause any component to be permanently
damaged.  Spark plug replacement would be an example of emission-related
maintenance, since a malfunctioning spark plug can greatly increase
hydrocarbon emissions.  A malfunctioning spark plug can also cause
catalyst activity to deteriorate at a faster rate  than normal and such
deterioration would not be reversed by replacement with a good spark
plug.

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                                  —2—
II.  Potential Intervals for Emission-Related Maintenance

     The following maintenance Items are • considered  to be  emission-
related under the definitions stated in the preceding section.  The
reasons why these maintenance items are considered to be emission-
related are also shown.

     Gasoline-^fueled engines:

     1.   Cleaning or replacement of spark plugs - misfiring  substan-
          tially increases hydrocarbon emissions and can overheat the
          catalyst, speeding up its deterioration.

     2.   Replacement or adjustment of 0?  sensor - failure has a sub-
          stantial effect on emissions; a  key component to the three-way
          catalyst.system.

     3.   Cleaning or replacement of PCV and EGR valves —  malfunction
          can substantially affect crankcase and NOx emissions, respec-
          tively.

     4.   Replacement of emission-related  hoses and  tubes  - rupture or
          plugging can disable emission control devices causing sub-
          stantial increases in emissions  (e.g., EGR vacuum lines).

     5.   Inspection or replacement of ignition wires - faulty wires can
          cause misfiring of spark plugs (see -?1).

     6.   Cleaning of injector tips - improper injection can  cause
          substantial increases in emissions.

     7.   Replacement of catalyst -   failure  or loss  of activity can
          cause substantial increases in emissions.

     8.   Adjustment of the idle air-fuel  mixture -  maladjustment can
          cause substantial increases in hydrocarbon and carbon monoxide
          emissions.

     Diesel-fueled engines:

     1.   Cleaning of injector tips - same as ?6 above.

     2.   Cleaning or replacement of PCV and EGR valves —  saiae as £3
          above.

     3.   Servicing or replacement of turbocharger - malfunction can
          significantly change air-fuel ratio and substantially increase
          emissions.

     4.   Replacement of injectors - sane as i-6 above.

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                                   -3-

     Other maintenance items, such as oil filter,  air filter,  fuel
filter, and drive belt replacements, adjustments of the idle speed,
valve lash, and engine bolt torque and cooling system maintenance are
not considered to be emission-related maintenance  under the definitions
of Section I.  None of them are believed to have a lasting effect on the
durability of the engine with respect to emissions.  That is,  once the
maintenance is performed, even belatedly, the deterioration of emissions
will return to normal.  Also, while some of the above items can affect
emissions, the effect is not large enough to merit an emission-related
designation.

     The rest of the report will be devoted toward determining the
potential intervals between the performance of these maintenance items.
The method used to determine these potential intervals is a very simple
one.  If a vehicle currently exists which utilizes a given interval  for
a maintenance item, that interval would be assuaed to be potentially
available to all vehicles.  An exception to this would be a case where
it was known that the reason this particular vehicle was able  to have
such a long maintenance interval was either:  1) not available to all
vehicles, or 2) prohibitively expensive to be extended to all  vehicles.
The time and resources available for this study did not allow  any dura-
bility testing of"components, either in-use or_in  the laboratory.  Data
from other sources on the durability of emission-control- systems is_not
readily available, but what data were available have been incorporated
into the discussion.

     Spark plugs

     The use of unleaded gasoline has allowed extended intervals for
spark plug replacement, primarily due to the absence of lead deposits on
the spark plug tip.  Prior to 1975, when light-duty vehicles and trucks
were still being operated on leaded gasoline, their spark plug replace-
ment intervals were around 12,000-15,000 miles. With the use  of unleaded
gasoline, these intervals have been extended to 30,000 miles for many
vehicles (e.g., all of Chrysler's 1978 vehicles with domestic  engines).
California also recently received a waiver from the U.S.  EPA regarding
the requirement of more restrictive maintenance intervals for  light-duty
vehicles and light-duty trucks (1).*  The interval for the replacement
of spark plugs that California found to be technologically *feasible  was
also 30,000 miles.   A potential interval for spark plug replacement for
light-duty trucks should then be 30,000 miles.

     Most heavy-duty engine manufacturers currently recommend  spark  plug
replacement every 12,000 to 18,000 miles.  These engines are operated on
leaded gasoline.  Since their spark plug replacement interval  corresponds
to that of light-duty vehicles and trucks using leaded gasoline, it
would appear that the spark plug replacement interval is independent of
vehicle type.  Because the heavy-duty engine emission standards to be
proposed for 1983 should require catalysts on all  gasoline engines,
unleaded gasoline will be used in all these.engines.  This should allow

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                                   -4-

spark plug replacement intervals to be extended to 30,000 miles for
heavy-duty engines.

     An exception would have to be made for any light-duty trucks or
heavy-duty engine which could meet the standards to be proposed without
the use of catalysts.  These vehicles could still be operated on leaded
gasoline and there is no guarantee that spark plugs could last 30,000
miles under these conditions without an increase in cost.

     Oxygen sensor

     Oxygen sensors are a recent addition to motor vehicles in the U.S.
They are an integral part of a three-way catalyst system which is used
to reduce NOx emissions as well as hydrocarbon and carbon monoxide
emissions.  In early 1977, the California Air Resources Board (CARS)
found that it was technologically feasible to produce an oxygen sensor
that would only need replacement every 30,000 miles (2).  This deter-
mination was not successfully challenged in the hearings that followed
its proposal (1).  Recently, Ford certified a 1979 Pinto equipped with a
three-way catalyst- system., having-^a-50,000-mile -replacement interval-for
its oxygen sensor-, - demonstrating- that- a -50,000 mile oxygen sensor is
technologically feasible" for" light-"duty""vehicles.

     To extend this finding to light-duty trucks and heavy-duty vehicles,
the mode of sensor failure should be examined.  The most common modes
are electrical failure and thermal cracking, due to sudden cooling
(i.e., water splash) and load cycling of the engine.  There is no reason
to expect that oxygen sensors on light-duty trucks and heavy-duty vehicles
should experience any more electrical failures or water splashes than
light-duty vehicles.-  Failures by these modes should be just as likely
in either case.  It may be possible, though, that a heavy-duty oxygen
sensor may experience more extreme temperature cycling due to the more
extreme loads experienced by heavy-duty engines.  This difference should
not be large, though, and should be able to be handled by sound sensor
design.  There appears .to be no significant problems in applying light-
duty sensor technology to heavy-duty applications.  Thus, oxygen sensors
should be able to last 50,000 miles on light-duty trucks and on heavy-
duty vehicles as well as on light-duty vehicles.

     PCV and EGR valves, emission-related hoses and tubes, and
     ignition wires

     The inspection, cleaning, or replacement of PCV valves, EGR valves,
emission-related hoses and tubes, and ignition vires were all examined
by the CARS in their analysis of automotive maintenance (2),  The CARS
found that it was technologically feasible for a light-duty vehicle or
truck to go without this maintenance for 50,000 miles.  As was the case
with oxygen sensors, this determination was not successfully challenged
in numerous CARB and EPA hearings held afterward (1).  With respect to
heavy-duty engines, General Motors did not reconaend any maintenance on
their 1979 EGR system through 50,000 miles, and Ford did not reconrnend

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                                  -5-
any maintenance on their emission-related hoses and tubes or their
ignition wires through 50,000 miles.  Since a PCV valve on a heavy-duty
engine carries the same compounds as a PCV valve on a light-duty vehicle,
there should be no reason for the former to have more plugging problems
than the latter.  It then appears that PCV valves, EGR valves, emission-
related hoses and tubes, and ignition wires on light-duty trucks or
heavy-duty engines only require-maintenance at 50,000 mile intervals.
If it is assumed that there is no difference between gasoline-fueled and
diesel-fueled engines with respect to the durability of these items,
then the above conclusion can apply equally well-to diesel-fueled
engines.

     Injectors

     Injectors can require periodic cleaning and possibly even replace-
ment if they fail to function properly.  Cummins recommends that the
injector tips on their heavy-duty engines be inspected and cleaned every
90,000 - 150,000 miles depending on the specific engine being serviced.
Caterpillar-recommends this same maintenance every 100,000 miles.  Using
Cummins recommendatiohs, 150,000 miles should be~a" feasible interval
between injector~inspection and cleaning! forrsorae, and: possibly; all
applications./  A;.more_ conservative figure which would apply to all
heavy-duty applications would be 100,000 miles, using the Caterpillar
recommendation.  It also appears that most heavy-duty diesel manufac-
turers, including Cummins, do not recommend the periodic replacement of
the injectors.  Thus, no periodic replacement should have to be allowed
in the maintenance provisions of the NPRMs for heavy-duty engines or
light-duty trucks.

     The maintenance schedules for light-duty trucks usually only extend
to 50,000 miles.  .Throughout this interval, it would appear that no
injector maintenance is needed.  For example, neither General Motors nor
Volkswagen recommend any injector maintenance on their vehicles through
50,000 miles.  To project past this mileage, the heavy-duty experience
must be extrapolated to light-duty trucks.  Periodic cleaning of the
injector tip is usually required because of coking which occurs during
the combustion process.  This coking predominantly occurs at light loads
(i.e., idling).  It would be expected that diesel engines in light-duty
trucks would undergo less idling than those in heavy-duty applications;
such as diesels in tractor-trailers which are idled during rest stops or
delivery trucks which are idled during deliveries.  Injectors in light-
duty trucks may even need less frequent maintenance than injectors in
heavy-duty vehicles.  To estimate any increase in maintenance interval
for light-duty injectors over the heavy-duty interval would be impos-
sible, though, without more data.  Thus, the maintenance interval for
cleaning injectors on light-duty engines should be able to be at least
as long as the heavy-duty intervals, which is 100,000 miles.

     Catalysts

     In their analysis of light-duty vehicle maintenance requirements,
the CARB determined  that catalysts did not require maintenance over
50,000 miles  (2).  The CARB did not attempt to show feasibility past

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                                   -6-

 this point,  though.   Because the useful life of light-duty trucks and
 heavy-duty engines will likely be greater than 50,000 miles under the
 proposed regulations, it is important to determine if catalysts can go
 longer intervals without replacement.

      Two seta of data are available from light-duty vehicles which show
 that current catalysts do not deteriorate at a faster rate after 50,000
 miles than before  50,000 miles*   The first study consisted of two certi-
.fication-type vehicles run over  the AMA durability schedule for 100,000
 miles (4).   A Dodge  Aspen and a  Ford Pinto were both equipped with
 catalysts which do not require maintenance over 50,000 miles.  A com-
 parison was  made between the average emissions over 100,000 miles using
 the current  EPA certification method and that using an integral method.
 The EPA certification method consists of fitting a leasts-squares line
 through all  of the data between  5,000 and 50,000 miles.  The point where
 the line crosses 50,000 miles then becomes the average emission level
 over 100,000 miles.   It is assumed that the emissions continue linearly
 through 100,000 miles.  The integral method sinply connects each con-
 secutive pair of data points between 0 and 100,000 miles with a straight
 line and finds the integral beneath the curve.  This area under the
 curve' is; then ^divided-^by-100,000 miles: to farid the^ average~:eraissions per"
 mile;" Tf"~the~rtwo: methods"yield*,the sam¥~re~sultp"t^
 the deterioration  rate from 50,000^to_100,000 miles was about the same
 as that from ~0~ to  50,000'miles""   "

      The results of  the comparison are shown in Table 1.  The two
 methods yield quite  similar results.  The certification method tends to
"overestimate the actual emissions of the Aspen (i.e., the deterioration
 over the. last half of the useful life is less than that over the first
 half).  This is reversed in the  case of the Pinto.  For hydrocarbon and
 carbon monoxide emissions, which are the only ones affected by the
 catalyst, the certification method underestimates emissions by an average
 of 3.5%.  From this  limited data base, it would appear that the deteri-
 oration rate over  a  vehicle's second 50,000 miles, including the catalyst,
 is no different than that over the first 50,000 miles.  Thus, under
 current test procedures, catalysts in light-duty vehicles appear to be
 durable over 100,000 miles.

      The second set  of data was  available from the EPA's Restorative
 Maintenance  program.  In this program in-use vehicles are first tested
 in an as-received  condition and  then tested after various stages of
 repair and maintenance.  Along with 300 low-mileage vehicles, nine high-
 mileage catalyst-equipped vehicles were tested (average mileage of
 105,000 miles). No  data was available on the low-mileage emissions from
 these high-mileage vehicles, so  an attempt was nade to find lotf-mileage
 data from other vehicles of the  same engine family.  Data of this kind
 could be found for only four of  the high-mileage vehicles.  Both the
 low- and high-mileage data for these four vehicle-engine types are shown
 in Table 2.

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                                  -7-
                                  TABLE 1


             Average 100,000 Mile Emissions in Grams  per Mile


                 Current           Integral           Difference
Vehicle        Cert. Method         Method              (Percent)
                                      0.40                 -2.5%
                                      4.01                -11;2%
                                      1.69                   0   %
                                      0.30                   6.7%
                                      1.63                  20.9%
                                      1.66                   4.8%
Dodge
Aspen

Ford
Pinto

HC
CO
NOx
HC
CO
NOx
0.41
4.46
1.69
0.28
1.29
1.58
     Integral-Cert
       Integral

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                                 -8-
                                  TABLE 2

                 Emission Deterioration of Well-Maintained
                      In-Use 1975 Model-Year Vehicles
Vehicle
               Mileage
   FTP Emissions
                                                  HC
                                                            CO
Plymouth
  Duster
Plymouth
  Station Wagon
Mercury
  Monarch
Ford
  LTD
                  4»9222
                  8,789!:
                138,000
                In-use d.fe
                Cert, d.f.'

                 10,968*
                 77,000
                In-use d.ft
                Cert, d.f."

                 13,135:?
                104,000
                In-use d.fe
                Cert, d.f.'

                 12,375?,
                 13,135^
                111,000
                In-use d.fj
                Cert, d.f.'
0.65 g/tni
0.55 g/rai
3.00 g/iai
2.48
2.31

0.48 g/mi
0.74 g/mi
1.40
1.30

1.33 g/mi
1.52 g/mi
1.08
1.67

1.23 g/rai
1.33 g/rai
2.04 g/oi
1.29
1.17
 9.4  g/mi
 5.42 g/mi
22.9  g/mi
 1.76
 1.41

 6.87 g/mi
 4.60 g/mi
 0.77
 0.93

 7.28 g/mi
 8.03 g/mi
 1.05
 0.92

11.2  g/mi
 7.28 g/mi
11.0  g/mi
 1.09
 1.04
1

2

3


4

5
"Evaluation of Restorative Maintenance on 1975 and 1976 Light-Duty
Vehicles in Chicago, Illinois", EPA, January 1977, EPA-460/3-76-030.
"Evaluation of Restorative Maintenance on 1975 and 1976 Light-Duty
Vehicles in Washington, D.C.", EPA, March 1977, EPA-460/3-76-031.
Results from testing of high-mileage catalyst-equipped vehicles
performed under Work Effort #6, Contract 68-03-2612 by Automotive
Testing Labs for the EPA in St. Louis, 1978.
d.f. = deterioration factor, ratio of emission rate at 50,000 miles
to that at 4,000 miles.
Durability test results from EPA certification of 1975 model-year
vehicles.

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                                 —9—
     Data was chosen from the Restorative Maintenance program because
the vehicles are-.in-use vehicles and show in-use deterioration,  but at
the same tine the effects of maladjustments and failed components
(excepting catalysts) have.been removed.   In determining catalyst dura-
bility from whole vehicle data, it is important to remove the effects of
rich idle-mixture settings, plugged EGR valves, etc.   The data  shown in
Table 2 are from tests of vehicles which have been "restored" in this
way unless the vehicle was already meeting all emission standards-  No
maintenance was performed on the catalysts.  The deterioration  seen on
these vehicles includes the deterioration of the catalyst, plus the
basic deterioration of .the engine (rings, valves, pistons, etc.).  While
it would be preferable to have low- and high-mileage  data on the same
vehicle, using data from two or three different vehicles of the same
engine family can affect the results in either direction.   It is expec-
ted that on the average this effect would tend to cancel itself and be
negligible.

     To show-that-catalysts-can (and do)  operate for  100,000 miles,- the
deterioration of emissions up- to the-high mileage data point (average of
107,500 miles) is compared to the deterioration determined over 50,000
miles in the EPA certification process.  To put both  measures of the
deterioration in .the same format, the in-use deterioration was  put in
the format of the certification deterioration factor  (i.e., ratio of
emissions at 50,000 miles to that at 4,000 miles). Only hydrocarbon and
carbon, monoxide emissions have been shown since these are the only emis-
sions affected by oxidation catalysts. The averages  of the ratios of
in-use deterioration to certification deterioration are nearly  equal to
unity; 0.975 (HC) and 1.066 (CO).  This result shows  that the average
deterioration rate of the catalyst and engine over 100,000 miles in-use
is the same as that over 50,000 miles using the EPA's durability test
procedure.  The conclusion would appear to be that current-technology
catalysts can last for 100,000 miles with the same deterioration rate
(per mile basis) as occurs over 50,000 miles.

     While the above two sets of data seem to indicate that current
technology catalysts can operate 100,000 miles with the same deterior-
ation rate as over 50,000 miles, some data examined by the California
Air Resources Board (CARS) seem to indicate that the  deterioration rate
increases after 50,000 miles.  The CARS examined the  carbon monoxide and
hydrocarbon emissions of 256 1975 and 1976 catalyst-equipped vehicles of
all makes, sizes and mileage (5).  About  19% of the vehicles had mile-
ages over 50,000 miles and 11% had mileages over 55,000 miles.   A quad-
ratic curve was fit to the data using two techniques; 1) weighted least-
squares, and 2) log-trans formed least-squares.  Both  of these techniques
weighted the more consistant data more heavily, which was the data at
low mileages.  Extreme scatter in the data was found  at high mileage.
The resulting curves showed positive quadratic terras, indicating that
emissions deterioration was increasing with mileage.   This result was
vehicle dependent, with some engine families and product lines  showing
very poor high-mileage emissions and some showing very good high-mileage
emissions.  This was evidenced in the resulting coefficients of cor-
relation of the regression curves, which were very low.  Mileage was not
the primary factor affecting the emissions of the vehicles in this
study.

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                                   -10-
     The above studies indicate that catalysts can last 100,000 miles-
on light-duty vehicles, though they do not indicate that the current
catalysts of all manufacturers can operate efficiently through 100,000
miles.  Some manufacturers may have to upgrade the durability of  their
catalyst systems.  However, no similar data are available on catalyst
life in light-duty trucks or heavy-duty vehicles,  so extrapolation will
have to be made from light-duty vehicle experience.  There are two
potential causes of catalyst deterioration, poisoning and over-heating
(6,7).  Poisoning here does not only include gross poisoning (i.e.,
continued use of leaded gasoline), but also includes gradual poisoning
from small amounts of lead, phosphorus, and other  metals-contained in
unleaded gasoline and motor oils.  Over-heating can occur when exhaust
that is too rich in hydrogen, carbon monoxide, or  hydrocarbons, reaches
the catalyst.  The ignition of these compounds releases enough energy to
raise the temperature of the catalyst high enough  to sinter the alumina
substrate.  This drastically reduces the conversion efficiency of the
catalyst.

     The occurrence of poisoning should-not be any different for  either
light-duty trucks or heavy-duty vehicles than for  light-duty vehicles,
since poisoning is primarily related to fuel and oil use and not  engine
size or operating conditions.  However over-heating occurs during speci-
fic operating modes of the engine (6).  These modes are sustained engine
misfiring and high-speed, closed-throttle coasting.  A well-maintained
heavy-duty engine should not misfire any more than a light-duty engine.
Neither is it expected that light-duty trucks would undergo prolonged
motoring any more than light-duty vehicles.  The EPA tests both light-
duty vehicles and light-duty trucks over the same, driving cycle,  so this
would imply that both types of vehicles would experience the same amount
of motoring.  Ikwever, heavy-duty vehicles may be  motored in-use  more
than the other two classes of vehicles.  While heavy-duty vehicles are
driven on the same roads and must follow the same  general traffic pat-
terns as light-duty vehicles and trucks, there are two differences in
heavy-duty drive trains which could result in increased motoring.   One
is the predominance of standard transmissions in the heavy-duty fleet,
which results in engine motoring when current automatic transmissions
would not.  The other difference is that heavy-duty vehicles usually
have higher gear ratios than light-duty vehicles which could result in
higher engine speeds during motoring.  These two factors could result in
a somewhat more severe environment for catalysts.   With the lead  time
available, though, it is expected that any increase in severity can be
overcome and that heavy-duty catalysts can be made as durable as  light-
duty catalysts.  Thus, heavy-duty catalysts should be able to last
100,000 miles without maintenance or replacenent.

     While a catalyst may last 100,000 niles with  no maintenance,  its
activity does not remain constant.  A 100,000 mile emission standard
would need to take into account the added deterioration of the catalyst
occurring over the second 50,000 miles.  The deterioration rate shown in
Table 2 includes that of the engine in addition to the deterioration of
the catalyst, so it would only show an upper limit for catalyst deter-
ioration.  Any improvenent in catalyst activity and durability over 1975

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                                 -11-
technology that would occur by 1983 would, of course, reduce the need to
take the-deterioration over the second 50,000 niles into consideration.

     Air-Fuel Mixture

     The CARB examined the need for adjusting the idle air-fuel mixture
and found that it was technologically feasible that a light-duty vehicle
or truck not require such an adjustment over its useful life (50,000
miles).  A survey of the adjustment intervals recommended by heavy-duty
engine manufacturers shows that no Ford engines, and only one Chevrolet
engine require this adjustment over '50,000 miles.  It appears that a
50,000 mile adjustment' interval for the air-fuel mixture should be.
easily attainable for either light-duty trucks or heavy-duty engines.

     Turbochargers

     Caterpillar currently recommends an inspection of the turbochargers
on all of their heavy-duty engines so equipped at 200,000 miles with
possible rebuilding or replacement, if necessary.  Other heavy-duty
manufacturers-recommend this maintenance-earlier^between 90,000 and
150,000 "miles""."" At" this" "timey no inherent and immutable' differences
between Caterpillar and other- heavy-duty engines are known to exist
which allow Caterpillar to have a more durable turbocharger.  Thus,
200,000 miles should be an acceptable maintenance interval for turbo-
chargers on heavy-duty engines.

     No light-duty trucks are currently equipped with turbochargers, so
no in-use experience can be cited in this area."  Turbochargers usually
fail because of bad bearings or because of wear on the turbine blades
from particle impingement.  Neither of these problems should be more
likely to occur in light-duty applicatons than in heavy-duty applica-
tions.  Light-duty diesels currently must control crankcase emissions,
while heavy-duty diesels are not currently rquired to control these
emissions, and this could cause more foreign matter to be introduced to
the inlet of the turbocharger.   With these changes in allowable mainte-
nance intervals will also be a proposed change to control of crankcase
emissions from heavy-duty diesels, removing any differences in this
area.  For both classes of vehicles it should be possible to filter out
any foreign matter from crankcase blow-by and also from any recirculated
exhaust gas which may arise due to future control of nitrogen oxides.
There seems to be no reason, then, that turbochargers on light-duty
trucks should not be able to have the same maintenance interval as those
on heavy-duty vehicles, 200,000 miles.

     Most light-duty trucks are not expected to have useful lives in
excess of 200,000 miles, so to prohibit maintenance over the useful life
might have the same effect as a 200,000 mile maintenance interval.   How-
ever, to protect any light-duty trucks with useful lives in excess of
200,000 miles, the 200,000 mile maintenance interval should be kept for
light-duty trucks.

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                                 -12-
III. Summary

     The previous section investigated the maintenance intervals of
certain emission-related components which should be achievable by heavy-
duty engines in 1983.  These maintenance intervals are shown in .Table 3.
Some extrapolations have been made from light-duty vehicle experience
due to a lack of light-duty truck or heavy-duty engine experience.  This
notwithstanding, given the current level of technology and the lead time
available, these intervals should be technologically feasible by 1983 or
the time that the certain emission-related components are necessary to
meet emission standards (e.g., 1935 for heavy-duty oxygen sensors).

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                                 -13-
                                  TABLE 3
             Intervals for Emission-Related Maintenance Items
                       Which Should be Achievable by
             Light-Duty Trucks and Heavy-Duty Engines in  1983
Maintenance Item                                  Interval-Miles


Spark Plugs - clean or replace                        30,000

Oxygen Sensor - adjust or replace                     50,000

PCV and EGR Valves - clean or replace                 50,000

Emission-Related Hoses and Tubes - replace             50,000

Air-Fuel Mixture - adjust                             50,000

Injector Tips - clean                                100,000

Catalyst - replace                                   100,000

Turbocharger - rebuild or replace                    200,000

Injectors - replace                                  Total Useful Life

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                                References
1.   "California State Motor Vehicle Pollution Control Standards -
     Waiver of Federal Preemption", Federal Register,  Vol. 43, No.
     143, Tuesday, July 25, 1978, pp. 32182-32185.

2.   Exhibit A - Public Hearing on Proposed Changes to Regulations
     Regarding Allowable Maintenance During New Vehicle Certification
     of Light-Duty and Medium-Duty Vehicles, Calif. Air Resources
     Board, May 26, 1977, CARB #77-12-1.

3.   "Motor Vehicle Emission Control Status Report  for the U.S. EPA,"
     A.B. Volvo, January.1978.

4.   Hellman, Karl H., Chief, TES, "Comparison of Cert^-Type Projections
     of Emissions to Actual 100K Data," Memorandum  to  Charles Gray,
     Acting Director, ECTD, EPA, May 18, 1978.

5.   Cheung, M., "Deterioration of HC and CO Emissions with Use of
     Catalyst-Controlled Vehicles (Update)," CARB Memorandum to R.
     Ingels, Manager, Data Analysis Section, CARB,  December 22, 1978.

6.   Mondt, James R., "A Guard System to Limit Catalyst Coaveiter
     Temperature," February 1976, SAE #760320.

7.   Klimisch, Richard L., et. al., "The Chemistry  of  Degradation in
     Automotive Emission Control Catalysts," G.M. Research Labs, Feb-
     ruary 4, 1974, presented at the Third North American Meeting of the
     Catalysis Society, San Francisco, February 4-6, 1974.

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