EPA-AA-TEB-80-17
Effectiveness of Idle Adjustment on Light-Duty
Trucks at Commercial Repair Facilities
by
John C. Shelton
June 1980
Test and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise, and Radiation
U.S. Environmental Protection Agency
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-2-
Abs tract
This paper describes the results of a project on Light Duty Trucks to evaluate
the effectiveness of idle adjustment at commercial repair facilities. This
effort involved a total of 96 trucks and vans tested by Automotive Testing
Laboratories (ATL) during 1979. These vehicles were a subset of 370 vehicles
tested in St. Louis as a part of the FY 78 Light Duty Truck Emission Factor
Program. Vehicles which arrived for testing without limiter caps were chosen
to participate in the survey. After the complete laboratory test, a
contractor employee took each vehicle to a service station or independent
garage and asked simply that the idle mixture and speed be adjusted to
manufacturer's specifications. Upon return to the laboratory, the work
performed by the Facility was evaluated using a tachometer and garage-type
emission analyzer. The sequence was completed when the contractor's mechanic
performed the idle adjustments to the best of his ability. The data obtained
illustrates the inability of the majority of independent repair facilities to
properly set idle mixtures. The results of this project point to the need for
mechanic training in reducing vehicle emissions through correct maintenance
procedures.
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—3—
Background
According to the Clean Air Act and its Amendments, the Environmental
Protection Agency (EPA) is required to encourage and implement programs which
will assure that properly maintained vehicles will meet their emission
standards throughout their useful life. Inspection/Maintenance programs are
the primary force behind this effort to control emissions from in-use vehicles
with the work to be performed by the commercial repair industry. It is well
known that a substantial number of in-use vehicles will not meet their
emission standards when tested in an as-received condition. (Reference 1)
One of the major reasons is that the idle mixture and speed has been
maladjusted. In order for these vehicles to meet their emission standards,
these adjustments must be made correctly. The typical places for these
adjustments to be made include dealerships, service stations, and independent
garages.
Purpose
This study was designed to evaluate the ability of the commercial repair
industry to set idle adjustments to manufacturer's specifications.
Selection and Test Procedures
Vehicles selected for this project were recruited primarily for the FY78
Light-Duty Truck Emission Factor Program. Trucks which arrived at Automotive
Testing Laboratories' (ATL) St. Louis facility missing idle mixture limiter
caps were chosen for this study. Ninety-six out of a total of 370 trucks
tested which had their limiter caps missing were taken to .commercial
facilities by various persons in the ATL organization (secretaries, lab
personnel, engineers, technicians, etc.). The following procedures were
employed:
Before Leaving ATL - Vehicle identification information was recorded on
worksheets provided by EPA. Idle readings (CO, HC, RPM) were also measured
and recorded. Any evidence that the vehicle was in a testing program (e.g.,
data packets or exhaust connectors) was removed from the vehicle. A repair
facility was contacted to set up an appointment to have idle mixture and speed
adjusted. If possible, all adjustments were to be performed while the driver
waited. No reference was made to any affiliation with an emission testing lab
or that this was to be part of an EPA study.
At Repair Facility - The person requested that the idle mixture and speed be
adjusted to manufacturer's specifications. If questioned why, it was stated
that they had been informed in some way (by a friend, magazine article, etc.)
that this is a very important adjustment from a number of standpoints, such as
fuel economy and engine performance. If the mechanic insisted that other
maintenance be performed, it was stated that the person wanted only the idle
adjusted at this time to see what difference it made. If the mechanic said
that he did not know how to set it to specifications, he was asked to set it
as best he could. Notes were made (although not in his presence) of any
comments and actions taken by the mechanic. Observations regarding
instruments, tools, and cost data were also recorded on the worksheets.
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-4-
After Returning to ATL - ICO, IHC, and IRPM were .measured and recorded, as
were the number of % turns necessary to lightly seat the idle mixture screws.
The mixture screw settings were not measured prior to sending the vehicle to
the commercial repair facility. Idle parameters were then adjusted to
manufacturer's specifications by ATL mechanics and the location of the idle
mixture screws relative to the lightly seated position was recorded. ICO, IHC
and IRPM were again measured and recorded. New limiter caps were installed in
the center position. The vehicle was then returned to its owner.
Follow-Up - ATL personnel performed a follow-up inspection approximately 30
days later. The presence and position of the limiter caps were checked at
that time. The owner was also asked several questions relating to the
performance of his vehicle.
Results
Idle tests - Nine 1979 model year trucks were taken to commercial repair
facilities. The results of these adjustments are summarized in Figure 1.
After adjustment at commercial repair facilities, idle HC concentration
increased by 80% and idle CO increased by 50%. The engine RPM values,
representing the average absolute difference from manufacturer's
specifications, were essentially unchanged. The average cost for these
adjustments was $2.17.
Eighty-seven trucks from the 1975-1978 model years were also taken to
commercial repair facilities. Their results are summarized in Figure 2.
After adjustments at commercial repair facilities, idle HC concentration
decreased by 25% and idle CO decreased by 9%. Again, the engine RPM values,
representing the average absolute difference from manufacturer's specification
were virtually unchanged. The average cost was $4.23. Almost one-quarter of
these visits resulted in no charge.
A follow-up limiter cap inspection was accomplished approximately 30 days
later on a total of 82 trucks. The new limiter caps on 55 trucks were found
to be unaltered. Limiter caps had been removed on 22 trucks and 5 trucks had
their settings altered with the limiter caps still installed. The results of
the follow-up are summarized in Figure 3.
The results of each of the 96 trucks involved in this project are listed in
the Appendix.
Results of the Federal Test Procedure - Although the Federal Test Procedure
(FTP) was not performed on these vehicles after they returned from the repair
facility, the FTP emissions for the fleet were collected and averaged based on
the presence of limiter caps upon arrival at the laboratory. These averages
are listed in Table 1. The values here indicate that vehicles without limiter
caps have average HC and CO emission levels which exceed those where the
limiter caps are intact.
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-5-
Conclusions
1. Only minor adjustments would be required to allow most vehicles to pass a
basic I/M test.
2. The commercial repair industry does not currently adjust idle mixture and
speed properly.
3. A lack of training and proper equipment (tachometers and exhaust
analyzers) is apparent in the performance of this type of maintenance.
4. In order to conduct successful Inspection/Maintenance programs, some form
of incentive or a major effort in mechanic training will be required to
ensure that idle adjustments are made properly.
References
1. J.T. White, "An Evaluation of Restorative Maintenance on Exhaust
Emissions from In-use Automobiles", SAE Paper 780082, March, 1978.
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-6-
Table 1
Emission levels and Fuel Economy versus Presence of Limiter Caps
Model Year(s)
1975-1978
1975-1978
75-78 Totals
1979
1979
79 Totals
Limiter
Caps on?
Yes
No
Yes
No
1
159
100
259
95
15
110
HC_
3.73
5.74
4.50
.97
1.17
.99
CO
39.3
58.9
46.9
13.2
14.2
13.3
NOx
3.87
3.88
3.87
1.89
2.02
1.91
MPG
12.7
12.1
12.5
12.9
12.2
12.8
HFET
16.5
16.0
16.3
16.5
16.5
16.5
IHC
240
380
290
76
103
80
ICO
1.4
3.5
2.2
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-7-
Figure 1
Effectiveness of Idle Adjustments
at Commercial Repair Facilities
Nine 1979 Light Duty Trucks
200 _
IHC 100 _
(ppm)
0 _
189
105
136
3.0
2.0 _
% ICO 1.0 _
0_
Before After After
Repair Repair ATL
2.1
1.4
.33
Before After After
Repair Repair ATL
100 -i
100 _
IRPM*
50 _
0 .
* These numbers are the average absolute
difference from manufacturer's specifications
24 -,
20 -
]
1
83
Before
Repair
7S
After
Repair
75 _
Percent
of
Sample
24
After 2b
ATL
0_
Sfi7
_Average Cost $2.17
22%
11%.. ! 11%
i
Free up to 2.01- 5.01-
$2.00 5.00 10.00
Cost of Adjustment
Number
of
Trucks
16 -
12 -
8 .
4 -
0 -
[| 1975-1978 Models
g£3 1979 Models
17
2 0 2 4 6 8 10
Richened Leaned
Number of % turns required for proper adjustment after return from
commercial repair facility
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-a-
Figure 2
Effectiveness of Idle Adjustments
at Commercial Repair Facilities
Eighty-Seven 1975-1978 Light Duty Trucks
393
tuu
IHC
(ppm) 300'
200.
100.
0.
!
1
295
238
4.O.,
% ICO
Before After After
Repair Repair ATL
3.0_
2.0.
1.0.
3.3
3.0
.54
Before After After
Repair Repair ATL
*IRPM
100 -
50 -
100'
75
— Average Cost $4.23
86
yo
Percent 50-
of
Sample
25
17
1 o
22%
7%
•3Q7|
jy /o>
\
1
777.
5%
J
Before After After
Repair Repair ATL
* These numbers are the average absolute
difference from manufacturer's specifications
Free Up to 2.01- 5.01 Over
$2.00 5.00 10.00 10.00
Cost of Adjustment
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-9-
Figure 3
Results of 30 Day Follow-Up Inspection and Questionnaire
Eighty Two 1975-1979 Light Duty Trucks
Limiter cap status at 30 day
follow up inspection
100%-,
Satisfied with present performance?
50%_
0%.
150%-,
67%
50%_
27%
6%
0%J
91%
9%
same missing adjusted
position
yes
no
Is performance different than before test?
100%,
74%
50%_
0%J
Has there been a change in fuel economy
100%.
15%
50%.
11%
69%
15%
16%
Change
for the
worse
No Change
notice- for the
able better
change
Change for No Change for
the worse notice- the better
able
change
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-10-
Appendix
-------
Before
Vehicle' Repair Facility Typo of
,,JjaibFy.^U!ib&UiatL-'A'~Ilj.9. ^n _.lm'* r^-m ty
rffectiveneR8~oi Idle Adjustments
at CommerclaL Repair Facilities
F/*?3 ,££ .4*4*1 * T^^fter
Service Person's Repair Facility
•Cor.jnic-nts ' , Co.'it IliC ZICO JKI'il1''
•i
Differences' in
' !5 Turns o£
Lab Set Mixture Screws''"''
t.UPM l.crfl: Ui.;;h'.-
Aildltioail
C;)-.i;r.'.-.nt:'i
- -3,93-
#off£
o
,2«r 730
/fc
It.
//
/T.
''c look'td
hood .of *i
,'clt *M Kun
y;J*lt»tt
zs* - .IO-
A/tf
frw)
•jood
fiord-' floO
*>*•- -of ~
10 • 10
-------
lif fcctivcrtOPHrfff~Iclr. Adjustments
at c
... ._!
j;- , Date i
j| Vehicle
i ^&%kP.L..-i&&g-&
.
BQfore
Uepnir Facility Typo of
IHC%ICO IRVM* Facility
Service Person's • •••'•
: Consents : :
Difference*!,, •
. Alurn.sof ^
Rep.iir Facility Lab Set Mixture Screws **
Cost IHC>,IC'J ::::!" IJJC /TICO IRPM T.c.'r. R;,-.:'.v
Additional
Consents
7Z -i.
fltte/ity-fc
d
V'45-
tzi "too*
-.25 -
*• .25 -100
> {-So
. 7 • -
f)/f
a.
'*/lfa
i-farfibn
Sop - 1.0 -
- .20 -
lf>tC*9r)i'£ S«>;a •/(,,. ..-,.-. ,.f .
tJiikptJ. ftJySita
10
/5
II
(+5oo
US- 2.1 _
«
I • 1
6/20
-700
St^f/
ovi
is- -<>y- 700
/ o to
77?
Sar-j
Heei
/i *«**»*/
?h/2i
-2,76 -
/ 300 -,i5 -
n
r»«e /)a^»'c uiej aw // - i, ie. 4 *« iV.t
3*1rli/lft/ -/itti/ha /'t/ff t+l'IffHb"
° "i.c'riC' .^•|v*.'"7i j"/ T
(+10°)
•frit m stop -/Ton-, -fair
«I35
*J
f I
IHC ZtCO IRPM* .
_jy.ii&.,-.jfti[fi..
7V<> - 1,0 -
"a. 0
AVKKAOES
'-Number shown it/ parenthesis ia
• tlie difference in RFM fron the
manufacturers sj>ccif acntions<
(H-"j;rcafcr thc:i,-=.l-:i>f: ii).'!n)
Cost IHC SICO IKl'M* JHC ZiCO
to it MjCJ!i*<»"+" - ncr-.bor of !£
in the "rich" d.irocti
"-" ° r.unbcr of '< turn
in tiic "lonv." divecti
-------
rt '-f-,rr
'3&
, ^
Vehicle
M;ike
Before
Repair Facility Type of
IHCXICO 'IRVH* Facility
Ff-
nffcctivences of Idle Adjustments
at Commercial Row ** J^}"^".^
-7&~^T. £<*m /*<$££
Repair Facility
Cunt 1IIC21CO IKHI*
Service Person's
Comment.",
Differences in
* Turns of
tab Set Mixture Screws**
JIIC '/, ICO IRPM I.oft Hi. .-.],::
A»!dlt:I.oiinl
Consul:;:
v\\
fecfomc
a
"ff
tl.bo
-l-7-t.io
{-no.
/oo- .70- 75' -8/0
Sunoco
• J
foec.n)hi'e.
ta»i twa
Uj,«A
>« «••'(-
«»e
/feo- ^5-75-0
7. •
3 3
t,
a
1-fov tob.'vwf
Crdl/ "to fWa,
W? forj-F/op
MA -W^
10 /3
i »»>/»« e/ji^V' rff/j
j
-------
Dace £.
Vcihir.la
.li- rx-.ility Type of
.-:u:o IIU'M*' Vacilil-y
-14-
Effgctivoncus of Idle Adjustir..::-.ts
at Corai.-.orcial Repair. Facilities
F/: 76-
Service Person's
Common l«
-------
Effectiveness oTIdle Adjustments
at Coimnavcial Repair Facilities
\ Bate & Before
; Vehicle Repair Facility Type of
, ;-;i;i::i;cr M:.iV.i: fcModel IIIC /;tCO JIU'M* Facility
' J-•*'.''»y'_'^j •••>_.—^•g>-f^-JL~i''T_"'^'^""- ' "-I'tTT^-TJii i --_.-!.. _-uj-L •-. .i-ji^_-n.-j.-. ;- J
33 -.56
Service Person1.1?
Difference.'! in
*4 Turns of
Repair Facility Lab Set Mixture: Sc.ircw.i'
Cos!: 1HC %ICO IRl'M"* I1ICX1CO IRFM I,-,!'c K-?'*:
tf/95
r.
c/i,
ff/Z.So
(+!•)
/z
/VUIit.l.on.1.1.
**
o/f
II.
/so y,?o
.0! <(
ti '>fO
50 .
50 .50
ti i^ctl
(0)
/OS
'0
.600
/oo >C t- 500
/o
/o
//
10
lA/O
'b 3S-po/*>7'i
no , of 700
tii/r-0
(w)
5- 5-
A/AS
3?0 • 20
«? 8-
/v h
(•ftfo)
74/0
- C20
u/ tp/u'tf
1 '
tt'D TVwt/fe
3 3P- 7, (, -500
T.IIC /:tCO IRFM-
.so • 7to
frico).
//
j KfSl/fQ
V/o
-9-0 7to
/P.-
Xi-.AiM'lS
''•'N'lir.ibc): sl\ov.-n in parenthesis is
r.lu1 (Mllfuroncc i:< Ri"! from tliu
cost IHC rato ii
-------
-In-
effectiveness or lule Adjustments
at Coir.naro.ial Repair Facilities
l)atl- ''
Viiiir.l.o
Before
Ro.|):ii.r Facility Type of
Service Person's
Comiiionts
O«-.r
Repair Facility
UK'. 21C.I1 IK:1!!"
Lab Set
IMC. 2 ICO IRFM
Differences in
l-t Turns of
Mixture Sr.vcwa *'*
I..'ft Rir.liv
Additional
Ccnir.cn l" s
;.72./7
•S////79
,
^^
*&-""
•
.v;:-,.,KS
/2' /fW."%r0
l$7-2.%-4OO
me ;u.co IRP:
II
Sf * 6
iJi'.Ln<.i'.[ ZDlk. />#•> A'JJJ'; ^tiMvfy
MfC/SA'iStL 9/)fP IDLE To F/t$/'
-
**;Muniber slicv/ii in p.'iriinthGii.s is
tlio djfforcnce in U1?M frori the
manufacturer ^ spcctfacatlons.
*. • (,l C. tt ti... t IK.u , . .i.t...... tlK.il/
O,OO
l.oO
Cos
//£ /,io /^o
i/OO
-------
-17-
Kf(!octtveno.':s of Idle Adjustments
at Cowir.arcinl Repair Facilities
Da«* beforc
; Vehicle . Repair Facility Type of .
;;u:::b.;r Iljike JcMs.\lol. 7110 MV.O IKI'M'' r.-ir. il.lCv
Service Person's
Coira-u-ntn
***,- 4«
:;ln..
Repair Facility L.ih Set Mixture Screws'11* A(Ulii..i...:wl
Cost T1ICZICO Mil':;-'' T.IIC 7, ICO TRf.V i..:i> r,:-,ii! i>r>;r--Mi-s
Mo 6/1
fflecfito'C-. "»"*" f"fr A*'^ i/_ ««"j[/f FA
t It 't lib •*•»«» •aa^fif'T tl*tt€ TC/fctC I
<* '^.\l / ~J* ~ Jt*^ / * / Ji .\J
At J '9 n ul W C.HI 9f/Cait- & *j& W'b-
at /it'. L. ^ fM° ^ t * * ft
frl cJ/A *l* t*K.&*ft .^r1 •&**¥ ftlt J.OO
-- (,
>y,iffi+e. ft I/ •' • i :
end /ui h'»M s - -fj ir
J7/Z5/7?
Uojee.- t>IOO
12 S -V- 7fo
/SZ -3-03 ,
-------
-18-
csa of I
Effectiveness of Idle Acijustnients
at Comr.arcurl Renair Facilities
•Vehicle
Before
Repair Facility Type of
TUC W.?. T.R'.':.!ft FariUtv
Service Person's
Coir.nu-iii.-J
Repair Facility
Cost II!!J?;I~0 JRS:""
Lab Set
JHC •;:!« T.UFM
Differences in
•i, Turns of
Mixture Screws**
Additional
f.l--
She.//
Jnc/
tit
$7,00
Zoo- .? -
*
iff* ten c
f J'*-je
J
tys/7?
- . 5 -
*
/zo
ft/00}
3oz.-S.V1-
3/.2/21
35V?- -5 -
ifaft
thef- CIO
-t,,63 - (,00
were -fair.
75 -
&30)
object./ t'/lH"
ns -t.
300 -/;y _
ft, •
//
(-<*:
-«
30* -
- »oV- 600
x. /<>•
•7-* ff
Ii!C 21.00 IV.VM*
Av;cKAr;i;s
•:Kur.:ber shov.-fl in parenthesis is
the tlif forcncc in RPM t"ro;;i tho
naiiufacturers spcicifncntiQns.
(•i--'i'.rcr.tcr thcri,-»lcas than)
floo..
Cost II!C ZICO 1-ltPM* IHC ZICO Loft il3!lL:v,v".|.'' = ncr.ber ol k turi)
in the "rich" diroct?
"-" •> nur.iber of k turr
in tiie "lean" dirccj;!
-------
•I U;!te " Before
Vehicle Rnpair Facility Type of
L.u^!^^L,..J:!a^Jii!afeL..-.Ilic ^Ico lR^ft Facility
.
Effectiveness bTTdle Adjustments
at Corair.::rci;il Repair Facilities
fy-ia-ST.ionts - "
Service Person's
Corn-lent s
After
Repair Facility
Lab Set
Different-fin1 in
!i Turns of
Mixture Screws**
- s://- 700
%&!/
Cost IHC %1CO lUi'H1'' IHC J!ICO IRPM Loft F.xijhf.
Additional
Co'."ients
300 -
Jjlt -fuA
Xood
-fair
- 7.0 -
/t
7
Id
7
/(/tf
iff
Ihrt-fto
1780 -7.0S- 580
- .85-700
'/ I/
7 7
b.k'f'Y
atY- Co
1t>.^e
me zico
shown in parentiiosl;; is
tlic difference in RPM fron Lhc
urcrs specifacnuions.
.or tlicn.—-.1.f-:.:s t!;c:!-.)
Cost JilC %ICO 1RI',"." IHC ZICO
^" n nunb-^r of k turn
in the "rich" divncti
-" = nur.iber of k .tutrr
-------
Vehicle
lie fore
Repair Facility Type of
Till". 2H:0 IIU'M" Faclli'tv
-20-
I'.f. foclivencf.s' of Idle Adjustments
at Coiacarcial Repair Facilities Differences in
fi-TQ $7, Lorii Tfatit'* After -'s Turns of
Service Person's Repair Facility Lab Set Mixture Screws**
Convener; Cost IHC 21CO _ IRl'U*. IHC Z ICO -IRPH Loft R.i.shf.
Atldition.il
Corar.cnts
- .3 -
(ZS /.6l
(o)
. (0}
6370
flit 'if/we
C*eti.
50 '80 750
(0)
6
y
6^73
V5/79
/
ft/7£/
/•TO
(.to)
A/P
5.00
too
50t>
mo
'•N'umbcr shown in parenthesis is
the tliffcronce in lU'ii from the
•.r.anufacture.rs specif'. mentions .
cost me ;aco IHPM* me zico
Lefl: M£]lt ft*"v „ iu:r;lbcr oi >j turil
in ti;o- "ric'x" dirocti
"-" = nunbcr cf !; turn
ii: the "le.-i!i" uiract^
-------
Date £• Before
'•Vehic.le Repair Facility Type of
.,.,^!^-ji.i:.^JJil'-c-&;-!pc!c.l. IHC %ICO IIU'M^ tVicility
f//W^7
325 -7.05 -£,2,0
F.ffectivenor.a' of Idle Ailj'.iftir.ents
at Commercial Repair Facilities Differences in
FY-78 S7~, tov\j 7,'?VCitS After k Turns of . f>
Service Person's Repair Facility Lab Set Mixture Screws'** Additioail
Comments On.-.!: TilC %ICO IU\\':' IHC 2 ICO IRPM I.oft K:li:h:-, Corrr.cr.ts
\r.oo
smaU
300
-2.05
IsL
•/06
500
(-loo)
156 Z.
;# LL
50
• of hoc
'V
metJiaitic.Si'J oefi.J
<;< |