Archive-name: autos/chrysler-faq/general/part3
Posting-Frequency: 15
Last-modified: 1995/6/7
Version: 2.5
Modifications have been split off to form their own FAQ. We expect to
see it soon. To suggest additions to the modifications FAQ, write to
Gary Hamel <ha…@cl.uh.edu>.
See the very last part of this section for reading ESA computer codes
without a scan tool! Useful for those without the key-turn-watch-light
feature (e.g. 1985 Caravans) — and those with it! Courtesy of Bohdan
Bodnar.
Contents: 1. Engine Codes
2. Engine types
3. Body types
4. Acronyms
5. Info from the Center for Auto Safety
6. Reading codes without a scan tool
(Diagnosing/tuning cars with computer controlled,
carbureted engines)
DISCLAIMER:
While every effort has been taken to insure the accuracy of the
information contained in this FAQ list compilation, the author and
contributors assume no responsibility for errors or omissions, or for
damages resulting from the use of the information contained herein.
The information below may be reproduced in any way PROVIDED that
credit is given to the writers and the maintainer; and that it is not
published in book or magazine form without the prior written
permission of the maintainer; that the maintainer receives, without
needing to ask, a FREE copy of the final material; and that no changes
are made (except for formatting) without the express permission of the
maintainer (vali…@mordor.com = David Zatz).
– - – - – - – - – - – -
Please note that, if you did not obtain this FAQ from one of its
newsgroups or from the rtfm.mit.edu archives, it is probably
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ftp rtfm.mit.edu
[Name:] anonymous
[Password:] [your e-mail address]
cd pub/usenet/rec.answers/autos/chrysler-faq/general
dir
get part1 part2 part3 part4
cd ..
get neon [or whatever other FAQ might be there]
bye
– - – - – - – - – - – -
FAQ for rec.autos.makers.Chrysler - Part III
********************************************************
COMPUTER CODES
Start with the ignition off. Within five seconds, switch the key on,
off, on, off, on. (On is not start!)
The "check engine" light will flash. Count the flashes Each code is a
two digit code, so a (for example) 23 would be FLASH FLASH <pause> FLASH
FLASH FLASH <loong pause>
It will never flash more than 9 times, watch for pauses!
55 is end of codes, 33 is normal if you dont have air conditioning.
When the computer indicates major failure, it will activate Limp In
mode, which substitutes guesses for data to compensate for sensor
failure.
Please note that some codes are NOT included below, this
is not a complete listing, but it IS very close to complete.
The following was leeched from Herb. 
[some additions by cho...@astro.ge.com Charles Hobbs)
[modified later]
* Activates Power Limited/Check Engine light.
11 No ignition reference signal detected during cranking (bad Hall
effect)
OR timing belt skipped one or more teeth;
OR loss of either camshaft or crankshaft position sensor
12 Battery or computer recently disconnected
13* MAP sensor or vacuum line may not be working
14* MAP sensor voltage below .16V or over 4.96V
15 No speed/distance sensor signal
16* Loss of battery voltage detected with engine running
17 (1985 turbo only): knock sensor circuit
17 Engine stays cool too long (bad thermostat or coolant sensor?)
21 Oxygen sensor signal doesn’t change (stays at 4.3-4.5V)
Probably bad oxygen sensor
22* Coolant sensor signal out of range
- May have been disconnected to set timing
23* Incoming air temperature sensor may be bad
24* Throttle position sensor over 4.96V (SEE NOTE #3)
25 Automatic Idle Speed (AIS) motor driver circuit shorted
or target idle not reached, vacuum leak found
26 Peak injector circuit voltage has not been reached
(need to check computer signals, voltage reg, injectors)
(SEE NOTE #4 BELOW)
27 Injector circuit isn’t switching when it’s told to (TBI)
OR (MPI) injector circuit #1 not switching right
OR (turbo) injector circuit #2 not switching right
OR (all 1990-) injector output driver not responding
- check computer, connections
31 Bad evaporator purge solenoid circuit or driver
32 (1984 only) power loss/limited lamp or circuit
32 EGR gases not working (1988) – check vacuum, valve
32 (1990-92, all but Turbo) computer didn’t see change in
air/’fuel ratio when EGR activated
- check valve, vacuum lines, and EGR electrical
33 Air conditioning clutch relay circuit open or shorted
(may be in the wide-open-throttle cutoff circuit)
34 (1984-86) EGR solenoid circuit shorted or open
34 (1987-1991) speed control shorted or open
35 Cooling fan relay circuit open or shorted
35 (trucks) idle switch motor fault – check connections
36 (turbo) Wastegate control circuit open or shorted
36 (3.9/5.2 RWD) solenoid coil circuit (air switching)
36 (Turbo IV) #3 Vent Solenoid open/short
37 Shift indicator light failure, 5-speed
OR
part throttle lock/unlock solenoid driver circuit (87-89)
OR
solenoid coil circuit (85-89 Turbo I-IV)
OR
Trans temparature sensor voltage low (1995 and on; see NOTE 2)
41* Alternator field control circuit open or shorted
42 Automatic shutdown relay circuit open or shorted
42 Fuel pump relay control circuit
42 Fuel level unit – no change over miles
OR
42 Z1 voltage missing when autoshutdown circuit energized (whatever
that means)
43 Peak primary coil current not achieved with max dwell time
OR
43 Cylinder misfire
OR
43 Problem in power module to logic module interface
44 No FJ2 voltage present at logic board
OR
44 Logic module self-diagnostics indicate problem
OR
44 Battery temperature out of range (see Note #1!)
45 Turbo boost limit exceeded (engine was shut down by logic module)
46* Battery voltage too high during charging or charging system
voltage too low
47 Battery voltage too low and alternator output too low
51 Oxygen sensor stuck at lean position (lean condition)
OR
51 Internal logic module fault (’84 turbo only)
52 Oxygen sensor stuck at rich position
OR
52 Internal logic module fault (’84 turbo only)
53 Logic module internal problem
54 No sync pickup signal during engine rotation (turbo only)
OR
54 Internal logic module fault (’84 turbo only)
55 End of codes
61 "Baro" sensor open or shorted
62 EMR mileage cannot be stored in EEPROM
62 PCM failure SRI mile not stored
63 Controller cannot write to EEPROM
64 Catalytic converter efficiency failure
65 Power steering switch failure
88 Start of test (not usually given, don’t expect it)
These codes cover multiple years and engines (2.2l, 2.5l, 3.0l).
NOTE #1.
The power module has an air-cooled resistor which is used to sense the
incoming air temperature. This information is fed to the logic module
and is used to control the duty cycle of the field current in the
alternator. This code applies ONLY to alternators whose voltage is
computer regulated. The battery voltage is sensed by the logic module
— there is an internal takeoff from the wire feeding the NVRAM
keep-alive power circuit which is fed to a voltage comparator. So…if
you lose the feed to keep RAM information stored when the engine’s off,
you also lose battery voltage sensing. — Bohdan Bodnar
NOTE #2
From the 1995 TRUCK (Ram) manuals: the trailer towing package includes a
transmission coolant temp sensor while the standard package doesn’t. I
imagine that the fault code detection system is the same for both
models. This would cause the low (no) voltage indication….no sensor
to send any voltage. — J.E. Winburn
NOTE #3
Matt Rowe <st92i…@dunx1.ocs.drexel.edu> comments: The throttle
postion circuit is a sensor which tells the computer how far the
accelerator is depressed. So a fault in this that is intermitent is
probably due to a loose wire or connector. The Throttle Position Sensor
(TPS) is located on the throttle body on the opposite side of the
throttle cable. The connector should have a round rubber cover over the
connections. Clear the fault codes, start the car and try jiggling the
wires/connectors to try to trip a fault code. Since this sensor is the
only way the computer can tell where the throttle is so a loss of this
signal could cause the other problems so start with trying to fix this
one.
NOTE #4
During cranking, the computer will test the current through the
injector to see whether there’s too much resistance in the injector’s
path. If there is, code 26 is set.
In my Le Baron, the problem was cured with copious use of
television tuner
cleaner on the Bosch connector and the injector’s connector.
For TBI engines, the injector’s cold resistance should be between
0.9 and 1.2 ohms (specs vary with year). This is a peak-and-hold
injector. On a properly operating system with the engine idling the
peak period should be about 1.2 milliseconds whereas the hold period
will vary with parameters such as temperature, MAP reading, etc. If
it’s lower than this at idle, then either the injector’s shorted or
there’s a defect in the injector driver circuit. (Bohdan Bodnar)
***********************************************************
From Lloyd Parker:
Engines used in Chryslers since 1966:
4-cylinders: (MMC=Mitsubishi, CC=Chrysler, VW=Volkswagen)
1.4 SOHC (MMC) — Colt, Champ
1.5 (Sunbeam) — Cricket (British)
1.5 SOHC (MMC) — Colt, Summit
1.6 SOHC (MMC) — Colt, Champ, Challenger, Sapporo, Arrow
1.6 SOHC (Peugeot) — Omni, 024, Charger, Horizon, TC3, Turismo
1.6 SOHC turbo (MMC) — Colt
1.6 DOHC (MMC) — Colt, Summit
1.6 DOHC turbo (MMC) — Colt
1.7 SOHC (VW) — Omni, 024, Charger, Horizon, TC3, Turismo
1.8 SOHC (MMC) — Colt, Vista, Summit, Laser, Talon
2.0 SOHC (MMC) — Arrow, Vista
2.0 SOHC (CC) — Neon, Stratus, maybe 96+ minivans
2.0 DOHC (MMC) — Laser, Talon
2.0 DOHC turbo (MMC) — Laser, Talon
2.0 DOHC (CC) — Neon, Sebring, Avenger, Talon
2.2 SOHC — Omni, 024, Charger, Horizon, TC3, Turismo, Aries, Lancer,
Reliant, Shadow, Sundance, 400, 600, Caravelle, Caravan,
Voyager, LeBaron, Laser, Daytona, New Yorker, E-Class
2.2 SOHC turbo – LeBaron, New Yorker, Limousine, Laser, Daytona,
Lancer, TC, 600, Shadow, Caravelle, Sundance, Omni,
Charger, E-Class, Shelby
2.2 DOHC turbo – Spirit, Daytona (joint venture with Lotus)
2.2 DOHC turbo – TC (joint venture with Maserati)
2.2 SOHC (Renault) — Medallion
2.4 SOHC (MMC) — Vista, Summit
2.4 DOHC – Stratus, 1996+ minivans, (Cirrus and Breeze?)
2.5 SOHC – Caravan, Voyager, Aries, Reliant, Shadow, Sundance,
Duster, 600, Lancer, Dynasty, Daytona, Spirit, Acclaim,
LeBaron, Caravelle
2.5 SOHC turbo – Caravan, Voyager, Spirit, Acclaim, Shadow,
Sundance, LeBaron, Daytona
2.5 (AMC-derived) — Wrangler, Cherokee, Premier
2.6 SOHC (MMC) — New Yorker, E-Class, Executive, Limousine,
LeBaron, 400, 600, Aries, Reliant, Caravan, Voyager
2.6 SOHC turbo (MMC) — Conquest
2.5 is 2.2 with balance shafts, minor changes. 2.0 (CC) is 2.2 with
different heads, fuel system, some tweaks. 3.9 V-6 (below) based on 318.
2.4 is 2.0 with balance shafts, minor changes.
———————————-
V-6s:
2.5 SOHC (MMC) — Sebring, Avenger, Cirrus, Stratus (from 3.0)
3.0 SOHC (MMC) — LeBaron, TC, minivans, New Yorker, Spirit,
Dynasty, Daytona, Stealth, Shadow ES, Acclaim, Duster
3.0 DOHC (MMC) — Stealth
3.0 DOHC turbo (MMC) — Stealth
3.0 SOHC (Renault) — Premier, Monaco
3.3 SOHC (CC)– New Yorker, Dynasty, LH series, minivans
3.5 SOHC — Concorde, New Yorker, LHS, Intrepid, Vision
3.8 SOHC — New Yorker Fifth Avenue, Imperial, minivans
3.9 SOHC — trucks
———————————-
The SLANT SIX:
2.8 (170) — Dart, Valiant
3.3 (198) — Barracuda, Challenger, Dart, Valiant, Duster, Scamp
3.7 (225)– Polara, Monaco, Coronet, Charger, Mirada, Diplomat, St.
Regis, Challenger, Dart, Aspen, Fury, Belvedere, Satellite,
Barracuda, Valiant, Duster, Scamp, Volare
Note that slant sixes came with a variety of carb configurations, but
single and dual barrel were most common. Double barrel increased economy
and performance with a progressive opening. Plug: join the Slant Six
Club!
———————————-
The AMC straight six crowd:
4.0 IL-6 (AMC-derived) — Cherokee, Wagoneer, Wrangler, Grand Cherokee
4.2 IL-6 (AMC) — Wrangler
———————————-
V-8s:
4.5 (273) — Dart, Valiant, Barracuda, Coronet, Belvedere, Satellite
5.2 (318) — Polara, Monaco, Coronet, Charger, St. Regis, Magnum,
Mirada, Challenger, Dart, Aspen, Fury, VIP, Belvedere,
Satellite, Road Runner, Barracuda, Valiant, Scamp, Duster,
Volare, Cordoba, LeBaron, Newport, New Yorker, Gran Fury,
Imperial, Grand Cherokee, Grand Wagoneer, Diplomat
5.6 (340) — Charger, Challenger, Dart, Barracuda, Duster, Road Runner
5.9 (360) — LeBaron, Newport, New Yorker, 300, Cordoba, Diplomat,
Polara, Monaco, Challenger, Dart, Aspen, Fury, Gran Fury,
Barracuda, Duster, St. Regis
5.9 (361) — Coronet, Charger, Belvedere
5.9 (360-AMC) — Grand Wagoneer
6.3 (383)– Newport, 300, Town & Country, Polara, Monaco, Coronet,
Charger, Challenger, Dart, Fury, Belvedere, Satellite, Road
Runner, Barracuda, Magnum
6.6 (400) — Newport, New Yorker, Town & Country, Monaco, Fury, Road
Runner, Gran Fury, Charger, maybe Cordoba, Magnum
7.0 (426, Hemi & Wedge) — Belvedere, Road Runner, GTX, Barracuda,
Challenger, Charger, Coronet, Daytona, Superbird
7.2 (440) — Newport, New Yorker, 300, Town & Country, Imperial, Polara,
Monaco, Coronet, Charger, Challenger, Fury, VIP, Belvedere,
Road Runner, GTX, Barracuda, Daytona, Superbird
Get this — 440 was base engine on Daytona, Superbird.
8.0 V-10 — Viper (488 cid)
***********************************************************
BODY TYPES
(Below list courtesy Lloyd R. Parker)
A — Valiant, Dart, Barracuda, LeBaron (sedan), Scamp, Duster
B — Coronet, Charger, Magnum, Monaco, Premier, Belvedere, Satellite,
GTX, Road Runner, Fury, Cordoba
C — Polara, Monaco, Fury, VIP, Gran Fury, Newport, 300, Town & Country,
New Yorker, Imperial, Dynasty
D — Talon, (Plymouth) Laser
E — Barracuda, Challenger, 600, Caravelle, E-Class, New Yorker
F — Aspen, Volare
G — Daytona, (Chrysler) Laser
H — Lancer, LeBaron (hatchback)
J — LeBaron (coupe/convertible), Cordoba, Imperial, Mirada
K — LeBaron, Executive, Limousine, Aries, Reliant, 400, 600
L — Omni, 024, Charger, Horizon, TC3, Turismo
M — Diplomat, LeBaron, New Yorker, Fifth Avenue, Gran Fury
P — Shadow, Sundance, Duster
Q — TC by Maserati
R — St. Regis, Gran Fury, Newport, New Yorker
S — Town & Country, Caravan, Voyager
Y — New Yorker Fifth Avenue, Imperial
LH — Concorde, New Yorker, LHS, Intrepid, Vision
PL — Neon
JA — Cirrus, Stratus
FJ — Sebring, Avenger
SR — Viper
XJ — Cherokee, Wagoneer
YJ — Wrangler
ZJ — Grand Cherokee, Grand Wagoneer
SJ — Grand Wagoneer
PJ — Talon
***********************************************************
From: Joe Schaffer <schaf…@mopac.amd.com>
MOPARCRONYMS=========================================
* Modified items followed by /daz; list shortened considerably
\6 = Slant six (cylinder layout pattern)
ABS = Anti lock Brakes (from German) /daz
A/C = Air Conditioning
ACR = American Club Racer (showroom stock race package for the Neon)
AT = Automatic Transmission
ATDC = After Top Dead Center
AWD = All Wheel Drive
BHP = Brake Horse Power
BTDC = Before Top Dead Center
CAFE = Corporate Average Fuel Economy legislation
CC = Chrysler Corp; Cruise Control; Cubic Centimeter (cc)
CID = Cubic Inch Displacement
CO = Carbon monOxide
CO2 = Carbon diOxide (oxide, being plural constitutes the "2")
DC = Direct Connection
DIS = Distributorless Ignition System
DMV = Department of Motor Vehicles
EGR = Exhaust Gas Recirculation
ET = Elapsed Time
FSM = Factory Service Manual
FORD = Fix Or Repair Daily / Found On Road Dead
4WD = Four Wheel Drive (now usually AWD, these days)
FWD = Front Wheel Drive
FYI = For Your Information
GLH = Goes Like Hell (origional Hi-performance Dodge Omni)
GLHS = Goes Like Hell Somemore (next Hi-Po Shelby Omni)
GVW = Gross Vehicle Weight
HC = HydroCarbons
HP = Horse Power
IMHO = In My Humble Opinion (see IMO)
LH = not an an acronym, a platform name (Concorde, Intrepid, Vision)
MMC = Mitsubishi Motor Corp.
MML = Mopar Mailing List
MOPAR = Mainly Out Performs All the Rest
MP = Mopar Performace (Mopar’s performance parts)
MP = Mounted Police, Multiple Personality, Member Parliament /daz
MT = Manual Transmission
NHTSA = National Highway Traffic Safety Administration
NOS = New Old Stock (40 year old part still in factory wrapper!)
NOX = Nitrogen OXides (NO, NO2, etc)
OEM = Original Equipment Manufacturer
P/S = Power Steering
PB = Power Brakes
PCV = Positive Crankcase Ventilation
PS = Power Steering
PSI = Pounds per Square Inch
RPM = Revolutions Per Minute
RWD = Rear Wheel Drive
S/N = Signal to Noise ratio (garbage posts vs. useful)
SBEC = Single Board Engine Controller
SMEC = Single Module Engine Computer
T/A = That’s Awesome
T/A = Trans Am (a racing class)
TDC = Top Dead Center
TPS = Throttle Postions Solenoid
TSB = Technical Service Bulletin
WOT = Wide Open Throttle
***********************************************************
CHRYSLER INFO from CENTER FOR AUTO SAFETY
Note: this is just a summary, we suggest you contact CAS at 2001 S
Street NW, Washington, DC 20009 for more info. Ask for this factsheet
and provide a self-addressed, 55 cent stamped envelope and, if you like,
a donation. Comments in parentheses are editorial remarks/questions.
* FIRES – recalls on 1985-87 turbo models for bad fuel hose connections.
* Valve cover gaskets on 1989-90 FWD models
* FIRES – fuel reservoir leaks on 87-89 Omni/Horizon.
* STALLING – Omni/Horizons mostly, drivability kits issues (2.6?)
* TIMING CHAINS – 1981-86, 2.6 liter engine. Chrysler often paid at
least partly.
* POWER STEERING – various FWD models (including minivans), 1981-89.
Problems in Saginaw & TRW steering units. TSB 19-01-83.
* SUSPENSION: 1981-83 K-cars, front crossmember corrosion.
* SEATS – 1985 Laser, LeBaron, 600, Lancer, Daytona power driver’s seat
attachment failure.
* PARK – in column-mounted automatic trans — 1981-90 vehciles — NHTSA
investigation closed.
* BRAKES – 1978-92 models, rear brake lockup and master cylinder
failure. Pressure may get repairs out of warranty.
– ABS in many 1991 vehicles: recalled 91V-1991
– disc brake pad separation in 1989 Daytona and LeBaron – recalled
– ABS in 1992 minivans: may lose fluid, lose ABS – recalled
* SEAT BELTS: difficulty latching front belts, all 1991 models
(recalled)
– inoperative automatic belts in 1988-89 Shadow/Sundance (recalled)
* A/C: clutch failure, 1985-86 4-cylinder models. TSBs 24-01-85,
24-02-86.
* TRANSMISSION: 1989-91 models with 4-speed auto are unreliable (big
surprise). Write to CAS-Ultradrive for more info with a 55 cent stamped,
addressed return envelope.
=========================
DIAGNOSING PROBLEMS IN COMPUTER CONTROLLED
CARBURETED ENGINES
From: boh…@uscbu.ih.att.com (Bohdan L Bodnar)
This is a description of the procedure I’ve used to diagnose air/fuel
mixture problems in computer controlled carbureted engines; the
outlined procedure can also be used to set the idle air/fuel mixture
without resorting to infrared exhaust gas analysis. The procedure is
based on the General Motors "System Performance Test" which was
developed for diagnosing problems in GM’s carbureted engines. This
procedure will not work with carburetors which use a stepping motor to
control the a/f mixture (e.g., Ford’s variable venturi carburetors).
THEORY
The a/f mixture is controlled by a MIXTURE CONTROL SOLENOID (MC
solenoid). This is a valve which operates at a fixed frequency
(typically, 10 Hz) and whose duty cycle (valve’s ON time divided by
period) is varied. That is, the valve is pulse width modulated. When
the valve is turned on, the incoming a/f mixture is fully leaned; when
off, fully enrichened. The former is called a "lean command" whereas
the latter is called a "rich command." By varying the duty cycle of the
MC solenoid, the AVERAGE a/f mixture can be varied. In GM products,
this valve directly varies the incoming fuel and air flow. In Fords,
only the incoming air is directly varied. In Chryslers, only the
incoming fuel flow is directly varied.
The valve has a two wires electrical connector. On wire is connected to
switched battery voltage whereas the other is connected to a power
transistor in the computer and is a source of switched ground.
During closed-loop operation the following will occur (assume the oxygen
sensor is sensing a lean condition — its voltage will be low):
1). The computer gradually decreases the MC solenoid’s duty cycle.
2). The exhaust eventually becomes rich enough that the oxygen sensor’s
output will swing high (about 1 volt).
3). The computer gradually increases the MC solenoid’s duty cycle.
4). The exhaust eventually becomes lean enough that the oxygen sensor’s
output will swing low (about 0 volt).
The cycle now repeats. A device for monitoring the solenoid’s duty
cycle (such as a dwell meter) will show a constantly varying duty cycle.
The frequency of the oscillations will depend on the how fast the
computer varies the duty cycle and the engine’s RPM. An AVERAGE duty
cycle of 50% corresponds to, on the average, NO average a/f correction.
Stated differently, everything is operating correctly. An average duty
cycle of LESS THAN 50% corresponds to, on the average, a rich command
(the computer is compensating for a lean condition). An average duty
cycle GREATER THAN 50% corresponds to, on the average, a lean command.
DIAGNOSIS AND SETTING IDLE A/F MIXTURE
Monitoring the MC solenoid’s average duty requires (for most people) the
use of high impedance dwell meter. A low impedance dwell meter may be
used unless it affects engine operation; my recommendation is to not
use a low impedance dwell meter (that is, stay away from self-powered
dwell meters). Following the GM procedure, set the dwell meter to the
six cylinders scale REGARDLESS of the number of cylinders in the engine.
At this setting, 30 degrees will correspond to a 50% duty cycle, 60 to a
100% duty cycle, and 0 to a 0% duty cycle. Run the engine until closed
loop operation is present; this will be indicated by a varying dwell
(see footnote 1 for deviations from this procedure). Once the engine is
hot, not the average dwell — the reading should vary equally above 30
degrees and equally below 30 degrees. The following is a brief trouble
listing:
1). DWELL NOT VARYING: system is operating in open loop.
2). DWELL STUCK AT 10 DEGREES OR LOWER: full rich command is present;
the computer is compensating for WHAT APPEARS TO BE a massive fuel flow
reduction (check for dirt in carburetor, air injection system stuck in
upstream position, vacuum leaks, improper a/f mixture setting…).
3). DWELL STUCK AT 50 DEGREES OR HIGHER: full lean command is present
(check for float stuck low, valve seat damage, oxygen sensor’s sense
lead shorted to battery voltage, etc.)
4). DWELL OSCILLATING, BUT AVERAGE READING IS BELOW 30 DEGREES: average
rich command is present (check for vacuum leaks, dirt in carburetor’s
jets, improperly set a/f mixture…)
5). DWELL OSCILLATING, BUT AVERAGE READING IS ABOVE 30 DEGREES: average
lean command is present. Check for incorrectly set a/f mixture, float
stuck low, valve seat damage, clogged air filter, etc…).
Based on the above descriptions, it should be fairly clear on how to set
the idle a/f mixture: merely set the mixture so that the average dwell
is 30 degrees. Now, suppose the system’s dwell is not varying, but the
sensors are working properly, the upper radiator hose is hot…
Several cars with small engines have the oxygen sensor mounted fairly
far away from the engines. Indeed, during idle conditions, the sensor
may cool off to the point that it will not operate (I had this
experience in a 1986 Mustang with 2.3 liters engine and EEC-IV system).
My recommendation is that all electrical accessories be turned off (so
as to provide a minimal load on the engine) and use the idle stop screw
on the carburetor to gradually increase the idle rpm until the sensor
begins oscillating. Ensuring a negligible load on the engine guarantees
that the carburetor will be operating mostly on its idle circuit. Now,
set the a/f mixture so that the average dwell is 30 degrees. On the
Mustang, this was done at about 1500 rpm.
Note that the a/f mixture setting procedure assumes that NO fuel
delivery problems (vacuum leaks, clogged carburetor, etc.) are present.
FOOTNOTES
[1] In some engines (e.g., GM cars with the "min-T" system — Chevette)
the a/f mixture is varied REGARDLESS of whether the engine is in closed
loop operation or not. Consider setting the a/f mixture or diagnosing
at a slightly increased rpm.