Immediately after a cold start, between predeter-
mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the
pump by drawing air into the pump cavity and also
closes the vent seal. During non test conditions the
vent seal is held open by the pump diaphragm
assembly which pushes it open at the full travel posi-
tion. The vent seal will remain closed while the
pump is cycling due to the reed switch triggering of
the three port solenoid that prevents the diaphragm
assembly from reaching full travel. After the brief
initialization period, the solenoid is de-energized
allowing atmospheric pressure to enter the pump
cavity, thus permitting the spring to drive the dia-
phragm which forces air out of the pump cavity and
into the vent system. When the solenoid is energized
and de energized, the cycle is repeated creating flow
in typical diaphragm pump fashion. The pump is con-
trolled in 2 modes:
Pump Mode: The pump is cycled at a fixed rate to
achieve a rapid pressure build in order to shorten the
overall test length.
Test Mode: The solenoid is energized with a fixed
duration pulse. Subsequent fixed pulses occur when
the diaphragm reaches the Switch closure point.
The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5” H20.
The cycle rate of pump strokes is quite rapid as the
system begins to pump up to this pressure. As the
pressure increases, the cycle rate starts to drop off. If
there is no leak in the system, the pump would even-
tually stop pumping at the equalized pressure. If
there is a leak, it will continue to pump at a rate rep-
resentative of the flow characteristic of the size of the
leak. From this information we can determine if the
leak is larger than the required detection limit (cur-
rently set at .040” orifice by CARB). If a leak is
revealed during the leak test portion of the test, the
test is terminated at the end of the test mode and no
further system checks will be performed.
After passing the leak detection phase of the test,
system pressure is maintained by turning on the
LDP’s solenoid until the purge system is activated.
Purge activation in effect creates a leak. The cycle
rate is again interrogated and when it increases due
to the flow through the purge system, the leak check
portion of the diagnostic is complete.
The canister vent valve will unseal the system
after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.
Evaporative system functionality will be verified by
using the stricter evap purge flow monitor. At an
appropriate warm idle the LDP will be energized to
seal the canister vent. The purge flow will be clocked
up from some small value in an attempt to see a
shift in the 02 control system. If fuel vapor, indicated
by a shift in the 02 control, is present the test is
passed. If not, it is assumed that the purge system is
not functioning in some respect. The LDP is again
turned off and the test is ended.
MISFIRE MONITOR
Excessive engine misfire results in increased cata-
lyst temperature and causes an increase in HC emis-
sions. Severe misfires could cause catalyst damage.
To prevent catalytic convertor damage, the PCM
monitors engine misfire.
The Powertrain Control Module (PCM) monitors
for misfire during most engine operating conditions
(positive torque) by looking at changes in the crank-
shaft speed. If a misfire occurs the speed of the
crankshaft will vary more than normal.
FUEL SYSTEM MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide. The catalyst works best
when the Air Fuel (A/F) ratio is at or near the opti-
mum of 14.7 to 1.
The PCM is programmed to maintain the optimum
air/fuel ratio of 14.7 to 1. This is done by making
short term corrections in the fuel injector pulse width
based on the O2S sensor output. The programmed
memory acts as a self calibration tool that the engine
controller uses to compensate for variations in engine
specifications, sensor tolerances and engine fatigue
over the life span of the engine. By monitoring the
actual fuel-air ratio with the O2S sensor (short term)
and multiplying that with the program long-term
(adaptive) memory and comparing that to the limit,
it can be determined whether it will pass an emis-
sions test. If a malfunction occurs such that the PCM
cannot maintain the optimum A/F ratio, then the
MIL will be illuminated.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
Normal vehicle miles or engine misfire can cause a
catalyst to decay. This can increase vehicle emissions
and deteriorate engine performance, driveability and
fuel economy.
The catalyst monitor uses dual oxygen sensors
(O2S’s) to monitor the efficiency of the converter. The
dual O2S’s sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its effi-
ciency can be indirectly calculated. The upstream
DR
EMISSIONS CONTROL
25 - 3
EMISSIONS CONTROL (Continued)
Summary of Contents for 1997 Ram 1500
Page 7: ...Fig 5 FASTENER IDENTIFICATION 6 INTRODUCTION DR FASTENER IDENTIFICATION Continued ...
Page 8: ...Fig 6 FASTENER STRENGTH DR INTRODUCTION 7 FASTENER IDENTIFICATION Continued ...
Page 10: ...Fig 7 METRIC CONVERSION CHART DR INTRODUCTION 9 METRIC SYSTEM Continued ...
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Page 319: ...Fig 3 Cooling System Circulation 5 9L Diesel Engine 7 4 COOLING DR COOLING Continued ...
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Page 1560: ...Fig 23 FRAME DIMENSIONS DR FRAMES BUMPERS 13 17 FRAME Continued ...
Page 1561: ...Fig 24 140 5 IN WHEELBASE HEAVY DUTY 2 WHEEL DRIVE 13 18 FRAMES BUMPERS DR FRAME Continued ...
Page 1562: ...Fig 25 140 5 IN WHEELBASE HEAVY DUTY 4 WHEEL DRIVE DR FRAMES BUMPERS 13 19 FRAME Continued ...
Page 1563: ...Fig 26 160 5 IN WHEELBASE HEAVY DUTY 2 WHEEL DRIVE 13 20 FRAMES BUMPERS DR FRAME Continued ...
Page 1564: ...Fig 27 160 5 IN WHEELBASE HEAVY DUTY 4 WHEEL DRIVE DR FRAMES BUMPERS 13 21 FRAME Continued ...
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Page 2288: ...Fig 16 VEHICLE LEAD DIAGNOSIS AND CORRECTION CHART DR TIRES WHEELS 22 9 TIRES Continued ...
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Page 2398: ...Fig 10 DASH PANEL DR BODY STRUCTURE 23 103 SEALER LOCATIONS Continued ...
Page 2399: ...Fig 11 LOWER DASH PANEL 23 104 BODY STRUCTURE DR SEALER LOCATIONS Continued ...
Page 2400: ...Fig 12 ROOF PANEL DR BODY STRUCTURE 23 105 SEALER LOCATIONS Continued ...
Page 2401: ...Fig 13 CAB BACK PANEL 23 106 BODY STRUCTURE DR SEALER LOCATIONS Continued ...
Page 2402: ...Fig 14 LOWER DASH PANEL DR BODY STRUCTURE 23 107 SEALER LOCATIONS Continued ...
Page 2403: ...Fig 15 FLOOR PAN 23 108 BODY STRUCTURE DR SEALER LOCATIONS Continued ...
Page 2404: ...Fig 16 FRONT FLOOR PAN DR BODY STRUCTURE 23 109 SEALER LOCATIONS Continued ...
Page 2405: ...Fig 17 FLOOR PAN 23 110 BODY STRUCTURE DR SEALER LOCATIONS Continued ...
Page 2406: ...Fig 18 PICKUP BOX DR BODY STRUCTURE 23 111 SEALER LOCATIONS Continued ...
Page 2412: ...Fig 28 REAR DOOR INNER PANEL DR BODY STRUCTURE 23 117 STRUCTURAL ADHESIVE LOCATIONS Continued ...
Page 2413: ...Fig 29 SILL RAIL STD CAB 23 118 BODY STRUCTURE DR STRUCTURAL ADHESIVE LOCATIONS Continued ...
Page 2414: ...Fig 30 SILL RAIL QUAD CAB DR BODY STRUCTURE 23 119 STRUCTURAL ADHESIVE LOCATIONS Continued ...
Page 2419: ...Fig 31 FENDER BRACE 23 124 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2420: ...Fig 32 STEERING COLUMN SUPPORT DR BODY STRUCTURE 23 125 WELD LOCATIONS Continued ...
Page 2422: ...Fig 35 DASH PANEL Fig 36 LOWER PLENUM PANEL DR BODY STRUCTURE 23 127 WELD LOCATIONS Continued ...
Page 2423: ...Fig 37 FRONT FENDER Fig 38 DASH PANEL 23 128 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2424: ...Fig 39 FRONT FENDER Fig 40 DASH PANEL DR BODY STRUCTURE 23 129 WELD LOCATIONS Continued ...
Page 2425: ...Fig 41 HEADLAMP MOUNTING PANEL 23 130 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2427: ...Fig 43 AIR BAG MODULE BRACKET STANDARD CAB 23 132 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2429: ...Fig 45 REAR FLOOR CROSSMEMBER STANDARD CAB 23 134 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2432: ...Fig 49 FLOOR SILL STANDARD CAB DR BODY STRUCTURE 23 137 WELD LOCATIONS Continued ...
Page 2433: ...Fig 50 AIR BAG MODULE BRACKET QUAD CAB 23 138 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2435: ...Fig 52 REAR FLOOR CROSSMEMBER QUAD CAB 23 140 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2440: ...Fig 58 A PILLAR REINFORCEMENT STANDARD CAB DR BODY STRUCTURE 23 145 WELD LOCATIONS Continued ...
Page 2449: ...Fig 75 FLOOR SILL STANDARD CAB 23 154 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2450: ...Fig 76 BACK REINFORCEMENT STANDARD CAB DR BODY STRUCTURE 23 155 WELD LOCATIONS Continued ...
Page 2454: ...Fig 82 OUTER BODY SIDE APERTURE QUAD CAB DR BODY STRUCTURE 23 159 WELD LOCATIONS Continued ...
Page 2455: ...Fig 83 OUTER BODY SIDE APERTURE QUAD CAB 23 160 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2456: ...Fig 84 REAR FLOOR CROSSMEMBER QUAD CAB DR BODY STRUCTURE 23 161 WELD LOCATIONS Continued ...
Page 2457: ...Fig 85 CAB BACK REINFORCEMENT QUAD CAB 23 162 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2459: ...Fig 87 A PILLAR REINFORCEMENT QUAD CAB 23 164 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2460: ...Fig 88 B PILLAR REINFORCEMENT QUAD CAB DR BODY STRUCTURE 23 165 WELD LOCATIONS Continued ...
Page 2461: ...Fig 89 FRONT ROOF HEADER QUAD CAB 23 166 BODY STRUCTURE DR WELD LOCATIONS Continued ...
Page 2462: ...Fig 90 INNER BODY SIDE APERTURE QUAD CAB DR BODY STRUCTURE 23 167 WELD LOCATIONS Continued ...
Page 2465: ...Fig 93 TAPPING PLATES SHORT CARGO BOX ONLY 23 170 BODY STRUCTURE DR WELD LOCATIONS Continued ...
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Page 2516: ...Fig 3 Blower Motor Electrical Diagnosis DR DISTRIBUTION 24 29 BLOWER MOTOR Continued ...
Page 2517: ...Fig 4 Blower Motor Noise Vibration Diagnosis 24 30 DISTRIBUTION DR BLOWER MOTOR Continued ...
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Page 2627: ...Dealer Technical Operations 800 Chrysler Drive CIMS 486 02 76 Auburn Hills MI 48326 2757 ...