A8 emission control systems
Postcombustion control
Emission control systems that clean up the exhaust gases after the fuel has been burned.
Precombustion control
Emission control systems that prevent emissions from being created in the engine, either during or before the combustion cycle.
Checking the OBD II system usually consists of three parts:
MIL operation, checking for DTCs, and a readiness monitor check
as the fuel mix goes rich what reading drops and stays low
O2
as the mixture goes lean what levels increase
O2
when CO readings go up what reading goes down
O2 goes down
If there is high HC and low CO in the exhaust because of a lean misfire
O2 will be high
The common precombustion emission control systems are the
PCV, engine modifications, spark control, and exhaust gas recirculation (EGR) systems.
if a egr system is restricted it can cause 5
Rough idle can be caused by a stuck open EGR valve, a clogged EGR vent, dirt on the valve seat, or loose mounting bolts (this also causes a vacuum leak and a hissing noise). No-start, surging, or stalling can be caused by an open EGR valve. Detonation (spark knock) can be caused by any condition that prevents proper EGR gas flow, such as a valve stuck closed, leaking valve diaphragm, restrictions in flow passages, disconnected EGR, or a problem in the vacuum source. Excessive emissions can be caused by any condition that prevents the EGR from allowing the correct amount of exhaust gases into the cylinder or anything that allows combustion temperatures. Poor fuel economy is typically caused by the EGR system if it relates to detonation or other symptoms of restricted or zero EGR flow.
what does SCR (Selective Catalytic Reduction) do
Selective Catalytic Reduction systems. the high O2 content in diesel emissions means a regular cat wont work. the reductant removes O2 from NOx and makes water
Vehicle emission control information (VECI)
This information is normally used to identify and calibrate the emission controls on a vehicle.
what is VECI
Vehicle Emission Control Information. its a decal that explains what the vehicle is equipped with and how well it should perform. located under the hood
how does the pcm on a diesel know to activate a regeneration cycle for the pm filter
back pressure sensor
what happens when engine wear allows more blowby than the pvc can handle
backs up pressure in the clean air line of the pvc system. can cause oil in the air filter
Positive Backpressure EGR Valve testing
bring engine to 2000rpm and apply vacuume rpm should drop 100 or more
heated pvc systems
can be heated electrically or with the coolant systems. just used to make sure the system doesent freeze
what is a preconditioning mode
car is ran at high idle 2500rpm or at 35 on a dyno for 20-30 seconds
CO2 what is it what causes it
carbon dioxide. it is a mark of idea combustion . with leaner mixes there is less of it
what is CO what causes it
carbon monoxide caused by not having enough O2 in the mixture
what are the benifits of the ASM test or the RG-240 over the I/M 240
cheaper dynos no computer control for the ASM just a chassis dyno and a 5 gas analyzer
how do you check the canister purge soleinoid itself 2
check it for resistance with it removed. apply 10in hg to vacuum port shouldnt be any restriction when blowing through valve side
functional checks of the pcv system.
check part number make sure right one is in use. then pull valve out of head and idle the engine. should hear hissing cover with finger should feel vacuum. if not something is restricted. try a rattle check
what service can be done to a fixed orifice pvc system?
clean the orifice with pipe cleaner
what does the pcm do to monitor vapor purge.
dutie cycles the purge soleinoid and monitors stft. unrelated changes are a red flag some times the pcm reads for pressure differances between the purge side of the charcol can and the rest of the system
how are the ASM and ASM 2 tests done
dynamometer is used to load the vehicle while an exhaust gas analyzer measures hydrocarbon, carbon monoxide, and nitrogen oxide levels. The ASM test accelerates the vehicle to 15 mph using 50% percent of the vehicle's horsepower and the second test accelerates to 25mph using 25 percent of the vehicle's horsepower.
cant add fuel to a half way empty tank?
evap test might be in progress and the pressure stops the pump
what is a big way diesel piezio injectors reduce noise
fire up to 3 times a revolution
two main checks if there is oil in the air filter
first chck for restricted pcv. second do a compression test
Consequences of a restrictived PCV valve
force blowby gases into the air filter.
EEGR system
he EEGR system uses an electric motor in the EGR valve. Normally the EEGR valve is water or air cooled. The PCM controls the stepper motor that controls the position of the EGR valve's pintle valve. The position of the valve determines the rate of EGR flow. A spring keeps the valve closed and must be overcome by the force of the motor.
what is the risk of lowering CO emitions
higher NOx
high readings of HC is the result of
incomplete combution
hw does a Positive Backpressure EGR Valve function
it has a larger hollow pintle shaft. exhaust gasses pass through and close the valve higher vacuum opens it.
how does a negitive back pressure egr system open
it opens and closes with the pulses from exhaust valves.
what will happen to the pm filter in a diesel if a high sulfer fuel is used
it will destroy it
I/M 240 test checks
leakage test functional test of the evap system and a visual test. simulates short in town milesand long high way miles. through all drive cycles and colects exhaust through a CVS hose. car is driven on a dyno
Consequences of a stuck open PCV valve
lean air mix. rough idle or stalling
high NOx readings are a result of
lean mix of high combustion temps of CO and HC are low
tbi systems use intake heat control systems why and how
lower HC and CO emissions. electronic resistance grid in the throttle body
what is the main function of the egr system? how does it operate
lower combustion temperature to reduce NOx. only added at light load conditions. adds non combustable gasses to the intake
Before attempting to troubleshoot or repair a suspected EGR system on a vehicle
make sure that the engine is mechanically sound, that the injection system is operating properly, and that the spark control system is working properly.
what is a I/M test cutpoint
maximum allowable amount of each gas. nearly all vehicles have some speeds or conditions where gasses go over the cutoff
what does the I/M 240 test for
measures HC, CO, NOx, and CO2
I/M 240 failures without running full test
mil light or readiness code is not at a normal or ready state
what is NOx what causes it
nitrogen oxides caused by high combustion temps
what kind of adjustments can be done to a pvc system?
none isolate problem replace part.
pvc valve operation
normally closed. vacuum opens the small part of the valve so it is only engaged durring deceleration and idle. at higher loads blowby gas pressure builds opening the valve more
if you cant run specific emission test what might be the problem 2
not equipped with that type of emission device of scan tool doesn't support it
how can you tell the differance between a positive and negitive back ressure egr valve?
one has a p next to the part number the other has a n
when one gas test too high what else should you look for
other gasses that almost fail the test
what is O2 and what do high readings mean in emissions
oxygen not a pollutant. high readings indicates a lean fuel mix
air injection reactor (AIR) system does what for the cat converter
pulls outside air in to more fully burn hc in cat converter. AIRB valve controlls amount of air
high readings of CO
rich fuel mix
if the pvc valve is stuck open
rough idle
what happens when the evap system purges at idle or low speeds
rough idle worse in high heat
what happens with a charcol canister that has a saturated filter or is completly full of fluid
rough idle, flooding, fuel system back pressure,
difference between advanced evap and regular evap systems
smaller leak detection .020in system leaks and adition of a Fuel level input sensor so the system know when to run pressure test and how long it takes to create a vacuum based on fuel level
how does a solinoid operated egr system function
still uses vacuum to open the valve but a solinoid controlls when the valve gets vacuum
testng a older egr valves 2
test the engine to see if it is making enough vacuum. then use a hand vacume pump to valves vacuum port to 18in hg diaphram should move and should hold the pressure
using different tail pipes and pm filters runs what risk with diesels
the wrong size or mud buildup can destroy the pm filter
what is a digital egr valve?
they have 2-3 solenoids and part of the valve is always open. only found in gm cars.
why dont alot of late model engines have egr valves
they use variable valve timing
when will a dtc code be set for a emission related issue. When is it cleared
two failed drive trips. code is cleared after three good trips
The three emissions controlled in gasoline and diesel engines are
unburned hydrocarbons HC , carbon monoxide CO, and oxides of nitrogen Nx
what causes hydrocarbons HC
unburnt fuel
testing a digital egr valve. 3
use a scan tool energize solenoids one at a time each should drop rpm. if it doesent make sure it has 12v going to it. then check windings for resistance
pvc systems operation
uses engine vacuum to draw fresh air through the engine. from the head to the crank case mixes with blowby gasses and is drawn back through the head to the pvc valve to the intake manifold
whats the reason pvc system need to be so different in diesel systems
vacuum building in a diesel is reversed and lower in general. little to no vacuume at idle. alot at heavy load
what is done in addition to analyzing tail pipe emissions during a smog check
visual inspections. verify all emissions equipment is in place, vacuum lines, fuel leaks, and emission control decals
what is a diesel regeneration cycle
when the soot in the filter of the cat converter is burned off. actively(adds fuel) or passivly
after 2000 how small of a evap leak can systems register?
.02 in
modes of I/M 240 test
1 Mode one—idle, no load at 0miles per hour 2Mode two—acceleration from 0 to 35 miles per hour 3 Mode three—acceleration from35 to 55 miles per hour 4Mode four—a steady cruise at 35 miles per hour Mode five—a steady high cruise at 55 miles per hour Mode six—decelerations from 35 miles per hour to 0 and from 55 miles per hour to 0.
FTP testing includes
1 Nondispersive infrared (NDIR) tester for measuring CO and CO2 2 Flame ionization detector (FID) for measuring HC 3 Chemiluminescence detector for measuring NOx
sensors that stop egr operation
1 TVS thermal vacuum switch senses air temp 2 ported vacuum switch measures coolant temp 3 delay timer 4 WOT valve wide open throttle
what does the I/M 240 test consist of
1 a transient, mass emission tailpipe test HC, CO, CO2, NOx 2 evap purge test 3 evap pressure test
a typical diesel emission emits (6)
1 carbon(soot) 2 NOx 3 water 4 CO 5 Sulfur 6 hydrocarbon-based compounds
steps to running emission test with a scan tool. 15 steps
1 check for codes. 2check service info look for software updates. 3 check monitor status. 4 turn off all accessories. 5open hood set tranny in neutral or park. 6 open idle for 2 min. 7 close hood test drive. 8 light accelerate 45 to 50mph. 9 lightly accelerate to 55. 10 decelerate for ten seconds. 11stop and idle for ten min. 12 turn off let sit for 45 min. 13 check monitors with scan tool. 14 if all test ran retreve codes. 15 repeat if test wernt ran.
normal obd2 evap systems include 9 items
1 domed tank 2canister vent colinoid valve 3 filter limits amount of fuel that can be added to tank 4 vacuum or pressure sensor 5 vapor lines 6 vapor separator 7 charcoal can 8purge lines 9purge solenoid valve
EGR system with a DPFE sensor.
As exhaust gases pass through the valve, they must also pass through the orifice. The DPFE sensor measures the pressure drop across the orifice and sends a feedback signal to the PCM. Based on this signal, the PCM can make corrections to the operation of the EGR valve. Normally the voltage signal from the DPFE sensor is 0 to 5 and the voltage is directly proportional to the pressure drop.
at 2000 rpm how much vacuum should there be?
16in hg
Before diagnosing the cause of excessive emissions 10
1check battery 2air filter 3charcoal can 4idle speed 5timing 6fuel pressure 7engine condition 8electrical 9 vacume lines 10 pcm grounds evap, egr, pvc hoses and seals
three steps to checking a charcoal canister
1lose the purge port, gently blow into its vent port, and check that air flows from the port. 2Close the vent port and gently blow into its air inlet port. Check that air flows from the purge port. 3With the purge port and air inlet port closed, apply low air pressure (about 2.8psi) to the vent port. Make sure that the canister can hold that pressure for at least minute. If any of these fail replace the can
how many times must a evap error occor before a code is sent?
2
when is a emission code completely erased
40 warm ups without issue
Oxidation catalyst
A catalyst that breaks down substance when oxygen is introduced.
Reduction catalyst
A catalyst that removes oxygen from a substance.
Greenhouse gas
A name given to the effect that certain gases have on global warming.
egr positive back pressure transducers diesel
A positive backpressure EGR valve has a bleed port and valve positioned at the center of a diaphragm. A spring holds the bleed valve open. An exhaust passage connects the lower end of the valve through the stem to the bleed valve. When the engine is running, exhaust pressure is applied to the bleed valve. At low engine speeds, exhaust pressure is not high enough to close the bleed valve. Because the vacuum supplied to the diaphragm is bled off, the valve remains closed. As engine and vehicle speed increase, the exhaust pressure also increases. Eventually exhaust pressure closes the bleed port and vacuum lifts the diaphragm and opens the valve.
Charcoal canister
A small plastic or steel container filled with activated charcoal that can store gasoline vapors until the right time for them to be drawn into the engine and burned.
Digital EGR valve
An EGR valve that is controlled digitally by a computer.
Air injection reactor (AIR)
An emission control system responsible for adding outside air to the catalytic converter or exhaust stream
what replaces a pvc valve in diesels how does it work
CDR Crank case depression regulator. it is designed to operate at lower vacuum and regulates pressure to reduce oil consumption. operates off a diaphragm and return spring
how does a negitive back pressure egr valve work
In a negative backpressure EGR valve, the bleed port is normally closed. An exhaust passage connects the lower end of the tapered valve through the stem to the bleed valve. When the engine is running at lower speeds, there is a high-pressure pulse in the exhaust system. However, between these high-pressure pulses, there are low-pressure pulses. As the engine speed increases, the high-pressure pulses become closer together. The negative exhaust pressure pulses decrease and the bleed valve closes and opens the EGR valve.
early evep systems that didnt use the pcm where controlled bywhat and what was the problem with them
a ported vacuum purge port, a vacuum check valve, and a thermo vacuum valve (TVV) the thermo valve stoped purging on a cold engine. the problem was the purging the same volume at all load conditions
whats the big difference in diesel egr systems?
a separate cooler for the egr system
how does a evap leak test work when using a seperate tester
adds .5 psi of n2 to the system and waits for leaks. hook tester to evap service port. to localize the leak use soapy wateror, dye, or smoke
by obd2 standards when is a pending code erased
after a full trip with no errors
If there is a high O2 reading without a low CO reading
air leak in the exhaust might be the issue
testing a negitive back pressure egr system
at operating temp but key off... apply 18 in of vacuum to egr valve. valve should open and hold vacuum for 20 seconds. then try starting the engine vacuum should drop to zero and close the valve
measuring crank case pressure on dessils
attach a water manometer to dip stick. if pressure is less than one in. raise rpms to 2000. if pressure drops 4-5 in pcv is fine
