A8 Engine Performance
jumper specific pins in a diagnostic connector
count the amount of times the MIL flashes to reveal DTC.
crankshaft end-play noise
deep knocking sound that is usually most obvious at idle but diminishes under a load
power loss
defective coil late ignition timing not enough timing advance engine misfire
mechanical fans are
designed to slip when cold and rotate the fan at maximum speed when hot.
ignition switch can be tested with a
digital multimeter (DMM)
as the primary current decreases, a high voltage is induced in the secondary winding of ignition coil,
directing a spark through the rotor, to fire the spark plug.
during cranking compression test
disable ignition system and fuel system. then you can crank up to four compression strokes.
if worn valve guides are suspected
disconnect PCV system and inject some propane into the valve cover. the engine speed will increase and vacuum readings should rise.
replace fan clutch if there is no
viscous drag either hot or cold, or turn smoothly or at all.
ignition system inspection
visual inspection of spark plug, spark wires, cap and rotor, firing order, check coils for cracks, car on tracking, oil leakage, check primary circuit wiring, and inspect distributor.
preliminary inspection
visually inspect and adjust v-belt or belt tensioner. check battery and cables.
if fan does not work.
visually inspect wiring & connectors in the circuit then check with direct power
when control valve receives a backpressure signal from the exhaust
when EGR valve closes, full vacuum signal is applied directly to EGR valvediaphragm, opens the valve and allows EGR.
positive back pressure continued.
when control valve receives a backpressure through EGR valve pintle, pressure on the bottom of control valve closes it.
the more common magnetic pick up coil design
when the teeth of the rotating timer core and pole piece align, or the reluctor and the single tooth of the pick up.
always use the manufacturer's suggested key off drain specifications
when trying to determine the proper amount of current draw when vehicle is off
Rack and pining inspection
while in normal running position, movement is felt between the tie rod stud and the socket while the tire is moved in and out
tall firing lines indicate high resistance
while short firing lines indicate low resistance
while at TDC on the exhaust stroke
while the crank is moved slightly back and forth, both intake and exhaust valve should move. if not then valve timing is incorrect.
exhaust leak
whistling, hissing or popping noise, even a tapping sound that sounds like a valvetrain noise
carburetor is out of adjustment
will cause vacuum readings to slowly float above and below idle reading.
bad piston ring
will make the engine smoke worse when accelerating
Lowering the temperature of combustion
will reduce NOx. this could happen by running rich fuel/air mixtures or lowering thermostat temp. burning leaner mixtures produce high temperatures
blue grey smoke is least likely caused by
worn piston rings
NOx is formed by Nitrogen and Oxygen
@ 2500°F (1371°C) / composition process.
primary coil resistance for DI system coils should approximately be
0.5 to 15 ohms, the secondary side will range from 800 to 10,000 ohms.
EI system waste spark ignition coil
1 coil provides spark for 2 cylinders.
to check starter ground circuit
1st place the black lead of voltmeter on the negative battery post. crank the starter and place the red leaf on starter housing.
a properly operating clutch should stop from spinning within
2 seconds of shutting off a hot engine.
pick up coil continuity resistance is
500 to 1500 ohms.
During a leak down test, air could be heard coming from the tail pipe.
An exhaust valve not sealing
exhaust gas analyzer monitors
CO2, O2, HC, CO, also NOx leves
DTC
Diagnostic Trouble Code
DPFE
Differential Pressure System Feedback system
Distributor Ignition(D1) or
Electric Ignition(EI)
ECM
Engine Control Module
during the combustion process
HC (unburned fuel), CO (carbon monoxide), NOx (Oxides of Oxygen), SOx (Oxides of Sulfur and engine particules
100% fuel
Hydrocarbon(HC), unburned fuel in exhaust means the complete combustion is not occurring.
MIL
Malfunction Indicator Light
PCM
Power Control Module
PFE
Typical Pressure System
hydrometer uses
a calibrated float to measure the specific gravity of a liquid.
PCV system is basically
a controlled air leak from the crankcase to intake manifold.
To get the most consistent and accurate results, perform
a cranking compression test at normal operating temperature. remove all of the spark plugs. remove air cleaner and hold down throttle blade. check battery.
Piston must be at TDC on the compression stroke when performing
a cylinder leak down test
overcharging can be caused by
a defective voltage regulator a short field wire and a battery that is internally shorted.
a system that is not charging or undercharging is usually indicated by
a discharged battery that does not have enough power to operate the starter or cause the starter to crank slowly, dim headlights, a dash warning light that illuminates or flickers or an ammeter that indicates low charging.
connect a battery load tester for 15 sec.
a good battery voltage should read 9.6 volts or higher.
if artificially enriching the mixture makes no difference and engine performs sluggishly suspect
a leaking EGR valve, late ignition or valve timing.
isolation testing
by replacing the regulator with manual control of the field, diagnosis of the alternator and regular circuits can be accomplished.
connecting rod noise
a light metallic tapping most noticable when engine is under a light load. becomes louder and occurs more frequently when engine speed is increased. will quiet down if you eliminate timing or fuel injection
when NOx is struck by sunlight,
a photochemical smog is formed
the intermediate section shows
a series of diminishing patterns that represent residual coil energy. problems with ignition coil will be indicated.
sticking valves will cause
a substantial but very intermittent drop during vacuum readings
loose torque converter
a thumping noise at the back of the engine, most noticable in park or neutral
some distributors use a photocell, Light Emitting Diode (LED) and
a wheel with slits to provide an rpm signal to a light sensitive photoreceptor.
check cable corrosion & damage
add some petroleum jelly to prevent corrotion.
black exhaust smoke
air/fuel mixture is too rich, can be caused by restricted air I take, leaking fuel pressure regulator diaphragm, defective fuel injector or electronic sensor misleading the computer to add more fuel than is needed. strong sulphur smell
excessive CO emissions could be caused by
air/fuel ratio too rich, clogged air filter, leaking fuel injector or fuel pressure regulator diaphragm, fuel pressure is too high, crankcase oil is contaminated with fuel, engine is running too cool, faulty sensors such as ECT/IAT
distributor pick up coils
aka as a magnetic pick-up coil assembly, or startor.
starter current draw test
allow the engine to warm up. disconnect ignition or fuel system. connect ammeter to negative cable and negative post. connect voltmeter to battery.
the burn voltage indicates the
amount of energy required to sustain the flow of current across the plug electrodes.
injecting propane into the induction system
an engine running lean should speed up and a engine too rich fuel mixture will slow down.
pick up cool continuity is tested using
an ohmmeter (on low range) between the pick-up coil connector leads.
the radiator should be warmest near the inlet
and coolest near the outlet
1 distributor design contains a permanent magnet, a pole piece with internal teeth and a pick-up coil, a rotating timer core is used with this type
another contains a permanent magnet and a single tooth pick-up coil. a reflector or armature is used with this type.
pick up coil test
any resistance measurement less than infinity requires the replacement of pick up coil.
Torsion bars, exception
are not interchangeable
EGR is not required when engine is cold,
at idle(warm or cold) and at WOT.
coolant protection level
at least -34°F (-37°C) aka 50/50 mixture of antifreeze and water
undercharging can cause the
battery plate to sulfate and can cause a high water content in the electrolyte, allowing the battery to freeze in cold weather.
low compression on all cylinders could
be a sign of worn rings, also an indication of valve timing that is out of specification. compare cranking compression test results to idle vacuum readings.
starter current draw test should
be around 150amps for 4 cylinder, 200amps for 6 cylinder and 250amps for V8 engines
a no charging or low charging system can
be caused by a broken or slipping alternator drive belt, defective voltage regulator, defective diodes or starter winding, an open alternator field circuit, excessive resistance or an open in wiring between the alternator and battery.
neutral safety switch can
be located on the steering column, shift leveler or transmission.
different length pushrod can
be used to restore the plunger-to-lifter body relationship.
sometimes its hard to identify a key off battery drain
because the drain wont be enough to discharge the battery when vehicle is off.
starter relay
between ignition switch and starter solenoid.
on some distributors the pick up coil gap requires adjustment
between the coil and the reluctor using non-magnetic feeler gauge. if not you could have misfire or no start.
Interference engine
broken timing belt or timing chain, or one that has excessively jumped time, can result in valve to piston contact.
air leaks in 1 of 4 places
bubbles in the radiator, air hissing out of intake system(disconnect PVC valve), air thats comming from tailpipe, air blowing into crankcase.
spark line should be 3/4 after the firing voltage
burn voltage is the height on the voltage scale of the spark line.
engine performance can be affected
by decreased valve lift.
high levels of NOx can be caused
by lean air/fuel mixtures, a malfunctioning EGR system, q cooling system problem.
carburetor or throttle body leak could
can affect each cylinder to a different extent, resulting into erratic and unpredictable rpm drops during Power Balance Test.
0 or no start cranking vacuum
can also be caused by a severe exhaust restriction (easy way to test remove 02 sensor/exhaust pipe. strong puffs of air from mounting hole during cranking can indicate restricted exhaust
higher than normal current draw test readings
can be caused by a short circuit in the starter motor or mechanical problems causing binding in the engine.
changes in valve stem height
can cause a pushrod to move the plunger lower in the lifter body and possibly bottom out in its bore.
computers, programmable radios, and any other solid-state memory unit
can have there memory erased when disconnecting the battery
rich or lean air/fuel ratio will
cause CO2 levels to drop.
worn valves can also
cause a lean condition by allowing additional air to enter the combustion chamber.
leaking EGR valve will
cause a low unsteady reading, not as unsteady or erratic as a burned or sticking valves.
rattling noise
caused by loose exhaust system heat shields, loose clamps, or an exhaust pipe interfering with another component
a low resistance wire insulation, which allows low spark voltage to flow to ground
causes a miss and makes the coil overheat, shortening its life.
if battery failed a load test
charge it for 3 minutes @ 40amps. if voltage is greater than 15.5v replace the battery.
22r check modulator for vacuum then
check EGR valve, if car dies EGR is good. clean all ports afterwards.
When a cylinder head with an overhead camshaft is discovered to be wrapped, what is the repair option?
check for cracks, straight in the head, and then surface the head
if rotor or cam moved when the crank was turned
check for excessive movement, if so suspect a loose chain or belt or worn gears.
clutch switch testing
check switch for adjustment. check for voltage on the input side & output side.
a hydrometer can be used to
check the specific gravity of the batterys electrolyte
bad wires are the primary cause of
coil failures
EGR is not required constantly when the engine is
cold, at idle(warm or cold) and at WOT(wide open throotle) so must be controlled.
blowby
combustion gases leak past the piston ring into crankcase.
even when engine is warm, there is no need for EGR at idle because
combustion pressures are relatively low and NOx is not formed. EGR will stall the engine because of too much dilution.
test starter relay
compare voltage at relatively switch terminal and starter terminal
high levels of CO2 means
complete combustion
to prevent relearn
connect 12v battery in cigarette lighter or power point
ignition coil testing
connect 12v test light to coil negative terminal and ground. key on test light should be on. while cranking light should flicker if not test with ohmmeter. if ok the. module is defective. use spark tester tool.
check for voltage drop in ground side of the system
connect negative lead to the negative battery cable end. connect positive lead to alternator grounding point. normally voltage drop should not exceed 0.1 volts
ignition coil secondary resistance test
connect ohmmeter leads to negative terminal and high tension wire terminal.
ignition coil primary resistance test
connect ohmmeter leads to positive and negative terminals.
ground the negative lead of the DMM to distributor.
connect positive lead to the power wire at the module. when ignition is turned to on or start position. reading should be at least 90% of battery V.
voltage drop test
connect the black lead to the battery cable connection at the starter. disable ignition or fuel system & crank the motor. while cranking the engine touch the red lead of the voltmeter to positive post of the battery.
check high resistance in voltage side of the system
connect voltmeter negative lead to positive battery cable, connect positive lead to alternator cable end. voltage drop should not exceed 0.2 volts
hydraulic lifters
consistent ticking sound. excessive clearance in valve stem & rocket arms. mimic the noise of worn valvetrain parts
B -type alternator
controls current on the positive side, while the ground on the other side of the field is constant. B - before
oscilloscope
converts the electrical signals from the ignition system into a visual image showing voltage changes over a period of time.
excessive white exhaust smoke
coolant is leaking into 1 or more cylinders. Most common cause is bad head gasket. Catalytic Converter will hide the problem.
2 weak cylinders also
could be related because they are closest cylinders to an intake air leak or leaking EGR valve.
pick up coil testing
disconnect electrical connector, set ohmmeter on the high scale. connect 1 lead of the ohmmeter to ground and probe each lead of the pick up coil connector.
when disconnecting the battery always
disconnect negative cables first.
ignition coil test continued.
disconnect spark wire from the distributor cap and connect spark tester to the wire.
raster or
displayed places all cylinder patterns on top of one another. helpful to check timing or dwell variations between cylinders.
oscilloscope
displays a graph(or waveform) of an electrical signal to see how it changes
main bearing noise
dull or deep sounding metallic knocking most obvious right after the engine starts up.
piston noise
dull or muffled metallic rattle at idle or during light engine loads. will increase if you eliminate ignition or fuel injection.
nitrogen can bond with O2 molecules
during the combustion process and form NOx.
ammeter battery test
enables full battery voltage to the vehicle.
disabling the ignition on an erratically cranking engine
engine cranks smoothly again means ignition or valve timing problem.
blue-gray or gray-white smoke
engine is burning oil, caused by PVC system malfunction, worn valve guides and/or seals, and worn piston rings and cylinders
valve timing has jumped
engine lacks power, has low manifold vacuum and low compression readings on all cylinders
poor milage
engine misfire late ignition timing not enough timing advance
electric fan is activated when
engine reaches a certain operating temperature also on most vehicles when A/C is turned on.
overcharging can cause severe corrosion and warpage to the battery positive plates
excessive heat in the battery that can also damage plates, and electrolyte depletion.
charging system voltage drop can be caused by
excessive resistance on voltage and/or ground sides. usually caused by defective cable from alternator to battery.
valvetrain noise
excessive valve train clearance, worn rocker arms, shafts, lifters, camshaft or lack of lubrication
worn valve guides/valve stem seals
exhaust smoke during deceleration caused by high intake vaccum that draws the oil through the worn guides or seals
low pressure on the 1st puff and remains low during a wet compression test.
expect problems such as valves misadjusted, burned valves, sticking valves, a hole in the piston, etc.
4 types of ignition coils
external coil, conventional coil, EI system waste spark coils, and DI coil on plug (COP).
on EI systems the coils are signaled to
fire in the proper order by the ignition control module and or PCM/ECM. which also controls spark timing and advance.
the secondary scope pattern has 3 sections
firing, intermediate and dwell
sea level pressure
for every 1000 ft above sea level remove 1 in. of vacuum
positive backpressure EGR
have a control valve controls the amount of vacuum to the EGR diaphram chamber.
engines with mechanical lifters
have a valve lash(clearance) setting that must be set specified to those of the manufacturers.
most engines with hydraulic lifters
have non-adjustable valvetrains.
the pcv system keeps pollutants from being released into the atmosphere, and also
helps to keep engine oil clean, keeps crankcase pressure from building up and prevents oil leaks.
loose drive belt
high pitched squealing noise when engine is accelerated
negative backpressure EGR valve, a vacuum signal is supplied through a
hose connected in the upper part. manifold vacuum is also applied at the bottom through an intake port.
resistance test may not always determine
if a coil is faulty. some defects only reveal themselves during scope testing
Manifold Vacuum test contin.
if idle vacuum is ok disconnect EGR valve port and plug it. At 2500 rpm, the vacuum reading should be equal or greater than the idle reading.
spark wire testing
if tester fails to fire there is a problem in spark plug wire , distributor, cap or rotor
engine will not start
if timing belt has jumped enough teeth or breaks
if HC is high and CO is normal
ignition misfire, incorrect ignition timing, air/fuel ratio is too lean or too rich, low compression, bad head gasket. internal engine mechanical problems: bad valves, valve guides, lifters, pistons, piston rings, etc.
0 or nearly 0 cranking vacumm
improperly adjusted throttle blade, a loose or cracked carburetor or intake throttle body, stuck open PVC valve or cracked PVC hose, secondary throttle blades that are stuck open, a leaking intake manifold gasket.
the glass tube of the hydrometer is scale calibrated to specific gravity
in a range of about 1.100 to 1.300
leakage greater than 20%
indicates a problem cylinder
adjusting valve lash on pushrod engines calls for
inserting a feeler gauge between the tip of the valve stem and the rocker arm. an adjustment nut or screw is turned to change the clearance.
the pick up coil is located
inside the ignition distributor
carbon monoxide(CO)
is a colorless, odorless, poisonous gas produced by combustion due to the lack of air or excessive fuel
COP coil
is a distrubutorless system, where secondary resistance is minimized with the design because spark wires have been eliminated.
fusible link
is a fused wire that protects a particular circuit from high currents, and may be either in a harness, or mounted separately.
a carbon track
is a small line of carbon that conducts electricity and can cause voltage to short to ground or to the wrong plug wire. causing a misfire.
the combustion process
is heated to approximately 2500°F
internal ignition coil
is located inside or a part of the distributor cap or distributor.
checking timing mark adjustment
is the best way to see if the engine has jumped time.
the most effective way to check for a key off battery drain
is to use an ammeter with the negative battery cable and the negative battery post
Exhaust Gas Recircularion(EGR) valve
is used to meter the exhaust into the intake air stream.
A-Type alternator
key on, engine off, you will have voltage in both terminals. A- After
very high HC with very low CO means
lean misfire, also likely to have rough idle, stalling, hesitation and poor fuel economy, a lower than normal manifold vacuum at idle, uneven rpm drops in power balance test, and will idle faster and smoothly when you artificially enrich the mixture.
cylinder power balance test
let engine idle and short out the ignition to each cylinder, 1 at a time. compare the output of each cylinder to solve rough idle complaints.
if drain is not found continued.
locate and disconnect all circuits that use a fusible link.
starter ground and connection continued.
locate the problem by moving the red leaf closer to the battery post in steps. Repeat voltage test each time. Always remove the red lead before you stop cranking the engine.
to determine a low CO2 level
look at the O2 levels, higher O2 levels indicate a lean mixture while low O2 levels mean a richer mixture.
check for electrolyte conditions
look for cloudy or muddy discoloration of the fluid. add distilled water.
check distributor cap and rotor
look for cracks or evidence of carbon tracking
no start or hard start
low or no primary voltage at the coil. defective coil open coil wire defective distributor cap/rotor defective triggering mechanism defective ignition module fouled spark plugs
engine misfire
low primary voltage, defective coil, defective distributor cap/rotor, worn distributor, high resistance in spark wires, firing order, defective spark plugs
running rich air fuel mixtures and lowering thermostat temperatures would
lower the temp. of comb. but also produce high leves ot HC and CO emissions and lower fuel economy. and contradict stroicheometry.
positive backpressure EGR system has a control valve/vacuum regulator valve which
manages the amount of vacuum to the EGR diaphragm chamber by bleeding vaccum to the atmosphere during certain conditions.
key on engine off, key on engine running.
max millivolts = 100 mv.
amperage that is low during current draw test
may be caused by starter circuit resistance.
if module is found below the coils it
may be damaged as the energy finds it's way to ground.
if engine runs hotter than normal
may cause detonation or overheat the engine.
poor cranking vacuum could also
mean that compression is low in all cylinders due to normal engine wear caused by valve timing or timing belt problem.
another method to test for key off battery drain.
measure voltage drop across a 1-ohm resistor connected in series between the negative battery cable and the negative battery post.
spark knock
metallic pinging or ringing noise mostly under a heavy load or low rpm. preignition spark knock is caused by excessive combustion deposit or engine too hot
when disconnecting & reconnecting battery the car may also
need a relearning process when engine & transmission are performing erratically
use a 12v test light to test
neutral safety switch, the light should only be on when gearshift is in Neutral or Park. check device that accurate the switch
ignition system failure symptoms
no-start, hard-start, misfire or stumble under acceleration.
an open wire(high resistance) forces the coil to find an alternative path to ground
often through the coil case, ruining the unit and bleeding coil energy to ground.
triggering mechanisms in ignition system location
on DI system they are inside the distributors, on EI they are mounted in the engine near the crankshaft.
OBD II system
on board diagnostic system to detect problems before they can result in increased emissions.
most vehicles with 2 fans
one is dedicated to the A/C system
exhaust gas should theoretically contain very little, if any.
oxygen because it should have been consumed during the combustion process.
check starter control circuit
place black voltmeter lead on the relay control voltage terminal. crank engine over and place red lead to positive battery terminal.
if engine runs cooler than normal
poor fuel milage and excessive emissions.
EGR systems include
ported, positive backpressure, negative backpressure, pulse width modulated and electronic.
there are several types of EGR systems including (6)
ported, positive backpressure, negative backpressure, pulse-width, modulated and electronic.
start/clutch switch
prevents the starter from operating unless the clutch pedal is depressed.
EI system coils resistance will be lower
primary resistance will range between 0.2 to 2.0 ohms. the secondary side will fall between 4,000 to 7,000 ohms.
running lean mixtures
produce high temperatures.
always check relay ground
quite often they are mounted on non metallic inner fender panels and require a good round to the metal car body.
fan clutches improve gas mileage and
reduce noise levels.
if excessive drain is displayed
remove 1 fuse at a time until high voltage reading is stabilized to a normal one.
engines with distributor ignition
remove distributor cap, rotate crankshaft by hand while watching the distributor rotor turn.
engines with distributorless ignition
remove the valve cover, rotate crankshaft by hand while watching camshaft turn.
if voltage drop test exceeds 0.5V for the entire starter circuit.
repeat the test, moving the black leaf toward the battery one connection at a time. when you get past the bad one, voltage drop readings will sharply decline.
to test b-type(internally grounded unit)
send battery voltage to the field winding for a moment, and watch for a rise in the voltage system. if so the regulator circuit is out of adjustment or defective.
2 consecutive cylinders in firing order that are weak or dead often
share an ignition problem
overcharging is indicated by
short light bulb life and a battery that continually needs water.
firing line represents amount of voltage required to jump the spark plug and
should be 7-13kV, with no more than 3kV variation between cylinders.
cylinder leak down test
shows you the location of a compression leak.
@ WOT the need for power outweighs the need to control NOx emissions, and
since WOT needs richer, cooler mixtures. NOx is minimal anyways.
replacing oxygen with inert gas comming from EGR will
slow and cool the combustion process.
spark knock
spark plug heat range too hot firing order ignition timing too advanced
firing section will indicate problems with
spark plugs, plug wires, distributor cap and rotor.
Wet Compression Test
squirt a spoonful of clean engine oil into the cylinder and spin the engine over to spread oil around cylinder. repeat cranking compression test.
ignition systems suffer from the same problems that afflict electrical circuits
such as high resistance connections, open circuits, wire-to-wire shots, and shorts to ground. always check for DTC's
Damaged or worn out distributor caps and rotors can cause a variety of problems
such as no start condition, hard starting, missing, lack of power, rough idle, high emissions, and poor fuel economy.
EGR is designed slow and cool the combustion burn and reduce NOx by
supplying the intake system with inert gas.
when 2 cylinders right next to each other are dead
suspect a blown head gasket or a cracked head. perform compression test and cylinder leak down test.
the dwell section begins when the
switching device turns on to allow current flow to the ignition coil.
the primary circuit is common to EI and DI and includes
the battery, the ignition switch, the primary windings of the ignition coil(s), and a triggering mechanism and switching device to turn device on and off
primary circuit triggering
various methods are used to turn primary circuit on and off.
1 or more compression leaks
the compression air volume will drop momentarily, the cranking speed will increase momentarily, the starter current draw will decrease momentarily. (Perform Cylinder Leak Down Test).
an induced voltage in the pick up coil signals
the electronic module to open the coil primary circuit.
very high HC levels means
the engine is misfiring.
DI system the secondary system consist of
the ignition coil, the coil wire, distributor cap and rotor, spark plugs and spark wires.
when adjust valve lash under cold specifications
the lash setting requires no further adjustment once the engine is warm.
the primary scope pattern shows
the low voltage changes in the primary circuit of ignition system
at WOT the need for power outweighs
the need to control NOx emissions. also means its richer=cooler mixture, NOx formation is minimal.
when adjusting valve lash for 1 cylinder
the piston must be TDC on the compression stroke to adjust cam lobe with filler gauge.
freewheeling engine
the pistons cannot contact the valves regardless of there positions.
if you find a high resistance when checking starter ground
the presence of engine to starter shims, or an engine to battery ground cable, check carefully for a poor connection or even corrosion.
all ignition systems are divided into 2 circuits
the primary and secondary
during wet compression test gauge improves substantially
the problem may be worn compression rings, a worn piston, and/or a worn cylinder wall.
if voltage is as specified in the switch terminals but not the starter terminal
the relay should be replaced.
the higher the CO level
the richer the mixture. helpulf for diagnosing fuel economy complains.
if neutral safety switch operates in gear positions other than Neutral and Park
the switch may only need adjustment
if valve clearance is too tight
the valves will be held open. causing compression loss and/or valve burning.
if valve clearance is too loose
the valvetrain will be noisy and the cam will experience shock loads and premature wear.
exhaust restriction will cause
the vehicle to become very sluggishly and a substantial drop in the vacuum readings at 2500 rpm.
if voltage is less than specified at the switch terminal
there is a problem in the control circuit upstream of the relay.
dwell section is where the magnetic field build up in the ignition coil.
there should be a short downward drop followed by oscillations. problems with triggering mechanism and ignition module will be indicated here.
positive crankcase ventilation
this system vents crankcase gases into the engine air intake where they are burned with fuel air mixture.
every ignition coil performs the same function
to convert a low primary voltage(battery) into a high secondary voltage supply to the spark plug.
check wiring diagrams
to isolate a current draw.
atmospheric pressure enters crankcase tru breather hose and pushes crankcase blow-by vapors
towards the low-pressure point offered by the PCV valve and intake manifold.
general testing
use inductive probe to check the alternator output at the alternator oit
engines with hydraulic lifters
use valve adjustments to properly position the hydraulic lifter plunger within the lifter body.
a healthy cylinder
usually builds most of its pressure on the first stroke and continues building to good compression reading.
Manifold Vacuum Test
vacuum gauge connected to a manifold vacuum port at normal operating temperature produce 17 to 21 in Hg reading at idle.
cranking vacuum test
vacuum gauge to intake manifold should read 3 to 5 in. Hg or more. the better the rings and valves are sealing the stronger the vacuum
leaking valves will cause
vacuum readings to drop much lower than normal readings
if all vacuum checking are good the problem can be caused by
vacuum switch valve
changes in valve stem height are a result of
valve and seat grinding or excessive cylinder head or block deck resurfacing
when adjusting valve lash under a hot setting
valve lash will have to be readjusted once the engine is at normal operating temperature.