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.