A8 (Engine Performance, Tune Up) Questions

EGR passages clogged with carbon (no EGR flow)

An EGR valve diaphragm is raised with the engine idling and there is no effect on idle speed (should stall out). What's up with that?

Distinctive O2 sensor normal closed loop, adaptive fuel management pattern.

O2 sensor voltage on a scope analyzer. Pattern observed, changes from 0.25 volts to 0.8 volts in a regular series of flat-topped hills.

sine wave form

Type of waveform produced by two-wire, reluctor (permanent magnet) sensor

Why no EGR at cold engine???

Until the engine is warm, there is no need because combustion is still sufficiently cool

Defective coil pack, breaking down under acceleration stress

V6 engine with distributor less ignition breaks-up on acceleration, but get's smoother when reaching cruise. Roughness in the idle is detectable. What's up with that? (most likely)

Unmetered air entering the engine. More air than the amount for which the engine is delivering fuel

Vehicle can be started with great difficulty, but lacks power and will not idle. What's going on?

Stuck open thermostat. Cold engine will run too lean. (Technically, the ECT will report cool temperature to PCM which then makes the air/fuel mixture richer)

Vehicle gets piss poor fuel milage and has poor heater performance. What's going on? (most likely)

Vacuum leak at the intake manifold

Vehicle running at normal operating temp. Idling too high. IAC shows zero. What's (most likely) going on???

Intermittent open in the pickup coil leads

Vehicle with electronic ignition hesitates and stumbles during acceleration. Problem goes away when vacuum advance hose (on the vacuum advance distributor) is disconnected and plugged. What's up with that?

Hall Effect vs Magnetic Reluctance sensors

____ ______ switches are equipped with a 3-wire connector. ________ __________ types are equipped with a 2-wire connector. They create voltage and are also known as PM (permanent magnet) generators.

excessive connecting rod bearing clearance

an engine has light metallic knocking noise during light engine loads. When the cylinder with the noise is disabled during a cylinder balance test, the sound diminishes. What's going on???

TBI fuel injector stuck open

Crank-no-start, fuel is POURING from the TBI injector when the engine is cranked and even when the cranking is stopped until pressure runs out.

Testing a ported, or negative back-pressure EGR valve

Engine off. Apply vacuum with a hand pump to the EGR. Valve should open

This may indicate a defective sensor

Erratic readings, or a momentary infinite readings

Systems prior to EVAP systems

Fuel vapors were emitted to the atmosphere from vented gas caps and carburetor float bowls

Test the fuel injector circuit in the order of the manufacturers dx procedure

Hard fault found in ECM for a fuel injector circuit. What should you do?

SFT will be a negative number

IF: -There is less oxygen in the exhaust -Injector pulse width has shortened -there is increased voltage signal from the O2 sensors

Wet compression test

If a piston ring is leaking, this type of test will indicate some compression. If a valve is burned, this type of test will make no difference and indicate the same readings

Closed Loop Operation

If the coolant temperature sensor tells the PCM/ECM that the engine has not yet warmed up, even though it has, the system will not go into ______ ____ _________ and will run rich

Testing a positive back-pressure EGR valve

Needs exhaust back pressure to open. This can be simulated by placing a restriction in the exhaust pipe, starting the engine and placing the transmission in gear. The engine should stall when pressure opens the valve at idle.

Adjusting valve lash

Rotate the crankshaft until the piston is at top-dead-center on the compression stroke (valves closed). This will position the intake and exhaust valve lifters or cam followers on the base circle of their respective cam lobes. Then adjust.

Fuel Pump Electrical Diagnosis

Simply having system voltage at the tank is not enough to condemn a pump. A multimeter puts virtually no load on a pump circuit. Before energy reaches the fuel pump, it must pass through the pump harness, pass-through connector, and pump wiring. A high resistance in any of these places can keep the pump from running properly. A test light can load the circuit in place of the pump, to determine if there is a resistance which will cause a significant drop in voltage available to the pump. Typical resistance could be from relay contacts which are burned or have insufficient pressure

Catalytic converter inspection

Strike it with a mallet. If you hear a rattling sound, it means ceramic substrate has come loose and is disintegrating

Muffler inspection

Tap on it with a mallet and listen for the sound of loose rust particles. It may not appear rusty on the outside, but they tend to rust from the inside.

Customer states the MIL light is on. When you pull it into your bay, the light is off? What's going on?

The monitor responsible for the DTC has run three times in a row (or a specific number of warm-up cycles) without seeing the same failure.

Checking an NTC (negative temperature coefficient) sensor

The resistance varies with temperature. Check the function by measuring resistance between the sensor terminals. General rule: 3000 ohms @ room temp. Can also be checked with voltage drop. More voltage dropped across the sensor when it is cold and less when hot.

EGR stalling

This would be caused by too much EGR or EGR at the wrong time

Bubbles in the radiator coolant during cylinder leakage test

This would indicate a cracked head, cracked block and/or blown head gasket during a cylinder leakage test

Causes of airflow problems through a radiator core

-Broken shroud -Debris build-up -Bent fins

Ways to determine if valve timing has jumped:

-Check valve movement with the piston at TDC on the exhaust stroke (quickest) *WHY??? Both valves should be open because of "valve overlap". The exhaust should close a few degrees after TDC and the intake should open a few degrees before. -Look at timing marks on cam and crank sprockets

Conditions in which exhaust gas recirculation is NOT required:

-Cold engine at part throttle -warm engine at idle -warm engine at WOP

PCM/ECM replacement PRO TIPS:

-Disconnect Negative Battery cable prior to replacement -Test the vehicle driver circuits for low resistance (to be certain that no circuits will draw excessive current).

Causes of vehicle running at normal operating temp to have rough idle and blow black smoke from the exhaust

-EVAP canister purge solenoid stuck open (canister improperly purging at idle) -fuel pressure too high (too much fuel injected during injector opening) -fuel injector(s) stuck (fuel flow when not energized)

Intake manifold vacuum readings that indicate restricted exhaust

-Engine gradually accelerated to 2000 RPM and vacuum reading drops to zero before slowly returning to normal -Throttle closed and vacuum doesn't increase -Engine is accelerated to 2500 RPM and vacuum drop 3 inHg below original reading after a few minutes.

Crankshaft end-play noise (excessive clearance between the thrust bearing and the machined faces of the thrust journal)

-Engine may make a deep knocking sound -Usually most obvious at idle but diminishes when a load is placed on the crankshaft, e.g. disengaging the clutch -measure using a pryer and a dial indicator

Testing alcohol content of fuel

-Fill 100mL container to 90mL with fuel -Then fill to the 100mL mark with H2O -Shake vigorously for 15 seconds and allow to settle -Take the new amount of H20 and subtract the original amount. The difference is the amount of EtOH -e.g. the container now shows 15mL of H2O. This means there is 5% EtOH

Things that can interrupt OBDII PCM/ECM reprogramming

-Getting an automatic update (like virus protection) -Opening the car door -Carrying the key fob in your pocket

Normal Mechanical Fan Clutch Operation

-Has viscous drag, regardless of temperature -varies fan speed according to engine temperature (not speed) -Stops fan from spinning within 2 seconds after turning off a hot engine.

EVAP Canister Vent Solenoid Facts

-It is activated by the PCM/ECM to block the entrance of outside air into the canister during the EVAP leak test -It is used only on vehicles with enhanced EVAP systems -It is located in the fresh air supply hose to the canister

Starter current draw (amperage) higher than normal

-May be short circuit in starter motor -May be mechanical issue causing binding in the engine

Fuel Pressure Regulators:

-Most are not adjustable -Most are connected to manifold vacuum and vary the pressure according to engine load -If its diaphragm ruptures, a rich running condition may occur -Pressure is higher if the vacuum line is disconnected

Vehicle with "no-start" condition. Coil wire from distributor cap is disconnected and spark tester is hooked up. Why would there be no spark???

-Problem with ignition coil primary circuit -A bad coil -A bad distributor pick-up coil

Possible causes of crank-no-start to have no spark at all (distributer vehicle)

-Problem with the ignition primary circuit -a bad coil (part if primary circuit) -bad distributer pick-up coil (part of primary circuit)

Signs of overcharging

-Short light bulb life -Battery constantly needs water

Signs of catalytic converter problems:

-Signal from catalyst monitor fluctuates high and low (should be stable) -Converter shell appears blueish (has overheated) -Converter makes a rattling noise when struck (ceramic substrate has come loose) -There is little difference between the inlet and outlet temperatures (outlet temp should be hotter)

Piston noise (piston slap, excessive piston-to-wall clearance)

-Sounds like a dull or muffled metallic rattle at idle or during light engine loads -May disappear after warm-up due to expansion -Should be corrected if doesn't disappear after warm-up -Eliminating ignition or fuel from the the cylinder will not eliminate the noise. IN FACT: It may grow louder.

Symptoms of insufficient EGR

-Spark knock -Surging at cruise -Increased NOx emissions

No-start vehicle. Tech connects test light between the (-) side of the coil and ground. Cranks engine. Test light flutters. What conclusions can be drawn from this?

-The pickup coil signal is okay -the ignition module (shown) is okay -the module is triggering the col to fire. *Cannot ascertain that the coil is actually good. Just that it is being triggered to "fire".

~200 amps

= typical starter current draw for 6 cylinder engines

~250 amps

= typical starter current draw for 8 cylinder engines

Main bearing noise (too much bearing clearance)

-Usually indicated by a dull or deep sounding metallic knocking -Increasing engine load or RPM will increase the frequency -Usually most obvious right after the engine starts up, under heavy load, or during acceleration -FUN FACT: Engine may exhibit low oil pressure

Connecting rod noise (excessive bearing clearance / lack of lubrication)

-Usually sounds like light metallic rapping -Most noticeable when the engine is running under light load, relatively low speed -Becomes louder and more frequent as engine speed is increased -Diminishes when ignition or fuel is removed from that cylinder

Excessive resistance in the voltage and/or ground side of the charging circuit

-Will cause low charging rate -Will cause higher than normal voltage drop

A vehicle with multlport fuel injection has a stalling problem. When the throttle body is inspected if is found to be contaminated with sludge buildup. What's going on????

-Worn Rings -Clogged or restricted PCV valve Why??? Worn rings can cause excessive blowby into the crankcase which may be more than the PCV can handle. So, instead of going into the intake manifold, these gases find their way through the fresh air intake and into the air cleaner. Oil deposits then mix with air and for sludge.

Causes of blue-gray smoke from tailpipe during DEceleration:

-Worn valve guides and / or bad valve stem seals (high intake vacuum during this time draws oil through the worn guides and seals) -May also be caused by plugged oil return holes leading to oil accumulation in the head

Hydraulic lifter noise

-a consistent ticking sound -may sound like worn valvetrain components

Intermittent Faults

-a malfunction that occurred in the past, but is not present at the time of the self-test -May need to recreate conditions described by the driver in order to reset it -They are often caused by damaged wiring and connectors, so tapping and wiggling them can sometimes get problems to reoccur

Spark knock

-caused by 2 types of abnormal, uncontrolled combustion -sounds like metallic pinging or ringing -Occurs most often under heavy load and being run at too low an RPM or accelerating, OR an engine that is running too hot and/or has excessive combustion deposits

Valvetrain noise

-caused by excessive valve clearance, worn rocker arms, shafts, lifters, camshaft or lack of lubrication -usually a light ticking noise at idle that occurs at a frequency slower than engine RPM

Piston Pin Noise

-makes a light, but sharp metallic rapping at idle -may be more obvious at low-speed driving eliminating ignition or fuel will change frequency or possibly intensity of the noise

Starter current draw (amperage) lower than normal

-may mean there is abnormal starter circuit resistance

Signs of undercharging

-slow cranking -dim headlights -low ammeter indication

'Pending' Codes

-these are recorded if monitor results indicate a failure after one drive cycle, or 'trip' -these should be checked to verify repairs

Causes of Engine detonation (knock)

1. A lean air/fuel mixture 2. Advanced ignition timing 3. Excess carbon in the combustion chambers 4. A stuck-closed EGR valve

2 Types of MAP sensors

1. Analog Signal type-tested with a voltmeter 2. Frequency signal type-tested with a hertz meter or digital tachometer

Proper procedure for checking starting circuit

1. Check crank speed 2. Check starter current draw 3. Check battery voltage while cranking 4. Check voltage drop of the starter motor circuit

voltage drop of the starter motor circuit

1. Connect black lead of voltmeter to battery connection at starter 2. Disable the ignition and crank engine. As doing so, touch red lead to battery positive 3. Quickly switch the volt scale to lower scales until a reading is seen 4. If drop exceeds 0.5V for entire circuit, repeat the test, moving the black lead toward the battery, one connection at a time

Causes of turbocharged vehicle performing poorly and lacking power:

1. Restricted intake duct 2. Wastegate stuck open 3. failed turbocharger shaft bearings

500 - 1500 ohms

= normal resistance reading when an ohmmeter is connected to the pick-up coil leads

~150 amps

= typical starter current draw for 4 cylinder engines

Secondary Superimposed Scope Pattern

A quick way to compare secondary ignition patterns of each cylinder of a V8. A scope pattern that places all patterns on top of each other to check for uniformity.

Thermistor

A type of variable resistor that changes resistance according to the change in temperature (may also have the resistor squiggle in it when depicted on a wiring diagram

Check operation of the air bypass valve

A vehicle with AIR system backfires during acceleration. What should be checked????

EVAP Canister Purge Solenoid

Activated by the PCM to allow the flow of fuel vapor from the EVAP canister to the engine.

>9.6 volts

Battery voltage should remain above this level during the starter current draw test and the engine should spin rapidly.

Voltage test of TP sensor

Best accomplished using a scope, as even the smallest dropouts can be seen as the throttle is moved. These moments may be skipped by the processed data of a scan tool.

Testing a voltage generating Vehicle Speed Sensor (VSS)

Check the sensor's resistance with an ohmmeter. OR Check with a lab scope. Should be a sine wave pattern because this is a permanent magnet sensor that produces AC signal.

Lean Condition Exhaust Gasses

CO2 lower than normal, O2 level is high, NOx is high

Maybe a bad 02 sensor or intake air temperature sensor. Both of these relay signals to the PCM/ECM that directly affects control of the fuel

Car with electronic fuel injection gets piss poor gas milage. Measured value blocks show the engine is running rich. What could be the cause?

Low manifold vacuum causing the fuel pressure regulator to restrict fuel return

Car with electronic fuel injection system has too high fuel pressure at idle. What's the deal?

Crank-no-start diagnosis

Do not jump to conclusions. Test until the defective component is identified

No-crank car's starter solenoid is being tested with a jumper wire between the battery and the solenoid "S" terminal. The engine finally cranks. What's the problem?

Problem in starter control circuit

PCV Valve testing

Remove from the hose and give it a shake. If it rattles, it is not stuck open or closed.

Causes of large leak test failure in enhanced EVAP system

The PCM/ECM opens the canister purge valve to cause vacuum in the EVAP system. All of the following would prevent vacuum from being created: -Loose fuel cap -cracked vapor line -stuck open canister vent solenoid

No-crank car's starter solenoid is being tested with a jumper wire between the battery and the solenoid "S" terminal. The solenoid makes a clicking noise but the starter doesn't engage. What's going on? What's the problem?

The starter is defective

Why no EGR at warm engine idle?

There is no need at this condition because combustion pressures are relatively low and NOx is not formed. If it occurred at this point, it would stall the engine because of too much dilution.

Why no EGR at WOT?

There is no need for it at this point because the need for power outweighs the need to reduce NOx emissions and because this condition needs a richer, slightly cooler mixture (NOx formation is almost minimal)

"0" codes (P0XXX)

These fault codes are considered "generic", SAE standard.

"B" fault codes (BXXXX)

These fault codes indicate a problem with body control modules

"C" codes (CXXXX)

These fault codes indicate a problem with chassis components

"U" codes (UXXXX)

These fault codes indicate a problem with the network (module to module communication)

"P" codes (PXXXX)

These fault codes indicate a problem with the powertrain

"1" codes (P1XXX)

These faults are consider OEM, or manufacturer specific.

Adjusting hydraulic lifters

These must be adjusted to position the lifter plunger within the lifter body, therefore the adjuster must be turned farther than zero lash

Quick way to distinguish a Hall Effect Sensor

These use 3-wire connectors

Quick way to distinguish Magnetic reluctance sensors

These use a 2-wire connector. They create a voltage. They are also known as PM (permanent magnet) generators

Thermal Vacuum Switch

This component is used to prevent EGR when the engine is cold. If operating properly, it should not allow vacuum flow until the engine reaches a specific operating temperature

Timing light with ignition advance meter

This is the best, most accurate way to measure spark advance

Manifold vacuum found to be low, but steady

This manifold vacuum reading could mean the air/fuel mixture is too lean OR too rich.

MAF (mass air flow) sensor

This sensor can be checked by measuring the pulse width of the fuel injector (how long the fuel injector is open). Restrict the air intake and look for a change in fuel control

Oscilloscope and Spark Plugs

This tool can be used to determine spark plug firing voltage as well as the condition of the ignition coil

Frequency type MAP sensor

This type of MAP sensor measures pulses per second (Hz) and converts them to revolutions per minute. Therefore, it will have a constant signal voltage.

High MAP sensor voltage (~5 volts) at idle

This would indicate atmospheric pressure inside the intake manifold, which should only happen when the engine is off, or at wide open throttle (WOT). The PCM will respond by richening the fuel mixture.

Air blowing into crankcase during cylinder leakage test

This would indicate worn piston, rings and / or cylinder during a leakage test

EVAP System Purpose

To prevent HC emissions from escaping the fuel system to atmosphere. Captures vapors and routes them to the engine where they are burned with the air/fuel mixture

Faulty purge solenoid power circuit

Vehicle with normally closed canister purge solenoid is not purging the EVAP canister when engine operating conditions for purging are met. The purge solenoid is removed from the vehicle for testing. It allows vacuum when voltage is applied. What's going on there???

Voltage Check with DMM

When doing this, the DMM should be connected in parallel

Amperage check with DMM

When doing this, the DMM should be connected in series

100 F or 38 C

When testing a catalytic converter with an exhaust pyrometer, or temperature probe and DMM, the difference between the surface of the converter inlet and outlet should be ___ F or __ C with the engine at normal operating temperature. Rear should be hotter than the front.

Reason for EGR

When the engine is warm and above idle speed, it is required to prevent spark knock AND reduce NOx emissions.

PCV is either stuck closed, or the hose between the intake manifold and PCV could be plugged

While the engine is running, the PCV valve is pulled out of the valve opening. Placing a finger over the valve, NO vacuum is felt. What's going on there?

Fuel mixture is likely too rich. Too high voltage indicates a rich mixture.

With a DMM connected, an O2 sensor reads above 550 millivolts, constantly. What's going on?

Intake manifold vacuum readings that indicate good exhaust system

With the throttle closed, vacuum momentarily increases and then resumes normal readings

piston slap, or excessive piston-to-wall clearance

an engine has light metallic knocking noise during light engine loads. When the cylinder with the noise is disabled during a cylinder balance test, the sound does NOT diminish (perhaps even grows louder). What's going on???

White Exhaust Smoke

caused by coolant leaking into one or more cylinders, such as when a head gasket goes bad

Causes of "tapping" noise coming from top end of V8 engine

could be caused by worn valve train components or excessive valve train clearance, like a valve needing adjustment could be an exhaust leak at the manifold/cylinder head junction

PCM driver for the TBI injector is shorted out

crank-no-start, fuel is POURING from the TBI injector when the engine is cranked. Disconnect the connector to verify. The injector should hold the fuel back on its own.

Importance of pick-up coil gap

if too small, or too large, it may cause a misfire

Secondary Air Injection System

injects air into the exhaust system.

Excessive Alcohol in Fuel

it can degrade rubber fuel system components, clog the fuel filter and cause lean air/fuel mixtures

multi port fuel injection

know the differences

Look into "checking initial timing"

look into "checking spark advance" and vacuum advance.

Loose torque converter bolts or a loose or cracked flexplate

most likely cause of thumping at the back of the engine that is most noticeable when in park or neutral

infinity ohms

normal resistance reading when ohmmeter is connected to ground and either pick-up coil connector lead

Preignition Spark Knock

occurs when a hot piece of carbon or metal inside the combustion chamber ignites the air/fuel mixture too early. Then, the spark plug ignites the remaining mixture at the normal time. When the 2 burning portions meet, there is a sudden rise in cylinder pressure which causes vibration

Detonation Spark Knock

primarily caused by fuel with too low an octane rating for the engine (fuel burns to quickly), ignition timing that is too far advanced, high engine temp or excessive carbon build-up in combustion chamber. In this case, the spark fires, the mixture begins burning and pressure rises in the cylinder. The normal rise in pressure causes part of the mixture to self-ignite elsewhere in the combustion chamber. Then, the two flames collide.

Square wave pattern

the type of waves pattern produced by Hall effect sensor

AIR system air bypass valve

this AIR system component momentarily exhausts the air pump's output by diverting it to the atmosphere during engine acceleration.

DSO reading of disconnected or open spark plug wire

this DSO reading would show a higher by comparison spike line reading when compared to the other spark plugs

DSO reading of closed spark plug gap

this DSO reading would show a very low spike line in comparison to the other spark plugs

Worn valve guides and vacuum readings

this condition would cause the vacuum gauge needle to fluctuate at idle, but the needle would steady when the engine speed is increased.

Weak or broken valve spring and vacuum readings

this condition would cause the vacuum gauge needle to fluctuate or jump from low to high readings

Distributer cap carbon track

this is a likely cause of "spark miss" on distributer equipped vehicle

Blue Smoke

this means the engine is burning oil. Could be caused by worn piston rings

Propane introduced to an air fuel mixture that is too rich

this will make the engine slow down and the vacuum reading drop

Propane introduced to an air fuel mixture that is too lean

this will make the engine speed up and the vacuum reading will rise

Ammeter

tool used to troubleshoot a slow drain in an electrical circuit

10 megaohm impedance

when testing computer-controlled systems, a DMM should be used with an input impedance of at least this much, for max protection.