Engine Performance Diagnostics

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Paul Danner Sixth Edit io n

Introduction Hello, my name is Paul Danner. I am an ASE Ll certified master technician with 20 years of field experience in driveability diagnostics and computer systems troubleshooting. For the past 11 years I have been an instructor for Rosedale Technical Institute near Pittsburgh, PA where I developed this book for training my students. Before entering my class students are expected to have a basic understanding of the 4 stroke engine and also some basic electrical background . Although this is important, it is not completely necessary to understand most of the topics and testing methods taught in this book. One of the main focuses in this book is what I like to call the "anti-flowchart". I hate engineer written flow charts! These are step by step procedures that some pencil pusher thinks is the best way to troubleshoot a particular problem on a car. For the most part they don't give us technicians enough credit. They are certainly never written with speed in mind . How could they be when half of them start off with disconnecting the computer and the sensor and checking the wire for opens and shorts? Do they realize that step one could take more than a half hour to just get to the computer? This is ridiculous! There has to be a better way! I think I have said that to myself thousands of times over the past 20 years. Well guess what, I have found a better way and I want to share it with you. Some of my methods are a little unorthodox, but if used correctly there is no faster or more accurate method for computer systems trouble shooting than what I have outlined in this book. Do I still use engineer written flow charts? Of course, but only as a guide and almost never literally. Maybe someday engineers will wake up and figure out that some of us can handle more information than what they are providing. Until then we must develop a more complete understanding of sensors and circuit designs. Once we have these fundamentals we will be able to troubleshoot ANY computer controlled system, not just a fuel injection computer. I even fixed my furnace at home using these same principles!

Table of Contents Universal Testing Methods SVl'itch Inputs Transistor Drivers and Output Solenoids Oxygen Sensor Introduction Oxygen Sensor Testing Thern1istors Potentiometers Pressure Sensors The 5 Volt Reference Circuit Signal Circuit Integrity T esting Substituted Values A.irOow Sensors Types of Fuel Injection Fuel Delivery Designs Fuel Pun1p Electrical Circuits Fuel Pressure Testing Fuel Injector Driver Designs Fuel Injector Testing No Injector Pulse, No Start Problems Idle Speed Controls Ignition Systen1 inputs No Start, No Spark l'roblen1s No Start, Good Spark and Injector Pulse Condition EGR System Problen1s Con1n1on Tern1s and Abbreviations

Section l Section 2 Section 3 Section 4 Section 5 Sl-'Ction 6 Section 7 Section 8 Section 9 Section 10 Sl-'Ction 11 Sl-'Ction 12 Section 13 Section 14 Section 15 Sl-'Ction 16 Section 17 Section 18 Section 19 Section 20 Sl-'Ction 21 Sl-'Ction 22 Section 23 Section 24 Section 25

1- 29 1 -30 1 - 30 1 - 21 1-27 1-17 1 - 15 1 - 10 1-6 1-7 1-6 1- 17 1 -8 1 -9 1 - 19 1- 16 1 -7 1 - 26 1 -5 1- 29 1-33 1- 26 1 -2 1 -8 1-2

Universal Testing Methods Section 1

Where Do I Start? •

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Fuel - Is the engine running rich or lean? - Is there enough fuel delivery under a load? Ignition - What is causi ng the misfire? • Is it lack of spark, fuel or compression? - What are some quick tests to identify the cause of the misfire? Mechanical - Is there a compression problem? - Is there a jumped timing belt/chain? - Is there a vacuum leak? Electrical - Is there a bad diode in the alternator? - What is the computers response to low battery voltage? Emissions - Is the EGR va lve stuck open? - Is the exhaust restricted? - Could the air pump or evap. system be causing problems?

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Question customer. Test drive to verify customer complaint. The symptom must be duplicated for an accurate diagnosis. Scan for diagnostic trouble codes. (DTCs) - Check freeze frame data (if available) to determine the engine load and temperature set by the fault code. Check for technical service bulletins (TSBs) RESEARCH!!! You must know the description and operation of the system or component before diagnosis begins. (*The main resources I use as an aftermarket technician: Shop Key, Mitchell, iATN.net, Snap-on's Troubleshooter and the Component Meter of the Vantage Pro) • Find the specific fault code and read or print the step by step "flow chart". Even if you don't follow it completely you will still gather valuable information about why the code is set and what the possible causes are. • Print the wiring diagram for the system you are troubleshooting. • Research theory and operation of the components being tested. Never forget to perform a visual inspection. This can save you significant time if you just take a look first!

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Fuel trim •

Short term fuel trim is used to keep the 02 sensor moving slightly rich I lean from stoichiometric. This provides the catalytic converter w ith the necessary gases to properly reduce the maj or pollutants.

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Long term fuel trim is learned from the short term fuel trim. Its primary functions are: -

To keep the short term with as much correction capability as possible. This is achieved by keeping the short term close to 0°/o.

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To reta in fuel trim corrections in memory

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Use the long term fuel trim values to determine if the engine is delivering fuel normally or if it is correcting for an overly rich or lean condition. Keep in mind that every load/rpm combination will have a different "learned" long term fuel trim numbers.

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Positive numbers (numbers above Oo/o) mean the computer is adding fuel. This is a rich command in response to a lean condition .

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Negative numbers (numbers below 0%) mean the computer is subtracting fuel. This is a lean command in response to a rich condition.

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Oxygen sensor malfunctions w ill cause the computer to add or subtract a disproportionate amount of fuel. If the 02 sensor voltage is fixed lean (below 450mv), the computer w ill severely richen the mixture. This will result in poor gas mileage, black smoke and poor low rpm performance. If the 02 sensor voltage is fixed rich (above 450mv), the computer will severely lean-out the mixture. This will result in low power and hesitation problems. In either case the eng ine will run good cold and at wide open throttle (WOT) because the 02 sensor is not used du ring these times .

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Understanding ST/L TFT •

STFT (short term fuel trim) - #1 job is to keep 02 sensor near (a little above/below) stoichiometric is a command from the PCM to alter injector pulse - Oo/o = no fuel corrections from factory preset value is only used in closed loop

L TFT (long term fuel trim) - #1 job is to keep STFT as close to 0°/o as .possible and to retain any fuel corrections 1n memory. PCM "looks" at L TFT first to know where to start injector pulse width learns from STFT% is a command from the PCM to alter injector pulse 0°/o = no fuel corrections from factory preset value +/- 10 °/o is considered normal on most systems may be used in both open and closed loop

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NOTE* With left and right bank upstream 02 sensors , the PCM uses left and right bank STFT & L TFT (individual bank fuel trim control)

Total fuel trim is the sum of the LTFT and STFT

Pre-OBDll GM used Block Learn (LTFT) and Integrator (STFT) binary numbers. 128 = 0°/o

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02 and Fuel Trim Example Fixed lean 02

• 1994 CHRYSLER CAR AA IT 3.0L V6 MPI A/C 51 sustained LEAN F/A CO ITION 704 02S(V)_0.04 INJ(mS)_ 3.5 0 RPM IGN CYCLES 1 3 IGN CYCLES 2 134 IGN CYCLES 3 0 OPEN/CLSD LOOP CLSD MAP SNSR(V) 1.2 MAN VAC("Hg)_ 19.2 BARO PRES("Hg)_28.9 THROTTLE( 0/o) O TPS(V) 0.82 MIN TPS(V) _ _0.82 2.3 COOLANT(l1F) 199 COOLANT(V) ST ADAP( 0/o) 24.8 LT ADAP( 0/o) 24.8 EXHAUST EAN VEH 0 SPEED(MPH)

Rich command (limit reached as indicated by both ST and LTFT o/o being high .

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This is a data capture of a vehicle with a bad 02 sensor. (signal fixed lean) The computer's response to a lean 02 sensor is to add fuel. This process of adding fuel will continue until the 02 sensor moves back to the rich side of stoichiometric or until the fuel trim has reached its limit. This limit of control is different on every car and is necessary to prevent severe over or under fuelling conditions. This engine ran well cold and at WOT and also during a forced open loop condition. - A forced open loop condition will occur when an 02 sensor will not respond to the computer's command. A trouble code will also be set at this time. 6

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Fuel Trim After Replacing 02 Sensor This vehicle had a bad (fixed lea n) 02 sensor. The below picture is a scan data capture of what the fuel trim numbers looked like with the new 02 sensor and the computer's memory not cleared . Why is the LTFT commanding rich and the STFT commanding lean? The computer is in the process of relearning. The memory (L TFT} was to add fuel from a bad (fixed lean) 02 sensor. The new 02 is able to react and is telling the computer there is too much fuel. The computer immediately responds using the STFT command to lean-out the mixture . *I like to see this reaction, this tells me that the vehicle is fixed! My preference after a repair for a lean condition is to watch the STFT and see how much it counters what the L TFT memory is commanding. For an example, see the following video: http://www.youtube .com/watch?v=Hmt LNJ9Gkl

Examples after a repair for a lean condition: •

LTFT 30°/o STFT -25°/o = you fixed the problem (Total fuel trim is 5°/o, after the relearn process the LTFT will be 5o/o and the ST FT will be 0°/o)

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LTFT 30°/o STFT -10°/o = you still have a lean condition . (Total fuel trim is 20°/o, after the relearn process the LTFT will be 20% and the STFT will be 0°/o) It's better but there is still a problem . 0 2 Sens o r 112 Volts

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For Low Power Complaints The upstream 02 sensor must be functional (switching rich/lean) to use the following test: • At WOT every engine runs rich, so the 02 sensor should be reading over 800mv. Just because the computer ignores the 02 sensor at WOT doesn't mean you have to. You can use this as a guide to fuel delivery under load conditions. • Test drive while watching 02 sensor millivolts at wide open throttle (WOT) -

If the 02 drops lean (under 1OOmv) there is a fuel delivery problem. This is most commonly caused by a dirty mass air flow (MAF) sensor or a low fuel pressure/volume problem. http://www.youtube.com/watch?v=Hmt LNJ9Gkl

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If the 02 stays rich (above 800 mv) then fuel delivery is good and you most likely have a plugged exhaust causing the low power problem. http://www.youtube.com/watch?v=9TlygJMxTps

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Vacuum leak testing without a smoke nold'fine~ In general a Speed Densi ty engine (MAP only) will idle high (Figure 1) and a MAF engine will idle low with a vacuum leak (Figure 2). This will change what the follo wing data parameters (PIDs) look like. http://www.youtube.com/watch?v=RFQBa-nqBPo

NOTE* Some vacuum leaks (especially manifold gasket areas) can on ly be located while the engine is cold • External vacuum leaks - Check for diagnostic trouble codes (DTCs). Look for lean exhaust and idle adaptive limit codes . (Figure 3) - Look at scan data • 02 mv • LTFT • Idle A ir Control (IAC) motor position (see Section 20 for further /AC information) • RPM and Desired Idle Speed - Carefully spray propane around the intake and all vacuum hoses (FIRE HAZARD!!!!) • Listen for RPM changes • Watch 02 mv I STFT 0/o, (02 will go rich and STFT will go negative if you find the leak) - If you find a lea k and are having difficulty pinpointing the exact area » Spray the sa me areas w ith water. You w ill be able to see and hear the water getting sucked into the intake and no you won't hurt the engin e w ith a small amount of water. • Internal vacuum leaks (V-type engines only) causing a single cylinder misfire - Remove PCV valve and plug PCV port in the valve cover. - Block off PCV breather port to the air cleaner. (Figure 3) - Remove engine oil dipstick and install a vacuum gauge on the dipstick tube . • There should be NO vacuum in the crankcase. Crankcase pressure will actually . increase. 9 • If you read vacuum, there is an internal vacuum leak .

(Return)

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(Return)

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Description and operation Hot wire type Conta ins a heated resistor (hot-wire) that is maintained at a predetermined temp. above ambient temp. As air flow increases the current required to maintain hot-wire temp . also increases. This increasing current is converted to a signal and sent to the PCM as a measurement of mass air flow . • Signal can be analog or digital As with a VAF, all incoming air must pass th ru the sensor. Vacuum lea ks and air intake tube problems will cause "un-metered" air to enter the engine causing mild to severe lean a/f ratio problems . Unique to the hot-wire MAF is problems with contaminates . Dirt, dust, pollen and PCV gases cause the hot-wire to become "dirty" which acts as an insulator covering the hotwire causing the MAF signal to be wrong under all conditions . • Causes lean running conditions (symptoms noticed more when engine is cold) If this is a " honeycomb" type screen, DO NOT TOUCH IT!

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Scan Data MAF Testing • • •

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Look at MAF signal (voltage or frequency) Look at MAF grams/sec (th is is the signals converted value) Ford - look at BARO HZ (lower than normal HZ = possible dirty MAF). Sea level readings should be near 160HZ. Barometric pressure is calculated off of the MAF at WOT. http://www.youtube.com/watch?v=h5KAHv4 7viw (Using Fuel Trim data to determ ine type of lean condition) 1. Check at idle and WOT (redline) 2. May need to test drive for the WOT test if scan data baud rate is slow • Pay close attention to the WOT redline values • Look for near 150 grams/sec for most GMs and Fords (some systems will be less than th is. http://www.youtube.com/watch?v=Hmt LNJ9Gkl (Toyota Dirty MAF) http://www.youtube.com/watch?v=-5L5tp4NDqO (Cracked air intake tube) • Ford, Nissan, and Toyota signal voltage should go over 4 volts • GM frequency should increase to 8,500 HZ or more (see pages 1Q, 12. and .Ll. for case stud ies) 3. Check 02 mv at WOT (test drive) • 02 should read rich (800 mv +) if the MAF is clean • 02 indicates lean then possible dirty MAF or other fuel delivery problems 4. Check fuel trim • Generally a dirty MAF will have normal fuel trim numbers at id le and higher than normal (positive) fuel trim numbers with higher RPMs • On occasion a dirty MAF can over estimate air-flow at idle . The contaminants cause an increase in surface area , which under low airflow conditions cause a greater heat transfer. The PCM "sees" higher airflow so it provides more fuel. This causes the fuel trim at idle to be negative. 5. Can try the unplug it test if the signal is out of range . If the eng ine runs good with MAF unplugged = suspect faulty MAF • The above test is NOT always accurate. Some systems do not provide good back6 up strateg ies for MAF failures . (N issan , Toyota, Subaru)

Scope Testing MAF Sensor~~~ • • •

0 G

•

~

Digital Type To determine if the MAF sensor is dirty you must measu re peak frequency . Peak frequency is best measured using a graphing multimeter (Snap-on Vantage, Picoscope 4000 series) which allows the digital signal to be converted to analog for easier measurements. (see page 11) 1. Measu re signal frequency at idle and WOT redline (see examples) Look for over 8500 HZ at WOT (newer GMs) If frequency is low then remove sensor and inspect hot wire for contaminants (see picture on pg. 14) Clean with brake cleaner and a soft paint brush (hot-wire type only) - BE CAREFUL! Do not clean any other type of MAF sensor with brake or carb . cleaner! http://www.youtube .com/watch?v=h5KAHv47viw (Digital MAF test with Picoscope) If signal is out of range or no signal appears 1. Measu re MAF power feed KOEO or KOER Should be near 12v 2. Measure MAF ground KOEO or KOER Should be less than 100 mv 3. GM only, disconnect the MAF sensor and measure signal voltage harness side w ith the KOEO Should read 5 volts The PCM sends 5 volts down the signal wire to the sensor and the sensor pulls it to ground to create "square wave" signal. (see switch inputs for more details) If no voltage you have a PCM or a signal wire problem , NOT a MAF sensor problem. http://www .youtube .com/watch ?v=p2QLxxstRn8 7 http://www.youtube .com/watch?v=E8sBg7kMbOw

Scope Testing MAF Sensom" • •

•

0 G

8

Analog Type To determine if the MAF sensor is dirty you must measu re peak voltage 1. Measu re signal voltage at idle and WOT redline (see examples on pg. 1...§. and 1§.) Look for over 4 volts at WOT (Ford, Nissan, Toyota) If voltage is low then remove sensor and inspect hot wire for contam inants (see picture on pg . 14) Clea n with bra ke cleaner and a soft paint brush - BE CAREFU L! Do not clean any other type of MAF sensor with bra ke or carb. cleaner! http://www.youtube.com/watch?v=H mt LNJ9Gk I If signal is out of range or no signal appea rs 1. Measu re MAF power feed KOEO or KO ER Should be near 12v 2. Measure MAF grou nd KOEO or KOER May be more tha n one grou nd Ford uses two grounds . It has an MAF ground and a PCM ground . The PCM gets its ground th rough the MAF sensor . This is important to know when performing signal circu it integrity testing because the PCM w ill not respond to any test with the MAF sensor unpl ugged . All grounds should be less than 100 mv Some MAF sensors conta in an internal intake air temperature sensor identified by the number of w ires . 1. Ford 4 wire = MAF signal , MAF ground , PCM ground, MAF power feed . 2. Ford 5 or 6 wire= MAF signal , MAF ground, PCM ground , MAF power feed, IAT signal , and IAT signal return (which may be sha red w ith another ground wh ich would eliminate one wire) 3. Testing this IAT sensor is no different than any other therm istor

8

m

'V """"'

MAF signal low with good MAF senSor •

o.

Vehicle exhibits similar symptoms as a dirty MAF sensor however the sensor is clean. (Ford BARO HZ will also be lower than normal) 1.

0

-~

2.

G

..

Plugged exhaust • If the engine cannot "exhale" it cannot "inhale" so intake air volume will be low under all conditions. • A quick test to identify this condition is test drive at WOT and watch 02mv 02mv fixed rich (over 800mv) at WOT suspect plugged exhaust 02mv fixed lean (under 1OOmv) at WOT suspect low fuel pressure Intake restriction This condition will show a weak/low MAF signal no matter how you test • it.

,.~

(

.,-

MAF OTC with good MAF sensor Usually sets a "range/performance" code and may be caused by the following: 1.

TPS problem

2.

Vacuum or air intake leak

3.

Oil cap or dipstick problems

4.

PCV system leaks

5.

Dirty/plugged air cleaner

9

(Return)

Digital MAF Sensor Case Study 97 B uick LeSabre 3800 series II 3 wire sensor Scan Data

Clean MAF

Dirty MAF

0 0

•

1997 BUICK

•

3.8L V6 BUICK SFI

AJC A/T 0

100

•

RPM_5699 TPS(V)_ 4.22 TPS( /o)

•

•

OPEN/CLSD LOOP_OPEN 17 02 B1-S2(mV) 02 B1-51 (mV)

•

ST TRIM(o/o}

•

MAF(gm/Sec)

•

AJC A/T

•

1997 BUICK

•

3.8L V6 BUICK SFI

•

RPM_5530 TPS(V)_ 4.22 TPS( 0/o)

•

100

35

•

OPEN/CLSD LOOP_OPEN 946 02 B1-S2(mV) 02 81-51 (mV)

16

•

ST TRIM(%}

84.1 MAF(Hz)

7473

•

MAF(gm/Sec)

MAP(V}

4.43 MAP("Hg}

27.8

•

MAP(V}

4.49 MAP("Hg}

28.1

•

BARO(V)

4.64 BARO("Hg)

29.0

•

BARO(V)

4.64 BARO("Hg)

29.0

•

COOLANT(°F)

63

•

COOLANT(°F)

203 INTAKE AIR(°F)

77

•

IAC POSITION

775

•

IAC POSITION

95 DESIRED IDLE

600

•

INJ PW(mS)

4

•

INJ PW(mS)

0 LT TRIM(0/o}

151 INTAKE AIR(°F) 120 DESIRED IDLE 11.4 FT CELL

0 LT TRIM( 0/o} 143.0 MAF(Hz)

942 16 8886

4

19.6 FT CELL

10

(Return)

Digital MAF Sensor Case Study (cont.) 97 B uick L..:::e-=S-=a""b""'re::;.._ _ _ _~-------I 3800 seri es II I I 10k 3 wire sensor I I I Scope Captures

I I I

10k

I I I I

I I

I I

I I I I I I I

I I I

I I I

•

WOT snap w ith clean

WOT snap with dirty

0

MAF

MAF

0 •

0

6.72k

6.84kHz

G

8.32k

8.52kHz

I I I I

10k

I

Digital Waveform at idle

Graphed digital waveform at idle both before and after cleaning no change/

.. .:

... .. ..

=

I I

•

... .

I

I I

5.01V

5.01VDC

-1

2 .40k

..• .. .. ..• ... .

0

2 .41 k Hz 11

Before cleaning MAF sensor

lni PWM Avg Bank 1 lni PWM Avg Bank 2

14.47

I I I

=ec 4829 rpm

0 868

ensOf v

(Return)

22

m

894 22

ensor v

7665 requency

2000 Chevy S-10 4.3L e Study

z

21 15 l l l 25

3 .9

-

.

.

lni PWM Avg Bank 1

msec

488 4

fter cleaning MAF senor

rpm

634 981 56 994 87 8572

requency

z

2429 154 23

s

5 .33

12

I I I

•••

'

•

Before cleaning MAF sensor

•

~ ngine Speea

5460 rpm

n IRl! ,,; ~

~

en•or l

••• • •

.ri

898 m\I

J:)

ICMl

•

~

• •

•

(Return}

•

MAI"

Hz

t=::l.9

frequency

Mat t All

....

••• • •

• flow

1W.t>ll

al•

••• •• 1r

. . . . ..

0 CD After cleaning MAF senor

-..

WOT

••

1 Volt

•

"

5506

\

•• ••

18. 16

n1 Pulse Width

•• •• •

I

Frequency

;;;

8783.7

1!'iO:

8783.7

Hz

•

11" Semorv

.. . . ..

4.16 ..

-

2821.8 144 93

g/s

••• •

~

msec 2.84

•

144.93

17 19.68

•• • Mass Alf

747 916

mV

898

I

6 45

-

•• •• • ~ensor

103 69

43

rpm

t--.

28091

Redline RPM • • •

I~ ng1n e Speed

1 4 31

416

4.16

~ enscwv

~

7859 .9

••• •

•

22

msec 4 12

10.74

ntPul• e...?ldih

745

6.58 4.16

v

0.43

.

13

(Return>

Clean I Dirty Hot Wire

14

m'7 ~

~

Analog MAF Sensor Scope Testing (Return)

5

1:::::::::-1.::tru·

Known Good 94 mustang 5.0 ns ... 0.12 v 4.04 v ;:~~r:~s:

Known Good 96 altima 2.4 1. 49 Hz

Initial peak

4

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3

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z

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.

1

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.

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z

0

Initial peak was s lightly low, however there where no drivability problems on this engine 0

I

3

Mechanical Returnless

Pressure G.1uge

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Fuel Fi lrer

m~

Pressure G.1uge

Fuel Filter/Psi Regulator

lnjecrors

Injecrors

Fuel Pressure Regulator

Fud rump

rud Pump lult'I

Technically there is still a return , its just not attached to the fuel rail.

Fuel Tank

4

Electronic Return less ffivr ~ PCM

PressL1re G ASD and Fuel Pump Relavs will be • energized

•

Too only pt1rpose for 1his destgn

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