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Fuel Systems. A.S.T. Training By: John Forro. Course Agenda. Discuss the various types of fuel systems 1) Carbureted 2) TBI 3) MPI 4) SFI 5) SCFI 6) Return-less Discuss various fuel pump testing procedures 1) Pressure 2) Volume 3) Dead head 4) RPM 5) Amperage. Course Agenda.

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fuel systems

Fuel Systems

A.S.T. Training

By: John Forro

course agenda
Course Agenda
  • Discuss the various types of fuel systems
  • 1) Carbureted
  • 2) TBI
  • 3) MPI
  • 4) SFI
  • 5) SCFI
  • 6) Return-less
  • Discuss various fuel pump testing procedures
  • 1) Pressure
  • 2) Volume
  • 3) Dead head
  • 4) RPM
  • 5) Amperage
course agenda3
Course Agenda
  • Discuss various injector testing procedures
  • 1) Resistance
  • 2) Flow rate
  • 3) Drop/leakage
  • 4) Voltage waveforms
  • 5) Amperage waveforms
  • Tool showcase
  • Diagnostic Strategies Tips and Tricks
  • What were the big problems with these systems?
  • 1) Linkage wear
  • 2) Fuel atomization
  • 3) Poor fuel control
  • How did the PCM control fuel delivery?
  • 1) Mixture control device
  • 2) External vacuum control valve (Honda)
  • What were the players?
throttle body injection
Throttle Body Injection
  • Where are these injectors located?
  • Inside the throttle body.
  • How many are there?
  • Typically 1-2.
  • Are these systems high or low pressure?
  • Both
  • What improvements did this bring over Carburetion?
  • Better fuel control.
  • Lack of mechanical wear.
  • What did this system lack?
  • Fuel vaporization.
  • Exact fuel delivery to reduce emissions.
  • What system components are needed?
typical known good tbi pattern
Typical Known Good TBI Pattern
  • This is a typical peak and hold injector pattern.
  • Why do we use a peak and hold injector?
  • What does each section of this waveform represent?
  • What can I read into this pattern?
  • Where might I expect to see this pattern fail?
multi port fuel injection
Multi-Port Fuel Injection
  • How does this system differ from TBI?
  • More injectors, 1 per cylinder and sometimes a cold start injector.
  • Different injector resistance/composite makeup.
  • How many injector drivers are in the PCM?
  • Two
  • Are these systems high or low pressure?
  • Typically high pressure.
  • What do we gain when we use this type of injection system?
  • Better fuel atomization.
  • More prone to carbon build up.
  • What do we still lack?
  • Fuel control for emissions.
  • What system components are needed?
typical known good mpi pattern
Typical Known Good MPI Pattern
  • This is a known good Multi-Port injector. “Saturated Switch”
  • How does this pattern differ from the TBI pattern?
  • Why doesn’t this pattern produce the second spike?
  • What can I read into this pattern?
  • Where would I look for a problem with this pattern?
sequential injection
Sequential Injection
  • How does this system differ?
  • Fires only once per 4-stroke cycle.
  • Less prone to carbon build up.
  • Better fuel delivery.
  • What are the added main players?
known good pattern
Known Good Pattern
  • This is a typical known good sequential injector waveform.
  • What can be assumed by viewing this pattern?
  • What other diagnostic tips can be read into the pattern?
vortec cpi scpfi
Vortec (CPI/SCPFI)
  • How does this system operate?
  • What used these systems?
  • What goes wrong with these?
  • How does OBD II {SCPFI} systems differ?
  • What is the minimum fuel pressure and speed needed for this type of system to operate?
return less fuel systems
Return-less Fuel Systems
  • How do these systems operate?
  • There are three types of return-less systems, mech. Electrical and demand delivery.
  • Mechanical will simply use a bypass regulator to return fuel to the tank usually mounted by the fuel filter.
  • Electrical will incorporate the use of a sensing pressure regulator mounted to the fuel rail. This will enable the controller to modulate the pulse width of the pump speed to control fuel pressure based on inputs from its load and demand sensors.
  • The Demand Delivery System will follow the same principle with the exception that the demand pressure regulator be located downstream of the rail to maintain a constant fuel pressure.
  • Why do we use these systems?
  • Less expensive.
  • Safer.
  • How do we test this system?
  • Same
fuel pump testing
Fuel Pump Testing
  • Pressure testing
  • Key on
  • Cranking
  • Running
  • Non-regulated vs. regulated.
volume test
Volume Test
  • 1 pint in 30 seconds unless a manufacturer specification is provided.
  • Why is this test so important?
dead head
Dead Head
  • How do we achieve this test?
  • Squeeze/block return line.
  • Why is this test important?
fuel pump speed
Fuel Pump Speed
  • Why do this?
  • How do we do this?
  • Count how long it took for all the commutator bars/humps to be displayed on screen.
  • Multiply this by the current time base setting on the scope. Example if 8 humps took 6 divisions at 2 ms it would look like this 6x.002= .012
  • Then divide 1, for 1 second, by .012 or whatever your figure happened to be to arrive at a pump speed of 83.3 revolutions per second.
  • Finally multiply this figure by 60 seconds and we will arrive at our fuel pump speed in revolutions per minute.

Average speed should be about 6,000 RPM

current ramping pumps
Current Ramping Pumps
  • Why do this?
  • Looks into the future.
  • Finds tough driveability problems.
  • What should we be looking for?
  • Uniformity.
  • Overall amperage.
  • Shorted/open commutator bar segments.
  • Speed.
  • What should this look like?
  • Uniform.
injector testing procedures resistance
Injector Testing Procedures Resistance
  • How do we do this?
  • When do we do this?
  • Is this the best test?
  • Can we do this on all cars?
injector testing procedures flow rate
Injector Testing ProceduresFlow Rate
  • Why do this?
  • How can this be done at our level?
injector testing procedures drop leakage
Injector Testing ProceduresDrop/Leakage
  • What are the various ways to achieve these tests?
  • What are our diagnostic clues that these tests may need to be performed?
injector voltage waveforms tbi
Injector Voltage Waveforms TBI
  • How do I obtain this waveform?
  • What does each section of this waveform represent?
  • What are my diagnostic clues?
  • What about ringing?
injector voltage waveforms pfi sfi
Injector Voltage Waveforms PFI/SFI
  • How do I obtain this waveform?
  • What does each section represent?
  • What are my diagnostic clues?
injector amperage waveform tbi
Injector Amperage Waveform TBI
  • Why should I look at this type of pattern?
  • How do I obtain this pattern?
  • What must I know?
  • What is this pattern trying to tell me?
  • Where are my bulls eye points?
injector amperage testing pfi sfi
Injector Amperage Testing PFI/SFI
  • What is this pattern trying to tell me?
  • Where are my bulls eye points?
tool showcase
Tool Showcase

Injector tester



Fuel System Analyzer

fuel system tips and tricks
Fuel System Tips and Tricks
  • Replace Multec injectors with Bosch DRI.
  • Check the pump ground on all Vortecs
  • All injectors will restrict their final filter over time = Sell cleanings.
  • A good Multec will draw less then 1 amp, a bank of three will be less then 3 amps.
  • Be careful using a noid light, remember there is no load involved.
  • Load battery with AVR or vehicle loads to find marginally bad injectors. { use gas analyzer, ignition scope or listen to exhaust.}
fuel system tips and tricks27
Fuel System Tips and Tricks
  • Shorted injectors will often steal voltage from other cylinders when bank fired.
  • Check supply voltage to pump and injectors while cranking and at idle.
  • Wrong PCV valves will give low IAC counts.
  • TBI base gaskets suck in.
  • Low IAC counts indicate lean condition, vacuum leak and or low fuel pressure.
  • Carbon buildup on valves acts as a sponge. “ cold start ups.”
fuel system tips and tricks28
Fuel System Tips and Tricks
  • Ford TBI fuel pumps will have about 3 amps draw-PFI will have about 5 amps draw.
  • Carbon on throttle plates will cause High IAC counts. (less then 30)
  • If fuel filter is installed backwards, it will act like a restricted exhaust.
  • Use four gas wand inside spark plug holes to find leaking injectors.
  • Defective alternators will likely cause injectors to run rich.
  • Tempos and Topaz use an inlet filter screen on their throttle body systems. #E53Z-9F525-A
fuel system tips and tricks29
Fuel System Tips and Tricks
  • Sloping up spark lines could mean a restricted injector.
  • GM Dual TBI injectors will read about 2 ohms at operating temperature.
  • Install a capacitor to cure the injector ringing.
  • TBI pressure regulators springs corrode and fail.
  • Surging after TCC lockup on 3.8 GM can be caused by dirty injectors.
  • Fuel pumps need at least ¼ tank of fuel to operate efficiently.
thank you
Thank You

Be sure to use the supplied specifications manual for quick references.

Thank you all for coming tonight, and I hope to see you all again real soon!

John Forro