Fuel Systems
A.S.T. Training
By: John Forro
Course Agenda
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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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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
Carburetion
• 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
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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
• 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
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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
• 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
• How does this system
differ?
• Fires only once per 4stroke cycle.
• Less prone to carbon
build up.
• Better fuel delivery.
• What are the added
main players?
• CID/CAM
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)
• 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
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How do these systems operate?
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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.
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Why do we use these systems?
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Less expensive.
Safer.
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How do we test this system?
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Same
Fuel Pump Testing
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Pressure testing
Key on
Cranking
Running
Non-regulated vs.
regulated.
Volume Test
• 1 pint in 30 seconds
unless a manufacturer
specification is
provided.
• Why is this test so
important?
Dead Head
• How do we achieve
this test?
• Squeeze/block return
line.
• Why is this test
important?
Fuel Pump Speed
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Why do this?
How do we do this?
1.
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.
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4.
Current Ramping Pumps
• Why do this?
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Looks into the future.
Finds tough driveability problems.
• What should we be
looking for?
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Uniformity.
Overall amperage.
Shorted/open commutator bar
segments.
Speed.
• What should this look
like?
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Uniform.
Injector Testing Procedures
Resistance
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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
• Why do this?
• How can this be done
at our level?
Injector Testing Procedures
Drop/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
• 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
• How do I obtain this
waveform?
• What does each
section represent?
• What are my
diagnostic clues?
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
• What is this pattern
trying to tell me?
• Where are my bulls
eye points?
Tool Showcase
Fuel System Tips and Tricks
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6.
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 Tricks
1. Shorted injectors will often steal voltage from
other cylinders when bank fired.
2. Check supply voltage to pump and injectors
while cranking and at idle.
3. Wrong PCV valves will give low IAC counts.
4. TBI base gaskets suck in.
5. Low IAC counts indicate lean condition, vacuum
leak and or low fuel pressure.
6. Carbon buildup on valves acts as a sponge.
“ cold start ups.”
Fuel System Tips and Tricks
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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 Tricks
1. Sloping up spark lines could mean a restricted
injector.
2. GM Dual TBI injectors will read about 2 ohms at
operating temperature.
3. Install a capacitor to cure the injector ringing.
4. TBI pressure regulators springs corrode and
fail.
5. Surging after TCC lockup on 3.8 GM can be
caused by dirty injectors.
6. Fuel pumps need at least ¼ tank of fuel to
operate efficiently.
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
Fuel System
Specifications
By: John Forro