Holley Avenger EFI series User manual

AVENGER EFI
4 BBL MPFI SYSTEMS
SINGLE PLANE 4BBL SMALL BLOCK CHEVY MULTI-PORT EFI SYSTEMS
550-811 (Early/Late Models)
550-816 (Vortec Heads)
SINGLE PLANE 4BBL BIG BLOCK CHEVY MULTI-PORT EFI SYSTEMS
550-831 (Std Deck, 1000 CFM Rect. Port)
550-836 (Std Deck, 1000 CFM Oval Port)
HARDWARE AND FUEL SYSTEM
INSTALLATION MANUAL –199R10553
NOTE: These instructions must be read and fully understood before beginning installation. If this manual is not fully understood,
installation should not be attempted. Failure to follow these instructions, including the pictures may result in subsequent
system failure.

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TABLE OF CONTENTS
1.0 INTRODUCTION.....................................................................................................................................................................3
2.0 BEFORE YOU BEGIN.............................................................................................................................................................3
3.0 WARNINGS, NOTES, AND NOTICES ....................................................................................................................................3
4.0 SKILL LEVEL REQUIRED.......................................................................................................................................................4
5.0 ADDITIONAL ITEMS REQUIRED FOR INSTALLATION ........................................................................................................4
6.0 TOOLS REQUIRED FOR INSTALLATION.............................................................................................................................. 4
7.0 AVENGER EFI SYSTEM OPTIONS........................................................................................................................................4
8.0 PLANNING THE INSTALLATION............................................................................................................................................4
9.0 REMOVAL OF EXISTING FUEL SYSTEM..............................................................................................................................5
9.1 Preparing the Manifold for Installation..................................................................................................................................5
9.2 Installation of AVENGER EFI Manifold ................................................................................................................................5
9.3 Installing the distributor........................................................................................................................................................ 7
9.4 Vacuum Line Connections ...................................................................................................................................................7
10.0 SUPPLY AND RETURN FUEL SYSTEM INSTALLATION....................................................................................................7
10.1 Fuel Supply/Return System Description.............................................................................................................................7
10.2 Fuel Pressure Regulator ....................................................................................................................................................8
10.3 Fuel Pump Installation........................................................................................................................................................ 9
10.4 Fuel Line Mounting.............................................................................................................................................................9
10.5 Fuel Filters .........................................................................................................................................................................9
10.6 Return Line Installation .................................................................................................................................................... 10
10.7 Oxygen Sensor Installation ..............................................................................................................................................11
10.7.1 Oxygen Sensor Mounting Procedure.......................................................................................................................... 11
10.7.2 ECU Mounting........................................................................................................................................................... 12
11.0 WIRING ...............................................................................................................................................................................12
11.1 Important Wiring “Do’s and Don’ts” .................................................................................................................................. 12
12.0 WIRING HARNESS INSTALLATION................................................................................................................................... 12
12.1 Main Power/Battery Connection.......................................................................................................................................12
13.0 PRIMARY HARNESS INSTALLATION AND SENSORS CONNECTION............................................................................13
13.1 ECU Connectors.............................................................................................................................................................. 13
13.2 Harness Routing .............................................................................................................................................................. 13
13.3 Sensor Connections & Outputs........................................................................................................................................14
13.3.1 Throttle Position Sensor (TPS)..................................................................................................................................14
13.3.2 Manifold Air Pressure Sensor (MAP).........................................................................................................................14
13.3.3 Coolant Temperature Sensor (CTS)..........................................................................................................................14
13.3.4 Manifold Air Temperature Sensor (MAT)................................................................................................................... 14
13.3.6 Wide Band Oxygen Sensor (WB02) .......................................................................................................................... 14
13.3.7 Fuel Pressure (Fuel)..................................................................................................................................................15
13.3.8 Oil Pressure (Oil)....................................................................................................................................................... 15
13.3.9 CANbus –Handheld (CAN).......................................................................................................................................15
13.3.10 Knock Sensor (Knock)............................................................................................................................................. 15
13.3.11 Ignition (IGN) –........................................................................................................................................................16
14.0 PRIMARY OUTPUTS .......................................................................................................................................................... 16
14.1 Idle Air Control (IAC)........................................................................................................................................................16
14.2 Fuel Injector Outputs (INJ) and Fuel Injector Harness.....................................................................................................16
15.0 LOOSE WIRES.................................................................................................................................................................... 16
16.0 IGNITION/ENGINE SPEED INPUT..................................................................................................................................... 17
17.0 WIRING ...............................................................................................................................................................................18
18.0 ADDITIONAL OUTPUTS..................................................................................................................................................... 21
APPENDIX 1.0.............................................................................................................................................................................. 22
Pinout........................................................................................................................................................................................ 22

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1.0 INTRODUCTION
Holley has written this manual for the installation of the AVENGER EFI manifold and fuel system. Wiring harness and ECU
installation, sensor connections, startup, and tuning are contained on the disc supplied with AVENGER systems. Please read
all the WARNINGS, NOTES, and TIPS, as they contain valuable information that can save you time and money. Should you
need information or parts assistance, please contact our technical service department at 1-270-781-9741, Monday through
Friday, 8 a.m. to 5 p.m. CST. Please have the part number of the product you purchased when you call.
WARNING! The AVENGER EFI systems consist of a number of sophisticated components. Failure of any one
component does not constitute, nor does it justify, warranty of the complete system. Individual service
items are available for replacement of components. If assistance is required or if you need further
warranty clarification, you can call Holley Technical Service at the number shown above.
WARNING! To preserve warranty, these instructions must be read and followed thoroughly and completely before
and during installation. It is important that you become familiar with the parts and the installation of the
AVENGER EFI system before you begin. Failure to read and understand these instructions could result
in damage to AVENGER EFI components that are not covered by the warranty and could result in serious
personal injury and property damage.
WARNING! Use of leaded fuels will degrade the oxygen sensor and will result in incorrect exhaust gas oxygen
readings and improper fuel delivery. Failure to follow these directions does not constitute the right to a
warranty claim.
WARNING! Failure to follow all of the above will result in an improper installation, which may lead to personal injury,
including death, and/or property damage. Improper installation and/or misuse of this or any Holley
product will void all warrantees.
WARNING! Use of some RTV silicone sealers will destroy the oxygen sensor used with this product. Ensure the RTV
silicone sealant you use is compatible with oxygen sensor vehicles. This information should be found on
the RTV package.
2.0 BEFORE YOU BEGIN
Fuel injection systems have proven to increase engine performance by allowing the engine to operate to the best output it is
capable of producing. Make sure your engine is in good basic running order before installing the AVENGER EFI fuel injection
system. Anything that increases the power of your engine demands more from all the components and systems. If your engine
is in poor condition before you begin this installation, you won't get the results you want.
Fuel injection is more efficient, but also less forgiving than a carburetor. A properly tuned EFI system can disclose hidden
problems your carburetor may have concealed. Corroded terminals or a weak battery, alternator or ignition system will not
adversely affect your carburetor, but they will interfere with the precision functions of an EFI system.
The engine cooling system must have a working 160F to 210F thermostat. The intake manifold needs to be hot enough to
completely vaporize the injected fuel.
3.0 WARNINGS, NOTES, AND NOTICES
WARNING! For the safety and protection of you and others, the installation, adjustment, and repair must be performed
only by a trained mechanic having adequate fuel system experience. It is particularly important to
remember one of the very basic principles of safety: fuel vapors are heavier than air and tend to collect in
low places where an explosive fuel/air mixture may be ignited by any spark or flame resulting in property
damage, personal injury and/or death. Extreme caution must be exercised to prevent spillage and thus
eliminate the formation of such fuel vapors.
WARNING! These instructions are provided as a general guideline for installation. Each user must use his own
judgment to determine whether his own, or the engine's safety will be endangered by any procedure
selected. The user should consult factory engine manuals to ensure compliance with fastener torque and
other important specifications unique to each engine.
WARNING! This type of work MUST be performed in a well-ventilated area. Do not smoke or have an open flame
present near gasoline vapors or an explosion may result.

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4.0 SKILL LEVEL REQUIRED
Installation of the AVENGER EFI intake system and the ECU requires approximately the same level of skill and experience to
replace or service an induction system consisting of a carburetor and conventional intake manifold (as well as basic wiring skills
for the installations of the ECU).
Adequate skills for modifying the vehicle fuel supply are critical, and will vary widely, depending upon the selected components
and methods of fuel line plumbing. The most basic level will require the user to plumb a high-pressure supply fuel line and a
tank return fuel line to the fuel rails. The most complex level may require the user to modify the fuel tank, re-route or add fuel
lines, or mount various combinations of electrical and/or mechanical fuel pumps. Some fabrications may be required, depending
on applications, for throttle cable assemblies, throttle cable bracket and thermostat housings.
NOTICE: If you are not absolutely certain that you have the skills and experience required to perform these
procedures, we strongly recommend you have this system installed and tested by a technician with
specialized training in EFI and fuel systems service.
5.0 ADDITIONAL ITEMS REQUIRED FOR INSTALLATION
The following is a list of materials that are needed, depending on the application.
3/8" fuel hose (must meet SAE J30)
Parts to mount the throttle cable
3/8” steel fuel line (must meet SAE J526) RTV sealant (O2sensor compatible)
Various Electrical Connectors Selection of 1/2" and 3/8" pipe plugs
PTFE pipe sealing compound Heat Shrink
Mechanical fuel pump block off plate
0-50 psi fuel gauge or Holley 0-100 PSI pressure transducer (recommended)
6.0 TOOLS REQUIRED FOR INSTALLATION
The following is a list of materials that are needed, depending on the application.
Standard wrench set Small & Medium blade screwdriver Timing/Advance Light
#2 Phillips screwdriver Digital Volt meter Drill and assorted bit sizes
Hole saw (2”) Allen Wrench Set 10” adjustable wrench
Gasket Scraper Factory service manual
7.0 AVENGER EFI SYSTEM OPTIONS
AVENGER EFI systems offer several optional brackets and spacers designed to simplify installation in certain applications.
These parts can be ordered separately by contacting our technical service department at 1-270-781-9741.
8.0 PLANNING THE INSTALLATION
Before starting the installation of the AVENGER EFI system several things must be decided:
Mounting location of the fuel pump
Mounting location of the fuel filters
Routing of the fuel supply line from the tank, to the filter, to the pump
Routing of the high pressure fuel supply line from the pump to 10micron fuel filter to the fuel rails on top of the manifold
Routing of the fuel return line from the pressure regulator to the fuel tank
Mounting locations of the ECU
Proper throttle cable installation
Proper thermostat housing clearance

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9.0 REMOVAL OF EXISTING FUEL SYSTEM
1. Disconnect the ground side of the battery.
2. Drain the cooling system. Remove the cooling system hoses and thermostat housing.
3. Drain the fuel tank, then disconnect the fuel supply line or disconnect the fuel supply line and plug the hose.
4. Disconnect all throttle linkages.
5. Identify or number the ignition wires. Numbering the ignition wires will help in reconnecting them during MPI system
assembly. Remove the ignition wires from the coil and spark plugs.
6. Remove the ignition cables and distributor cap as one unit.
7. Note the position of the rotor and the distributor housing. Mark rotor position on the distributor and mark distributor housing
position on the engine block to ensure accurate re-assembly. After marking the position of the rotor and the distributor
remove the distributor. It is easiest if the rotor points directly towards the firewall.
8. Loosen all manifold bolts before removal. Remove the manifold bolts.
DANGER! FROM THIS POINT FORWARD, USE EXTRA CAUTION TO ENSURE NO GASKET MATERIAL OR OTHER
FOREIGN MATTER ENTERS OIL PASSAGES, HEAD PORTS, OR ANY OTHER LOCATION WHERE AN
OBSTRUCTION MIGHT CAUSE DAMAGE.
9. Remove the existing manifold. If required, remove valve covers.
10. Remove the mechanical fuel pump and push rod and install a mechanical fuel pump block-off plate.
9.1 Preparing the Manifold for Installation
1. Protect the lifter galley with clean shop rags. Close off the ports by stuffing them with clean shop rags.
WARNING! Failure to cover the intake opening with a clean towel could result in dirt or debris entering the engine.
Dirt or debris in the induction system can cause engine damage, which may require a complete engine
overhaul.
2. Using a gasket scraper, remove gasket material from heads and block. When all loose material is removed, carefully
remove the shop rags from the ports, ensuring that no material falls into passages. Using a shop vac, remove all debris
from the lifter gallery.
3. Inspect carefully. Use a flashlight to inspect the interior of all air, oil, and water passages.
4. Soak a clean shop rag with solvent, and clean all sealing surfaces. Surfaces must be completely clean to ensure a reliable
seal between the components and gaskets.
9.2 Installation of AVENGER EFI Manifold
WARNING! Use new gaskets. Be sure you are using the proper gasket for your engine, for aluminum manifolds, as
recommended by the manufacturer.
1. The manifold comes with the rails, fittings, and crossovers loosely installed in the proper locations. The crossover lines will
have to be removed in order to install the intake manifold bolts. The injectors, fittings, rails, and crossovers should be
assembled and tightened after the manifold is installed on the engine.
2. Install the manifold gaskets, carefully following the instructions provided by the gasket manufacturer.
3. Use O2sensor compatible RTV (again following manufacturer's instructions) around all water passages and for end seals
if end seal gaskets are not used.
4. Carefully position the manifold on the heads, so the bolt holes in the manifold are centered over bolt hoses in the heads.
5. Hand start all the bolts.

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6. Tighten down the manifold bolts in the proper sequence and torque as recommended in the engine manual.
NOTE: Consult your engine manual for proper fastener torque, bolt tightening pattern and other manifold installation
specifications.
7. Remove the fuel rails. Install the fuel injectors. Lubricate the fuel injector top and bottom O-rings. Do not use synthetic,
animal or vegetable oils. Use of an O-ring specific lubricant is recommended. Use motor oil if you do not have a good
O-ring lubricant. Be careful not to damage the O-rings.
WARNING! Damage of the O-ring can cause fuel leakage. A fuel leak may result in a fire or an explosion hazard, which
could cause serious injury or death.
8. Carefully install the injectors into the rails and then install the injectors and both rails into the manifold. Reinstall the four
1/4-20 x 1” Allen head screws that held the rails in place and tighten securely.
9. Make sure that the four end fittings in the fuel rails (they should already be installed but not tightened) are threaded in to an
adequate depth.
10. Reattach the front and rear crossover tubes. Tighten completely hand tight.
11. After the crossover tubes are installed, tighten the nut on the four fittings that go into the fuel rails. Tighten securely.
12. Securely tighten the front and rear crossover tubes with a wrench.
13. The regulator should already be installed. Make sure that the two Allen head screws securing it to the fuel rail are tight.
Also check that the regulator fitting it tight and is pointed in the desired direction. Do not overtighten the fitting in the
regulator or it will leak.
Figure 1
14. Next install the throttle body. The throttle body is in a separate box in the kit, which contains the gaskets needed. First
install the gasket that matches the manifold base. Next install the steel plate included with the throttle body. Next install the
gasket that matches the plate. Install the throttle body with the 4 5/16-18 bolts and washers included. The MAP sensor
bracket is attached by the rear, passenger side bolt. Install the MAP sensor first with the two 10-32 x 1” screws and #10
washers. See Figure 1. The throttle cable bracket is attached with the rear driver’s side bolt. The bracket in the kit works
with most throttle cables and transmission cables.
15. Tighten throttle body bolts securely.
16. Check the front fuel rail cross over tubing. This line may shift during the foregoing operations, so ensure that the line
cannot interfere against the manifold runner or the water cross-over. Adjust if necessary.

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17. Install new thermostat housing gasket, replace thermostat housing, replace the coolant hoses and refill the cooling system.
18. Attach the throttle cable.
9.3 Installing the distributor
Follow the manufacturer’s recommended procedures for the following steps:
1. Drop in the distributor making sure that the rotor aligns with marks made during disassembly. If you are installing a new
distributor, you will have to make sure it is properly timed.
2. Align distributor housing with marks made on block during disassembly.
3. Ensure the distributor seats properly against
manifold.
4. Ensure the distributor shaft is fully engaged in the
oil pump.
5. Bolt the distributor hold down clamp to the
manifold.
6. Replace the distributor cap.
7. Replace the spark plug wires and check that they
are in the correct firing order.
9.4 Vacuum Line Connections
1. Install vacuum hoses to the appropriate port on
the throttle body (See Fig 2). Use the diagrams
made during removal of the existing fuel system
to locate the correct port. The vacuum ports of
the throttle body are labeled in the figure to the
right.
Figure 2
10.0 SUPPLY AND RETURN FUEL SYSTEM INSTALLATION
The MPI fuel system is a fuel metering system based on a time/pressure principle. The longer the injector is open the lager the
amount of fuel per fueling event is delivered to the engine. Fuel pressure also plays a direct role in how much fuel is delivered
to the engine. The higher the fuel pressure the more fuel is delivered during the fueling event. It is crucial for the proper
operation of a high performance MPI system that the fuel system be installed and sized correctly. Unlike a carburetor where
low-pressure fuel is delivered at an "as need" rate, the MPI supply system must continuously deliver fuel at the correct high
pressure in a volume greater than the engine requires at maximum load. The excess fuel the injectors do not use is returned to
the fuel tank. At idle, most of the fuel is returned to the tank, but a wide-open throttle (WOT) under full load nearly all of the fuel
is used by the engine and only a small amount is returned to the fuel tank. An improperly installed or sized MPI supply fuel
system may deliver enough fuel at low engine speeds but will starve the engine at WOT.
10.1 Fuel Supply/Return System Description
The high pressure fuel supply system consists of the following sub-systems: the fuel pick-up, a coarse fuel pump pre-filter, the
high pressure electric fuel pump, the 10 micron high pressure fuel filter and a 3/8” ID fuel line (See Fig.3). The fuel pick-up
delivers fuel from the tank to the inlet of the fuel pump filter. From the filter the fuel line supplies filtered fuel to the high pressure
pump inlet. The high pressure electric fuel pump delivers pressurized fuel to the 10micron fuel filter, which in turn delivers
filtered pressurized fuel to the fuel rails, fuel injectors, and the fuel pressure regulator. The function of the regulator is to
maintain a constant fuel pressure of 300kPa (43.5psi). The outlet of the regulator returns the excess fuel back to the fuel tank.
The following section covers the installation of an in-line pump. Holley PN 12-920 is included with this kit. Holley includes both
a pre and post filter with the AVENGER MPFI system. Both of these filters are designed to connect to an EFI pressure rated
rubber hose. They are not designed for “AN” style plumbing. If AN lines and fittings are used, obtain AN style filters. AN fittings
are available for the 12-920 pump. PN 26-160 contains two -6 pump fittings and PN 26-180 contains two -8 pump fittings.

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All of the fittings on the intake manifold are -6 AN fittings (except the internal threads of the fuel pressure regulator which have a
“Saginaw” thread. There are barbed adapters included that can be installed on the inlet and return fittings that can be used to
connect to high pressure rated rubber fuel hose.
10.2 Fuel Pressure Regulator
The function of the fuel pressure regulator is to provide constant fuel pressure for the fuel injectors. Constant fuel pressure is
essential to ensure an accurate fuel metering process. The fuel pressure regulator of the system is set to 300kPa (43.5 psi) to
match the flow characteristics of the fuel injectors. The pressure regulator is reference to the manifold pressure to ensure the
required differential pressure for the metering event. Thus at high manifold vacuum (i.e. idle) the fuel pressure gage will read a
fuel pressure that is slightly lower than 300kPa (43.5 psi) because the gage is referenced to atmospheric conditions and not to
the intake conditions. The pressure reading at idle will vary with the application as manifold vacuum changes from engine to
engine and from application to application.
The regulator included is adjustable. To adjust the fuel pressure: remove the vacuum reference line and turn the screw
clockwise to increase the pressure (or counter-clockwise to decrease the fuel). Fuel pressure can be lowered slightly or raised
to reduce or increase the amount of fuel the injectors add. This is usually only done when the injectors used need to have their
flow decreased at idle or increased at wide-open throttle. Make sure you input the actual pressure into the software in the
“Engine Parameters” section.
NOTE: Increasing the fuel pressure by 10 PSI (43.5 to 53.5) results in a fuel metering increase of about 10%. The same is
true when reducing the fuel pressure.
NOTE: If the fuel pressure is changed, make sure to change the “Actual System Pressure” in the Engine Parameters setup in
the software.
DANGER!INCREASING THE FUEL PRESSURE BEYOND THE OPERATING POINT OF THE FUEL PUMP MAY RESULT
IN POOR ENGINE PERFORMANCE AND COULD CAUSE FUEL LEAKAGE ON COMPONENTS THAT ARE
NOT RATED FOR EXCESSIVE HIGH FUEL PRESSURES. LEAKAGE OR BURSTING OF FUEL SYSTEM
COMPONENTS MAY RESULT IN A FIRE OR EXPLOSION HAZARD, WHICH COULD CAUSE SERIOUS
INJURY OR DEATH.
Figure 3

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10.3 Fuel Pump Installation
DANGER! NEVER GET UNDER A VEHICLE SUPPORTED ONLY BY A JACK. SERIOUS INJURY OR DEATH CAN
RESULT FROM VEHICLES FALLING OFF OF JACKS. BEFORE WORKING UNDERNEATH A VEHICLE,
SUPPORT SOLIDLY WITH JACK STANDS.
Most in-line high-pressure fuel pumps have limited suction characteristics, so they need to be mounted as low as possible and
should be mounted no higher than the bottom of the fuel tank. The pump can be mounted either horizontally or vertically. When
mounting the fuel pump, check to make sure that you have the fuel flow in the correct direction. This may sound like a foolish
reminder, but it is a common installation error. To prevent damage to the fuel pump before the fuel system is filled with fuel,
drip/spray some light lubricant (such as 10w motor oil) into the inlet side of the pump.
1. Make sure fuel tank is properly vented.
2. Mount the electric fuel pump as close to the fuel tank outlet as possible. Mounting the fuel pump in this manner will insure
that the pump will prime easily and purge fuel vapors in the fuel lines to insure faster starts.
DANGER! TAKE PRECAUTIONS TO ENSURE THAT ALL FUEL LINE ROUTINGS ARE AWAY FROM HEAT SOURCES,
SUCH AS THE ENGINE, CATALITIC CONVERTER OR EXHAUST PIPES. A FIRE OR EXPLOSION HAZARD
COULD CAUSE SERIOUS INJURY OR DEATH.
DANGER! ENSURE THAT THE FUEL PUMP MOUNTING LOCATION WILL NOT INTERFERE WITH ANY UNDER THE
VEHICLE COMPONENTS, ESPECIALLY AT THE EXTREME LIMITS OF THE SUSPENSION TRAVEL. A FIRE
OR EXPLOSION HAZARD COULD CAUSE SERIOUS INJURY OR DEATH.
3. Connect the pump to the tank using 3/8” I.D. fuel hose. Connect the outlet of the pump to the steel line which runs to the
front of the vehicle with 3/8” I.D. fuel hose, depending on the diameter of the steel fuel line. All fuel hose used must meet
SAE J30 performance standards.
10.4 Fuel Line Mounting
DANGER! FAILURE TO USE A FUEL HOSE THAT MEETS SAE J30 STANDARDS COULD RESULT IN FUEL LEAKS. A
FUEL LEAK MAY RESULT IN A FIRE OR EXPLOSION HAZARD, WHICH COULD CAUSE SERIOUS INJURY
OR DEATH.
1. If using existing fuel lines, inspect and replace any hose, clamps, or fuel line showing any sign of aging or does not meet
SAE J30 fuel hose specifications. If you are not using existing fuel lines, you will need a fuel line routed to and from the
engine compartment and fuel rails. Use a 3/8” steel fuel line available at any auto parts store. All steel fuel line must meet
SAE J526 standards. Any time a rubber hose is connected to a steel fuel line, the steel fuel line must have a “barb” or
“nipple” on it to properly retain the hose (along with hose clamps). Either use the proper tool to put a “nipple” on the end of
the tube (similar to the ends of the fuel filters), or use a compression fitting and a barded fitting adapter that is the proper
size for the lines used. Clamping a rubber hose to a steel line that has the end squarely cut off does not ensure a safe
connection.
DANGER! FAILURE TO USE STEEL FUEL LINE THAT MEETS SAE J526 STANDARDS COULD RESULT IN FUEL
LEAKS. A FUEL LEAK MAY RESULT IN A FIRE OR EXPLOSION HAZARD, WHICH COULD CAUSE SERIOUS
INJURY OR DEATH.
DANGER! TAKE PRECAUTIONS TO ENSURE THAT ALL FUEL LINE ROUTINGS ARE AWAY FROM HEAT SOURCES,
SUCH AS THE ENGINE, CATALYTIC CONVERTER, OR EXHAUST PIPES. A FIRE OR EXPLOSION HAZARD
COULD CAUSE SERIOUS INJURY OR DEATH.
DANGER! RIGID FUEL LINE TUBING SHOULD BE USED FOR UNDER VEHICLE RUNS, SUCH AS ALONG VEHICLE
FRAME RAILS OR UNDER FLOOR PANS. FAILURE TO DO SO IS A POTENTIAL FIRE OR EXPLOSION
HAZARD, WHICH COULD CAUSE SERIOUS INJURY OR DEATH.
2. Anchor all fuel lines securely to solid chassis members at 1 ½ foot intervals using rubber coated steel clamps. Use of only
approved steel fuel line tubing will afford maximum fuel line protection against road hazards, gravel bombardment and
premature wearing due to flexing, temperature extremes, road salt, weather, etc.
10.5 Fuel Filters
WARNING! It is very important the fuel filters have the proper flow capacity, burst pressure rating and filter size. The
flow capacity of the filters must at least 60 gallons per hour (gph), and the filter size must be no bigger
than 10 microns for the high fuel pressure filter and not bigger than 75 microns for the fuel pump inlet
filter. The high-pressure fuel filter should be rated for at least for 150 psi burst pressure.

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DANGER! FAILURE TO USE HIGH PRESSURE FUEL FILTER LINE RATED FOR A MINIMUM OF 100 PSI BURST
PRESSURE COULD RESULT IN FUEL LEAKS OR BURSTING OF THE FUEL FILTER. A FUEL LEAK MAY
RESULT IN A FIRE OR EXPLOSION HAZARD, WHICH COULD CAUSE SERIOUS INJURY OR DEATH.
The fuel filter supplied by Holley meets or exceeds the above specifications. Most filters for carburetor systems do not.
The fuel pump inlet filter (marked WIX 33033) must be plumbed between the fuel tank and the fuel pump. It should be mounted
as close to the fuel tank as possible and should be mounted no higher than the top of the fuel tank. The high-pressure fuel filter
should be plumbed between the fuel pump and the fuel rail. It should be mounted as close to the fuel rail as possible but should
not be mounted above the fuel rail level.
Be careful to ensure the suction part of the fuel system contains no air leaks. Air leaks are caused by holes and/or crevices so
small that they will not leak fuel. Just because fuel is not leaking out does not mean air is not leaking in. Common causes of air
leaks are not using thread sealing compound on fittings and cracks or holes in fuel lines. Air leaks could potentially cause fuel
pump failure and or inadequate fuel supply to the fuel rails.
10.6 Return Line Installation
DANGER! DO NOT USE THE VAPOR CANISTER LINES AS A FUEL RETURN LINE. POSSIBLE FUEL LEAKS MAY
CREATE A FIRE OR EXPLOSION HAZARD, CAUSING SERIOUS INJURY OR DEATH.
WARNING! Use only approved steel fuel line. The return fuel line should enter the fuel tank at the “fuel level sending
unit flange” or at the “filler neck”. The connection should be made below the flapper valve of the filler
neck. The filler neck or sending unit must be removed from the tank to perform this operation.
DANGER! PROPER INSTALLATION OF THE FUEL RETURN LINE MAY REQUIRE THE COMPLETE REMOVAL OF THE
FUEL TANK. THIS WORK SHOULD BE DONE BY A FUEL TANK SPECIALIST, WHO REGULARLY DOES
THIS WORK AND IS FAMILIAR WITH SAFETY REGULATIONS AND PRECAUTIONS NECESSARY TO DO
THIS WORK. IF A PERSON ATTEMPTS THIS WORK
WHO IS NOT FAMILIAR WITH THE SAFETY
REGULATIONS AND PRECAUTIONS, AN
EXPLOSION HAZARD MAY RESULT CAUSING
SERIOUS INJURY OR DEATH.
The fuel return line from the fuel pressure regulator must go back to
the fuel tank and enter the fuel tank with a fitting that has an internal
diameter of at least 3/8".
The internal thread on the fuel pressure regulator is a “Saginaw”
style thread and is internally sealed with an O-ring. This fitting
should not be over-tightened in the regulator or it will leak.
Returning fuel should be routed back to the tank away from the fuel
tank pick-up tube. This will allow air bubbles from the returned fuel
to dissipate before they are drawn into the pick-up tube.
There are several options including the following that meet the
above criteria for returning the fuel to the fuel tank.
Figure 4
Use a fitting already in the fuel tank
Use the vent fitting. Be very careful not to block the fuel vapor from escaping the tank.
Route the return line into the filler neck. This can be done by cutting the filler neck, Inserting a welded "T" fitting, and
securing the neck with multiple clamps.
Drill and weld a new fitting into the tank
NOTICE: For best performance of your fuel supply system an in tank pump is recommended. Such an installation can
be achieved by either buying a late model fuel tank or have your tank modified by professional companies
that install an in-tank pump with the required swirl pods and baffles.
DANGER! MODIFICATIONS TO FUEL TANKS SHOULD BE DONE BYFUEL TANK SPECIALISTS, WHO REGULARLY DO
THIS WORK AND ARE FAMILIAR WITH THE SAFETY REGULATIONS AND PRECAUTIONS NECESSARY. IF
A PERSON ATTEMPTS THIS WORK WHO IS NOT FAMILIAR WITH THE SAFETY REGULATIONS AND
PRECAUTIONS, AN EXPLOSION MAY RESULT CAUSING SERIOUS INJURY OR DEATH.