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32 Posts
Discussion Starter · #1 ·
I've a 302 wit TFS Heads and Stage 1 Cam, want to convert from Carb to EFI, plan ist to by a Cobra Intake and simple wiringharness, which throttle body i should take and which injectors size, is the the a9p computer the right one, and which inline fuelpump i should take, perhaps i will go later to supercharged.

and greatings from germany

3,408 Posts
I'd use a Trick Flow street intake over the Cobra, but either will work. A cheap alternative is the Professional Products line of intake manifolds, which are basically Chineese clones of the Edelbrock Performer intakes.

65 or 70mm throttle body is plenty. Again either will work. I like Accufab.

24lb injectors with matching mass air meter for naturally aspirated.

19lb might also be enough actually.

Go with 30's and matching MAF if supercharger in the future. Using 42's is probably possible if you eliminate the FMU from the system but you may need dyno tuning to get it to run right. Not sure on that one.

190 or 255lph pump - go larger if supercharger in your future.

You will also need an EFI distributor with the TFI module on it. Make sure it has a steel gear. A stock Mustang distributor would work fine.

You will need the ACT sensor for the intake, a TPS sensor on the throttle body, a coolant temp sensor in the intake, a BAP sensor, and of course the MAF sensor in the MAF meter mentioned above. You will also need O2 sensors ( a pair ) and bungs in the exhuast system, preferably as close to the exhaust ports as possible.

Let me see...you'll need an IAB valve on the throttle body and either an EGR block off plate or an EGR valve as well. I would run the valve and put the sensor on it, and attach it to the harness. The EEC likes having this hooked up unless you custom program a chip.

Man.....that's about all I can think of right now.

Senior Charter Member
3,086 Posts
A9L is the correct EEC for a manual. The A9P is for an automatic, but will usually work OK with a manual.

To really get 42s running right you will need some tuning. They tend to overfuel at startup and during warmup. They can dump a lot of fuel, sometimes the computer just can't trim them up.

However if you are serious about a supercharger the 42s are a good investment.

One comment on the 255 pump, I just installed one and my fuel pressure is too high. My pressure is close, but does not behave properly at idle (sits at 40 and won't move). I have torn out the 1/4" return and installing a 3/8" return. Long term the high fuel pressure at low loads is a tuning problem, so I am correcting now, before tuning.

FFCobra Captain
11,720 Posts
I've read here that the A9P is better than the A9L. I don't remember the exact reason, but I think there's something different in the programming that will give you more power.

FFCobra Fanatic
7,022 Posts
JR I had 30#injectors with the matching 75 MM MAF,TFS stage 1 cam,and a 155 LPH fuel pump. It worked great. It did run a little rich. It needed a tune.

I am upgrading to a Vortech S/C 8-10 pounds of boost. 30's and 155 LPH pump would not have ben enough. If you have no plans on S/C this set up is fine.


FFCobra Master Craftsman
8,694 Posts
I thought one computer was for automatic and one was for 5 speed? I can't remember which was which - A9L or A9P

32 Posts
Discussion Starter · #9 ·
Hello Wulf, as you mentioned, I should place the O2 Sensors close to the exhaust ports, is it posible to install them in one off the header tubes befor it goes in to the collector, because i've got 4 in 4 sidepipes an i dont want the sensors to be seen in the sidepipe at the outside wheer the collector is.

Junior Charter Member
815 Posts
From the Ford Racing Catalog, page 114-116:

• Always disconnect the battery before doing any wiring!
• The single leading cause of most electrical problems is due to poorly grounded circuits.
The ground for the fuel injection system should connect DIRECTLY TO THE BATTERY at the negative post. Using the steel chassis or engine block as a ground will commonly create
excessive resistance causing the computer to function improperly.
EFI computers measure the voltage returned from the engine sensors to directly infl uence the parameters for proper air/fuel ratio and spark timing for the engine.
An example of how a high ground or connection resistance can have a serious effect on an engine is as follows. This particular case applies to a 2005 Mustang GT, but can easily be
extended to any electronically controlled Ford vehicle:
Very small changes in the MAF return voltage can have a huge and potentially catastrophic effect on the engine. Consider the case where a PCM is reading a MAF signal of 4.1 V (due to a
high ground or connection resistance) when it should really be reading 4.3 V. This equates to a difference in measured air mass of 13%. That is, the MAF will be telling the PCM that there is
13% less air entering the engine than there really is. Let’s say this happens at WOT, where air/fuel ratio is critical not only to performance, but also to engine durability. The result is that the
actual air/fuel ratio can go from a safe 12.5:1 to a potentially damaging 14.1:1…all from a 0.2 V change in the MAF return signal!
All PCM sensors, not just the MAF, are affected in a similar fashion, so it is absolutely imperative that all electrical connections are solid and that the grounds are reliable. The potential
penalty for a bad ground can range from strange drivability issues that are diffi cult to diagnose all the way to a damaged engine, as in the above example.
• Doing a resistance test should be done with the key OFF. Having voltage going through the system can return a false reading of excessive resistance. Additionally, it is possible to have
a ground that may test acceptable while the engine is cold, but can test poorly when the engine is hot. Heat increases resistance, so as a rule of thumb, you should run these tests on
a warm engine when possible.
To test for an adequate ground circuit in the fuel injection system for a 1986 to 1995 Mustang, use a Volt/Ohm meter to check the resistance of the following circuits.
– To verify a proper ground to the computer, check the resistance from Pin 40 and Pin 60 DIRECTLY to the negative side of the battery. Resistance should be no greater than 0.2 ohms.
– To verify a proper ground to the main computer harness, check the resistance from the Mass Air Flow (MAF) meter at pin ‘B’ DIRECTLY to the negative side of the battery.
Resistance should be no greater than 0.2 ohms.
– To verify a proper ground to the engine harness, check the resistance from the black wire at the Throttle Position Sensor (TPS) DIRECTLY to the negative side of the battery.
Resistance should be no greater than 0.3 ohms.
– While 0.2 ohms is desirable, the resistance can be considered ‘acceptable’ up to a reading as high as 0.5 ohms. If you have 0.51 ohms or more, this would be considered
completely unacceptable and is susceptible to drivability concerns.
• A weak ground connection can also cause the computer’s internal reference voltage regulator to function incorrectly. This can be checked at the Throttle Position Sensor (TPS) by
checking voltage between the Black ground wire and the Orange reference voltage wire. With the key ON, this voltage signal should be somewhere between 4.7 and 5.3 volts.
General Procedures and Settings
• The Powertrain Control Module (PCM), or ‘computer’, should be mounted inside the vehicle whenever possible, to protect the PCM and connections from water damage. The PCM
module should be mounted with the connector at the bottom to avoid trapping any water.
• When setting the voltage at the TPS, you should check the voltage between the Black and Green wires. This voltage should be somewhere between 0.96 and 0.98 volts. If the key
is on while the engine is off, set the voltage at 0.96 volts. If the engine is running, set it at 0.98 volts. The TPS can be set by loosening the mounting screws and slightly rotating the
sensor. If you are unable to achieve the proper setting, you may need to elongate the TPS mounting holes.
• If you ever need to lengthen any of the harness leads for your specifi c application, it is strongly advised that you lengthen only one wire at a time. This will help avoid mistakes.
• If you are using long tube headers, and need to lengthen the leads of the harness to reach the Heated Exhaust Gas Oxygen (HEGO or O2) sensors, NEVER lengthen the wires of the
O2 sensor itself. These wires are made up of a unique material and you will disrupt the signal coming from the O2 sensor even if they are soldered correctly! If you must alter the
length of the leads to the O2 sensor, always lengthen the wires on the wiring harness side of the O2 sensor. Many aftermarket companies offer O2 Sensor extensions that work quite
well and are an easy solution to this problem.
• When soldering two or more wires together, you should “tin” the bare ends to be soldered. This will prevent cold solder joints and make the process easier. “Crimp” style or “solderless”
connectors are not recommended. Over time, these have a tendency to loosen and permit corrosion. Additionally, these connectors can commonly allow short circuits to develop
within the connection. Many of these problems within the harness can be diffi cult to locate. Use weather-tight heat shrink over all soldered joints.
• If the factory coolant tubes are not used, the Engine Coolant Temp (ECT) sensor should be installed directly into the threaded boss in the intake manifold near the thermostat. This is a
coolant passage.
• The ACT sensor should not be moved from the factory location. Some after-market companies offer ACT relocation kits while making false claims of increased horsepower by reading
cooler air. While it is true that a cooler engine can make more power, this “trick” is not cooling the incoming air charge. It is merely reading the air temp from a different location. Since
the computer is no longer measuring air from the position that it was originally calibrated for, it will offer a false reading of the incoming air temperature to the computer, and can have a
negative effect on overall engine performance. On a forced induction engine the ACT sensor needs to be located after the power adder as additional heat is generated by the power adder.
• Protect the air fi lter element from turbulence created by the cooling fan. This is commonly referred to as “Fan Wash”. If you are using an open element air fi lter on the end of the mass
air meter, it is strongly advised that you use a shield to eliminate this problem.
• It’s best if the air fi lter gets cold air from in front of the radiator. If the fi lter is located in the engine compartment, as in many street rod applications, the inlet air temperature can be
up to 60 degrees hotter which can result in a 5% torque loss from the air density change. The PCM will also retard ignition timing for the hotter air which will result in an additional
5-10% torque loss.
• An improperly functioning charging system can cause engine running problems. Under-drive pulleys spin the accessories slower meaning that they consume less power from the
engine. This results in a greater net horsepower available at the fl ywheel. Normally this is not a problem, but some systems may not perform properly if you under-drive the alternator
excessively. If the alternator does not generate enough voltage to keep the system adequately charged, it can have an adverse effect on the fuel injection system PCM.
Fuel Pump Location
• This is a common problem that seems to be constantly ignored. Optimally, the fuel pump should be mounted IN THE TANK to eliminate cavitation. Cavitation is the presence of
vapor bubbles in the fuel. When a vacuum is introduced to a liquid, it lowers the boiling point of that liquid. Gasoline can actually begin to boil at around 72 - 76 °F. While this is not
a vigorous boil, this is where the fuel can actually “fl ash” to a vapor. Normally this is not a problem, as the vapors are contained in the fuel tank. Sometimes you may actually hear a
hissing sound when you remove the gas cap. This is due to the vapor being constrained. When liquid is under pressure, this will RAISE its boiling point, minimizing its ability to fl ash to
vapor. It is quite common to notice a substantial reduction in fuel economy if you do not use a gas cap.
• If you are unable to mount the fuel pump in the tank and need to mount an external fuel pump, you should make certain that the fuel pump is gravity fed, meaning that the fuel
can fl ow freely to the pump even if the fuel pump is not running. In a fuel system, if the fuel pump has to ‘pull’ the fuel, this creates a vacuum in the fuel pump inlet allowing vapor
bubbles to develop. These vapor bubbles are then drawn into the fuel pump and enter the high pressure side of the fuel pump. These vapor bubbles do not go away, they are merely
compressed. They travel the entire length of the fuel system and are expelled through the fuel injector. When these vapor bubbles exit the injector, they are no longer under pressure,
and they can expand. This expansion displaces the liquid fuel that the engine is intended to use. This displacement causes the engine to receive less fuel and runs lean, causing
potential engine damage. This problem has a common characteristic of seeming to run just fi ne, until the weather gets warmer. Sometimes the problem may seem to only develop
when driving on certain surfaces. This is because heat can be refl ected off of the pavement more so than from a 4x4 trail.
• Regarding fuel fi lters: if you are using an external mounted fuel pump, you should run a very coarse fi lter on the inlet side of the fuel pump. A paper fi lter is NOT recommended on the
inlet of the fuel pump because it can cause a restriction in fuel fl ow which can create a vacuum in the fuel pump inlet.
• BOTTOM LINE: If the fuel pump is not gravity fed or mounted IN the tank, you are susceptible to drivability issues that are VERY diffi cult to diagnose.
• The inside diameter of the fuel ‘return line’ should be at least 75% of the size of the inside diameter of the ‘fuel pressure’ line.

Seemingly, one of the most commonly misunderstood aspects of Electronic Fuel Injection is how to properly size fuel injectors, fuel pumps and mass air
meters. The following information is intended to offer a brief tutorial as to how to properly size the most common fuel system components.
Fuel Injectors
First and foremost, adding larger fuel injectors will NOT create extra horsepower! The addition of a larger fuel injector should only be introduced when you
have exceeded the horsepower capacity of the existing fuel injectors, and larger injectors are needed to support more horsepower.
You can use the following information to properly determine what size injectors are needed for various applications. For this example, we will use a naturally
aspirated 5.0L V-8 engine making 300 HP. Keep in mind that this is FLYWHEEL HORSEPOWER!!!!
Engines actually require a certain rate of fuel generally referred to as “LB/HR” which is determined from their Brake Specifi c Fuel Consumption (BSFC). By
defi nition, ‘BSFC’ represents how much fuel is required (in lb) per hour per each brake (or fl ywheel) horsepower the engine makes. Most gasoline engines
generally operate on a .42 to .52 lb/hp-hr BSFC. High-performance engines (12.5:1 and higher) which tend to be extremely effi cient can sometimes have
a BSFC as low as .38 to .42. The average naturally aspirated street engine usually runs about a .5 BSFC. More clearly stated, this means that if you have
an engine that makes 300 horsepower, its fuel requirement in lb/hr can be fi gured as follows: HORSEPOWER x BSFC
EXAMPLE: A 300 HP engine running a BSFC of .5 requires what size fuel injector?
300 x 0.5 = 150 LB/HR total fuel requirement
Divide this by the number of injectors being used. Since this an 8-cylinder engine using 1 injector per cylinder,
fi gure injector size as follows:
150 LBS/HR / 8 injectors = 18.75 LB/HR per cylinder
So, technically, the engine only needs a 19 lb/hr fuel injector to support 300 HP, but this will require that the injector is at nearly a 100% duty cycle in order
to achieve this horsepower level. A duty cycle refers to how much time is available to supply fuel vs. how much time you actually need to use. When you have
used the entire allotted time window available, this is referred to as a 100% duty cycle. Note that Ford injectors are fl owed at 40 psi delta pressure across the
injector, so an injector rated at 19 lb/hr means it is capable of fl owing 19 lb of fuel per hour at 40 psi delta pressure.
There seems to be a misconception that running an injector at a duty cycle in excess of 80% has a tendency to be bad for the injector, that it can possibly
overheat the injector. Since the injector has fuel constantly passing through it, this actually has a cooling effect on the injector. You could actually run an
injector at 100% duty cycle indefi nitely with no adverse effects whatsoever on the injector.
The problem is if the weather gets cooler, or the barometric pressure increases, the air will be denser, and therefore, the engine will receive more air
than it normally would. Under these circumstances, the engine will also make more power than it normally would, and the 19 lb injectors may no longer
fl ow enough. This is why it is generally recommended to not exceed an 80% to 90% duty cycle on the fuel injector. This will allow some ‘cushion’
to compensate for variables such as weather. So to fi gure out what size fuel injector will result in a 90% duty cycle, divide the original result by 0.90:
18.75 LB/HR / 0.90 = 20.8333 or ~ 21 LB/HR requirement
Since the next popular injector size available is 24 LB/HR, this is the correct size injector that you should choose for this application.
This can also be fi gured the other way around, meaning how much horsepower can a set of fuel injectors support. The following guide is a general rule of
thumb for sizing fuel injectors on an 8-cylinder engine using a BSFC of .50. Centrifugal supercharged engines commonly have a .55 BSFC, and most positive
displacement (‘Roots’ and ‘Twin Screw’ style) supercharged engines can have a BSFC of .65 or higher!
EXAMPLE: [(Injector Size) x (# of Injectors) x (Duty Cycle)] / BSFC
Naturally Aspirated: (19lb x 8 x .9) / .50 = 273.6 or approx 275 HP @ 90% capacity
Centrifugal Supercharged: (19lb x 8 x .9) / .55 = 248.7 or approx 250 HP @ 90% capacity
Roots Supercharged: (19lb x 8 x .9) / .65 = 210.5 or approx 210 HP @ 90% capacity
19 LB/HR 275 HP @ 90% Duty Cycle 210 HP @ 90% Duty Cycle
24 LB/HR 350 HP @ 90% Duty Cycle 265 HP @ 90% Duty Cycle
30 LB/HR 425 HP @ 90% Duty Cycle 330 HP @ 90% Duty Cycle
36 LB/HR 520 HP @ 90% Duty Cycle 400 HP @ 90% Duty Cycle
42 LB/HR 600 HP @ 90% Duty Cycle 465 HP @ 90% Duty Cycle
50 LB/HR 720 HP @ 90% Duty Cycle 550 HP @ 90% Duty Cycle
Note: These fuel injectors are rated at 40 psi using a fuel with a specifi c gravity of .72 @ 65° F
Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specifi c gravity
of the fuel being used.
Most fuel pumps for electronic fuel injection are rated for fl ow at 12 volts @ 40 psi. Most vehicle charging systems operate anywhere from 13.2v to 14.4v.
The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly
conservative fuel fl ow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.
As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion
since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be
performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specifi c gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the fi nal output of the fuel pump by
0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.
To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”
Safe “Horsepower Capacity” @ 40 psi with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower
Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases,
the fl ow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows fl ow rate versus delivery pressure.
That is, a 255 liter per hour pump at 40 psi may only supply 200 liters per hour at 58 psi (40 psi plus 18 lbs of boost). Additionally, if you use
a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH
at the pump may only result in 225 LPH at the fuel rail.
Mass Air Meters
If the MAF meter is not large enough, it will become a restriction in the intake path and will limit the overall horsepower output that the engine is capable of.
The MAF meter’s calibration is equally important. If you are using a different fuel injector than the engine was originally equipped with, the computer has no
way of knowing this. By introducing a properly calibrated MAF meter matched to your injectors, the computer can be ‘tricked’ into thinking that the engine
is receiving less air. If properly calibrated, this will cause the computer to generate a smaller injector pulse width, allowing the larger injectors to function
properly throughout the entire RPM range. The potential down-side to this method is that on Ford electronics, the PCM schedules spark advance as a function
of (among other things) engine speed and engine load. Engine load is defi ned as the mass of air entering a given cylinder divided by the mass of air that can
fi t in the cylinder, and is calculated directly from the MAF signal. If the MAF sensor is “tricked” into thinking the engine is receiving less air, then load will be
artifi cially low. Since required spark advance typically decreases as load increases, this “tricked” MAF will result in additional spark advance being scheduled,
which can result in spark knock.
Be aware that the MAF meter houses the single most important sensor in a Ford fuel injection system! The engine’s air/fuel ratio and spark advance are
primarily determined by the computer from the input received by the MAF meter. This is why it is of the utmost importance that there are no vacuum leaks
present in a MAF-based EFI system.
There are several ways to “trick” the MAF meter. The fi rst method is to change the MAF meter’s voltage output by manipulating the electronics of the meter.
For EEC IV electronics, this can be an extremely accurate way to calibrate a meter, since the meter’s “curve” can be precisely targeted to refl ect the needs
of the new application. A second method is to manipulate the signal from the meter by mechanically changing the amount of air that is permitted to pass by
the fi lament of the MAF meter by installing a different size ‘sampling tube’ or restricting the fl ow through the tube with a screw. While this method can be
effective, and can work quite well at wide open throttle, it is frequently the source of idle and low-speed drivability concerns. Another source of idle and
low-speed drivability issues is using a meter that has far too much capacity for the application. For example, don’t use a meter good to 750 HP if you only
plan on making 200 HP. The low-fl ow resolution of the high horsepower meter will not be as good as a meter designed for a 200 HP application, and issues
can result that are impossible to tune around.
There is also a method of using a mass air meter that has not been calibrated at all. However, these meters will usually require the use of an aftermarket
“chip” or “fl ash” to work properly. Using an “off-the-shelf” or “mail order” computer chip is discouraged with these types of mass air meters. If you do choose
this type of meter, it is strongly advised that you have the overall combination tuned on a dyno while monitoring the air/fuel ratio. Provided this is performed
by a competent tuner, this is the best method and will result in the best part-throttle drivability and idle. Additionally, before tuning on a dyno, you should BE
ABSOLUTELY CERTAIN that the ground circuits for the EFI system are in pristine condition. Otherwise, you are merely tuning around a problem, and a tune
that works well one day, can be substantially different if the ground signal varies. You can actually have a tune that works properly when tuned ‘around’ a poor
ground, and it is then possible to make it perform poorly by simply correcting the ground signal! It can’t be overstated that prior to the vehicle being tuned in
any way, all vacuum leaks, electrical issues, etc., need to be resolved. Fixing them before you go to the dyno will always be cheaper than paying for dyno time
while you’re wrenching on your car.
As a general rule of thumb, the following mass air meters will support the corresponding horsepower:
MASS AIR METER Horsepower Level
55mm (Stock 88-93 Mustang) 275 HP
70mm (Stock 94-95 Mustang) 350 HP
80mm (Stock Ford) 425 HP
90mm (M-12579-54) 540 HP

32 Posts
Discussion Starter · #11 ·
O2 Sensor Location Question,
as Wulf you mentioned, I should place the O2 Sensors close to the exhaust ports, is it posible to install them in one off the header tubes befor it goes in to the collector, because i've got 4 in 4 sidepipes an i dont want the sensors to be seen in the sidepipe at the outside where the collector is.
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