EFI wiring help on 86 5.0 (pin 30 & 46)

Pin 30 is used to tell the computer that the engine is in "Start mode". Where it connects is a function of the 3 character code on a label on the end of the computer. Some computers connect pin 30 to the Start section of the ignition switch to power it only at Start.


Mass Air A9L computer manual transmission cars connect it to pin 46 at start. The A9L is the most common manual trans Mass Air computer. It is used in 89-93 manual trans 5.0 Mustangs.


Pin 46 does indeed dead end at the computer diagnostic connector, but not before it connects to the Baro sensor, and engine fuel injection harness where it connects to the TPS, EGR, ECT and ACT sensors.





Diagram courtesy of Tmoss & Stang&2birds


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

66bronco said:

I'm not sure if it matters but I have a 86' "Speed Density" 5.0 not a Mass Air with a VJ1 EEC. So does effect the notion of hooking pin 46 up to the "start" like for a A9L?

When looking at the Veryuseful's EEC diagram of the 86' Mustang it does not show pin 46 going anywhere to pin 30. Is the the Veryuseful's 86' diagram incorrect with regards to tying 30 & 46 at start or did Ford make a change with that when switching to Mass Air EFI systems?

Thanks for all your time and help! Jeff

Click to expand...

Follow the information in Veryuseful's 86' diagram and you will be good to go when using the 86 computer.

Mass Air computers use a different wiring scheme from the 86 speed density system.

If you do not already have the 86 speed density computer and harness I would recommend a Mass Air computer (A9L) and a MAF from a 94-95 Mustang.

Keep in mind, that PIN 46 and 30 also tie together on the clutch position switch and the NGS switch in a manual trans setup. If PIN 30 carries start voltage, you can "NOT" tie 30 and 46 together or you will fry the ECM.

Further more, PIN 30 is used so the computer identifies an "In Neutral" or "In Gear" State.

PIN 30 only carries start voltage in an Auto Trans setup. Manual Trans setups are wired differently, and PIN 30 does not see the start voltage. Which is one reason why PIN 30 and 46 are used together in a Manual setup.

66bronco said:

Just so, I understand you right.

If I was running an auto trans I would have to take pin 30 to the "start" on the ignition switch and leave pin 46 un-tied to pin 30?

But if I would run a manual trans pin can't have "start" voltage but should have 30 and 46 tied together when the clutch switch is closed or in other words clutch pedal is pushed to the floor?

Sorry for my lack of understanding on all of this! So I do appreciate everyone help!!!
Jeff

Click to expand...

On Auto Trans setups, the start voltage sent to the small terminal on the starter relay is also whats sent to PIN 30. Which is hot in start of course, but shows as a ground when not in start. The ground is applied and broken by the NDS in the Auto setup. So yes, PIN 30 to start voltage.

Manual Trans setups, dont use a start voltage, and typically PIN 30 is at 5v when not in Neutral. Clutch Switch and NGS switch control the ground. They are wired in a parallel circuit. So you can have the trans in gear, but clutch down and the ECM gets a ground signal to show the car its "In Neutral". Or Trans in Neutral, and Clutch up gives the same ground signal.

Look at the second diagram JR posted. Top left corner shows the wiring differences between the Auto and Manual setups

So Yes to everything you said, I just thought I would explain it out for you. Id rather have an explanation rather than just a "Yes" or "No".

66bronco said:

As I'm finding out there is two schools of thought with these swaps.

First... simply tie 30 and 46 together.

Second... take 30 to ground and just leave 46 alone.

Honestly I have no idea which if all would be the best thing to do. I know there quite a few guys early Mustang and Bronco guys who have done these swaps that are working great. Also it seems to be a difference between the early EFI like 86-87's to 88 on up with regards to the pin 30 to 46. True or false? So what do you think my best option is with my 30 and 46?

Thanks again for the help and sorry for all the questions. Jeff

Click to expand...

I believe I have seen the difference you speak of on the 86-87 HO harness, and this will pertain to you more than likely. PIN 30 also travels through the 02 harness. And the manual and auto setups are wired differently. They both have a looped wire 02 harness on the later 88 and newer stangs that I have seen. This looped wire location is what determines how the signal is sent. Either start voltage sent to the ECM PIN 30 or no start voltage sent to PIN 30. Ive seen, and have a 87 02 harness, and it doesnt have that loop, So im going to assume, that the 86-87 setups didnt use a Neutral Sensing strategy like the later models do. Someone correct me if Im wrong about that.

So my first advice to you is to determine wether or not you have start voltage going to PIN 30 while cranking the engine. If you dont, you can do either tie PIN 30 and 46 together, or just ground PIN 30. Both give the same results. PIN 46 is a ground source from the ECM.

Fuel Pump Troubleshooting for 86-90 Mustangs

Revised 30Aug-2008 to update fuel pump wiring diagram

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 5-20 seconds and shut off. To trick the fuel pump into running,
find the ECC test connector and jump the connector in the upper RH corner to
ground.






If the fuse links are OK, you will have power to the pump. Check fuel pressure –
remove the cap from the Schrader valve behind the alternator and depress the
core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be
used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch
cars hide it under the plastic trim covering the driver's side taillight. Use the
voltmeter or test light to make sure you have power to both sides of the switch

B.) Fuel pump power relay – located under the driver’s seat in most stangs built
before 92. On 92 and later model cars it is located below the Mass Air Flow meter.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect
for fuel escaping while pump is running.

The electrical circuit for the fuel pump has two paths, a control path and a power
path.

The control path consists of the inertia switch, the computer, and the fuel pump
relay coil. It turns the fuel pump relay on or off under computer control. The
switched power (red wire) from the ECC relay goes to the inertia switch
(red/black wire) then from the inertia switch to the relay coil and then from the
relay coil to the computer (tan/ Lt green wire). The computer provides the ground
path to complete the circuit. This ground causes the relay coil to energize and
close the contacts for the power path. Keep in mind that you can have voltage
to all the right places, but the computer must provide a ground. If there is no
ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like
fuses, except they are pieces of wire and are made right into the wiring harness.
The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump
relay contacts. When the contacts close because the relay energizes, the power
flows through the contacts to the fuel pump (light pink/black wire). Notice that
pin 19 on the computer is the monitor to make sure the pump has power.
The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays
or injectors, but provides the ground necessary to complete the circuit. That
means one side of the circuit will always be hot, and the other side will go to
ground or below 1 volt as the computer switches on that circuit.


Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, bad ignition switch or ignition
switch wiring or connections. There is a mystery connector somewhere under the
driver’s side kick panel, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously
described. Look for 12 volts at the Light Pink/Black wire (relay controlled power
for the fuel pump). No voltage there means that the relay has failed, or there is a
broken wire in the relay control circuit.

Check the Red/black wire, it should have 12 volts. No 12 volts there, either the
inertia switch is open or has no power to it. Check both sides of the inertia
switch: there should be power on the Red wire and Red/Black wire. Power on the
Red wire and not on the Red/Black wire means the inertia switch is open.

Pump wiring: Anytime the ignition switch is in the Run position and the test
point is jumpered to ground, there should be at least 12 volts present on the
black/pink wire. With power off, check the pump ground: you should see less
than 1 ohm between the black wire and chassis ground.



The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds.
One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump
may be larger gauge wire that the fuel tank sender ground wire.

Make sure that the power is off the circuit before making any resistance checks. If the circuit
is powered up, your resistance measurements will be inaccurate.

You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what
a good reading is, short the two meter leads together and observe the reading. It should only be
slightly higher when you measure the black wire to ground resistance.

The Tan/Lt Green wire provides a ground path for the relay power. With the test
connector jumpered to ground, there should be less than .75 volts. Use a test
lamp with one side connected to battery power and the other side to the
Tan/Lt Green wire. The test light should glow brightly. No glow and you have a
broken wire or bad connection between the test connector and the relay. To test
the wiring from the computer, remove the passenger side kick panel and
disconnect the computer connector. It has a 10 MM bolt that holds it in place.
With the test lamp connected to power, jumper pin 22 to ground and the test
lamp should glow. No glow and the wiring between the computer and the fuel
pump relay is bad.

Computer: If you got this far and everything else checked out good, the computer is suspect.
Remove the test jumper from the ECC test connector located under the hood.
Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer
and everything else is connected. Turn the ignition switch to the Run position and observe
the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn
the key to the Run position. This can sometimes fool you into thinking the computer has died.
Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin.
With the ignition switch Off, jumper the computer into self test mode like you are going to dump
the codes. Turn the ignition switch to the Run position. The light will flicker when the computer
does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
Remove the test jumper from the ECC test connector located under the hood.

Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire
has shorted to ground. Remove the fuel pump relay from its socket. Then disconnect the computer and use
an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see
more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t
jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own
dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a
black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up
next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The
computers are very reliable and not prone to failure unless there has been
significant electrical trauma to the car. Things like lightning strikes and putting
the battery in backwards or connecting jumper cables backwards are about the
only thing that kills the computer.

See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

It's time to think...

Go back and read the tech note I posted on your fuel pump question. Everything you need to test and diagnose the problem is in there.

Since your present computer is toast, you might want to consider a Mass Air Computer and wiring harness, or Mass Air conversion harness.

MASS air conversion instructions from Mustang Mass Air Conversion « FREE
A9L (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, 5 Speed) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85

The whole thing is probably less than $300 using junkyard parts.

A9L computers are 5 speed only
A9P computers are automatic, but will work with a 5 speed.

The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, actually less work that swapping the wiring harness.
Conversion Harness kits & parts
Interactive Systems & Technologies Mass Air Home Page
Ford Fuel Injection » EFI Harness Pigtails

If the idea of moving & soldering wires scares you, here's a list of compatible Mass Air wiring harnesses.

Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (B/c of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)
Late 92 through 93 harnesses should be compatible (single dash connector, fuel pump relay under the hood)

Larger MAF to go with Mass Air conversion:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter Kurtz Kustomz Motorsports, Inc. KKM Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.
Try AutoZone and ask for 81413 - Spectre / 3 in. Aluminum Intake Mass Air Flow Sensor Adapter at $12.00. You may have to order it online.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Also see www.forfuelinjection.com for help with the harness parts RJM Injection Tech » Pigtails:, and connector pins, RJM Injection Tech » Ford Terminals: