My 1987 fox body 5.0 motor wont goes pass idle when trying to rev it

not a fox body

New Member
Apr 16, 2019
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I know this isnt the right place to ask about this so i have a 1982 mazda rx7 with a 1987 302 5.0 and 5 speed out of a fox body and it just rev up when you punch it or just try to rev it quickly but if you slowly rev it, it will rev but then try to stall sometimes and you have to give it gas before you start it or it takes a long time to start. ps this is my first time on this sit i just thought some 5.0 guys could maybe help me with my problem
 
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Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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How are you controlling the engine? Factory ECU? Or aftermarket? Did it ever run right? What ecu are you using and what wiring harness?
 

90sickfox

I didn't really have an issue with the stink...
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Mar 2, 2015
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Welcome to the forum....we get a little enjoyment from swapped vehicles here.

There are several things we need to know...like posted above.

Is there an aftermarket camshaft, heads, fuel system, or intake ?

How are you controlling it stock ECU, stick ECU with chip, stand alone ECU?

Will it do burnouts ?

Do you have pics ?

Pics of the car, beverages, or weird ones of yourself doing dumb ish accepted. Occasionally, animals are accepted too...as long as they haven't been seriously injured or maimed. Hair loss is OK.
 

not a fox body

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Apr 16, 2019
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Well is still fuel injected And has a stock ecu and stock harness out of the Fox body for the motor at least cause everything in the car works with gauges and stuff but I don’t have o2 sensor plug in so and I have herd that might be my problem and i don’t know if it ever ran right cause I just got it and the motor is stock but the fuel injectors look after market and it has a cold air intake and has steel braided lines going to the the electric fuel pump in the rear
5F33BCFD-AAF2-46B8-B86C-04C4F0B1D48B.jpeg
30C43015-2F4B-4168-AB7C-1DAEDB152003.jpeg
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
31,381
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Massachusetts
Sure that's an '87 motor? That's a 1986 Intake plate on it. I don't see a MAF, so it's still running speed density, but can you confirm the PCM number?

Are the test port plugs on it? Normall on the Mustang we'd suggest dumping codes.
 

not a fox body

New Member
Apr 16, 2019
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orangevale ca
Sure that's an '87 motor? That's a 1986 Intake plate on it. I don't see a MAF, so it's still running speed density, but can you confirm the PCM number?

Are the test port plugs on it? Normall on the Mustang we'd suggest dumping codes.
I
Sure that's an '87 motor? That's a 1986 Intake plate on it. I don't see a MAF, so it's still running speed density, but can you confirm the PCM number?

Are the test port plugs on it? Normall on the Mustang we'd suggest dumping codes.[/QUO
Sure that's an '87 motor? That's a 1986 Intake plate on it. I don't see a MAF, so it's still running speed density, but can you confirm the PCM number?

Are the test port plugs on it? Normall on the Mustang we'd suggest dumping codes.


I was told it was a 1987 motor and trans so I could tell you the details and I would love to try and pull codes but of course it doesn’t have a plug on it for me to do so, the pcm code is d6k16 I believe looking at it
image.jpg
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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VP1 ECU, which is the ECU out of a 1986 Mustang GT 5-spd. So more evidence it's a 1986 motor vs a 1987.

Look at the harness on the driver's side rear of the engine for a plug that looks like this. If you can find that you can run codes. I

5704x1__44958.1273431176.380.500.jpg
 

not a fox body

New Member
Apr 16, 2019
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orangevale ca
VP1 ECU, which is the ECU out of a 1986 Mustang GT 5-spd. So more evidence it's a 1986 motor vs a 1987.

Look at the harness on the driver's side rear of the engine for a plug that looks like this. If you can find that you can run codes. I

5704x1__44958.1273431176.380.500.jpg
I found it so how do I run codes cause see i have normal like obd2 plug ins but not this style
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
31,381
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Massachusetts
I found it so how do I run codes cause see i have normal like obd2 plug ins but not this style
Two ways

#1 is buy this code reader

View: https://www.amazon.com/INNOVA-3145-Ford-Digital-Reader/dp/B000EW0KHW/ref=asc_df_B000EW0KHW/?tag=bingshoppinga-20&linkCode=df0&hvadid=
{creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4583795260709503&psc=1

#2 is jumper wire and a test light bulb

https://foxstang.com/reading-mustang-trouble-codes-eec/
 

not a fox body

New Member
Apr 16, 2019
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0
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23
orangevale ca
Two ways

#1 is buy this code reader

View: https://www.amazon.com/INNOVA-3145-Ford-Digital-Reader/dp/B000EW0KHW/ref=asc_df_B000EW0KHW/?tag=bingshoppinga-20&linkCode=df0&hvadid=
{creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4583795260709503&psc=1

#2 is jumper wire and a test light bulb

https://foxstang.com/reading-mustang-trouble-codes-eec/
Ok thanks so is there anything else you think you could identify from what I have told you so far or no
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
31,381
7,635
224
Massachusetts
Fuel pressure is what i'd check first, but usually hot start issues are sensor related. ECT or ACT. Next time it won't start, floor the pedal to the firewall. This will send the TPS to near 100% and signal the ecu to turn off the fuel injectors during cranking for flood clear. If it's starts, your engine is flooding out due to a bad ECT/ACT sensor. Pulling the codes will tell you which, but they are fairly cheap sensors to just replace both although I hate firing the parts cannon at a car without properly troubleshooting
 
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not a fox body

New Member
Apr 16, 2019
16
0
1
23
orangevale ca
Fuel pressure is what i'd check first, but usually hot start issues are sensor related. ECT or ACT. Next time it won't start, floor the pedal to the firewall. This will send the TPS to near 100% and signal the ecu to turn off the fuel injectors during cranking for flood clear. If it's starts, your engine is flooding out due to a bad ECT/ACT sensor. Pulling the codes will tell you which, but they are fairly cheap sensors to just replace both although I hate firing the parts cannon at a car without properly troubleshooting
That’s the thing is it will start just fine hot or cold I just need to give it gas before it will start
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Is there a schrader valve on the fuel line someplace to check fuel pressure? Efi systems need 32 psi running, is this a return style fuel system?
 

jrichker

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Well I found out that my fuel pump only puts out 4 to 7psi and I herd that I need 94 psi in general I guess I don’t know I will look more into it
Fuel Pump Troubleshooting for 87-90 Mustangs

Revised 1-Dec-2015 to add fuse links diagram.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 1-3 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper LH corner to ground.

Foxbody Diagnostic connector


Foxbody Diagnostic connector close up view


Turn the ignition switch on when you do this test.



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 Mustangs built before 92. See the diagram to help identify the fuel pump relay wiring colors. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
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.

88241.gif


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

Control 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.


Power Path
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.

Fuse links
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Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect. Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.

View: http://youtu.be/uaYdCRjDr4A


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.

All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified

Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the EEC (computer) power relay. To be sure look for good 12 volts on the red wire on any fuel injector.
Good 12 volts means the EEC relay is working. No 12 volts and the ECC wiring is at fault.
Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch. Check the Red/black wire on the inertia switch, 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. Push the button on the side of it to reset it, and then recheck. Good 12 volts on one side and not on the other means the inertia switch has failed.

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.

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.


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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. In extreme ghetto cases, the pump relay may have been bypassed. 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.


a9x-series-computer-connector-wire-side-view-gif.gif


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
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
13,620
4,291
193
polk county florida
Well I found out that my fuel pump only puts out 4 to 7psi and I herd that I need 94 psi in general I guess I don’t know I will look more into it
Oh the painful reality of the internet truths! 94psi? :confused:
i don't think so unless you have a jet pack strapped to the hatch!
more like 42+/- koeo and 32-34 koer. I'm not trying to run you off just because this is a miata, it is 'Ford Tough' now, I'd look into a in tank type pump around maybe 240 lph, I'm going to guess here that the system is a one way affair and does not have a return line, right.
How bout a shot of the car, engine pics too, see if we can poke fun, I mean, help you spot any other troublesome issues.