Using Jrichker's Fuel pump test. Do I really have two bad computers?

MadMatt5oh

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jrichker said:
All the fuse links live in a bundle up near the starter solenoid. You have to
unwarp the wiring harness to find them. I would recommend that you use a
voltmeter to check them out before unwarapping the harness.


Fuel Pump Troubleshooting for 87-90 Mustangs

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 lower 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). 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.


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

Diagram courtesy of Tmoss & Stang&2birds



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.

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.

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.

Ok, Im not able to get my 1988 to run with either the A9L or the AEM EMS. In both cases I will get just a 3 second prime up of 38 PSI at the shrader which immediately drops off to 15 PSI or so..

Here are the results from both the fuel pump test I did on both computers.....

Test Orange/light blue wire for 12volts Key off....... AEM 12 A9L 12v

Light pink/black wire for 12v, key on, jumper ran.....AEM 12 A9L 12

Red/Black wire for 12v, key on.............................AEM 12 A9L 12

Inertia switch for 12v on both Red/black and Red....AEM 12 both A9L 12 both

Tan/light green for volts, jumper ran, key on..........AEM .109 A9L .74

Tan/light green with test light on batt + , jumper ran,
key on...........................................................AEM lite on A9L lite on

Tan/light green connection at ECM pin #22 with test
light also on ground, key on, jumper ran................AEM lite on A9L lite on


I dont understand why my computers are both suddenly bad? Please Jrichker or someone knowledgeble.. please help me figure this out! Ive been struggling with this a whole week now. Ive learned alot but solved very little. I really am not excited about giving up on this and selling everything off. I have invested almost 12 grand and a large part of my last 3 years into this hobby.
 
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MadMatt5oh

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Jrichker,
I reread my thread. It almost seems if Im criticizing your help. That I can assure you - I'm not!!

I tried your diagram and step by step but have my doubts on how I understood and performed the tests. Perhaps I was supposed to leave the key on or?

I have barely slept in the past week due to this car.
 

HISSIN50

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Im not JRichker, nor am I sure what you did exactly. You mentioned that it primed, so that suggests the wiring and circuit are intact to some degree.

I use a DMM to test the ground pulse from the computer to the relay (tan/lt grn) - this is due to workin on newer stuff where a test light overloading a control circuit is possible (and a fear for me). I might try a different method of testing if one doesnt work for you. That said, I'm sure JRichker's method works - I just havent done it like that (he knows about 1000 times more than I do about electronics).

There is a ground strap in the computer that creates continuity for that tan/lt grn wire to provide the ground to the control side of the relay. I doubt you lost that strap, given what you posted.

Good luck and bump for JR.
 

MadMatt5oh

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I do have spark and fuel now... I think the reason why I felt it wasnt is due to the pip#56 being mistaken for #45. AEM's diagram really helped me **** things up! So, I started running all sorts of tests that were not needed!!!

It seems the 60s are hosing down the plugs in pretty short order... at least I hope this is the issue! I really hope to get it to fire up as well!
 

HISSIN50

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MadMatt5oh said:
It seems the 60s are hosing down the plugs in pretty short order.
I suppose those big squirters could do that. :p Were you seeing a lack of pressure or priming before? Even though the wrong pins were being probed, if there was an issue with no priming, no cranking, no injector pulsing, etc, an issue of some sort likely exists.

Good luck with it!
 

MadMatt5oh

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HISSIN50 said:
I suppose those big squirters could do that. :p Were you seeing a lack of pressure or priming before? Even though the wrong pins were being probed, if there was an issue with no priming, no cranking, no injector pulsing, etc, an issue of some sort likely exists.

Good luck with it!
:D Yeah, there still are issues. Even now if I have someone turn the key the prime at the shrader still drops from 40 to 20 or sometimes from 45 to 30. I think the FPR is bad.

The issue before was that the ECU wasnt getting the signal to fire the injectors due to the connection being mistaken and miswired for a MAP connection. That has been corrected now. It just requires some tuning. I had help today and we did have it running. Tuning will start once the turbo setup is installed with the wideband...
 

HISSIN50

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If you think it's a bad FPR, you can use fuel line crimpers to carefully crimp the return line just as soon as it's done priming. Note if pressure stays at what it was before. If it does and you release the clamping tool, if pressure drops right off, you seem to have found a bad FPR.

Good luck.
 

MadMatt5oh

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HISSIN50 said:
If you think it's a bad FPR, you can use fuel line crimpers to carefully crimp the return line just as soon as it's done priming. Note if pressure stays at what it was before. If it does and you release the clamping tool, if pressure drops right off, you seem to have found a bad FPR.

Good luck.
I tried the suggestion. I crimped it immediately after primeup and let go.It didnt change the drop off situation one bit. It still went to 40 or 45 and puked to 25 or 30.

(In case Im a retard) The return line is "the one without the injectors mounted on" right?

I really dont want to buy extra FPR if I dont need another.

(^^see "retard clause above^^)

Is it normal for a car to not hold pressure when one cycles the key to prime without starting? Why is this thing such a pile of ****?
 
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