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manicmechanic007

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There are several codes related to ecu failure
And a few test procedures for no codes outputted
Better start there and have a NGS or the guessing game will continue
 
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General karthief

wonder how much it would cost to ship you a pair
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There are several codes related to ecu failure
And a few test procedures for no codes outputted
Better start there and have a NGS or the guessing game will continue
There is no 'guessing game' with the 'surging idle checklist '.
It has been proven here many times, @jrichker posted the checklist with contributions from others here because it works if done per instructions and has many posts from members that have found and fixed idle, surging and poor running issues with our cars.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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WTF 'Quack'?
I give a member a known diagnostic repair procedure and you want to argue? The ain't facepage, be supportive or move on.
 

jrichker

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@Jamie C.

Fuel pump pressure & regulator test

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 37-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.



Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground.

attachments\68357


Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.





Computer will not go into diagnostic mode on 91-95 model 5.0 Mustangs

Revised Dec 23 2017
1.) To clarify signal ground connections on the engine mounted fuel injector wiring harness and add diagram for the engine mounted fuel injector wiring harness
2.) To add warning about using an automatic transmission O2 sensor wiring harness with a A9L manual shift transmission computer.


How it is supposed to work:
The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self-test mode. As long as you are successful dumping the codes by using the gray/red wire on the diagnostic connector for the ground when dumping, the computer’s internal ground on pin 46 is good.

If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1 ohm when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe. [/b

Engine mounted fuel injector wiring harness sensors for a 5.0 mustang
63347.gif


What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.

OR

If an O2 sensor harness from an automatic transmission Mustang is used with an A9L manual shift transmission computer. The 12 volts from the automatic transmission starter circuit will damage the A9L computer.

The STI (Self Test Input) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
With the power off, measure the resistance between the computer test ground (grey/red wire) on the self- test connector and battery ground. You should see less than 1 ohm.

attachments\57945


If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector: it should be less than 1 ohm. More than 1 ohm is a wiring problem. If it reads 1 ohm or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1 ohm. More than that and the computer’s internal ground has failed, and the computer needs to be repaired or replaced.

See image below for help finding the burnt signal ground trace.
?hash=146a243133771eeba54f17b17d721b1f.jpg

The fix is some careful soldering of a small jumper wire across the burnt section of copper trace.

While you have the computer connector disconnected from the computer, turn the ignition switch to the Start position and look for 12 volts on pin 46 of the computer wiring harness. If you see 12 volts then you have an automatic transmission O2 sensor harness. That will damage the A9L manual shift transmission computer.

If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self-test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More than 1 ohms is a wiring problem

The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.
eec-iv-computer-connector-for-5-0-mustang-gif.gif


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


Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the grey/red wire goes. Almost every sensor on the engine except the MAF is connected to it.

91-93 5.0 Mustangs
91-93_5.0_EEC_Wiring_Diagram.gif




Complete computer, actuator & sensor wiring diagram for 94-95 Mass Air Mustangs
94-95_5.0_EEC_Wiring_Diagram.gif



See the graphic for the 10 pin connector circuit layout.
salt-pepper-10-pin-connectors-65-jpg.jpg



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine[/b]
 
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jrichker

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Quack
code 15 means dead processor
Is that in the checklist?


Wrong answer...

Code 15 or 511 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test Failure).

Revised 4-Jan-2019 to add removing any custom tuning chip for minimum configuration testing.

The voltage to the Keep Alive Memory (KAM) is missing (wiring problem) or the KAM is bad. The KAM holds all of the settings that the computer "learns" as it operates and all the stored error codes that are generated as a result of something malfunctioning while the engine is running. Use a voltmeter to check the voltage to the pin 1 on the computer - you should always have 12 volts. No constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM may be bad and the computer is faulty. Read on further to make this determination, since there are some exceptions.

Clearing the codes by pressing a button on the scan tool or disconnecting the test jumper used to start the code dump does not erase the “learned settings”. Disconnecting the computer from the wiring harness or disconnecting the battery (either power or ground cable) will erase the “learned settings” If the computer has to "relearn" all the optimum settings every time it powers up, the initial 15-30 minutes of operation may exhibit surges, poor low speed performance, and rough idle.

Note that some aftermarket chips will cause code 15 to set. Disconnect the battery and remove the chip, reconnect the battery and retest. If you have a custom burned chip using the data gathered from a dyno session, this may not be advisable since it may drastically alter the fuel/air and timing tables.

Disconnect the battery negative terminal for the next step.
Remove the passenger side kick panel and examine the computer. It is held in place by a diagonal plastic strap and 2 screws in the strap. The end of the computer opposite the wiring harness may have an accessory PC board with a big chip in a socket. That chip is a custom tune to accommodate the mods that affect fuel /air mixture, ignition timing and emissions equipment. If it is present, remove it and see if the engine runs any better. Remember that the car will need to be driven at highway speeds for at least 15-20 minutes in order for the computer to relearn the adaptive settings.

For stock engines or engines with minor modifications (OEM cylinder heads, stock 19 LB injectors, no NO2 or pressurized induction).
Before replacing the computer, remove the battery ground cable for about 20 minutes. This will clear all the codes and “learned settings”. Retest after several days of running. If the 15 code is gone, then don't worry about it. If it is still there, then you get to do some troubleshooting.

See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Diagram courtesy of Tmoss & Stang&2birds
88-91_5.0_EEC_Wiring_Diagram.gif


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/88-91_5.0_EEC_Wiring_Diagram.gif
 
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7991LXnSHO

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Never heard of anything in the fuel tank of a fox mustang called a 'fuel pump module '.
:shrug:@manicmechanic007
explain where my fuel pump module is in my 89 stang.
This is a module from a Vibe/Matrix, and it is still ordered it as a fuel pump. The plate to get to the tank under the rear seat is the size of a frisbee, and the cutout hole is none too big when also replacing the emission hoses and fuel line. Delphi and AC Delco are pretty proud of the assemblies.
So, we have a fuel pump.
 
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Mustang5L5

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This is a module from a Vibe/Matrix, and it is still ordered it as a fuel pump.

His comment made me scratch my head too, mostly because I've never heard the pump itself called a fuel pump module. Yeah...semantics i know.

In later Fords, there is a fuel pump relay module, which most folks on the forum pages for those cars just call "Fuel pump module".

So, for my 2014 Ford, if you told me to replace the "fuel pump module", this is what I would buy. These actually are known to fail so i carry a spare module in my glovebox.

-----------------

There is a small check valve in the fuel pump that prevents the fuel from immediately draining off in the line and allowing it to hold some pressure. This prevents extended crank while the pump tried to build pressure. These check valves fail and you'll commonly see the fuel pressure drop to 0 almost instantly when the pump turns off. Provided you can maintain the 39psi required pressure when the pump is operating, the vehicle should still run if holding pressure. Now, if the pressure is spiking up to 70, then there is an issue with your fuel system that needs to be addressed.

My car had a failed check valve in the pump and i drove that way for maybe 20-30K miles without issue. Pressure in the rail on my gauge would drop to zero instantly as soon as i turned off the car. I had no issues driving. I had to do a double-prime of the pump before cranking, otherwise it would be an extended crank, but once running the pump held 39psi at WOT. Eventually I did replace the pump and there was zero change other than having to not do my double prime before starting.

While you should probably put replacing the pump on the list, if the vehicle is holding proper pressure while running, then i wouldn't say this is the root cause of your issues. If you are spiking to 70psi, then there are other issues as well
 
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manicmechanic007

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Damn straight the new ones have a driver module for the pump to control the duty cycle
The one line systems came about to be lighter {no return line) and the transducer and FDM are light too
That combined with a leetle sheeken sheet pump has better fuel economy due to the weight savings
 

manicmechanic007

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You should get to know Ford Tech Makuloco on YouTube
He has tons of videos concerning your soon to fail FDM in your new Ford
The trucks and expeditions are way worse due to the mounting location
 

Mustang5L5

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hello, I just wanted to update my issue. I replaced the fuel pump and the problem still exists. for some reason the OBD1 scanner is not showing anything. someone told me you can use a jumper wire to get the car to flash out codes by jumping two posts on the OBD1 plugs. has anyone heard of that? Also, it seems to run crappy when it gets up to operating temperature, is it possible it could be the barometric sensor which is located on the firewall? I'm above my skill level here, any suggestions are appreciated!

Does your CEL come on when you turn the key to on and stay lit?

That code reader is pretty simple. Step #1 is to warm the car up to the best of your ability. Start it, go for a drive, idle it, etc. Then shut it off. Hook the code reader up and have someone sit in the car and push the clutch in (if applicable). Turn the ignition key to on. Press ON on the code reader.

Then hit TEST. You should hear a few solenoids click in the engine bay and the square on the display should light up. That idiciates the reader is beginning to pull codes.


This video is a bit long, but it also explains the process in more detail. At the end of the code reading process is what's called a "cylinder balance test". It's a really primitive type misfire detection tool. It will turn off the injectors one by one and look for a change at the o2 sensor. If one cylinder seems to be off, it will report it.

Good luck


View: https://www.youtube.com/watch?v=XmOgURm7iXI
 
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manicmechanic007

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Yes it could be the MAP baro sensor as you can call it
The spec is the sensor puts out hertz in a certain range for your altitude
You will have to check the pid specs in a book or some worm like me could find it for you
In the manual they talk about substitute a known good map sensor and retest
This is when you are fighting a map sensor code
I an talking about the pinpoint tests
For your 1991 you should be using a super star 2 tester or a NGS
You can fabricate a tester that incorporates a test lamp bulb
I know of no way to simply do it (red codes) with a test light alone as you have no way to latch and unlatch the test light
The asset boys all made one in school
I am sure you can find a schematic for one online
I keep a super star 2 in my toolbox because it is the only way to diagnose an old lincoln air ride system
Mine I got from Ford for free when the new ones came out NGS
You should be able to find one on ebay cheap (a super star 2)
You are fighting a super fat condition right?
Only a few things come to mind
Like an above post check the VREF and the TP sig RTN
Replace the map
Verify the processor ground out by the battery on some of the old ones
 

manicmechanic007

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sl5 is describing what happens when a star tester latches
that is correct and there are other testers that might work
I am just familiar with the Ford stuff
You should be able to figure it out
Check a few thermister sensors just for GP's (like the act and ect sensors)
 

manicmechanic007

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I assume it still runs ok for 5 minutes?
Usually only takes around 2 minutes but you are describing the car coming out of open loop into closed loop operation
IMHO this can be only caused by a incorrect sensor feed or a bad processor
Because the processor just uses a set of values to run the car while in open loop
And they are provided by the KAM in the processor
So I would be at the nearest junkyard looking for a spare processor and a map sensor to start with