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I have an 89 ford mustang gt with issues.

Car: Ford, Mustang GT, 1989, 5.0     -    Back to Fix-It    -    Ford Repair Manuals

Q.I have an 89 ford mustang gt with issues. I have pulled the fault codes and they are as follows. 15 51 22 53 54 67. These are the ON DEMAND codes, key on engine off. The code reader says I have to fix these codes before moving on. Code 15 is a failure in the electronic control assembly. Does this mean my ECA is toast? Car was running great then things went down hill so i pulled the codes. How do I deal with the code 15, is it fixable. There is a lot more to this car but for now I just want to know how to procede. The check engine light has never come on before and the computer is the stock EEC-IV OBD1 A9S.

I already checked/done: Pulled error codes in KOEO mode

Answer Code 15 is for Keep Alive Memory Test failure, usually it occurs after the battery or computer has been disconnected, because the continuous power to the EEC was interrupted. After clearing codes and retesting, this code should go away. If it does not, check for "hot at all times" power at pin 1 of the EEC connector, there should be 12v there key on or off. Check for good ground on pins 40 and 60. You can use a test light to verify good power and ground here, with the connector disconnected. A good terminal to pin fit is also essential for a good connection. It is possible that an internal computer fault could exist, first check for a bad solder joint where pin 1 connects to the main circuit board inside the EEC, resolder as necessary. If the fault remains after good power, ground, and connections are present, then replace EEC. To test itself, the computer runs memory tests and compares the results to saved values called checksums. If the results don't match the checksums, the computer is programmed to set a code 15. It's not common for memory chips to fail, but it does happen.
Code 51 is for ECT (Engine Coolant Temperature) Sensor being out of range, This code is usually because the test was run with a cold engine, and the computer is expecting to see the sensor reading an already warmed engine. (Technically you are supposed to warm the engine up, then shut it off before test is started).
Code 22 is for the MAP (Manifold Absolute Pressure) sensor reading incorrectly. There are 3 wires to the MAP, one is 5v reference voltage (VREF), the other is ground, and the middle wire is supposed to read 2.5v. However, if the sensor is disconnected or a wire is broken, you will get the code. The MAP sensor could be bad internally as well.
Code 53 is for the TPS (Throttle Position Sensor) out of range, reading above 4.5v during the test. The TPS is also supplied with 5v VREF and ground, and has a third wire that signals throttle opening by showing 1-4.5v, depending how much throttle is open. If the computer sees voltage over 4.5, the sensor is disconnected, broken, or a fault exists in the wiring between the sensor and the computer.
Code 54 is for the ACT (Air Charge Temperature) sensor out of range. This one could also be due to the engine not being warmed up. Or the sensor/wiring faults I have describe earlier. This sensor has 5v supplied to it, and returns a signal voltage based on temperature. If voltage from this sensor reads above 4.6v, this code sets.
Code 67 is for the Neutral Safety switch not reading Neutral position (manual trans) or Park position during the test. Again, this is usually due to the test pre-conditions not being met. It will probably not reset this code once you clear the codes and retest with gear shift in Neutral or Park.
First, clear the codes and get the car warmed up, then see if the check engine light is on. Then turn off the engine and place car in Neutral or Park, and run the KOEO again. Several or perhaps all these codes may go away.
Keep in mind not all engine faults will set a code, and since the check engine light was never on, there may not have been any stored codes relating to the problem you were sensing. It is still good practice to check for codes, and address them, but these codes you have found so far may not all be helpful.
About the only ones that seem legitimate are the MAP code and the TPS code. A TPS failure is pretty common, since it has a moving part inside it that slides back and forth on a variable resistance, and the wiper wears out a track and then the signal becomes inconsistent and noticeable engine running problems are noticed. One way to isolate a TPS problem is to simply disconnect the sensor and drive it. This forces the computer to shift to preset values for TPS instead of relying on the wrong signals from a bad TPS. If the problems seem to go away with TPS disconnected, the TPS is likely bad. Resistance tests while rotating the TPS will show that the resistance no longer changes steadily over its rotation range, large spikes occur where the track is worn away and there is an open circuit through the sensor.
The MAP sensor is also able to cause poor running if it is unplugged or a wiring fault cuts off its signal to the computer.
(SD stands for Speed Density)

Addition A little background for you to better help me. My car has 7000 original miles. I have extensively modified it. It has a vortech supercharger, afr heads, trick flow intake, 45lb injectors, msd 6al2 ignition, msd boost timing retard. It has had these modifications for at least a year and has run fantastic. I put the car on Jack stands to replace a leaking rear main seal and replace a leaking oil pan gasket. I disconnected the positive battery cable, not the negative. I put it all back together and when I started it up thats when the check engine light came on. When I shut it off it will turn over like crazy but not even try to start. After sitting for a while it will do the same thing over and over. Thats when i used a jumper wire and read the codes of the check engine light. The codes I gave you are the first set or ON Demand codes. It is my understanding from reading that these codes cannot be cleared like the second set of key on engine off codes or Continuous memory codes which i cleared last night. Are you saying that if I start the car now, warm it up, shut it off and run the codes again that the On Demand codes like the 15 code should go away if there is no longer a problem? I dont understand why the car doesnt start when warm. Is it really possible that all these faults happened at the same time from removing the 5 speed and clutch? As you are aware, to change the oil pan gasket you have to jack up the engine. I have checked endlessly for loose or disconnected wiring from jacking up the motor and there just isnt any. I did replace the o2 sensor harness because the wire to the oil level sensor was worn but with the problems i put the old one back on to see if that had anything to do with it, no change. I did move the battery to the rear of the hatchback but ran ground to the engine block. Is is possible I shorted things out? Sorry for the overload but thought you should have all the info. I am 53 and baby this car and it is very clean, not a beater. So.... again, if i clear the continuous memory codes, if everthing is ok will the On Demand codes go away or do I have to address them one at a time.

Answer Were you able to check the connection to the MAP? It has both electrical and vacuum tube connected to it. Make sure no vacuum leaks or damage has affected the MAP tube. If you can, check for the 5 volts VREF at least, to ensure the computer is turning on. Also, the TPS signal voltage is pretty easy to check. If you need more help with any electrical testing let me know, I can describe it in more detail.
Think of the on-demand codes as what the computer sees as a problem right now. Since it saw some unexpected values from several sensors due to not being warmed up first, these codes will probably not reset. So we really need to only concern ourselves with the "true" codes.
I really hope the 15 does not reset, because that could mean the EEC is going bad. It may still work even with failing memory, but it will not be 100%. I am pretty confident the temperature codes will not reset.
I don't think moving the battery caused a problem (the code 15 may have been the result of having the battery disconnected). You would have some blown fuses if you shorted any power wires, or at least some sparks. If you shorted a critical sensor wire, it will give us a code. So, let's see what happens when the test is re-run. Then if it goes like I suspect, we will have fewer codes to track down, and they will probably be the ones that lead to the problem.
By the way, it sounds like a really nice car. Fast and fun I bet. No need to apologize for too much info, it always helps to know and picture the car.
What are you running for fuel management to add fuel under boost conditions?

Addition I have not checked the MAP yet. I did reset the codes and checked to make sure they were clear. The first set of on demand codes hadnt changed, still 15 with all the rest. The second set of Continuous codes had reset and i was getting a 11 code meaning clear. I started the car and let it warm up to operating temp. The check engine light was still on. I shut the car off and set up and ran the koeo test again. All the demand codes were still the same and the same continuous codes had come back which are 22 51 53 54. Again, after i run the car and shut if off it will not start, turn over fine, just no attempt to start. I quite in discust at that point last night. I thought what I would do tonight is check the MAP. I will also pull the EEC and check for power and ground as you have described. Stupid question, I have never pulled the EEC before. I take it i just disconnect battery ground, unbolt the wire connector from the eec, then reconnect battery ground so I can check pin 1 for power and 40 and 60 for ground? I will also check the soldered connection for pin one inside the EEC. The code 15 never cleared so i am unclear just how to reset it before retesting to see if it appears again. I am not getting the code 15 in the second set of codes which are the ones that reset, the 15 only appears in the first set. Not to be redundent but what i am reading tells me those codes will not clear and must be fixed so i need help when you say to "clear the codes".

Addition quick update. Its getting wierd now. I just decided to go out before i hop in my car and go to work and check the MAP connections. Its plugged in but there is no vacuum line hooked up, and better yet, I cant find it for my life. I had AMP performance here in Phoenix install the supercharger, is it possible that for some reason they disconnected it. Its not pluged though.( Im trying to make them the morons and not me.) Where does the vacuum line for the MAP come from, maybe if I start there I will find it. Hey, Its something anyway!

Answer Since the car is modified, it is using a different style of fuel injection control than it originally had. I should have noticed this by the A9S code EEC you are running. That computer is a Mass Airflow computer. The original "speed density" system used a vacuum line to the MAP. This system is less tolerant to modification, although it is possible with the right computer reprogramming. Many Mustangs have been converted to Mass Airflow Sensor systems because they are more tolerant of modification, more "flexible" if you will. The Mass Airflow Sensor would look like this if equipped:

Since yours has been converted to MAF, it will have a MAF sensor in the air inlet tube, before the throttle body (it is sometimes mounted before supercharger, or it can be after).
So, since it is a MAF system, it uses a BARO (Barometric Pressure) sensor instead of a MAP, and it works the same way except without the vacuum tube. The code still refers to the BARO sensor signal being out of range, so the same faults could be affecting it except for the vacuum tube missing, since it doesn't use one).
BARO sensor simply monitors the air pressure the car is operating within. This allows the system to self tune if you were to drive up in the mountains, the air pressure drop would be detected by the BARO. The BARO sensor looks just like a MAP, and is essentially the same. It is only really different where the hose would have attached, instead of a barb for a hose, it has a different style end on its little tube. Some people just re-use the MAP sensor as a BARO when converting to Mass Airflow, and the hose is taken off on purpose. AMP Performance probably converted the car to MAF, which would mean they had to switch the computer, do some re-wiring, and add the MAF sensor.
As far as the code clearing goes, the surest way to clear them is to disconnect the battery temporarily. The codes are stored in memory by a chip that requires hot at all times power, so they are lost when the battery is disconnected.
You are correct in your plan of how to disconnect the EEC, just disconnect battery, remove the 10mm bolt from the 60-pin connector, and wiggle the connector as you pull it away from the EEC. Then go ahead and reconnect the battery so you can check power and ground to the EEC connector as described.
I went back to the diagrams, and all the things that are setting codes are on the same 5v VREF circuit. It is a gray/red wire (or possibly black/white) that comes out of pin 46 on the EEC connector. This wire comes off pin 46 and branches out to the ECT, BARO, TPS, ACT sensors. It also comes to the diagnostic connector, so you could check for that 5v there at the diagnostic connector. If this wire is broken, disconnected, or shorted, all these sensors are unable to provide valid signals. Look for problems right at the EEC connector where this terminal fits into the hardshell connector, check it for continuity to the sensors, and fo shorting to ground.
There is a wiring diagram below, you can see the sensors and circuit shows as gray/red on the bottom of the diagram.

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