I am unable to dump my computer codes on my 91 lx. I have tried this method jumping from the sti to the computer test ground with no success. I was able to jump from the computer test ground to the neg battery post and the check engine light flashed really fast and never produced a code 11 but went ahead and flashed all the other codes. Now I am unable to jump from the neg battery post to the computer test ground and get any data what so ever. Does anybody know what is wrong here. I have tried reading other post similar to my problem but couldn't find any solid answers.
Unable to dump codes
- Thread starter coffmaad
- Start date
The black/white wire is the computer power ground. It is one of the most important grounds on a EFI car.
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.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness
Picture courtesy timewarped1972 [/b]
The black/yellow is also a ground, but I can't find what circuit is for. See http://www.autozone.com/autozone/re...geId=0900c15280069677&partId=0900c15280069537
and chase it down if you want to.
Fix the grounds first and then recheck the computer to see if it will go into diagnostic mode & dump codes.
If it still won't go into diagnostic mode, then here's the test path for no code dump...
Computer will not go into diagnostic mode on 91-93 model 5.0 Mustangs
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. 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 1.5 ohms when measured from anyplace on the engine harness with the battery
pigtail ground as the other reference point for the ohmmeter probe.
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. Only an experienced electronics technician can open
the computer up & repair the trace if it burns up and creates an open circuit.
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
1.5 ohms.
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
1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms 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 1.5 ohms. More that that and the computer’s internal
ground has failed, and the computer needs to be replaced.
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 that 1.5 ohms is a
wiring problem
The following is a view from the computer side of the computer connector.
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.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring Mustang FAQ - Engine Information
If you feel like opening up the computer to attempt to repair the fried wire, see http://forums.stangnet.com/749974-computer-issue.html and joel5.0's comments for more help on fixing the computer innards.
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.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness
Picture courtesy timewarped1972 [/b]
The black/yellow is also a ground, but I can't find what circuit is for. See http://www.autozone.com/autozone/re...geId=0900c15280069677&partId=0900c15280069537
and chase it down if you want to.
Fix the grounds first and then recheck the computer to see if it will go into diagnostic mode & dump codes.
If it still won't go into diagnostic mode, then here's the test path for no code dump...
Computer will not go into diagnostic mode on 91-93 model 5.0 Mustangs
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. 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 1.5 ohms when measured from anyplace on the engine harness with the battery
pigtail ground as the other reference point for the ohmmeter probe.
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. Only an experienced electronics technician can open
the computer up & repair the trace if it burns up and creates an open circuit.
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
1.5 ohms.
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
1.5 ohms. More that 1.5 ohms is a wiring problem. If it reads 1.5 ohms 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 1.5 ohms. More that that and the computer’s internal
ground has failed, and the computer needs to be replaced.
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 that 1.5 ohms is a
wiring problem
The following is a view from the computer side of the computer connector.
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.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring Mustang FAQ - Engine Information
If you feel like opening up the computer to attempt to repair the fried wire, see http://forums.stangnet.com/749974-computer-issue.html and joel5.0's comments for more help on fixing the computer innards.
Yes.
Spend some time with the AutoZone link I posted and check to find the black/yellow wire and what circuit it connects to.
I checked from the red/grey wire to the computer ground near the battery and it was 3 ohms-failed. I then disconnected the computer and checked between pin 46 on the computer connecter and the red/grey wire and it was .01 ohms-good. I jumpered between pins 40 and 60 and then measured between those 2 to pin 46 and it is open. I think I may have found my problem.
Also, I am pretty sure that the plug I was questioning goes to the AC Clutch Relay.
Also, I am pretty sure that the plug I was questioning goes to the AC Clutch Relay.
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