Problems Dumping Codes

Nicklog

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Jan 25, 2016
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Hello, I'm recently bought a 1995 mustang gt automatic 5.0. It randomly threw a check engine light while on the highway but drove fine up until I parked it for two weeks. After sitting I tried to start it and it took a long time to start and it won't stay running. If you rapidly hit the gas it dies but if you do it slowly it will rev up but sounds as if it is missing. Checked spark and all cylinders were good, injectors all have 12v with key on, 40psi fuel at idle and key in Eng off. Cel is on the whole time, when I jump the computer test ground terminal on the eec and the sti terminal and turn the key on nothing happens. The cel still stays on and no flashing occurs. I've ohmed the computer test ground on eec all the way to the computer and all was good, 0.5 ohms. I checked the computer internal ground by ohming pin 40 to 46 and 40 to 60 both good. I've done a few more thing but don't recall. If someone could please steer me in a direction to at least pull the codes that would be great. Thank you
 
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You are on the right track, try jumpering the STI input to battery ground and see it things improve.

Check the computer ground next.
The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972
ground.jpg


Correct negative battery ground cable.
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3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its 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.

Testing the resistance between pin 46 and 40 or 60 is right on target. It sounds like you got good results, so check the computer connector wiring for evidence of water damage.

If you don't find anything suspicious, it is looks like it is time to swap the computer. Since you have an auto trans, you will need to find a 94-95 GT auto trans car to supply the computer.
 
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image.jpeg
So I jumped sti to batt ground and had no luck, still cel on and no flashing.

Checked the common ground point and it looked perfect. Test light confirmed good ground.

I checked the computer ground quick disconnect and it is clean and checked good.

The only thing I was a little confused about was when you said find the computers main power ground. In one part you said it was in close proximity to battery and another you said it was by the tarter solenoid. I didn't locate it. Were you referring to the connector I have circled at the top of picture?

Thank you so much for the help. I had hit the wall and was ready to give up!
 
image.jpeg
So I jumped sti to batt ground and had no luck, still cel on and no flashing.

Checked the common ground point and it looked perfect. Test light confirmed good ground.

I checked the computer ground quick disconnect and it is clean and checked good.

The only thing I was a little confused about was when you said find the computers main power ground. In one part you said it was in close proximity to battery and another you said it was by the tarter solenoid. I didn't locate it. Were you referring to the connector I have circled at the top of picture?

Thank you so much for the help. I had hit the wall and was ready to give up!
It looks like the connector you have circled at the top of the photo. Check to see if the wire and stripe colors match what I posted.
 
image.jpeg

The only thing I was a little confused about was when you said find the computers main power ground. In one part you said it was in close proximity to battery and another you said it was by the tarter solenoid. I didn't locate it. Were you referring to the connector I have circled at the top of picture?

Thats because he is giving information that is specific to the foxbody. Your ECM grounds are those two on the radiator support.

IIRC, there is another ground on the other side of the core support... but I dont know what it runs too. (never cared either... lol)