88 5.0 Computer Might Be Damaged ?

88droptop5.0 · Mar 5, 2015

I have recently acquired a 88 convertible 5.0 GT and I am thinking I did a bad thing. I was trying to pull codes and I think I jumped to the wrong single connector (dark connector with black/orange wire instead of the single gray connector) and may have damaged my computer. I cant get any codes to pull and I am now using a code scanner from Advanced Auto.
The car will start and run but very rough and will die out sometimes. I was having trouble starting the car when it was warm/hot and also fighting the surging idle monster. The car had a motor swap done at some point so I have no idea of what year the motor is, but it is a fuel injected engine. I can supply pics or whatever you need to help me wine the fight.....
Any help will be greatly appreciated ,
Thanks for your time and patients, Its been a while since I messed with cars..lol

88droptop5.0 · Mar 5, 2015

This is the single wire I jumped to by mistake

88droptop5.0 · Mar 5, 2015

I think this is what I should of jumped to, the single orange(ish) with red stripe wire with gray connector.
Help....please...

88droptop5.0 · Mar 5, 2015

I just picked up this code scanner, I can't get any codes to flash but that was after I accidentally jump to the wrong wire ( I think)..

88droptop5.0 · Mar 5, 2015

This is my computer ecm ecu or whatever we call them ..lol.. Anyway what is a suitable replacement for this? Will any manual 87 + unit work? Its a 5 speed GT convertabl ( if that matters). I need help with this , I found a few for sale but want to make sure I get the right one..
Sry the pic is upside down. .

88droptop5.0 · Mar 5, 2015

first off let me start by saying I apologize, I just started a thread on this but I think I put it in the wrong section. I have a 1988 5.0 Gt 5 speed,I've been having some issues with it idling serging, and I wanted to pull some codes out of it, but I think I accidentally jump to the wrong wire. the car still idles and reves but it's rough. I accidentally jumped to the dark connection with the red and orange wire instead of the gray connection with the orange and red stripe wire. I have sence bought a code reader can I get no code at all.when I first plug it in it lights up but as soon as I turn the key on the lake its very very dim and does nothing. I will post a picture of my computer and I will post pictures of the wire that I think I jumped wrong. if anybody could point me in the right direction as to what is a suitable replacement computer, or if there is any test that I can do to check my existing computer
Thanks...

88droptop5.0 · Mar 5, 2015

This is the wire that I think was the wrong one and might of caused some or all of my issues.
Also , this is the code reader that I purchased. keep in mind when I originally did the boo boo I was using a jumper wire and not the code reader. now I can get no coat at all when I first plug it in it lights up when I turn on me quita like its very very dim and does nothing, I watched it for a good 2 or 3 minutes...
Again thanks...

jrichker · Mar 5, 2015

If you used that wire, you probably burned the signal ground trace off the computer printed circuit board. That wire supplies 12 volts the under hood light on some models of Mustang. The computer is repairable if you have good soldering skills and a low wattage pencil type soldering iron.

See the test path below to determine if you did the suspected damage. In the test path is a link for repairing the damaged computer PC board trace that usually occurs with this problem.

Computer will not go into diagnostic mode on 86-90 model 5.0 Mustangs

Disconnect the battery positive terminal before making any resistance checks.
The voltage drop in the ground cable will cause incorrect resistance readings.

How it is supposed to work:
The black/white 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 black/white 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.

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 (black/white 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 black/white 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 repaired or replaced.

See View: https://www.youtube.com/watch?v=RsVcS0E_--8
for the how to solder tutorial

See Computer issue? | Mustang Forums at StangNet for Joel5.0’s fix for the computer internal signal ground.

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 wiring connector: it is for an A9L, A9P computer.

Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the black/white 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 - Wiring & Engine Info

See the graphic for the 10 pin connector circuit layout.

88droptop5.0 · Mar 5, 2015

Thanks so much for the reply, I did the first test with the positive cable off, negative still connect. I went from the black/white stripe wire in the self test connection to my battery negative. According to my Fluke on getting 2.03 for a ohm reading...I'll do more testing tomorrow as I assume that's a fail.. On a side note, I tested my known good and in spec at .85 v tps, its now like 4.07/5.03 and can't be brought in range..

88droptop5.0 · Mar 5, 2015

If the computer is shot, what can I replace it with. Any 87/95 manual or is it more specific?
I have a feeling that it is the computer, before my mishap it didn't run perfect but it was a whole hell of a lot smoother than it is now. but I will be doing more tests tomorrow, I assume the high ohm test of 2.3 is a fail?

madspeed · Mar 5, 2015

why start two threads containing the same thing??

madspeed · Mar 5, 2015

threads moved and merged

88droptop5.0 · Mar 5, 2015

I didn't mean to start to threads, i realized I may have posted in the rong section. I apologized when I started my 2nd thread .
Thanks for merging them.

madspeed · Mar 5, 2015

all good. Its tough to stay on topic and figure out whats going on with a particular issue when theres two going on at the same time. Got them merged together. Hope you get it sorted out

88droptop5.0 · Mar 6, 2015

Thanks, I'm working on it today after work. I'm testing the computer ground and everything that Jrichker suggested. I'm mad at myself because I caused the damage and I didn't look first before I started messing with stuff..
I appreciate all the help and will report back with my results this evening.

88droptop5.0 · Mar 6, 2015

okay, I perform the second test on my lunch break. I took a ohm reading from the black and white wire at the test connection to the number 46 pin on the computer harness not the computer. At first I got 00.3/00.4 ohms, then I tried again for the hell of it and can't get a reading now..lol what does that mean?.
I guess I'm going to pull the computer out and do the third test, just let me know if I'm on the right path here, thank you

liljoe07 · Mar 6, 2015

Just pull the computer and check it.

88droptop5.0 · Mar 6, 2015

liljoe07 said:
Just pull the computer and check it.

I plan on pulling the computer after work and testing it with the above procedure..

liljoe07 · Mar 6, 2015

You wont have to test anything, the issue will be clearly visible on the back of the board. I've fixed a bunch of these. And anytime you jump 12v to the SIGRTN, it burns the trace on the board.

88droptop5.0 · Mar 6, 2015

liljoe07 said:
You wont have to test anything, the issue will be clearly visible on the back of the board. I've fixed a bunch of these. And anytime you jump 12v to the SIGRTN, it burns the trace on the board.

Ok, thanks, i'm pulling it in a few. Any help with how to fix would be great. I'm good with soldering and have nothing to loose if its burnt anyway right..lol

88 5.0 Computer Might Be Damaged ?

Member

Member

Attachments

Member

Attachments

Member

Attachments

Member

Attachments

Member

Attachments

Member

Attachments

StangNet's favorite TOOL

Member

Member

Colonel Mustard

Colonel Mustard

Member

Colonel Mustard

Member

Member

Member

Member

Similar threads

Privacy & Transparency

Privacy & Transparency