So I think I fried another Computer :(

[mavmavv]

Jesus H.

So in my quest to get my car running properly and to be smoggable, ive been trying to fix codes 21, 94. ECT and AIR injection. Basically the car has never been running right.

I just have some bad luck with this car. I went through today and took off the upper intake to get to all the wiring and grounds. I went through and sanded down all the grounds, made sure they were clean, tried to trace the wires the best I could looking for shorts and couldnt find anything. I cleaned the large amounts of carbon deposits out of the upper intake and that seemed to help a bit.

But I bolted everything back up and took her for a test drive. I got on it a little after going down the road and I hear lots of pinging and see a CEL. Nothing new, so I get home and try to read the codes... nothing. No paperclip jump. The exact same issue I had when the previous computer was fried.

Bad wiring harness? Everything other sensor and component of the motor is pretty much new. I found a harness on Ebay for 30 bucks, its gotta be worth checking out. I seriously cant find a short in mine, but somehow it seems to be killing components.

 

[squeak93]

If it is the computers frying, then yes, it has to be either ur harness or something installed in/on the car that is doing it. I would find the source of the short b/f I went throwing more parts at it.

 

[jrichker]

No info about your car's model year, EFI or carb, no mods listed. Makes it hard to troubleshoot when we don't know what you have.

Therefore, no clue as to which wiring diagram or tech note you need for the computer will not go into diagnostic mode problem. The wiring changed several times between 86 & 95.

That's why it is a good idea to use the sig under the user control panel (User CP) option. It allows you to post your car year & mods, which help greatly when troubleshooting things. No, it is not there for us to snoop and see any "Secrets" you have hidden away under the hood. Be a good stangnetter and update you sig for future reference & don't keep us guessing.

 

[mavmavv]

I put in a sig a while ago. 88 LX 5.0.

 

[jrichker]

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

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. 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
(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 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 wiring connector.

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 http://www.veryuseful.com/mustang/tech/engine

 

[bloopbloob]

oops.

 

[mavmavv]

I went ahead and got another Harness at the Pick and Pull junkyard. Snapped it right in and boom, no more short. Computer codes were still there but atleast the computer wasnt dead. I noticed a kinked heater hose when I pulled the intake the last time, I went ahead and replaced it and burped the radiator.

Fixed my code 21! Looks like the water passage was blocked. Im scared to know what that did to the rest of the cooling system. I have the car unplugged right now to reset the ECU and im going to re-time it.

Hopefully it will run a little better. The last code I have is 94 which is AIR injection and that could just be some busted solenoids.

 

[mavmavv]

Woo man. Its Alive! God damn these things are slow as molasses stock, but atleast it runs! It will serve its purpose as DD just fine. I think I have 2.xx gears or something because it definitely has nothing down low. Once it gets past 2500 it starts to breathe pretty decent.