SIGRTN burnt on my A9L, I can fix it but whats the cause?

[86gtriceeater]

I recently converted to mass air and since Im having idling problems I tested for 5 volts reference at my tps. It was there, only .12volts. I opened the computer and sure enough the SIGRTN circuit is fried. I can fix it easily with some solder and a little wire but if I put it back in its gonna fry again. I just got done reading about 50 pages of different scenarios, different engine, transmission, and o2 harness combination that all only confused me more. I have an 86gt 5.0 manual that I converted to Mass Air and I'm utilizing the a9l computer. It sounds like there's differences in the o2 sensor harnesses from speed density cars to mass air cars but it was part any instructions I could find about the conversion. What do I test, look for ect??? What o2 sensor harness do I need? Can I re-pin mine if necessary?

Oh also I swapped out my worn out t-5 for a rebuilt SROD 4speed which doesnt have the provision or wiring for the VSS so I ran the wires for future use if I go back to the t-5 but I didnt connect them to the computer yet...I also recently discovered that my nuetral safety/start switch has been jumped because I can start it without the clutch in. I recently installed a stock 86 engine & headlight harness which did not come with the two little plugs that go into the sensor on the clutch pedal (clutch interlock/dissengage switch?) Sorry for the long un-organized post but I just put my 347 stroker in and I would really like to drive it!!!

 

[HISSIN50]

The difference in the O2 harnesses was for Auto vs manual cars IIRC.

Are you sure the trace was not burned before you got the EEC?

 

[86gtriceeater]

I'm not sure but its doing the exact same thing my other computer did, which I definitely fried but didn't know it at the time and sold it on ebay. The guy was pretty cool about it but I had gotten in from an un-molested 89 in the bone-yard so I know I definitely caused it...I went through my injector harness before installing it so I think there's something else Im missing....

 

[RangerJoe]

I went through this same thing man. Very frustrating. It took me about two weeks to get everything figured out. Honestly, I cannot remember exactly where my problem was. I hid my wiring harness and had cut and resoldered parts of the harness. It seems like I didn't wrap the harness well and caused a short somewhere. I googled, googled, googled, and read, read, read, before I got it fixed. I wish I could tell you exactly where to go to find the exact answer. However, I did still have this diagram saved. It should show you the differences between the two O2 harnesses, and you can repin it if that is your problem. Also, with computer out and battery connected, you can check pin 46 at the computer harness for voltage while you trouble shoot. You probably already knew that though...good luck with it!

Just to clarify...If you look at your connector# 40, it will be pinned for the Manual or the Automatic, but not both. If I remember correctly, you simply swap the pin from one to the other to fit your computer accordingly.

 

[86gtriceeater]

Pic of my connector #40

Heres my o2 sensor plug. The first top left is empty and the bottom two left are EMPTY!!!? What am I missing or how do I figure that out? Dang...

 

[HISSIN50]

Pic didn't come through. Do you only have one wire for each O2?

 

[86gtriceeater]

There's 3 wires on each plug that's going to each sensor...at the top where the engine harness plugs into the o2harness I have 5 pins. Looking at the female connector (on the o2sensor harness side) the top left is empty and on the bottom row the first two left ones are empty...there's a total of 5 pins there out of eight. is this correct? Id match the colors to the diagrams I've found but the colors are different. I'm confused...

 

[86gtriceeater]

I just read if the sigrtn is burnt then pin 42 is open to ground because people hook up the neutral safety switch wrong? Mine is bypassed so where/what do I check for so I can get this sucker on the road?

 

[86gtriceeater]

RangerJoe-is voltage at 46 while cranking computer out a good or bad thing. What will that be verifying exactly?

 

[86gtriceeater]

I discovered the stock computer that cam with my engine harness I have installed is a vj1 (automatic) for 86 gt 5.0!? Is there something I need to change on the harness to work with the a9l??? Id like to start a new thread as I'm butchering this one but I really need help...

 

[jrichker]

Originally Posted by 302EFI
The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU

See Oxygen sensor Harnesses - Manual/Auto differences and year differences - Ford Mustang Forums : Corral.net Mustang Forum for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a auto trans O2 harness with an A9P
Only run a 5 speed trans O2 harness with an A9L
90 model year harness only works with 90 model cars without inspection/rework.
The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.

 

[86gtriceeater]

On pin 46 I get between .02 and .30 volts while cranking. It fluctuates and doesn't seem to matter weather or not I have the 02 sensor harness plugged in...also the colors on that diagram of pin 40 are nothing like mine...

 

[86gtriceeater]

Is voltage at pin 46 good or bad?

 

[86gtriceeater]

I read about a jumper thats on a manual o2 sensor harness but mine doesn't have that, any ideas?

 

[RangerJoe]

I'm afraid I don't know enough about it to give you the solution. When I finally got mine fixed....I would have about .005 to .007 volts on pin 46. I was told by a friend of mine who does electrical that this is normal(these levels are insignificant). If you have voltage on pin 46, it means that you have a power wire grounded to your signal return somewhere.

Find a wiring diagram for your year model car. Several sensors run off of the Signal Return (pin 46). I believe the map sensor, the engine coolant sensor (the one in the heater tube), the air temp sensor, etc. See if you are getting voltage on these at the signal return. With battery disconnected, see if you have continuity between any power wires on sensors or injectors and your pin 46. If you can find this, you may have your problem. Also, I have heard of people trying to pull codes and jumpering the diagnostic port with the underhood light power supply. The connectors look similar...this will fry pin 46. I know the O2 harness is usually the culprit in this, but I am unfamilar with the setup you have. I really wish I could be more help. Please tell us what it is when you figure it out.

 

[jrichker]

See http://slantnosefox.com/picturehosting/jeremy/86 electrical & vacuum troubleshooting manual.zip you can download the whole set of electrical troubleshooting and diagrams for an 86 Mustang courtesy of Jeremy, AKA V8only.

It is a big 61 MB download that you get to unzip and save on your computer. It may take some time to download it, but the results are worth your time. Each page of the downloaded manual is a gif file that you can view with the picture viewer that is built into all versions of Windows. it takes a little effort to find what you want, but it is all in there.