Electrical Sensor Return, Messed Up Tps, Burnt Trace @ Pin 46, Auto To 5sp V8 Swap

Discussion in 'Fox 5.0 Mustang Tech' started by Project86, May 26, 2014.

  1. I'm remembering some of the electrical issues I've had in the past realizing they must be related to my current issue. Recently, I' m having the 5volts on the tps signal return issue. I just started working on my car again after years of sitting. I have aem ems and have been messing around with it off an on in anticipation off putting my supercharged motor back in the car, currently running a stock 92 5.0. Just got it up and running the other day after a bad ecm relay. With the aem computer, I have a high idle of 1400 and the tps voltage shows 4.9v ,wot. with a A9l, car runs ok but low crappy idle. I probed tps and the harness, and even without the sensor I have 4.9v on two of the three wires. I found a bad ground where the ecc harness grounds to to the pass kick panel. I fixed and now have 0 oms across the ground pins to the car body, but only when the ignition is off. When the key is on resistance goes up over 20. Im guessing it wasnt the problem. short circuit? Any way, sure enough with computer connected, koeo, pin 46 shows voltage. That goes for both an A9L and the aem. Last time i messed with the car a few years ago i didn't have this problem. I was running the stock motor with aem for purposes of learning the aem software. tps and other sensors worked fine.
    in another post it mentions the problems with using the 5sp computer on Auto cars. This car was a 4cyl auto to V8 tremec swap. In the past i had weird issues with the the starter triggering when in reverse, and clutch pedal causing a drop in idle. I cant remember what I did to fix that problem, but I definitely had some serious back feeding, or shorting issues. i must have just unhooked something. I also remember my diagnostic ports not working correctly. All the while tps and other sensor parameters were fine according to the feedback from aem ems. The clutch or neutralSS connections and the signal return thing has got to be my problem.. reading other posts, It seems like all the pieces to the puzzle are mentioned at various times, I just haven't grasped them yet. Not sure what to do next? cut wire to pin 30? Unplug the clutch pedal sensor? I think the neutral safety switch is currently disconnected, but the clutch pedal sensor is active. Did i blow out the ecm tracing to pin 46 on the A9L? I wonder if the aem is damaged? I dont remember there being a distinction between 5sp and auto part numbers. some people make jumper to ground at TPS. I know its not ideal, but would grounding pin 46 help? thanks
  2. update....the trace is burnt at pin 46. oxygen sensor harness is gone and the car has an aem wideband.
  3. You unloaded a ton of information right there, but I'm still confused on your actual setup. List your cars specs. Computer, trans, modifications, etc.
  4. yeah sorry..its a bunch of my desperate rants from another thread..

    it all started with an 86 5spd GT. bunch of usual bolts-ons, converted to mass air and running an A9l. tremec 3550, and eventually the old paxton. ran pretty decent for no tune. Yrs later put the whole combo in a 4cyl auto notchback. did the pedal conversion, brought over the ecm and engine harness from the 86. used most of the body harness from the 4cyl but i remember having to add a few harnesses here and there. it seemed to run fine. eventually killed bottom end and picked up a stock 92 5.0 from a wrecked GT. dropped that motor in and had electrical issues with reverse...when putting car in reverse the starter would engage... and when pressing in the clutch, there would be an engine miss and and dip in rpms then the ecm would come back to idle . I cant remember what it was but something got hooked up differently then it had in the past when I did the 92 5.0 install. I also cant remember what I did to correct it and get passed that. For a while the car ran like that and I put in an AEM ems i had laying around. I got it all working including a wideband o2 controller. Spliced in a VCC and was getting into some tuning. All sensors were within range and all was well. now a few years later go to run it as usual and cant fire. the ecm relay was bad. New one, fired right up and gave me a high 1400 idle, it also showed my tps at WOT, voltage was 4.9 . thought maybe I had flashed a tune that wasnt properly set up so I yanked the aem and swapped in the old trusty A9l. it ran but I could tell something wasnt right. Started probing tps and tps harness and got the high voltage on a multimeter just like the aem was seeing. so thats the background. so my main issue is the signal return being messed up... I can solder the trace, but is the issue in the past or am I gonna fry it again?.. once I get the a9l running ok, ill deal with the aem again..
  5. The trace inside the computer burns up for 2 reasons:
    1.) When someone dumped the codes, they used the brown connector instead of the gray one to dump the codes. The brown connector is for the under hood light and has 12 volts on it, this burns up the trace inside the computer.
    2.) Auto trans O2 sensor harness was used with an A9L computer.

    O2 Sensor harness interchange and modification

    Originally Posted by 302EFI

    Revised 16-Oct-2011 to add O2 sensor harness warnings
    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 http://forums.corral.net/forums/gen...manual-auto-differences-year-differences.html for more O2 sensor wiring harness info

    Basic premise to use with transmission swaps:
    Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
    Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems. There has been some debate about the no crank problem,and I haven't personally checked it out.
    See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

    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.
  6. thanks..awesome bit of info there...once i confirmed my O2 harness was long gone I was a bit lost. I haven't tried to pull any codes in a very long time, and I know this all was working a few years ago. I think the burnt 46 trace was a coincidence that happened along time ago. I finally isolated the problem. Battery relocation problem. It was a bad ground or ground loop or some kind of noise. I thought I was OK because I have a bunch of extra grounds and two different grounds that come all the way to the front of the car. everything worked previously but i moved some stuff the other day. I checked and double checked the grounds and cleaned and reinstalled. They all seemed really good when checking for resistance. The order i attached the ring terminals or something caused the issue. I tried a jumper wire direct to battery neg a few days ago but I didn't completely isolate the black/greens to the eec. I took that connector apart at the driver fender this time and direct grounded it and the aem is seeing good signal from the tps now. So... is there a chance I have some shorting to the grounds going on? Or is that eec ground that finicky and it was picking up ground loops or something? I guess i can leave it with a dedicated ground to the battery. I suppose thats what should have done in the first place, when I moved the battery.
  7. The fix is repair the burnt trace on the computer PC board.

    To keep it from happening again,:
    1.) Be careful when you dump the codes to use the single gray connector with a white red wire on it.
    2.) Make sure you have the proper wiring in the O2 sensor harness.

    Rear mounted battery ground wiring. Follow this plan and you will have zero ground problems.

    One 1 gauge or 1/0 gauge wire from battery negative post to a clean shiny spot on the chassis near the battery. Use a 5/16” bolt and bolt it down to make the rear ground. Use a 1 gauge or 1/0 gauge wire from the rear ground bolt to a clean shiny spot on the block.

    One 4 gauge wire from the block where you connected the battery ground wire to the chassis ground where the battery was mounted up front. Use a 5/16” bolt and bolt down the 4 gauge engine to chassis ground, make sure that it the metal around the bolt is clean & shiny. This is the alternator power ground.


    The computer has a dedicated power ground wire with a cylindrical quick connect (about 2 ½”long by 1” diameter. It comes out of the wiring harness near the ignition coil & starter solenoid (or relay). Be sure to bolt it to the chassis ground in the same place as you bolted the alternator power ground. This is an absolute don’t overlook it item for EFI cars

    Note: The quick disconnect may have fallen victim to damage or removal by a previous owner. However, it is still of utmost importance that the black/green wires have a high quality ground..

    Picture courtesy timewarped1972 [​IMG]

    Crimp or even better, solder the lugs on the all the wire. The local auto stereo shop will have them if the auto parts store doesn't. Use some heat shrink tubing to cover the lugs and make things look nice.

    For a battery cut off switch, see http://www.moroso.com/catalog/categorydisplay.asp?catcode=42225
    is the switch http://www.moroso.com/catalog/images/74102_inst.pdf is the installation instructions.
    Use the super duty switch and the following tech note to wire it and you will be good to go.

    Use the Moroso plan for the alternator wiring and you risk a fire. The 10 gauge wire they recommend is even less adequate that the stock Mustang wiring.

    There is a solution, but it will require about 40' of 18 gauge green wire.

    Wire the battery to the two 1/2" posts as shown in the diagram.

    The alternator requires a different approach. On the small alternator plug there is a green wire. It is the sense lead that turns the regulator on when the ignition switch is in the run position. Cut the green wire and solder the 40' of green wire between the two pieces. Use some heat shrink to cover the splices. See http://fordfuelinjection.com/?p=7 for some excellent help on soldering & using heat shrink tubing.

    Run the green wire back to the Moroso switch and cut off the excess wire. Try to run the green wire inside the car and protect it from getting cut or chaffed. Crimp a 18 gauge ring terminal (red is 18 gauge color code for the crimp on terminals) on each wire. Bolt one ring terminal to each of the 3/16" studs. Do not add the jumper between the 1/2" stud and the 3/16" stud as shown it the Moroso diagram.

    How it works:
    The green wire is the ignition on sense feed to the regulator. It supplies a turn on signal to the regulator when the ignition switch is in the Run position. Turn the Moroso switch to off, and the sense voltage goes away, the voltage regulator shuts off and the alternator quits making power.

    The fuse & wiring in the following diagram are for a 3G alternator. The stock alternator uses a dark green fuse link wire that connects to 2 black/orange wires. Always leave them connected to the starter solenoid even if you have a 3G alternator.


    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/ Everyone should bookmark this site.

    Ignition switch wiring

    Fuel, alternator, A/C and ignition wiring

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

    Vacuum diagram 89-93 Mustangs
    #7 jrichker, May 28, 2014
    Last edited: May 28, 2014