Please Help With Code 67

Discussion in 'Fox 5.0 Mustang Tech' started by apx, Sep 21, 2013.

  1. Hey everyone. Just got the car and it has a problem that I've haven't been able to figure out. The vehicle is a 92 Mustang GT that came from factory with a 5 speed. When I start the car up it will rev to about 2500-3000 rpm and the engine light will be on but some times (1 in about 5-6 starts) the engine light wont come on and the car will idle normal but as soon as I let the clutch pedal go the engine light comes on and it revs to 2500 rpms. I tried to jump both connectors at the neutral safety switch and same thing happens. I ran a KOEO test and got code 67 then in CM I get codes 22 and 34. I cant run a KOER test because of code 67. The previous owner has replaced the Bap sensor, egr solenoid and neutral safety switch and still the same. I did some research and checked pin 46 at the EEC and it has 12v when cranking. Checked the 02 harness and the jumper went between 1 & 5. I swapped the jumper to 1 & 6 then there was no voltage at pin 46 but when I started the car the check engine light came on and it had the codes 55, 22, 53, 54, 35 and 67 but the idle was only at 1500 rpm then it slowly came down to about 1000 so I put the jumper back to the way it was. I checked the EEC and it doesn't look like the circuit is burnt/fried at pin 46. If the battery is dis-connected and the NSS connectors are jumped I can get 2-3 starts before the engine light comes back on and the high rpms come back. Sorry for the long story but I dont know what to do anymore. Any help would be greatly appreciated.


  2. did you go through the surging idle checklist?
  3. Pull the cover off the passenger side kick panel and check the code label on the end of the computer opposite the wiring connector.

    Computer & interchange information for 5.0 Mustang

    Revised 16-Oct-2011 to add O2 sensor harness warnings

    The Mass Air computers from 89-93 are interchangeable with a few exceptions. Just be sure you use the MAF & MAF sensor from the same series computer. The auto transmission computers use a different start circuit than the manual computers. You can use an auto trans computer in a 5 speed car with no problems or changes. I have done it in my original 89 Mustang GT, and I know it works OK. I would recommend avoiding using a 5 speed computer in an auto trans car due to the possibility of damaging the computer’ internal signal ground circuitry.

    The odd duck is the 93 Cobra computer, labeled X3Z which is internally calibrated for 24 lb injectors. Use the MAF & MAF sensor from the X3Z computer to avoid problems with the computer's internal calibration. Try and avoid the 93 Cobra computer if you can.

    Some cautions about O2 Sensor harnesses need to be observed to avoid damage to the computer.
    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.
    See harnesses-manual-auto-differences-year-differences.html for more O2 sensor wiring harness info
    If you have a damaged computer with signal ground problems, See for Joel5.0’s fix to the computer internal signal ground.

    All the following are mass air unless they say Speed Density
    8LD - MANUAL 88 5.0L Mustang Mass Air - California
    8LF - Auto 88 5.0L Mustang Mass Air- California
    8LG - Auto 88 5.0L Mustang Mass Air- California
    A9L - 89-93 5.0L Mustang 5-spd Mass Air
    A3M - 93 5.0L Mustang 5-spd Mass Air
    A3M1 - 93 5.0L Mustang 5-spd Mass Air
    X3Z - 93 5.0L Cobra 5-spd Mass Air internally calibrated for 24 lb injector
    A9P - 89-93 5.0L Mustang Auto Mass Air
    A9S - 88-93 5.0L Mustang California Mass Air
    C3W - 89-93 5.0L Mustang Auto
    DA1 - 87 5.0L Mustang 5-spd Speed Density
    J4J1 - 94-95 5.0L SVT Cobra 5-spd
    T4M0 - 94-95 5.0L GT Vert 5-spd
    U4P0 - 94-95 5.0L GT Auto
    W4H0 - 94-95 5.0L GT
    ZA0 - 95 Cobra R
    D9S - 88 Lincoln LSC Speed Density

    See for more computer types

    Code 67 –
    Revised 2 Nov 2012 to add definition of the NSS functions for both 5 speed and auto transmissions

    Cause of problem:
    clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you from running the Key On Engine On tests.

    External evidence from other sources claims that a code 67 can cause an idle surge condition. Do try to find and fix any issues with the switch and wiring if you get a code 67.

    What the NSS (Neutral Safety Switch) does:
    5 speed transmission: It has no connection with the starter, and the engine can be cranked without it being connected.
    Auto transmission: It is the safety interlock that prevents the starter from cranking the engine with the transmission in gear.
    What it does for both 5 speed and auto transmission cars:
    The computer wants to make sure the A/C is off due to the added load on the engine for the engine running computer diagnostic tests. It also checks to see that the transmission is in Neutral (5 speed and auto transmission) and the clutch depressed (T5, T56, Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

    The following is for 5 speed cars only.
    The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector from the rear. Jumper the safety pin to the ground near the computer.
    Be sure to remove the jumper BEFORE attempting to drive the car!!!

  4. The 12v at pin 46 likely burnt the computer board up. Did you inspect the back of the board as well? It requires removal of the board itself from the case so you can flip it over. You cant see the burnt spot by just taking the top cover off.
  6. Thanks for the replies guys.

    jrichker thanks for that picture of the pin out. I was going off of another diagram that I found and pin 46 was in a different spot (55) than in that picture. I will do some more checking.

    liljoe07 thanks. I didn't know I had to heck the back also. I will check tomorrow. Hopefully I can figure this out and get a couple of weeks of driving in before putting it away for winter.
  7. Signal ground troubleshooting 91-93 5 Mustangs

    The computer pin 46 signal ground is a critical component: it provides ground for the Baro, TPS, ECT, EGR and ACT sensors. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground, although both may have a common connection origination point. Signal ground usually has some conditioning that reduces the electrical noise to prevent false readings
    The gray/red 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. What sometimes happens is that the test connector gray/red 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.

    See for Joel5.0’s fix to the computer internal signal ground.

    If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.

    Troubleshooting signal ground problems:
    Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
    1.) With the power off, measure the resistance between the computer test ground
    (Gray/red wire) on the self test connector and battery ground. You should see less than
    2.0 ohms.


    2.) MAP circuit: Check the resistance between the gray/red wire on the MAP/BARO sensor and then the gray/red wire on the EGR and the same wire on the TPS. It should be less than 1 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire. Next check the resistance between the gray/red wire and the negative battery cable. It should be less than 2.0 ohms.

    3.) Engine mounted sensor circuit: Check the resistance between the gray/red wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire.

    #7 jrichker, Sep 22, 2013
    Last edited: Sep 22, 2013
  8. Thanks jrichker. What I've come up with so far is that the circuit 46 at the eec is burnt just like in the link you sent. I got it repaired now. I traced the wires from the clutch and nss connector and there sems to be a problem with the nss connector. On the nss connector there are three wires all blue/red. One side of the connector has two of the wires exiting and gose off in the main harness to the eec. On the other side one of the wires goes out into the engine bay and connects to the starter relay at the top with a 90 degree elbow. The wire has been cut and wired into the elbow so i dont know if that's where it went from factory or if it went to a chasis ground. Now when I crank the car over i get 12v at the little connection where the elbow is on the starter relay which sends 12v through the nss connector and to the eec. But when I dont hook up the elbow on the starter relay the car wont crank over. I'm guessing when the nss circuit is closed that it's supposed to be grounded. I think this might be where my problem is.

    Thanks for all the help so far. I'll go check the ground signals from your post jrichker and go from there.
  9. There are two plugs on the clutch pedal switch. Or should be. The one with the red/blue wire, is for the starter solenoid. That one is supposed to have 12v when cranking the engine. And one with a blue and yellow wire, and a black/white wire. That is not to have 12v. Thats the conmector with the SIGRTN circuit in it.
  10. Thanks liljoe. I checked and there was 12v at that connector. Just got it fixed now. I did the ground test. The readings I got between all the sensors and the computer test connector all the way to the eec are good 0-.2 ohms. What i did was test the grey/red wire from the clutch pedal switch to #46 pin on the harness and got continuity then repaeted for all the sensors and the test connector all with good results. The problem I have now is when I test for ground between any of the sensors or the test connector to the batt neg there is no continuity. Just wondering if the grey/red wire is suppose to ground along the way to the eec some where.
  11. If you still have the computer out, then you won't get a continuity between 46 and battery negative or chassis grounds. There is no physical ground coming off pin 46. Its internally done in the ECM.
  12. He's right...

    That burnt trace on the computer circuit board is the one that connects pin 46 to the main computer power ground.
  13. Alright. I buttoned every thing up and tested for continuity and all is good. Fired the car up and took it for a nice test ride, so far so good. I hope this fixes the problem. What I found was the 02 harness had been changed and the jumper was in the wrong location. That caused 12v to be sent to pin 46 on the eec and it fried the circuit so that's why I had all the codes.

    Thank you jrichker & liljoe for all the help and your patience with me. I really appreciate it. Now I can enjoy the car a little before winter.