Tweecing Questions, Bad O2?

Discussion in 'Fox 5.0 Mustang Tech' started by mind, Jul 18, 2012.


  1. mind

    mind New Member

    Joined:
    Jul 18, 2012
    Messages:
    1
    Likes Received:
    0
    Trophy Points:
    1
    i'm messing with a '93 cobra, heads, cam, a9l, 24's, stock 5.0 mass air meter.

    Check engine light currently on because someone wired the fuel pump separately.
    I will fix that this weekend.

    It runs in open loop most of the time and is rough.
    It runs in closed loop briefly and runs smoother, but then switches back to OL after 1 minute or so.

    I have
    loaded an A9L bin
    disabled egr and thermatcor
    set the injector low slope to 24
    high to 30
    loaded the 89-93 maf file
    set the checksum base to 0

    I see the HEGO1 seems to function as I would expect, but HEGO2 is far less active and usually sits at .024 volts.

    Is this a clue?
    Or is there something else I'm missing or need to do?

    Any help appreciated!!

    If any tuners in DFW are interested in taking a look, i'll buy diner or beer.
    Thanks
    Tony
    #1
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

    Joined:
    Mar 10, 2000
    Messages:
    21,444
    Likes Received:
    334
    Trophy Points:
    134
    Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

    Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

    Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
    Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

    [​IMG]

    [​IMG]

    If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

    [​IMG]

    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

    [​IMG]

    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


    WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

    What to expect:
    You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

    Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

    Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

    Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

    Alternate methods:
    For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

    Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
    #2
  3. ruin41

    ruin41 New Member

    Joined:
    Jul 31, 2012
    Messages:
    2
    Likes Received:
    0
    Trophy Points:
    1
    Because the hego isnt responding to the computer in closed loop its unable to correct the A/F ratio, so its being forced into open loop to run off the default tables would be my guess.
    #3
  4. 2002BLGT

    2002BLGT Well-Known Member

    Joined:
    Dec 18, 2003
    Messages:
    2,949
    Likes Received:
    3
    Trophy Points:
    59
    Do you have a wideband ?
    #4

Share This Page