Engine Codes 18 And 96

Discussion in 'Fox 5.0 Mustang Tech' started by NC Firefighter, Jun 5, 2014.


  1. NC Firefighter

    NC Firefighter New Member

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    89 GT 5.0
    KOEO test shows continuous memory codes 18 and 96.
    The engine mainly only stumbles while trying to maintain speed on the road with minimal throttle, but seems to lack some torque under full throttle as well. The engine revs smoothly, and steadily holds at any reasonable RPM when not under a load without stumbling.

    Base idle is set around 600RPM, Base timing is at 14deg and TPS voltage is at 0.9v.

    Does anyone have any ideas on this? She's drivable, but just barely while maintaining speed.
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  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Code 18 - SPOUT out or wiring fault - look for short to ground in SPOUT wiring going
    back to the computer. Possible bad TFI or defective 22 K resistor in the IDM wiring

    Use a timing light to check the timing: remove the SPOUT and observe that the timing retards at least 4 degrees. Put the SPOUT back in place and observe that the spark advances at least 4 degrees.
    This code can disable spark advance and reduce power and fuel economy.

    Remove the passenger side kick panel and disconnect the computer connector.
    There is a 10 MM bolt that holds it in place.
    Disconnect the TFI module connector from the TFI and the measure the resistance between the yellow/lt green wire and ground.
    You should see greater than 100 K (100000) ohms.
    Check the resistance from Pin 4 on the computer connector (dark green/yellow) and the dark green/yellow wire on the TFI connector. You should see 20-24 K Ohms (20,000-24,0000 ohms). The resistor is located in the wiring harness about 6” from the connector. You will need solder and heat shrink to replace the resistor if it is bad.
    Next measure the resistance between the yellow/lt green wire on the TFI module connector and Pin 36 on the computer connector. With the SPOUT plug in place, you should see less than 2 ohms.

    The following is a view from the computer side of the computer connector.
    [​IMG]

    This diagram is the wire side of the computer connector.
    [​IMG]

    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]




    Code 96 for 86-90 model 5.0 Mustang – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump lost power at some time while the ignition switch was in the run position. The main power feed to the pump is what is losing power.

    Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under the passenger seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power may not have been wired correctly.
    See http://www.stangnet.com/tech/maf/massairconversion.html

    [​IMG]

    Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. . To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground.
    [​IMG]

    86-90 Models:
    Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so. If not, check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump body to tank wiring harness connector is the likely culprit since it is getting power. No voltage there, check the Orange/Lt blue wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the Pink/black wire, swap the relay.

    Keep in mind that the relay wiring and socket can also cause intermittent problems. Clean the relay socket with non-flammable brake parts cleaner or electrical contact cleaner. If you find damaged wiring at the relay socket, replacement pigtail socket assemblies are available at the auto parts stores. Be sure to solder the wires and cover the solder joints with heat shrink tubing if you replace the relay socket.


    [​IMG]
    Last edited: Jun 6, 2014
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  3. NC Firefighter

    NC Firefighter New Member

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    Thank you sir. I'll let you know what I find.
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  4. NC Firefighter

    NC Firefighter New Member

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    As far as the SPOUT code , here are my results thus far.

    With the SPOUT connector in place, the timing does advance approximately 4deg.

    TFI Yellow/Lt Green to Ground - 0 Ohm
    Pin 4 to TFI Dark Green/Yellow - 22.05k
    Pin 36 to TFI Yellow/Lt Green - 0.4 Ohm

    Obviously the TFI Yellow/ Lt Green to Ground is off, to say the least. I performed this test and all others with the computer disconnected and the SPOUT connector connected.

    Any insight into the cause of this would greatly be appreciated.
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  5. modulistic

    modulistic Member

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    That is telling you the yellow/light green wire is burnt through the plastic or the plastic itself got cut/scraped and the wires inside are touching the body of the car or the engine block. Trace the wire back from the tfi towards the computer and look for cuts or burns. Repair.
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  6. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    He has it right - start looking. The TFI wiring has a foil shield around it and it may have shorted internally. The place to start is nearest the TFI connector. Be sure to carefully wrap the foil shield back in place . It keeps the computer from picking up electrical noise that could make the timing skew at random.
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  7. NC Firefighter

    NC Firefighter New Member

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    Will do. Thanks guys.
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  8. NC Firefighter

    NC Firefighter New Member

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    Latest update....
    I can find no breaks in the Yellow/Lt Green wire from the TFI to pin 36. I do have continuity tone from pin 36 to Yellow Lt/Green wire at the TFI as well as 0.4ohm (which is the resistance that I get across a jumper wire that I cut of similar gauge and length).

    I still show no 100Kohm resistance from the Yellow/ Lt Green wire at the TFI to ground with the computer connector disconnected as per the instructions, but I don't see how that would be possible with the circuit open. With the computer connector connected (battery disconnected), I do show 4.2 Mohm from the Yellow/ Lt Green wire at the TFI to ground.

    As long as the weather holds out, I'm going to pull the TFI and check the resistances across its terminals this evening.

    One thing that I have noticed this week is that, when the throttle is released that the engine take a few seconds to completely return to idle, it will hang around 1500 RPM and then fall off to around 600RPM (which is where the idle is set).

    Do you guys have any other suggestions on this code 18 and stumbling issue.

    Thanks in advance.
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  9. modulistic

    modulistic Member

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    how are you testing the y/ltg wire to ground? are you probing into the tfi connector? if it is 0hms to ground, it is touching ground somewhere very solidly, and very close. look into the tfi connector itself, it may be burned or melted internally to the connector.
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  10. NC Firefighter

    NC Firefighter New Member

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    I've probed the connector side if the TFI, backprobed the TFI connector, probed the wire at the TFI, probed the wire at the SPOUT connector, as well as probed pin 36 of the computer connector to ground. All of which read 0ohm with both the computer connector and the TFI connector disconnected.

    I may be wrong or blatantly overlooking something, I have been many times before.... But it seems to me with one end of the circuit open that the only reading that I could get would be 0. And from what I can tell from the wiring diagrams, there's no resistor in the wire, so I don't understand where 100k of resistance would come from.

    Please correct if I'm just being stupid here, I started out in electronic engineering but switched majors to networking pretty early.

    Also I have taken the resistance measurements across the TFI module itself, I'll post them as soon as I get them typed up.
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  11. modulistic

    modulistic Member

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    so one lead is on y/ltgrn and the other lead is on an engine ground and it shows 0ohm?

    try this for me. pull the spout. put one lead on a ground. probe both directions from the spout connector and report back ohm measurements. if y/g wire is grounded, it will show up as 0ohms in one direction and high ohms in the other direction.

    0ohm means no resistance at all. if you touch the two leads together, no resistance, it will show 0hms. Is it possible it is showing OL? (out of limits) which would be very very high resistance? something, somewhere, is touching ground if its showing a true 0hms from y/ltgrn to ground.

    the test is trying to isolate y/ltgrn to just a single piece of wire - exclude everything else from the equation - and see if it is touching ground at any point. if it is broken/cut/pinched/melted and touching ground at any place, then electricity will flow from the lead, through the engine, into the wire at the break and back to your other lead.
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  12. modulistic

    modulistic Member

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    think of it like this... take a section of wire and lay it on the top of your motor. probe one end with a test lead, and the other end to engine ground. no electricity can flow from the engine block into the wire because it is protected by plastic covering. the resistance will be very very high - in the MegOhms.

    now

    take a bare shiny piece of copper wire and lay it on top of your engine. probe from the engine to the wire. since there is no protective plastic, the resistance will be minimal... 0 ohms or so.
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  13. NC Firefighter

    NC Firefighter New Member

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    Its raining here now, if it stops before dark I'll go out and probe the SPOUT connector and let you know.
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  14. NC Firefighter

    NC Firefighter New Member

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    image011.jpg
    Actual resistance across TFI module:

    A to B- 2.98k
    A to C- 4.14k

    Post A:
    to 1- 4.25k
    to 2- 10.03k
    to 3- 0.996k
    to 4- 2.89k
    to 5- 4.03k
    to 6- 0.0

    Post B:
    to 1- 1.16k
    to 2- 5.52k
    to 3- 5.75k
    to 4- 87.8 ohm
    to 5- 8.77k
    to 6- 4.79k

    Post C:
    to 1- 97 ohm
    to 2- 4.56k
    to 3- 6.73k
    to 4- 1.15k
    to 5- 9.84k
    to 6- 5.86k

    Anticipated resistance per resource:

    A to B- 11.5k
    A to C- 12.6k

    Post A:
    to 1- 12.8k
    to 2- 17.4k
    to 3- 1k
    to 4- 11.5k
    to 5- 4.2k
    to 6- 0

    Post B:
    to 1- 1.2k
    to 2- 5.8k
    to 3- 12.6k
    to 4- 100ohm
    to 5- 15.8k
    to 6- 11.6k

    Post C:
    to 1- 100ohm
    to 2- 4.7k
    to 3- 13.7k
    to 4- 1.2k
    to 5- 16.9k
    to 6- 12.7k
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