Need Help With A Code 18

Discussion in 'Fox 5.0 Mustang Tech' started by Travix, Jul 13, 2013.


  1. Travix

    Travix New Member

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    Here goes. I have a 1988 GT Vert with a 331 and a TKO 600. It has Trick Flow Track Heat heads, MSD 6AL, BBK SSI upper and lower intake, X303, 30# injectors, Long tubes, MAF conversion, roller rockers, electric fan, 6AL, 75mm throttle body, BBK CAI and probably a few more things. On the KOEO test I pulled a 95 and I wanna say an 85. The 95 is because when the MAF conversion was done we didn't wire in the secondary fuel pump circuit and the 85 is because I can't find where the dang canister purge solenoid is. I've looked everywhere for it. Moving on, with the KOER test I got a 18R, 33, 41, 91. The o2 codes I'm assuming is because of the larger injectors without a tune or they are bad, the 33 is because the EGR crap, I have no smog components on this car but I'd like it if it didn't throw the code. Not priority right now though. My big concern is the 18. If I remove the spout there is no difference in idle RPM, however I'm getting 22.2 kohms at pin 4 on the harness to the computer (I don't have the diagram in from of me so bear with me if I get the pins wrong) I checked for resistance at pin 36 with the spout plugged in I get .4 ohms and if I unplug the spout I get no resistance, so that tells me it has a complete circuit. I forgot I to say I was testing from the ignition module plug on the dizzy and the computer harness. I've replaced the ignition module and the coil. Still no advance and still a code 18. I've disconnected the MSD and went back to stock. Same problem. I've googled, searched forums, I'm lost and need some help with this. I have given you as much info as I have.
     
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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]

    If all the resistance readings are good, replace the TFI module.
     
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  3. Travix

    Travix New Member

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    I'll try the 100 kohm resistance check. That's the only check that I haven't run yet. Like I said, I've already replaced the TFI module, unless I bought a bad one. I'll give it a shot when it clears up outside. If it doesn't get the 100 kohms what is the problem? I have already checked pin 4 and pin 36. Both of those checked good. So that tells me its not the resistor right?
     
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  4. Strype

    Strype Cuthbert catcher Founding Member

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    I just had a code 18, 85, 33, 41 and 91. Changed the TFI and no more CEL. Exhaust no longer stinks. Runs great now.
     
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  5. Travix

    Travix New Member

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    Sorry, I wasn't clear. By ignition module I meant the TFI module. Its just what autozone calls it. There was no change. Still the code 18.
     
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  6. Travix

    Travix New Member

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    Ok, I don't know if there was confusion but when I checked the yellow/lt green wire I got hardly any resistance. But I checked the dark green/yellow to the ground I got 140,000 ohms. Where to next?
     
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  7. Strype

    Strype Cuthbert catcher Founding Member

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    What does the inside of your distributor cap look like? Mine was corroded too. You need to follow Jrichker's diagram. Return that TFI.
     
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  8. Travix

    Travix New Member

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    Distributor cap is fine. I don't know how that would throw a code. And the diagram said to test the plug, not the module. So I did. When I bought the part I had them test it on their tester thing they have and it tested good.
     
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  9. Travix

    Travix New Member

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    Ok, here's an update. I replaced the TFI module again, I thought perhaps I bought a faulty one. I put the new one in and the code 18 went away until I drove it and came back. I borrowed a friend's computer and drove the car and checked again. No code 18. I beat the crap out of the car too. I'm going to drive it tomorrow some too to see if it will come back. Let's cross our fingers. Oh I forgot to say, I'm throwing a code 92 & 33 if that's relevant to anything.
     
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  10. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Code 33 - Insufficient EGR flow detected.
    Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal changes. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
    Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1.5 ohm.

    Backside view of the computer wiring connector:
    [​IMG]

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif


    EGR test procedure courtesy of cjones

    to check the EGR valve:
    bring the engine to normal temp.

    connect a vacuum pump to the EGR Valve or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

    Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).


    apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

    if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.

    if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.

    if engine stumbled, connect EGR test jig to the hose coming off of the EGR Valve.
    Use your finger to cap the open port on the vacuum tee.
    snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
    did the vacuum gauge show about 2-5 in vacuum?
    if not the EVR has failed

    EGR test jig
    [​IMG]

    The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.


    Code 42 & 92 (engine running) System rich - Fuel control or (memory) System was rich for 15 seconds or more (no HO2S switching) - Fuel control. Look for leaking injectors, fuel pressure too high, cylinder(s) not firing due to bad ignition.
    Code 42 is the RH side sensor,
    Code 92 is the LH side sensor.

    Testing the O2 sensors
    Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

    There is a fuse link for the O2 sensor heater power. According to Ranchero50, it is in the wiring near the passenger side hood hinge. Measuring the voltages will give a clue if it has shorted to the O2 sensor signal lead. The O2 sensor voltage should switch between .2-.9 volt at idle.
     
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