Misses At Low Rpms And At Cold Start Up!

Discussion in 'Fox 5.0 Mustang Tech' started by Silver5.0Stang1990, Aug 28, 2013.


  1. Silver5.0Stang1990

    Silver5.0Stang1990 New Member

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    Just as the title says it misses at 1800 and below but up higher than that it runs great. Its not a hard miss but it does buck a little on occasion. It has started to smell rich could it be the O2 sensors?
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  2. mikestang63

    mikestang63 Mustang Master

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    Run the codes. Do a search for jrichker's writeup. It's easy to do and all you need is a paper clip and maybe a test light. Then come back and post the results.
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  3. Silver5.0Stang1990

    Silver5.0Stang1990 New Member

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    Forgot to mention the codes, I got codes 67 and 85 but because of the code 67 I can't get the KOER codes. Is there an easy fix for this? My car only starts in park or neutral so it works.
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  4. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    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
  5. Silver5.0Stang1990

    Silver5.0Stang1990 New Member

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    Car is an aod and I no longer have AC
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  6. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    In that case, you get to go hunting.

    I haven't mentally disassembled the neutral safety circuit in an auto trans car, so I don't have an answer for you at this time. I'll have to give it some thought, though. If I can find a diagram that doesn't try to combine the two types of transmission neutral safety circuits on one diagram, you'll have your answer. All that trouble to save a single sheet of paper and some ink to print it...
    #6

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