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  •  » FYI Ford, Classic Mustang Tech Discussion
  •  » 5.0 AC wiring to computer

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    8/05/2023 12:57 PM  #1

    soonerfan
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    From: St. Louis
    Registered: 7/18/2013
    Posts: 101

    5.0 AC wiring to computer

    I’m fighting a high idle from my computer.
    One of my sensor may be bad or I may have a stick idle bypass, but it may also be my ac compressor and the computer trying to adjust.
    Anybody have a 5.0, 5spd, and a/c installed? I have factory condenser (‘66) and a modern compressor with a single wire connection.
    Car was running fine idling correctly about 750-800ish. Then I got my AC leak fixed and drove twice with the air on and now I’m suffering a high idle of between 1500 and 2100.
    Should the wire from the computer tap into the wire coming out of my condenser that runs to the compressor or should it connect somewhere else to recognize AC compressor load?
    It may not be my compressor, that’s just the latest change to the car.

     

    8/05/2023 1:41 PM  #2

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,392

    Re: 5.0 AC wiring to computer

    If pin 10 going to the ECM has 12v applied when a/c is on for Foxbody ECM’s,
    idle compensation occurs.

    I don’t have mine connected with the Sanden compressor (serpentine) from Classic Auto Air.
    I have the daily driver under dash mount evaporator.

    It would be easy enough to remove, inspect/clean the IAC.
    2 bolts and electrical connector.

    Last edited by Nos681 (8/05/2023 1:45 PM)

     

    8/05/2023 1:51 PM  #3

    soonerfan
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    From: St. Louis
    Registered: 7/18/2013
    Posts: 101

    Re: 5.0 AC wiring to computer

    Thx NOS, that's what I thought.
    I've cleaned the IAB, tps, etc. Sounds like I need to go back and restart those idle troubleshooting threads to figure out my idle issues. I thought I had it licked, then got the AC fixed and it restarted again, so who knows.

       •Thread Starter
     

    8/06/2023 6:44 AM  #4

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
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    Re: 5.0 AC wiring to computer

    Another thought is to check all vacuum ports.
    Are any vacuum caps cracked or missing?
    I would also verify the seal at PCV is tight as well.

     

    8/06/2023 6:52 AM  #5

    soonerfan
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    From: St. Louis
    Registered: 7/18/2013
    Posts: 101

    Re: 5.0 AC wiring to computer

    I have checked the few vacuum lines and connections I have, but didn’t find any leaks. Iab, egr, and tps are all new within the last 5000 miles. Hegos we’re new with my install so there is probably 10000 miles or so.
    I did check the tps last night and noticed that the voltage dropped a little each time the throttle  opened and closed. I adjusted it slightly so the starting voltage is a little higher, .95 instead of .75.
    I found a large checklist for 5.0 mustang surging idles so I’ll try working through that list soon.

       •Thread Starter
     

    8/06/2023 9:38 PM  #6

    TimC
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    From: Wheaton, Illinois
    Registered: 4/01/2013
    Posts: 878

    Re: 5.0 AC wiring to computer

    It wasn't mentioned, so I must ask, did you run a scan to see if the ecm is throwing any codes?  I would start there before going through that lengthy idle surge checklist.  Been there, done that.

     

    8/07/2023 9:03 AM  #7

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
    Posts: 7,620

    Re: 5.0 AC wiring to computer

    soonerfan wrote:

    I have checked the few vacuum lines and connections I have, but didn’t find any leaks. Iab, egr, and tps are all new within the last 5000 miles. Hegos we’re new with my install so there is probably 10000 miles or so.
    I did check the tps last night and noticed that the voltage dropped a little each time the throttle opened and closed. I adjusted it slightly so the starting voltage is a little higher, .95 instead of .75.
    I found a large checklist for 5.0 mustang surging idles so I’ll try working through that list soon.

    The low end of TPS adjustment is 0.85.  Ideal is 0.99.  Once set it shouldn't move around.  I would keep an eye on that and see if it continues to vary.  I will only use Ford/Motorcraft sensors because of QC issues with aftermarket stuff.

    My thoughts would be backtrack to when this issue started.  I fin d a lot of issues are self inflicted due to previous work where you unplugged something and forgot to reconnect it, or possibly disturbed something without realizing it.  Or possibly a new part is bad out of the box (happens FAR more often now).
     

     

    8/10/2023 7:42 PM  #8

    soonerfan
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    From: St. Louis
    Registered: 7/18/2013
    Posts: 101

    Re: 5.0 AC wiring to computer

    I did think it was concerning that I was reading different voltages each time I moved the throttle plate.
    Was planning to pull codes and troubleshoot this week after I had the car aligned, but I was told by the shop they didn’t have enough bolt length to align the car, so now I need to look into that issue instead.
    Thx for the suggestions.

       •Thread Starter
     

     

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