Intermittent Stalling

Discussion in '1987 - 1991 Ford F150, F250 and F350 Truck Forum' started by austin_spafford, Feb 17, 2022.

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  1. austin_spafford

    Hey gang, I'm new to this forum. I have a 1990 f150 with a 5.0L V8 engine and need some input on a problem I've been having. Shortly after buying the truck, it stalled in a parking lot immediately after I fueled up. Assuming it had something to do with the fuel system, I checked the tanks for water and rust and then changed the fuel pump from each tank as well as the fuel filter (to my knowledge, they were the originals). I took it out for about 30 minutes to test out the pumps, and it ran like a top. A couple hours later, I went to start the truck so that I could move it out of the way of my garage and it stalled. After consulting the mechanic that my family has used for years, I decided to check the temperature of the engine, and found that it was running about 50 degrees below operating temperature. I removed the upper radiator hose and found that the thermostat valve was stuck open, so I replaced that and the gasket and again the truck seemed to be running fine. I ran around in the truck for a little over a week without any problems. On Tuesday evening, I went out to run an errand, and it stalled again. I tried starting it about 3 times, and each time it stalled. Finally, on the fourth try, the rpm's steadied out and the truck ran perfectly. I was able to run my errands with no difficulty. I was wondering if you guys had any advise? The problem is extremely intermittent and right when I think I got it fixed, it comes up again. It has so far never stalled when I'm moving fast, only when I'm almost completely stopped. The guy I bought it from said that he had replaced the starter and a hose that was cracked...but other than that didn't do any work on it. As I said above, I replaced the fuel pumps, fuel filter, and thermostat, and I checked to make sure there was no carbon buildup in the throttle body and that the air filter was clean. I would welcome any input!
    Austin
     
    austin_spafford, Feb 17, 2022
    #1
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  2. FTZ HAIC Staff Member Oregon Chapter Founding Member

    Clean and test the Idle Air Control valve. That cause cause problems like this. Its on the side of the throttle body.

    Carb or Maf cleaner sprayed into it will often to a good job of cleaning it and unsticking it. If this doesn't solve it, then try testing it and adjusting it.

    Testing:
    With the ignition off, unplug the IAC.
    Turn key on, don't start.
    Connect a multi-meter's black wire to the negative battery post.
    I don't recall which wire, but it's okay to test all. One wire should read about 10.5 to 12.5 volts. If not, replace.
    Measure the resistance across the IAC valve terminal, should be between 6 and 14 ohms, replace if not.

    If it doesn't need replacing, adjust.

    Adjusting:
    Pull the connector off while it's running. The engine should drop speed and turn off. If not, adjust the idle down with the idle screw a little at a time until it struggles and dies. If it dies quickly instead of struggling, adjust it up. You want it just on the edge of dying when it's unplugged.
     
    FTZ HAIC, Feb 19, 2022
    #2

  3. austin_spafford

    Thanks for the tip! When the problem lingered after doing the stuff with the fuel system, I wondered if it would have something to do with the idle control.
     
    austin_spafford, Feb 20, 2022
    #3
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