Electrical 99 4.6 Will Not Start Below 40 Degrees

Discussion in 'SN95 4.6L Mustang Tech' started by Indy Black Stallion, Dec 23, 2013.

  1. Hello, my sons 99 4.6, borla exhaust/h pipe only mods, wouldn't start last winter, which its not driven much then. Narrowed down after it ran fine all summer it will not start around 40 degrees F or below, the garage warmed to 54 last friday and it started fine,Sunday 41 degrees no start. Why/what does 40F have to do with it? Not showing any codes. Pumping pedal changes nothing, I am at wits end, move to Florida, car would run fine.
  2. Have you checked the cranking amps of the battery? It sounds simple but they get worse in the cold. If its not driven much it's likely "within spec" but not strong enough to crank a stone cold motor. Just something to look at.
  3. I will second the comment on the battery. You can go to any parts store and they can test the cranking amps of the battery. It is likely getting weak, so in warmer weather it has enough juice to start the car still.
  4. +1 on the battery. Bottom line. Today's cars simply will not run right without a strong battery and charging system.

    However, if you doubt that the battery is the problem, then MEASURE the voltage at the battery during cranking. Post the lowest reading. If the voltage is lower than 9 volts, likely this is the smoking gun.

    Also, try this. Cycle the key on/pause/off several times WITHOUT cranking. Listen for the fuel pump to run each time. Did this improve starting? If so, consider fuel pressure leak down as a possible problem source.
    #4 wmburns, Dec 24, 2013
    Last edited: Dec 24, 2013
  5. id be more inclined to look at coolant temp sensor..... when they go bad it usually defaults to -40 degrees..... that will dump fuel and cause a hard start..... just to see. hold the pedal to the floor while trying to start it. that puts it in flood clear mode....it should start but may run rough until it warms up some..,,
    trombonedemon likes this.
  6. I've started the car without the temp sensor hooked up, the car threw a code and the fan immediately activated.:shrug:
  7. Just back from the holidays' I will check the battery tomorrow, but expect it to be fine, it cranks good, hot off the charger lately. No fan or anything, tried holding accel, pumping accel etc. I have unplugged IAT sensor, normal rules of thumb aren't working, the more I read the more 1 of a kind problem this seems to be. All input is appreciated and welcome, such a strange situation...
  8. I will try everything posted tomorrow, the fuel pressure leak down could definitely be temp sensitive, something reacting, shrinking or 'sticky' when cold