Cold start problem

If the car cranks slowly when cold, look at something simple such as the oil viscosity you are using. If that is OK, then move to a weak battery or worn out starter (or corrosion on any cables attached).

I know this is 2 years old now but hopefully this may help someone out there. My son's 2005 Mustang 4.0 (V6) would not start when the weather dropped below 20 degrees and it was hard to start below 40 degrees. Very long story short our Mustang had a bad Crankshaft Position Sensor. If you want to test yours wait for a cold morning preferably a morning that you have not started the car. Heat up your CPS with a heat gun. Just long enough to get it warm if you hold that gun there too long you'll melt it and that won't be awesome. Once it's warm try to start the car. It may be a long start but if it starts and you haven't done anything else. You may have the same problem. Less that 20 dollars will buy you the replacement sensor but you will need to remove the belt and loosen the bolts holding your A/C compressor so that you can move it enough to access the bolts on the sensor. I hope this helps someone out there. I never would've expected that sensor to fail in the cold. My mechanic didn't suspect it either which is part of what took so long to figure it out. It's also important to not that we did not have a check engine light on. So even though the CPS was not functioning properly it was not throwing a code either. Good Luck. I hope this helps.

It was a first for me and my mechanic. My mechanic does this for a living and I've been working on my own cars for the better part of 20 years. Just because you've never seen it before doesn't mean it can't happen. However unlikely it may be. I used my own code reader multiple times and no codes were shown. My mechanic has a significantly nicer code reader than I do and he was able to show me that no codes were being thrown. But you don't have to believe me. I'm ok with that. I stand by my original statement and offered a test. Take it and try or don't. No skin off my back either way. I posted it to help anyone who may be in the same boat that I was. No logical answers worked in my case. So to my mind logic dictates that an illogical solution became my answer. A new CPS has my car starting reliably again no matter how cold it is outside. We did not get there with a code reader so the sensor did fail in such a way that the ECU did not recognize there was an issue. Beings that the internet is littered with stories of people who have Mustangs that won't start in the cold and several people out there still have not found a solution, I believe this may be worth taking a look at on their cars. Perhaps there is a larger problem with the design of Fords CPSs or ECUs. I do not know. I only know what happened to our car and how we arrived at the solution. I wish everyone having this problem the best if luck. It took us over a year and me changing out several other parts before my issue was solved. I literally feel the pain you are going through.

Issue fixed with the solution provided! I was facing the same problem since the last year, but I was not aware that this was a real problem (I thought this was due to cold temperatures and Mustangs), until I had to replace new spark plugs due to bad combustion on cold starts and potentially wasting more and more gas in the meantime. Also, I had to wait for my car to get warmer to avoid problems, like engine not responding appropriately (similar to cars with carburetors when cold). Chnaged the cranckshaft position sensor and now it starts no matter how much cold is outside. Thank you!