My 2006 Ford Fusion SE V6 has trouble starting in cold weather. Once it starts, it’s fine throughout the day, but once it sits a long time, like overnight, it has trouble starting in the morning. If it had a carburetor, I’d say the choke wasn’t working. The dealership couldn’t figure it out a few years back. I even tried a new battery and that didn’t help. Is there a sensor that detects cold weather and increases fuel flow or chokes off air flow for richer starting mixture that could be failing?
Bring the vehicle to a shop where it can sit overnight.
Then before the engine is started, they’ll look at what the coolant temperature signal from the sensor is being sent to the computer.
If the sensor is telling the computer the engine is already warmed when it isn’t, the engine can be hard to start and keep running while the engine is cold.
Tester
There is an engine temperature sensor which, if malfunctioning, can tell the computer the engine is warmed up when it isn’t.
This will cause the fuel system to run to lean, much like, as you said, a carburetor whose choke isn’t working.
I’m also wondering if the fuel pump check ball is leaking, allowing the fuel pressure to drop over night. A test would be to turn the ignition on, but don’t start the car, leave it on for a minute, turn it off for a minute, then try to start it normally. If it fires right up, the check ball is slowly leaking.
+1
I agree with the fuel pump check ball suggested by BustedKnuckes. If the car runs normally once it starts, this may be the cause. If the car stumbles until it warms up, then I would lean toward the sensor theory.
Thank you everyone for commenting. BustedKnuckels, I’m going to try your theory out tomorrow morning. I have noticed if I turn the key on and wait, it’s more likely to start. I don’t think I’ve ever waited a minute, turned off for a minute, and then tried. I will do that and let you know what happens. The only thing I wonder, BustedKnuckles, is the starting problem only happens when it’s cold. If the check ball is leaking pressure, would that still allow the car to start up warm weather but be difficult in cold, or would it be hard to start no matter the temperature?
I tried BustedKnuckels “fuel pump check ball” starting method and it does not help. The car still won’t start when it’s cold out in the morning. I’m wondering if it is the Mass Airflow Sensor. I’m going to get a MAS cleaner, take it out, clean the wires and then see if that helps. I will post again once I get a chance to do that (next weekend). If anyone else has ideas, let me know. Thanks!
A scan tool that can read sensors is the best bet to finding the problem. It would need to be hooked up on a stone cold engine, then the sensors can be read. The two I’d be most interested in are the coolant temp sensor (CTS) and the intake air temp sensor (IAT). These two sensors are used by the ECM to determine fuel load in colder temperatures. If they are sending erroneous data, that could be the problem.
Yup
Stone cold, those 2 sensors should be reading exactly the same temperature
BustedKnuckles and db4690, thank you very much for the advice! I will look into the CTS and IAT sensors. As soon as I can leave the car overnight at a garage, I’ll ask them to check the sensors on a stone-cold engine and we’ll see what happens. I’ll be sure to post an update when I do.
SOLUTION FOUND
It looks like the issue was with the MAS sensor. I cleaned the MAS with MAS spray and it did not help. I went to Pep Boys and asked to get a price on the IAT (intake air sensor) and they said it looks like it is part of the MAS. A mechanic at Pep Boys said to try starting the car with the MAS unplugged. If it starts, then that is the problem he claimed. I tried it and the car did start almost immediately even though my poor old battery was getting to the end of its life.
just to clarify, my car had trouble starting even when being jumped in the morning. It just cranked and cranked until it would finally catch. Therefore, I bit the bullet and replaced the MAS ($115 +tax) and the car started on the first turn even in a 10-15 degree morning but I still needed a jump start in the coldest of mornings. My battery is just hammered after 3-4 years of difficult, cold starts. I then went ahead and replaced the battery and the car starts like new again.
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@Vinonoir
Congratulations!
It is also surprising and nice to hear that the pep boys mechanic had some diagnostic skills.
After hearing and saying so many bad things about that place, and the people who work there, it’s nice to find an exception to the rule
Thanks for the update! It’s nice to hear what finally did fix the problem
You should be proud of yourself for fixing the car economically. $115 for the sensor is, in fact, a fair price.
Did you buy a battery with a 3 year “free” replacement warranty?
Thanks for the post. It does feel go to have this issue behind me for a very ninal price.
I got a battery right from Deka batteries who has a plant near us. Someone we know works there and they picked us up the biggest battery that would fit the car ($75 with old one). I didn’t see any cold cracking amps listed, but it was longer then the last battery and it fit fine, and snug, in the battery box. I don’t know about what kind of warranty it comes with, but our friend will help us out of anything goes awry.
Thank you for posting this. I’ve had the exact same problem with my 2008 Ford Fusion the past two weeks. Same symptoms. Yesterday morning my car wouldn’t start again so I unplugged the MAS sensor and it started right up. I bought some CRC MAF cleaner after work and followed a step by step video on YouTube. No problems this morning but the temperature was around 35 degrees. Hopefully the cleaning works or I’ll have to replace the sensor. Car runs good otherwise… needs to last me another 2 years if possible. 
So glad you were able to find my post. It stumped me for some time before I was able to figure it out from other, similar posts. I figure a lot of people with Fusions have this issue in the cold climates.
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Interesting. I’m sort of surprised the mass airflow sensor has so much involvement during startup. I’d have guessed the computer would just inject more or less gas depending on the air intake and coolant temperature and wouldn’t pay much att’n to the airflow sensor until after the engine was actually running.
I come to learn that this airflow sensor is actually what tells the computer the air temperature and airflow so it knows the mixture adjustments. That’s why starting the car isn’t an issue after it’s warmed up or in the summer. The fuel doesn’t need to be enriched in those cases. However, when it is cold, the defective sensor is failing to tell the computer to enrich the mixture.
Yeah, that makes sense. Glad you got to the bottom of it. On my Corolla the intake air temperature sensor (iat) is a separate gadget, but there’s no reason it couldn’t be incorporated with the airflow sensor. So it’s a combined maf/iat on your vehicle apparently. The downside by combining the two is that it may not be possible to replace just the failed iat component, which would make it a pricey repair.