Ok, here we go. My wife's 97 Explorer is having problems starting when below about 35 degrees outside. When it's under 35 degrees you have to depress the accelerator slightly and it'll start, but you have to hold it until it warms up before it will idle. That's problem #1. #2 is when it's below 25 degrees it will NOT start at all. Starter turns over fine, had the battery checked and replaced just a week ago. The starter motor works fine, it turns over, but will not fire up. After cranking for a couple minutes it'll give an intermittent fire off and then die right back out. You can smell excessive fuel going through the exhaust; then you get a couple shots of fire and it sets off the fuel in the exhaust and almost makes a backfire. The crankshaft position sensor has never been replaced, and from what I heard this could cause the problem. The crankshaft angle sensor has never been replaced either. What is the difference between the two. The 5.0 has both sensors and one has a gear like a distributor and one is just the sensor mounted on the front cover. HELP!!!!

 

You're actually referring to the Camshaft Position (CMP) sensor and the Crankshaft Position (CKP) sensor. The CMP is the sensor located in the distributor hole and is used for fuel and spark timing. The CKP is mounted at the front cover and is used for cylinder position. If the CKP is bad you will get no spark and no start. If the CMP is bad you may notice poor fuel economy and long crank times.

When the engine is running is it running smoothly, or does it have a rough idle like a vacuum leak or misfire?

From your symptoms I don't really suspect either a bad CKP or a bad CMP, but more likely a weak Idle Air Control (IAC) servo. You might try cleaning the Mass Air Flow (MAF) sensor and Intake Air Temperature (IAT) sensors first and check or replace the Engine Coolant Temperature (ECT) sensor first though as these are less expensive than the IAC. If you have a scan tool with the datastream mode you can monitor the operation of the ECT, IAT, and MAF sensors.

-Rod

 

When it does start and it's cold outside it idles very low, but not rough. The idle is normally around 800 rpm. When it's cold out it idles around 500 rpm. This morning I put the battery back in after charging it and tried just a dab of starting fluid in the air intake. It tried to start about twice then nothing. I tried more starting fluid and still nothing. I don't think it's getting fire to the plugs actually.

 

Try holding your foot on the gas a little and see if it starts. Could have a bad IAC.

 

Tried that already. It'll sputter on occasion but will not start.

 

As mentioned from another author I too suspect the IAC HOWEVER you mentioned that you removed the battery to charge it... heres the story, when the battery goes dead OR you remove it the KAM is erased what the kam does is as things like a dirty throttle body start to naturally occur then the kam learns to compensate for this by ramping up the percentage of the iac. when you erase that it now defaults to the original percentage which when cold AND mixed with a dirty or worn IAC gives you a no start condition when the throttle plate is in the idel position.
My question is this when was the last tune-up? more specificly when were the spark plugs last replaced...AND did you use Motorcraft spark plugs?. Most of that question is surrounding what you wrote "smells fuel" you can have lightning for a coil pack however if the plugs are dust old #7 just aint gonna start. As for using starting fluid throw that "stuf" away it is just to unstable in todays engines. I know extream cold and the challanges it can present, (at one time I lived in Minot N.D. and endured -45 degrees) there are several things that can cause a no start condition however it is amazing what a good tune-up can cure.
FYI when you smell fuel and have a no start condition I believe in your owners manual ( most published and least read publication) it states when suspect of "flooded" condition to hold throttle in wide open postion when cranking for X # of seconds to clear the engine of unburned fuel. (that procedure is an actual program within the engines computer).
** other items causing no start when cold, battery, starter, fuel pressure, restricted air filter, wrong engine oil for the ambient tempature, fuel quality, water in fuel, or software in the computer is corrupt (usally due to performance chip) I could go on. I recomend start with a quality tune and go from there, Good luck.

 

The last tune up was in August. Since then I checked the fuel pressure on the rail. The stats for it are supposed to be 35 to 45 psi on the 5.0L before running with the switch on. I got a reading of 18psi. I have purchased a fuel pump but haven't had the time to put it on yet. We'll see how that turns out before I go any further.