Wife has '01 Crown Vic. A couple times in last month, when she starts it, it won't run, but I hear a muffled pop/ thump in air system. Next try it starts and runs fine. Today, it would crank over fine, but not run, after several tries. I got in, pushed accelerator to floor, then it started normally. In a few seconds, I opened the throttle quickly several times, and it revved up fine. I went through repetitions several times, and it started/ ran fine. Once or twice, it would start, then there was a very short "stumble", but it would run fine. On some test starts, I'd hear the fuel pump run briefly, turn the key to start, and it would crank and run as normal. We've had 2 20 degree nights in a row, by the way.
OK, it's been about 30 minutes. I went out a started it 3 times with no problem. Waited a minute or two, started it 3 more times, again without problem. Each time before I started it this last series, I'd hear the fuel pump activate for a second or less. The pump sounds normal.
I'll wait until wife returns with my Vic, then test drive the '01 a ways. Anyone have any idea the most likely cause of this situation? Thanks much.

 

This could be one of those situations where you ask 4 or 5 different people and get 4 or 5 different answers.
Since the intake system is giving some indication of something unusual, why not just open the air filter assy and check if there is anything unusual going on there like maybe the filter is not properly installed or the cover is partially and not completely and correctly assembled. Fast and easy check, but will at least eliminate that possibility.

 

OK; I ran the car around for a couple miles last night. Started and ran fine. Got some "gas dry" and put in the tank. Came home and parked. Successfully started the car several times until bedtime.
THEN; went out this morning, and it cranked fine, but wouldn't start!! I did the same thing as yesterday; held accelerator to the floor, and PRESTO.... it started right up. Let it run a few minutes, cut it off, and then it started every time. Had an important errand, so I drove the car about 18 miles. Plenty of power, no stumbles or stutters or misses. Came back home, cut it off, cranked it again, and it started right up fine. The key thing here is that I've had to floor the accelerator to get it to start on the last 2 cold starts. Someone has mentioned the crankshaft position sensor as the possible culprit. I don't know what that device is suppose to control. I worked on vehicles over 20 years, but they had points, condensor, etc in those days. I changed occupations not long after electronics in cars came into use, though I had some training in the early systems.Any ideas from you modern wrench twisters? Thanks.

 

Most of the time, when a crank sensor is troublesome, is when the sensor gets heated or is hot. The things that change when you floor the pedal are you place the throttle position sensor in a different position and the idle air control valve is disregarded by the open throttle butterfly. You might try cleaning the throttle body air inlet and see if that helps any. Otherwise the idle air control valve itself may have a poor connection that is affected by cold temps or just may be full of accumulated carbon.

 

Well... the problem went away. It starts and runs fine, for almost 2 weeks now. I think what happened was: Wife put gas in the car.It sat through 2 cold nights/ days, and we used my 03 P71 for errands during that time. Must have been water in the gas, and it froze somewhere in the system. I put the "gas dry" in as mentioned previously, and it apparently took a little drive time to get the water out. So, thank you who made suggestions.

 

There are two types of dry gas, you may have picked the one that works. Hint: The good one costs twice as much! But that Techron complete stuff also works good, and you clean the combustion area too.

 

If you haven't had the fuel filter replaced recently, it's always a good thing to replace it before cold weather comes on because "dry gas" will not melt ice and if there is some water in the fuel filter it can freeze and the only way to get fuel up to the engine now is to thaw the fuel lines and filter out. Cheap insurance , and I don't know too many people that like to work on the road in the cold.

 

As I understand, modern fuel pumps usually just quit outright, not intermittenly. Correct? Had trouble with this 01 Vic again in some zero nights. Tried to start it on an 11 or so degree day, would only run on starting fluid. I put a small heater under the gas tank for about an hour. I pushed in the shrader valve stem in the fuel rail afterward, and gas came out with no bubbles. I then tried again, and it started right up. I let it warm some, drove about 3 miles, no problem. Put in some gas on top of Heet and STP fuel system clnr., and drove another 5-8 miles. The car never stumbles, stutters, misses, or loses power,ONCE it starts. It has started/ run fine for 2 weeks + now. I hope to change fuel filter tomorrow. Suppose to be near 60 degrees, before another Arctic plunge arrives. I'm old and have some serious ailments and can't do things like I once did, but hope to get that done.

 

There are two ways you can do this.
One way is to rap the inertia switch in the trunk, you should hear the ball roll. This shuts off the electric fuel pump in the tank. Then you crank the engine to reieive the pressure in the fuel line until the the engine will not run anymore. Now it is safe to remove the fuel filter without getting a fuel bath.
The other way is to remove the fuel pump fuse to accomplish the same thing.
Just don't forget to reset the inertia switch or reinstall the fuel pump fuse when done.

 

Thanks, all, for the help. Got the filter changed. Old one was not plugged up; I could still blow through it by mouth. There was some restriction, but not as much as I had expected.
Now: I started the car and let it idle, while laying under it, to check for leaks, which there were none. As I listened though, I could hear an intermittent "rattle", sound like it was coming from the fuel pump area. Not loud; kind of like 2 metal lines vibrating against each other. At the same time, I could detect engine idle varying in time with the rattle, VERY slightly, maybe 50 RPM or less. I thought it might be the system purging any air in the lines that may have gotten in when changing the filter. Any ideas? Also, I drove about 2 miles BEFORE changing the filter. The car had sit not running for about 30+ minutes while I prepared to change the filter. I did NOT disable the fuel pump as I should have, just left the ignition off. When I disconnected the fuel lines, there was some gas dribble, but no large stream or "gush". This stopped in a minute or less. Is THAT normal? Thanks much.