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My '04 Taurus has about 155K and CEL came on. Code is 0451 FTP (fuel tank pressure sensor)
Since you have to lower the tank to get to the sensor I am trying to do some trouble shooting first.

When I first purchased the car there was a loud "woosh" when you removed the fuel filler cap.
It doesn't do that any more.
I have cleaned the cap and it seems to be OK, fits tight and "clicks" as it should when you tighten it.

I tried putting a piece of cling wrap over the fuel filler. Nothing, no noticable pressure or vacuum at idle.
Something strange: with the filler cap off, a tapping sound coming from inside the tank after idling for a few minutes.
Lasts 5 or 6 seconds, stops for 10 seconds, starts again.

I believe if tank pressure is too high I should get a P0453 code, if pressure is too low, P0452
I don't seem to have any pressure or vacuum and I'm getting P0451
Any help would be appreciated. JayKay aka John


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contributions: 1957
Images: 37
Location: Oregon
P0451 means that the fuel pressure sensor in for the fuel tank changes greater than 14 inches of water in 0.10 seconds. (sensor + or - 1.7 inches )

with the tank at atmospheric pressure the FTP sensor should read 0, +/- 1.7 inches

you code will probably be an intermittent signal from the sensor. Look for a bad wire or connection. If not look at replacing the FTP sensor then it goes to the computer.

P0451 is the only code you have right?


   
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Yes, P0451 is the only code.

Unfortunately I have no way to measure the pressure. The system is supposed to operate under a vacuum right? That's why when you take the gas cap off you hear the "woosh" as air enters, well it doesn't create any vacuum when its running in my driveway.
If that's the case I would expect it to give me a different code?


   
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contributions: 1957
Images: 37
Location: Oregon
you use a scanner, usually the tool you got the code from, so see what the FTP sensor is doing. you have a 5V reference on one wire and ground on the other side wire. the middle wire is the signal back to the computer. At atmospheric pressure the FTP should be very close to 0, zero. the give you an offset, (I don't know why they went to use this term, it's just another way to say: allowable variance) of +/- 1.7 inches water. So if your gas cap is off, the FTP should be 0. The code you have says that the sensor signal is erratic. Moving to much in a short time. It could be a loose connection or an intermittent short to ground. It could be a bad sensor. Without a scanner or a volt meter, preferably a graphing one so you can see what is happening, hooked up to your car and see what the signals are doing when you are driving, to know what the problem is coming from you are reduced to replacing parts and see if that takes care of your problem.

the system is sometimes under vacuum and sometimes not. There is a vacuum switching valve that does allow vacuum into the system. However when that valve is closed and the vent valve is closed there may be a positive pressure condition. With the car stopped and sitting for a time the vent valve should be open and the system should be at atmospheric pressure or neutral.

http://www.youtube.com/watch?v=i0e-Uu4fXTs


   
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Problem solved. P0451 cleared and has not returned in 2 - weeks:

The problem was a damaged fuel tank.
Tank was badly dented in the vicinity of the plastic device next to the fuel pump. It extends down into the tank, almost to the bottom. When the tank was damaged, I suspect this device was pushed up and the seal at the tip where it extends throught the top of the tank was damaged.
Replacing the tank fixed the problem. I reset the P0451 code and it hasn't come back after about 2 - weeks of driving.
Beware! If you buy your tank fron Pick-N-Pull:
1. They lift the car with a forklift and in most cases damage the tank. I looked at at least 12 before I found a good one.
2. Or so I thought! The receipt said "Tank may be punctured" probably should have said tank will be punctured. (they drain the tanks by knocking a small hole in it)
My tank had a hole but not in the bottom of the tank and believe it or not I didn't notice it when I installed the tank. Everything seemed OK when I put it back together and with a couple of gallons of gas. When I put more gas in it, it started to leak out under braking.
Repaired the hole by cleaning carefully with coarse sandpaper, de-greasing with brake parts cleaner and applying a cone shaped plug of Loctite epoxy.
3. When you get your tank at the junk yard practice removing the fittings with the diabolical clips and make sure you take a couple of each size as you probably will beak some and the Ford dealer doesn't stock them.
4. When you re-start the car, the fuel pump is empty. The car runs very rough for a short time until the fuel is flowing properly. This was enough to set two more codes and the CEL on however it went off after a few miles and a couple of starts.


   
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