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Discussion Starter #1
Hello

I have a 2001 v6 Mustang. The "check fuel cap" light has mostly been on, off, and on for about 6 months. There's a leak where the fuel tank meets the fuel line used to pump gas into the tank. A Ford tech cleared the code, and the light remained off for months.

About 3 months ago, the "service engine soon" light came on, at about 65 MPH, with no performance issues. The light never went off. I figured this was related to the fuel vapor leak. About 1 month ago, the "check fuel cap" light came back on, again with no performance issues.

About a week ago, I started having a significant poor performance issue, "missing" is the best way I can describe it. It lasted from when I started driving until about 2 minutes later. Then the performance went back to normal. A couple days ago, the performance issue was there again, but this time it got worse, and the service engine light started blinking. Yesterday, when I drove to get the codes scanned, performance was slightly better (but still bad), this time with no blinking light (it just stayed on).

The following codes were displayed:

P0455 Evaporative Emission Control System Leak Detected
(Large leak)

P0457 Evaporative Emission Control System Leak Detected
(Fuel cap loose or off)

P0301 Cylinder 1 Misfire

The codes were cleared, and I drove for about 10 minutes, the lights both stayed off.

What confuses me is why this performance issue was so intermittent. First it resolved completely when the car got warm, then it was really bad with a blinking light (which I've never seen before), now it's slightly better with no blinking light (just the light staying on).

My instinct is to first replace the spark plugs and wires, but I'm curious if this pattern of on and off and on fuel cap light, and on and off performance problems, should be pointing me in a different direction.

Many Thanks
 

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Find a book or online guide to possible causes for error codes. Check one part at a time, and don't replace it if there is nothing wrong with it. Sometimes there are like 10 things that can cause a code to go off. I doubt it's your spark plugs, or your wires.
 

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Check the gasket on the fuel cap. Sometimes thats the culprit.. :scratchchin

Have you replaced the cap?

Check all the hoses in the EEC system ! The coal cannister is located behind the drivers side rear wheel.

Any funky smells in the garage or other enclosed areas of the car?

Good luck ! :happyhapp
 

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I don't mean to be offensive, but "buy a book" isn't very helpful. I came here to get helpful advice from people that have experience with similar issues.
I should have explained myself better. It's pretty easy. Find a book or call ford and ask one of their techs what the common causes are for code xx and code yy ect. Then ask here what is the best way to go about fixing it or where to start. It could be so many things. . . I've been trying to get the airbag light to turn off after i took apart the steering column to replace the ignition switches and remove the alarm, been working on that for about a month on and off. Once a week I go through a few more things that could be the cause.
 

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Discussion Starter #6
Check the gasket on the fuel cap. Sometimes thats the culprit.. :scratchchin

Have you replaced the cap?

Check all the hoses in the EEC system ! The coal cannister is located behind the drivers side rear wheel.

Any funky smells in the garage or other enclosed areas of the car?

Good luck ! :happyhapp
Thanks for the suggestions. I know what's causing the 455 and 457 codes, there's a leak where the gas tank meets the gas line used to fill the tank. That's an annoyance, but it was there before the performance issues. But let's look at the bright side: I have a fuel vapor leak. That would really annoy the tree huggers. :hihi:

My concern is the performance issue, which is apparently related to code P0301 "Cylinder 1 misfire". I don't see any noticible wear and tear on the spark plug wires, so I'm wondering what to fix first.
 

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A misfire may be due to a coil problem.

That would be the first place I would look after the spark plug. I bet the computer knows to throw a code because the culprit is the coil ! The computer wouldn't throw a code on a bad spark plug would it ?

Is the main harness in the engine bay ok? Anything wrong with the wires that goto the PCM?

Unless there's a valve spring broken or push rod bent then I don't know what else it could be.
 

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Thanks for the suggestions. I know what's causing the 455 and 457 codes, there's a leak where the gas tank meets the gas line used to fill the tank. That's an annoyance, but it was there before the performance issues. But let's look at the bright side: I have a fuel vapor leak. That would really annoy the tree huggers. :hihi:

My concern is the performance issue, which is apparently related to code P0301 "Cylinder 1 misfire". I don't see any noticible wear and tear on the spark plug wires, so I'm wondering what to fix first.
That leak could have got bigger and maybe the system cannot pressurize right. Looks like the check cap sensor is definitely showing that there is a problem with the pressure or whatnot. It probably thinks the cap is off because there is a leak. I have heard of misfiring because of a fuel pump/filter issue, but it could just be the system not getting the right amount of pressure.
 

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Discussion Starter #9
fixed !!

Okay, the spark plugs and wires seemed like the most logical place to start, the coil was going to be my next try. Anyway, I replaced the plugs and wires, and it's running fine now. In terms of expense, looks like I got lucky :shiny: (which is somewhat rare).

Thanks for all of the input.
 

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Glad you get her running right!
 

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Its may be the the rubber grommet in the tank thats what happend to mine first it was the check engine then the check fuel cap. I replaced the fuel grommet because it was leaking from their cleared the codes now its back to normal
 

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Discussion Starter #12
rubber grommet

What exactly is the "rubber grommet"? I know a little about electrical, but nothing about fuel tanks. There's a large external rubber o-ring at the point where the fuel line meets the fuel tank, but I can't tell if the leak is coming from the o-ring itself, or metal underneath/nearby the o-ring.

Thanks
 

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Ha Ha i had the same leaks and the same codes........ I changed that stupid i think $15.00 grommet and cleared the codes and viola alls good again
 

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...Same exact problem...

with my 01 conv. car. The technicians ran what they called a smoke test, replaced a rotting short air hose, and tested the gas cap. The next day the check engine soon and check gas cap indicators returned along with the fuel smell inside the car. I can taste the fuel vapor, its that bad! The only new development since they ran the check is an 8" diameter spot seen on my cement driveway. Possibly a fuel or antifreeze leak? IDK. Tomorrow I will replace the Auto Zone fuel cap with a better one to see if this helps. I will have someone check the grommet you're discussing, as well.
 
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