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Discussion Starter · #1 ·
I've been struggling with misfires ever since my intake manifold cracked. I replaced the manifold and still have problems. The misfire occurs during idle and low to medium rpm load, but not during WOT. It feels like shaking and sputtering.

Plugs have been gapped at .54, .56, and .60 with similar if not identical results. They are currently at .54.

The plugs have been replaced three times. The first time I replaced them, the misfire was gone and the car performed perfect. I took the driver side boots out after a short drive to see if there was any fluid down in the holes (this was actually BEFORE I replaced the manifold) and when I put them back in, the car misfired again. I took the second driver side boot out and repositioned it and put it back in. The car ran perfectly again... for about 3 days. Then it misfired again.

Since then I have replaced the intake manifold, the spark plugs, and the coils, paying special mind to that second coil and plug. I've repositioned it, wiggled the wires, replaced the coil and boot three times, and replaced the plug several times. The misfire won't go away this time.

I use only 93 octane and have been running fuel cleaner every time I fill up to clear up any clogged injectors.

I've also checked all readily reachable vacuum lines.

EGR is working properly as far as I know (I put a vacuum on the solonoid and it stalled out.)

Nothing is working. I don't know what to try anymore.
My mechanic can't figure it out either.
The problem only seems to get worse.

My car is a mostly stock 03 Mustang GT with 120,000 miles and FLowmaster mufflers (just got the mufflers yesterday so it has nothing to do with the problem.)
 

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I had a friend with a similar situation and it turned out to be one bad spark plug wire. No way of knowing (to the eye) until he put new wires on there. You already did that much just try a new set of wires.
 

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We dont have plug wires on new edge cars.

From what I can tell from searching 3 or 4 forums this is a common problem with the 99-04's. No one really has an answer. Some guys have full tuned, blown, built motors and still have the slight miss around 1500 rpms.

Some people say its the tune that ford put in, but theres other people with new tunes that still have the problem. So far I've never seen anything bad come out of it, mines done it since I bought it also. I'll look around for a few of the thread I was talking about and post them in here later.
 

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Discussion Starter · #5 ·
No codes thrown.
Also forgot to mention I cleaned the MAF.
It didnt used to misfire.
It performed like a dream when I got it.
I'm thinkin bad wiring somewhere since the one reposition set it straight for awhile.
 

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Discussion Starter · #7 ·
Thanks for the links, Slonlow. There's some good stuff in there. One popular solution was to replace the 02 sensors. Maybe I'll try that next.

Update: I popped the hood after a drive this morning and it looked like the first driver side fuel injector had gas on it while all the others looked dry. If the injector is clogged, could it overflow up out of the injector and past the o-ring like that?
 

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Mine does it to sum days it'll run good while others ittll miss fire or spudder at low rpms when I get in it it seems to have all of it's power, iv changed plugs coils traced wires o2sensors ect.ect. It's drivin me crazy!!!
 

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Discussion Starter · #9 ·
ani ideas for fixes or sources of the problem?
What all can cause a misfire?
And any answer to my injector question?
 

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Doc
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Well, to be honest, if you want a real answer you should get a wide band 02 sensor and a tuner so that you can data log.

That would tell you your issue real quick.
 

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Well, to be honest, if you want a real answer you should get a wide band 02 sensor and a tuner so that you can data log.

That would tell you your issue real quick.
+1
 

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Ive been having th esame problem for forever. Ive taken my car to my mechanic 6 times and he still cant figure out the problem.

So far Ive ran several bottles of fuel cleaner, mechanic did a fuel system flush, 8 new plugs, replaced a clogged injector, and I think he retuned the computer or somethin...Also replaced a sensor...

It threw a code for the #8 injector and we replaced that, but it still has the same problem with no code...

It just misses and sputters...it sucks lol
 

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Discussion Starter · #13 ·
okay. i guess i'll try the wide band o2 sensor and tuner when I get the cash.

Any input on the injector issue? could that be a probable cause of the misfire?
 

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If you have a clogged injector, that might cause you some problems.

I'm having the same problem as you. I thought it might be my injectors so I ran some injector cleaner through my car along with some good 93 oct gas. I put two bottles of slick 50 fuel system cleaner in. That didnt work...I guess theres more to it than my injectors.

It might be worth you trying it though. Its about 12 bucks a bottle. You might have some build up and that would clean it out.

Worth a shot!
 

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Discussion Starter · #15 ·
I just noticed a new symptom. when i yank on the throttle, it hesitates and makes an air sucking noise before actually revving. its a real quick thing. maybe a quarter of a second. but definitely noticeable. The air sucking is the air intake, but i never noticed this before, and i never noticed the hesitation before. is that normal?
 

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~C~, The Other White Meat!
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Did you pull the injectors and look at them? Try cleaning them outside the car. Did you try replacing the boots?
 

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Discussion Starter · #18 ·
IAC is working properly. I have not looked at the injectors. That can be a messy job. I'm not even sure how to tell if they are clogged or dirty or working properly. any tips?
 

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Mine did this too. Worked fine when i bought the car and then all of a sudden it started to misfire and sometimes it wouldnt start and t would backfire on startup. It pissed me off because i would never know when it wpuld do it and sometimes it would go away for like a month and then come back. Turns out it was my alternator. I took it off and had it checked and it wasnt putting out enough voltage. I replaced it and havent had a problem since. Try turning your ac on all the way and then checking your battery and the alternator should be putting out around 14.1-14.4 volts.
 

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Discussion Starter · #20 ·
Thanks for the tip! I tested the alternator and it was sporadically pulling values from 13.0 to 13.7 volts. Are these values too low? Could this be my problem?
 
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