Need help with intermittent misfire.

68stang351

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My 04 has been missing intermittently for about a week now. The CEL finally came on the other day and it's a cylinder 3 misfire. I know that about 98% of the time it's a coil. So I replaced the no. 3 coil, and the plugs. It still misses. It doesn't do it at idle, only about 1500-2000 rpm's, maybe higher, but it's most noticeable there. It's not a steady miss, but it's just kinda of jerky. When I've got cruise on 70 it feels like you are driving head on into intermittent 80mph gusts of wind.

So, I checked the new coil with an ohmmeter, and it checks out the same as my others, within specs in the manual.

I checked the connector to the coil, it is getting power.

I believe it is an injector problem. I checked the resistance in the injector, and it is the same as the others. I checked the connector for power, it is getting 12v with key on. I think maybe its gummed up or has trash in it or something.
The last thing I did was let the car run for a few minutes with the coil unplugged, and then killed it and took out the brand new spark plug. You would think it would smell like fuel right? NOPE! Not a trace of fuel smell on it. This leads me to believe that the injector is not getting fuel into the cylinder.

What do you guys think? Do you agree?
 
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02nightmaregt

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if youre fuel system is clogged try running a cleaner through it. I use seafoam about every time i change my oil (thats what they recommend) and i like it. Just an idea though.
 

68stang351

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Update:

I put a brand new injector on it from Ford and it's still missing. I questioned the coil and so I put a coil from a friend's car and another new plug in AFTER the new injector and it's still doing it. After the new injector, along with the cylinder 3 misfire, it also showed #3 injector circuit open. I plugged in a noid light to the injector plug and its flashing like normal. The noid is flashing the same as it did on cyl 1 so I don't see how the circuit is open.

So it's not the plug, not the coil, not the injector, I'm starting to think it's either got to be the ECM or the wiring harness. I have a friend that has a harness that he's going to let me use so I guess I'll try that. If not, ECM?:shrug:

Can anyone help me? This is my daily driver, I need it to run right as soon as possible.
 

BobHyatt

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My 04 has been missing intermittently for about a week now. The CEL finally came on the other day and it's a cylinder 3 misfire. I know that about 98% of the time it's a coil. So I replaced the no. 3 coil, and the plugs. It still misses. It doesn't do it at idle, only about 1500-2000 rpm's, maybe higher, but it's most noticeable there. It's not a steady miss, but it's just kinda of jerky. When I've got cruise on 70 it feels like you are driving head on into intermittent 80mph gusts of wind.

So, I checked the new coil with an ohmmeter, and it checks out the same as my others, within specs in the manual.

I checked the connector to the coil, it is getting power.

I believe it is an injector problem. I checked the resistance in the injector, and it is the same as the others. I checked the connector for power, it is getting 12v with key on. I think maybe its gummed up or has trash in it or something.
The last thing I did was let the car run for a few minutes with the coil unplugged, and then killed it and took out the brand new spark plug. You would think it would smell like fuel right? NOPE! Not a trace of fuel smell on it. This leads me to believe that the injector is not getting fuel into the cylinder.

What do you guys think? Do you agree?
I personally don't like to try guesswork, so my approach would be to pull that fuel rail and swap two injectors. If the problem moves, replace the injector, if not, then you have to keep looking. I would have done the same with the coil as well, as if it moves with the coil, the coil is bad...

This is by far the easiest and cheapest way to find a problem, otherwise you can toss a lot of money at the wrong area and still have the same problem when you are done. Intermittent miss has to be either spark or fuel. Spark covers plug and coil, fuel is the injector. Otherwise the next shot is a wiring problem which can be a royal pain to find.
 

chuck943

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Strange, the PCM grounds the injector to open it, if the noid light was flashing then PCM is grounding it,I suspect maybe your might have set that code(circuit open) while messing with the injectors. If u have tried new injector,another coil and plug, then u better do a compression test and a running comperssion test to make sure u have a hole.
 

68stang351

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I personally don't like to try guesswork, so my approach would be to pull that fuel rail and swap two injectors. If the problem moves, replace the injector, if not, then you have to keep looking. I would have done the same with the coil as well, as if it moves with the coil, the coil is bad...

This is by far the easiest and cheapest way to find a problem, otherwise you can toss a lot of money at the wrong area and still have the same problem when you are done. Intermittent miss has to be either spark or fuel. Spark covers plug and coil, fuel is the injector. Otherwise the next shot is a wiring problem which can be a royal pain to find.
I've already tried a new injector and two coils, please read my post! You are telling me things that I've already stated that I've done. I don't want to be a dick but you're not reading the thread very clearly and I need only helpful advice. Sorry.
 

68stang351

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Still no more help. Come on guys, I need to get this fixed.

If it helps here is the freeze frame data from when the CEL was last tripped.
P0303
Throttle Position 34.5%
RPM 2043
Load 68.2%
Air flow rate 47.72 GR/Sec
Coolant Temp 185
Intake air temp 75
Timing 20*
Short term fuel trim 1 2.2%
Long term fuel trim 1 0.7%
Short term fuel trim 2 20.59%
Long term fuel trim 2 72.6%
Short term fuel trim 3 38.2%
Long term fuel trim 3 72.6%
Short term fuel trim 4 85.9%
Long term fuel trim 4 30.1%
Speed 74mph
Fuel rail pressure 2.78 Kpa (this converted to only .4 psi, strange)
Fuel system Closed loop
02s1211 .695v
02sxx11 .695v
02s1212 .930v
02sxx12 .930v
Short term fuel trim (BX-xy)22 99.2%



Thats all I have please help.
 

Pearl02

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Strange, the PCM grounds the injector to open it, if the noid light was flashing then PCM is grounding it,I suspect maybe your might have set that code(circuit open) while messing with the injectors. If u have tried new injector,another coil and plug, then u better do a compression test and a running comperssion test to make sure u have a hole.
A Compression is the next thing you should check.(if low, do a wet compression test.)
I agree with both of these post. You should run a compression test to rule out any problem and go from there. Pearl02.
 

68stang351

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I agree with both of these post. You should run a compression test to rule out any problem and go from there. Pearl02.
Thanks. I'll try that. I've known that I should have tried that but I'm kind of afraid that I won't want to know the results. You're like the 3rd person that's suggested that so I guess I'll give in to it. I guess I'll dig up my compression tester in the morning and check it out.

I don't know what the hell I'm going to do if it has no compression.:shrug: Find a wrecked mach 1 maybe and transplant?
 

lewbud

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Question, have you just changed the plugs? The reason why I ask is that I had the same thing happen after the last time I changed plugs (looking at my records, it's time I got some new ones). You said you've replaced the coil and the injector, but is it possible you've got a bad plug? I would think that compression is fine in #3 because I did a dyno pull 04/07 (plugs were replaced 03/06) and the hp was where it was supposed be with the mods I've got: catback and pulleys best pull of the three was 239 hp (previous pull w/catback only was 230hp 05/05). If I'd dropped a cyl, the hp should have been way off. I wish I could tell you I did something to rectify the situation but I didn't. The CEL came on a couple of times after the new plugs were installed, I checked and cleared the code when it occurred and I haven't had a prob since. It's been about a year and a half since the last time this happened. Hate to tell you it'll go away, but that was my experience , or it's still there and the computer is ignoring the code. Sorry to muddy the waters even more.

Buddy
 

68stang351

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Question, have you just changed the plugs? The reason why I ask is that I had the same thing happen after the last time I changed plugs (looking at my records, it's time I got some new ones). You said you've replaced the coil and the injector, but is it possible you've got a bad plug? I would think that compression is fine in #3 because I did a dyno pull 04/07 (plugs were replaced 03/06) and the hp was where it was supposed be with the mods I've got: catback and pulleys best pull of the three was 239 hp (previous pull w/catback only was 230hp 05/05). If I'd dropped a cyl, the hp should have been way off. I wish I could tell you I did something to rectify the situation but I didn't. The CEL came on a couple of times after the new plugs were installed, I checked and cleared the code when it occurred and I haven't had a prob since. It's been about a year and a half since the last time this happened. Hate to tell you it'll go away, but that was my experience , or it's still there and the computer is ignoring the code. Sorry to muddy the waters even more.

Buddy
I didn't change them until it started missing, but I've changed the #3 plug twice to make sure it was a good plug.
 

chuck943

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Thanks. I'll try that. I've known that I should have tried that but I'm kind of afraid that I won't want to know the results. You're like the 3rd person that's suggested that so I guess I'll give in to it. I guess I'll dig up my compression tester in the morning and check it out.

I don't know what the hell I'm going to do if it has no compression.:shrug: Find a wrecked mach 1 maybe and transplant?
Also do a running compression test
http://www.misterfixit.com/dyncompr.htm
 

68stang351

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I think I found what is wrong with it. Last night I cleared the code when I was messing around with it. Of course it started missing again on my way to work this morning. When I got to work I took our code reader and checked it and it had the cylinder 3 misfire again, but also showed "injector open circuit cylinder 3". So with the key still turned forward I got out and started to make sure the #3 injector plug was plugged in tight. As soon as I touched the injector plug the injector started clicking like mad. Every time I wiggled the harness, even the main connector by the firewall, the injector was clicking like crazy. With the engine off! I have a spare engine harness here (from a friend that bought a PI 2v crate engine for his 98, couldn't use that harness) so I'm going to change the engine harness because I'm convinced that's what it is. On the way home it didn't miss a beat. I'm sure it is a connection problem or the injector's ground wire is somehow finding a ground when its not supposed to or vice versa. I will keep you guys updated.
 

68stang351

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:D:D:D:D:DHahahaha!

I found it. As soon as I started taking the engine harness off I found the problem. Right after I disconnected the three main connectors by the firewall and pulled them across the car, I noticed that the harness dropped down and was rubbing against the EGR tube. I looked and it had rubbed through the tape and conduit and had just barely started to show a bare wire. Guess which wire? The ground to the #3 injector! Brown with a yellow stripe. Since the injector always has a 12v and the computer grounds the injector to complete the circuit, it was getting grounded on the EGR tube and opening the injector when it did that! I spent about 2.5 hours replacing the harness (the last 30 mins was just trying to plug in the passenger side O2 sensor :nonono:).

I've never had a problem I couldn't fix and I'll be damned if a ****ing 4.6 Mustang is going to get the best of me!

Hope that made sense, I've been celebrating my victory if you know what I mean.:cheers::cheers::cheers::cheers::cheers::cheers::cheers::cheers:

Thanks for the help Stangnet!:SNSign:
 

chuck943

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:D:D:D:D:DHahahaha!

I found it. As soon as I started taking the engine harness off I found the problem. Right after I disconnected the three main connectors by the firewall and pulled them across the car, I noticed that the harness dropped down and was rubbing against the EGR tube. I looked and it had rubbed through the tape and conduit and had just barely started to show a bare wire. Guess which wire? The ground to the #3 injector! Brown with a yellow stripe. Since the injector always has a 12v and the computer grounds the injector to complete the circuit, it was getting grounded on the EGR tube and opening the injector when it did that! I spent about 2.5 hours replacing the harness (the last 30 mins was just trying to plug in the passenger side O2 sensor :nonono:).

I've never had a problem I couldn't fix and I'll be damned if a ****ing 4.6 Mustang is going to get the best of me!

Hope that made sense, I've been celebrating my victory if you know what I mean.:cheers::cheers::cheers::cheers::cheers::cheers::cheers::cheers:

Thanks for the help Stangnet!:SNSign:
Good Job!!