2003 gt misfire tried almost everything

Mustang with a miss · Mar 1, 2019

I’m new to this but I ran out of stuff to try I have a 03 mustang gt 5 speed and about a week ago it started missing under load when driving and now it’s missing at idle too Ive narrowed it down the the back cylinder on the passenger side and by unplugging coilpacks until one didn’t make a tone difference in the miss I know the plug is good and I put a brand new cop on it I even swapped them around and it’s still missing on that cylinder I listen to the injection with a screw driver and it sounds like all the over ones but I’m not ruling an injector out yet . I’m gonna pull the fuel rail off today and see if that injector is weak or clogged my buddy is also gonna bring his multimeter and check the resistance of the cop and injector i don’t know anything about that stuff but he said he knew a little. I also changed the fuel filter with little effect on miss. I fear it may be a pcm causeing my probably is there anything I’m missing here ? help would me very appreciated thank you

wmburns · Mar 1, 2019

Just wondering. What have you done to rule out a base engine problem? Consider running a compression test or cylinder leak down before looking at a bad PCM.

In addition you should confirm:

Primary ignition pulse
Fuel injector pulse

Using a "noid" style tester that can be rented from most any auto parts store.

If clogged injectors are suspected I have had great luck using a service such as InjectorRX.com. Once cleaned and flow tested they are as good as new (but cheaper).

Mustang with a miss · Mar 1, 2019

wmburns said:
Just wondering. What have you done to rule out a base engine problem? Consider running a compression test or cylinder leak down before looking at a bad PCM.

In addition you should confirm:

Primary ignition pulse

Fuel injector pulse

Using a "noid" style tester that can be rented from most any auto parts store.

If clogged injectors are suspected I have had great luck using a service such as InjectorRX.com. Once cleaned and flow tested they are as good as new (but cheaper).

Is using a multimeter gonna show us a correct reading on if the coils or injectors are getting enough power ?

Mustang with a miss · Mar 1, 2019

I don’t suspect a base engine problem cause i figured there would be some signs of it being a mechanical failure within the engine. Ik how bad 4.6 are with the coilpacks so I started there but I know my Coil pack is good . It’ll clear up and run fine for a couple seconds and then start missing again so I suspect a fuel problem or a wiring problem but it started this just all the sudden while driving

Mustang with a miss · Mar 1, 2019

I cranked it up today for the first time since yesterday and it ran perfect until I got it on the road and it started missing as soon a I gave it load and then it started missing at idle like it was doing yesterday after it got warm

Mustang with a miss · Mar 1, 2019

I let it cool off and it runs fine at idle when I rev it hard to give it a little load it misses then the spark on my sct tunner data log goes to like -7 degrees while it’s missing under load then goes back to 24 /25 when Idling And runs fine at idle ? Should I just break down and buy new coil packs ? I can’t get my buddy multimeter till tomorrow anyone have any suggestions?

wmburns · Mar 1, 2019

Mustang with a miss said:
Is using a multimeter gonna show us a correct reading on if the coils or injectors are getting enough power ?

No. How could you tell the difference between:

A bad device
a wiring fault.
a bad PCM.

Using a VOM as several problems.

It does not test as the circuit is actually being used.
It does not test the circuit under a load.
It does not test the wiring to/from the device
it does not confirm the ability of the PCM to control the circuit.

Mustang with a miss · Mar 2, 2019

I got it to idle normal for now the noid light didn’t tell me anything really everything was good with the light .It’s idling normal now( did it by itself?)but when I rev it hard and give it load it still try’s to sputter a little and the spark goes down on my tunner and when I drive it easy it don’t really sputter/hesitate until I give it load and the the spark goes down on the tunner as well getting tired of this issue been going on for couple weeks now , should I just break down and buy new coil packs ? I thought ab the intake being cracked and letting a little water in the cylinders and making it hesitant under load ? Ik the intake leaks a little but I’m positive my spark plug holes are dry

Mustang with a miss · Mar 2, 2019

Anything else I should watch on my tunner?

wmburns · Mar 2, 2019

Mustang with a miss said:
I got it to idle normal for now the noid light didn’t tell me anything really everything was good with the light

I strongly disagree with this. The test did give valuable information. It confirms that the wiring is good, As well as the PCM has "control' of the circuit. So we can move forward with the trouble shooting with the knowledge the basic circuit is sound.

Mustang with a miss said:
it don’t really sputter/hesitate until I give it load and the the spark goes down on the tunner

What does "spark goes down" mean? Are you referring to the spark advance? If so, that would be normal.

Mustang with a miss said:
should I just break down and buy new coil packs ?

If you are head strong to throw parts at the problem the buy a new set of COP boot insulators. A new set of COP boot insulators can be had for less than the cost of a single new COP.

Mustang with a miss said:
I thought ab the intake being cracked and letting a little water in the cylinders and making it hesitant under load ? Ik the intake leaks a little but I’m positive my spark plug holes are dry

If your intake is cracked, IMO the bigger problem is a vacuum leak causing a lean misfire.

What are the long term fuel trims (LTFT) at idle and at 2000 RPM's?

Mustang with a miss · Mar 2, 2019

wmburns said:
I strongly disagree with this. The test did give valuable information. It confirms that the wiring is good, As well as the PCM has "control' of the circuit. So we can move forward with the trouble shooting with the knowledge the basic circuit is sound.

What does "spark goes down" mean? Are you referring to the spark advance? If so, that would be normal.

If you are head strong to throw parts at the problem the buy a new set of COP boot insulators. A new set of COP boot insulators can be had for less than the cost of a single new COP.

If your intake is cracked, IMO the bigger problem is a vacuum leak causing a lean misfire.

What are the long term fuel trims (LTFT) at idle and at 2000 RPM's?

I put my buds cop on form his car that runs magnificent and it’s still has that hesitation under load and @ 2000 rpms it’s about 1.03 when it hesitates it goes down to 0.95 ish . I really appreciate the help man I’m only 18 and I have okayish knowledge ab mechanics from my dad and some tech school and I really helps to have some with tons of knowledge about my problem.and by down on spark it has spark on my tuner and it says degrees

wmburns · Mar 6, 2019

Have you cleaned the MAF? Usually a dirty MAF will over state flow at idle and under state under load. This results in LTFT's taking fuel away at idle and then adding fuel under load.

What have you done to rule out excessive EGR flow?

What have you done to rule out a clogged injector?

What have you done to confirm that the base engine is healthy?

If you are just starting out fixing your own car, I urge you to stop using the "parts changing" method as a primary way to fix cars. Fixing a modern car is a data driven activity that is greatly improved by learning HOW to use an ODB2 scanner. Here's some information on an affordable Windows based unit that will pay for itself with a single good part replaced without a fix.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Mustang with a miss · Mar 7, 2019

wmburns said:
Have you cleaned the MAF? Usually a dirty MAF will over state flow at idle and under state under load. This results in LTFT's taking fuel away at idle and then adding fuel under load.

What have you done to rule out excessive EGR flow?

What have you done to rule out a clogged injector?

What have you done to confirm that the base engine is healthy?

If you are just starting out fixing your own car, I urge you to stop using the "parts changing" method as a primary way to fix cars. Fixing a modern car is a data driven activity that is greatly improved by learning HOW to use an ODB2 scanner. Here's some information on an affordable Windows based unit that will pay for itself with a single good part replaced without a fix.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

I cleaned my maf with maf cleaner (didn’t do anything) I put my buddy’s maf on it still didn’t do anything, took all my injector out cleaned them out the back in the rails primed the fuel pump for pressure and got a little 9 volt battery and put positive wire and negative wire to check to see how the injections where spraying and they all where spraying good and strong. How to do I rule out the egr?

wmburns · Mar 7, 2019

Mustang with a miss said:
How to do I rule out the egr?

The best way is to monitor the EGR flow as reported by the DPFE using an ODB2 scanner.

The next best way is to disconnect and plug the EGR vacuum line. Does this improve performance? However this method won't work IF the EGR valve is stuck open.

Mustang with a miss · Mar 8, 2019

wmburns said:
The best way is to monitor the EGR flow as reported by the DPFE using an ODB2 scanner.

The next best way is to disconnect and plug the EGR vacuum line. Does this improve performance? However this method won't work IF the EGR valve is stuck open.

Can water get into my cylinders from the intake thats what one of my buddy thinks is happening

wmburns · Mar 8, 2019

Even the smallest amount of moisture in the spark plug wells will cause misfire. Further that if allowed to continue it will ruin the COP insulator boots. Usually best to replace just the insulator boots. A new full set of (8) is more cost effective than a single new whole COP.

From your opening post it was stated that a new COP was installed. You did clean out the spark plug wells right?

An alternative method to find leaks is by performing a cooling system pressure test. Frequently the cooling system pressure tester can be rented from your local auto parts stores.

Intake vacuum leaks will sometimes show themselves by looking at the long term fuel trims (LTFT) at idle and under load. A vacuum leak will have positive LTFT's (adding fuel) at idle. As the intake vacuum decreases the LTFT will decrease as there's a smaller pressure difference between outside air and inside the intake.

Mustang with a miss · Mar 20, 2019

I’ve been driving the car with hesitation now for a while it really just sucks ,this past weekend I pulled the intake off and cleaned everything up and put new gasket on it (old ones were shot)it didn’t help at all , we cut a peice of tin with no hole in it between the egr and the pendulum to block of the egr flow it didn’t make a difference at all . Me and all my buddies are stumped. I thought ab alternator but I can see my volts on my tunner and there good even at night with lights on .the only thing I’ve found that made a difference was driving the car as soon as you crank it during a cold start (I know it bad on the motor not letting it warm but I had to see if there was a difference between hot and cold ) it seems to have more power then and the hestion don’t set in till more load . Anyone have any ideas on what to try next?

Mustang with a miss · Mar 20, 2019

Well the car is fixed !so nice to have the power back !!all I did was take the plugs out check the gap clean the up and put the back in And smother the inside and out of the coilpack boots with dielectric grease and even all the connectors she runs like a champ so .weird that that fixed it. Tomorrow’s gonna be a full day of detailing it !

Loose nut · May 26, 2019

Ive had the same issue with my car twice and both times it was spark plug related.

wmburns · May 26, 2019

Mustang with a miss said:
!all I did was take the plugs out check the gap clean the up and put the back in And smother the inside and out of the coilpack boots with dielectric grease and even all the connectors she runs like a champ

I would have assumed from the title of this thread that ^^^ would have been one of the first "tried almost everything" done. Which automatically means that since the simplest and easiest thing has already been done you are looking for more "complicated" items.

Here's a very interesting TST Seminar on Ignition testing. If you can manage to get all the way through it, IMO one of the "take away" should be just how many things interact to create ignition system problems. Clogged fuel injectors, low compression, carbon loading. One of the more interesting things to me was how excessively high coil firing KV can lead to carbon tracking inside the coil. Thus one problem can "cause" additional problems.

Ignition Waveform Diagnostics with Jim Morton

View: https://www.youtube.com/watch?v=yCchGNQEMdE

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