Misfire, Sputtering, Rough Idle ... ?

Cincy12 · Sep 4, 2012

Hello Everyone,

I have a 2003 Mustang GT that was running strong until about 1 week ago. I replaced the battery (Cell 2 was dead) and an Advanced Auto. While there they went ahead and ran a diagnostic on my car. They said my alternator read "Phase 2 - Open" which I would assume is a bad diode. However, car maintains a solid charge and this issue goes relatively unnoticed with the exception of a radio light blink here and there.

As soon as I pulled out of the parking lot, I accelerated and the car immediately cut out, sped up, cut out, sped up, etc. in all gears until I would reach approximately 3500 rpm. During this 'Misfire?' the car jerks quite bad and the exhaust sounds completely different as if it was muffled - almost a farting noise. A quick Google search revealed basic tune up (Spark plugs, COP's, Rotor/Cap, Fuel Filter).

I replaced all 8 spark plugs, which showed no unusual signs upon examination. I examined the COP's at the same time and they looked brand new. I saw an interesting test on Troubleshootmyvehicle dot com where you unplug the injection wire one valve at a time. If you notice a reduction in rpm or vacuum, then the COP is working properly as the car is dependent on its power. I performed this test on all 8 valves and they all reduced the rpm. When I got back in the car, and took off to run an errand, the misfiring/sputtering/cutout is worse than ever in all gears through all rpm ranges. I verified that the injection wires are secure. Any idea where to go with this? Did I just diagnose that the injection valves are the issue? Sorry for a long and possibly confusing post but am trying to give as much detail as I can. Any help is greatly appreciated.

Jared

Cincy12 · Sep 4, 2012

So after further review, I came across another post that is making me question this entire problem all together. My car was running flawlessly on the way to the Auto store. Is it possible that the diagnostic test caused an issue with my ECU?

Kilgore Trout · Sep 4, 2012

Are the battery terminals connectors tight and corrosion free?

jibloni · Sep 4, 2012

When the people did the dignostic on it did he "delete" the code or ask you anything about him changing anything or something to that affect?

jcgafford · Sep 4, 2012

pull the negative battery cable and turn the lights on. leave it for 10 minutes. turn the lights off and reconnect the battery. it will clear codes and put the computer back at baseline. there is a short "learning curve" for the computer after you hook it back up. drive it casually for a while and see if it all returns to normal.

Cincy12 · Sep 4, 2012

Kilgore Trout: Yes, they are both tight. Thanks for the suggestion. I actually replaced the Neg. terminal recently due to corrosion.

jibloni: I actually didn't have a code, I had him run the test to be sure it was in fact my battery as opposed to my alternator though. The only thing he asked is if he could plug in some computer to the ECU that would 'maintain' my radio settings. The test was straight forward. I rev'd the engine twice for 5 - 10 sec @ 2500 rpm. with headlights and a/c on. The car was off for the remainder of the test.

Its just really ironic this started happening as soon as I pulled out of the parking lot.

Cincy12 · Sep 4, 2012

jcgafford thanks for the input. I will try this tomorrow and see if it helps.

jibloni · Sep 4, 2012

well bud i had a similar thing happen to a dodge i had it was an 04 1500 and it turned out that it was a setting that i deleted by accident. Just to save yourself money go back to the same place and see if they can return the car to the same settings you had before they hooked up the computer.

I have also herd a couple folks plug in computers or programmers and for some reason the ecu decides that that aint what it wants and it will screw it all up. It happened to a buddy of mine's ford truck and no the damn thing wont get over 9 miles a gallon.

trinity_gt · Sep 4, 2012

I'd like to know more about this alternator test that identified which of the three stator phases was open. I've been designing electronics for 20 years and know of no way to identify a dead phase without actually getting into the alternator and physically measuring each winding separately. If a diode in the bridge is open, same thing: No way to identify which particular one is open without getting into it.

If the alternator does have a bad phase or open diode it will be introducing a fair amount of what's known as "ripple" into the electrical system. This can play havoc with the sensitive electronics of the PCM. Get a second opinion on the alternator output (you can even use a DVM set to 'AC' to get a feel for the amplitude of the ripple voltage) and consider a new one if it's suspect.

g96v6-250k · Sep 5, 2012

ac leaking into chassis screwing with sensor signals.

Cincy12 · Sep 8, 2012

Thanks for the replies everyone. A little update:

I reset the ECU, took it for a spin. Ran like a beast for about 10 minutes. Then I did some testing.

Test 1:
I expect when going slow in a high gear and putting the pedal on the floor that it would just bog. However, this test proved that my problem still exists. For testing purposes, 5th gear 40 mph, pedal on the floor and the car starts jerking, speeding up, jerking, speeding up, etc. I can not only feel it but can see the shift knob shaking left and right quite violently. This only happens in 5th gear which I have never had any issues with. The jerking is quick and almost like its losing power for a brief second.

Test 2:
I got on a nice straight road and got on it through all the gears. This time it was even more noticeable. While the car still accelerated quite well, it was jerking/cutting out noticeably through all gears this time.

I still have this gut feeling it is the alternator due to the Auto Parts store test saying I have a diode/phase open. Any thoughts after this test? If I have to replace the alternator I will but no point in blowing $175+ if I don't have to. Also, here and there when I come to a stop, my radio lights blink and the rpms drop bounce low to normal like it could die. All help appreciated.

jcgafford · Sep 8, 2012

Cincy12 said:
Thanks for the replies everyone. A little update:

I reset the ECU, took it for a spin. Ran like a beast for about 10 minutes. Then I did some testing.

Test 1:
I expect when going slow in a high gear and putting the pedal on the floor that it would just bog. However, this test proved that my problem still exists. For testing purposes, 5th gear 40 mph, pedal on the floor and the car starts jerking, speeding up, jerking, speeding up, etc. I can not only feel it but can see the shift knob shaking left and right quite violently. This only happens in 5th gear which I have never had any issues with. The jerking is quick and almost like its losing power for a brief second.

Test 2:
I got on a nice straight road and got on it through all the gears. This time it was even more noticeable. While the car still accelerated quite well, it was jerking/cutting out noticeably through all gears this time.

I still have this gut feeling it is the alternator due to the Auto Parts store test saying I have a diode/phase open. Any thoughts after this test? If I have to replace the alternator I will but no point in blowing $175+ if I don't have to. Also, here and there when I come to a stop, my radio lights blink and the rpms drop bounce low to normal like it could die. All help appreciated.

test 1 doesnt hold much water. my past manual vehicles would all do that if i tried 5th too early. gotta have the speed to use the gear. test 2 on the other hand shows something weird going on. sounds like a miss or something on that line. i would be checking wires and plugs and move on from there.

Matt1323 · Sep 9, 2012

i am having the same problem with my 1999 gt it does exactly the same thing and i recently just changed one of the coils because i've been driving the car like this for the past month and every time i throw a CEL it gives me a cylinder # and usually its just a coil plug but i replace it and it keeps on doing the same thing and i just can't figure out what to do.

Matt1323 · Sep 9, 2012

In gear 1-3 i try to get past 3500rpm and it just stalls and can't go any more until i shift any ideas,...btw i also did that coil check where u remove the connector to see if the rpms go down and they all do...i don't know what the problem is on my car but it appears to be the same one u have.

Jeremy Smith · Jun 5, 2016

Cincy12 said:
Hello Everyone,

I have a 2003 Mustang GT that was running strong until about 1 week ago. I replaced the battery (Cell 2 was dead) and an Advanced Auto. While there they went ahead and ran a diagnostic on my car. They said my alternator read "Phase 2 - Open" which I would assume is a bad diode. However, car maintains a solid charge and this issue goes relatively unnoticed with the exception of a radio light blink here and there.

As soon as I pulled out of the parking lot, I accelerated and the car immediately cut out, sped up, cut out, sped up, etc. in all gears until I would reach approximately 3500 rpm. During this 'Misfire?' the car jerks quite bad and the exhaust sounds completely different as if it was muffled - almost a farting noise. A quick Google search revealed basic tune up (Spark plugs, COP's, Rotor/Cap, Fuel Filter).

I replaced all 8 spark plugs, which showed no unusual signs upon examination. I examined the COP's at the same time and they looked brand new. I saw an interesting test on Troubleshootmyvehicle dot com where you unplug the injection wire one valve at a time. If you notice a reduction in rpm or vacuum, then the COP is working properly as the car is dependent on its power. I performed this test on all 8 valves and they all reduced the rpm. When I got back in the car, and took off to run an errand, the misfiring/sputtering/cutout is worse than ever in all gears through all rpm ranges. I verified that the injection wires are secure. Any idea where to go with this? Did I just diagnose that the injection valves are the issue? Sorry for a long and possibly confusing post but am trying to give as much detail as I can. Any help is greatly appreciated.

Jared

My 2002 mustang gt had the same problem, changed all the plugs, alternator, and camshaft position sensor. Ran great for a week and the same problem occurred, once the check engine light started flashing I knew it was a misfire. Ran the code and sure enough the mid fire was in cylinder 1. Replaced the coil ($50) and it solved the problem and runs great.

Ramon510 · Apr 20, 2017

Cincy12 said:
Hello Everyone,

I have a 2003 Mustang GT that was running strong until about 1 week ago. I replaced the battery (Cell 2 was dead) and an Advanced Auto. While there they went ahead and ran a diagnostic on my car. They said my alternator read "Phase 2 - Open" which I would assume is a bad diode. However, car maintains a solid charge and this issue goes relatively unnoticed with the exception of a radio light blink here and there.

As soon as I pulled out of the parking lot, I accelerated and the car immediately cut out, sped up, cut out, sped up, etc. in all gears until I would reach approximately 3500 rpm. During this 'Misfire?' the car jerks quite bad and the exhaust sounds completely different as if it was muffled - almost a farting noise. A quick Google search revealed basic tune up (Spark plugs, COP's, Rotor/Cap, Fuel Filter).

I replaced all 8 spark plugs, which showed no unusual signs upon examination. I examined the COP's at the same time and they looked brand new. I saw an interesting test on Troubleshootmyvehicle dot com where you unplug the injection wire one valve at a time. If you notice a reduction in rpm or vacuum, then the COP is working properly as the car is dependent on its power. I performed this test on all 8 valves and they all reduced the rpm. When I got back in the car, and took off to run an errand, the misfiring/sputtering/cutout is worse than ever in all gears through all rpm ranges. I verified that the injection wires are secure. Any idea where to go with this? Did I just diagnose that the injection valves are the issue? Sorry for a long and possibly confusing post but am trying to give as much detail as I can. Any help is greatly appreciated.

Jared

Did you ever find out what the problem was? Im having the same problem with my 03 mustang and i dont know what to check for i dont wana spend money and for it to not work any suggestions?

wmburns · Apr 24, 2017

To Ramon510. Have you had the battery and alternator tested? No excuse to skip these steps as almost all auto parts stores will do the tests for free.

Bottom line. Today's cars simple will NOT run right without a strong battery and charging system. Cut corners here at your own risk.

Also check all the fuses inside the engine bay and driver's kick panel.

If $$'s are an issue, here's a way to save some real $$ rebuilding your alternator yourself.
https://www.stangnet.com/mustang-forums/threads/higher-amp-alternator-how-much-higher.897392/

Misfire, Sputtering, Rough Idle ... ?

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