03 Cobra hesistates/ backfires under wot or above 4000 rpms

rubior

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Hey guys i was wondering if i could get some opinions on my issue, when you give it 3/4 throttle or full throttle it starts bucking, hesitating & backfires, & if your idling & step on it it literally cuts at 3000 ish rpms, hesitates & backfires & the rpms slowly go down, i replaced the spark plugs with ngk iridiums & plugs with new motorcraft plugs, i cleaned the air filter, throttle body, changed the frps & nothing, theres been 2 times where it backfires & the car turns off, & once you pick up speed easing into it, if im able to get it at 3/4 throttle it has literally no power, other than that the car runs & drives good, only misfires super randomly, sounds kind of bubbly, & it smells really rich, i dont know what to do or how to diagnose it, ive googled & honestly nothings been helping,
 

slow98cobra

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Any codes?

Do you have access to a handheld tuner so you can do a little bit of data logging?

When is the last time the fuel filter has been changed?

Just throwing out some thoughts.
 

Black02GT

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100% stock? Usually cut out is dying pumps but if you are rich and back firing I'd guess voltage dropping. Most is pretty easy to pick out with a handheld and a laptop. Otherwise just mostly pissing into the wind and possibly doing damage.

Need way more info on the car and data logging makes life 1000 times easier.

Obvious ignition problems but why?
 

rubior

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Any codes?

Do you have access to a handheld tuner so you can do a little bit of data logging?

When is the last time the fuel filter has been changed?

Just throwing out some thoughts.
i dont man, ill try to find someone who could let me borrow their tuner or something, i bought the fuel filter but i havent replaced it yet
 

rubior

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100% stock? Usually cut out is dying pumps but if you are rich and back firing I'd guess voltage dropping. Most is pretty easy to pick out with a handheld and a laptop. Otherwise just mostly pissing into the wind and possibly doing damage.

Need way more info on the car and data logging makes life 1000 times easier.

Obvious ignition problems but why?
its just got bolt on mods, bbk 65mm throttle body, stock maf, cold air intake, & exhaust, supposedly the previous owner told me it was tuned, dont know with who, where, theres no dyno sheet, he didnt really remember either, i replaced the alternator & battery, ill do my best to try & find someone who can help me get the datalog & ill update once i find something
 

rubior

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Any codes?

Do you have access to a handheld tuner so you can do a little bit of data logging?

When is the last time the fuel filter has been changed?

Just throwing out some thoughts
Any codes?

Do you have access to a handheld tuner so you can do a little bit of data logging?

When is the last time the fuel filter has been changed?

Just throwing out some thoughts
no codes either
 

Black02GT

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its just got bolt on mods, bbk 65mm throttle body, stock maf, cold air intake, & exhaust, supposedly the previous owner told me it was tuned, dont know with who, where, theres no dyno sheet, he didnt really remember either, i replaced the alternator & battery, ill do my best to try & find someone who can help me get the datalog & ill update once i find something

Well that is scary. Hate to say it but starting to sound like you're spending way more money into throwing random parts at it vs bringing to a reputable Mustang shop. Not from my area area but I doubt there aren't a few in Tx.

Big DIY guy myself but need to know when you are digging yourself deeper.
 
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slow98cobra

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My first thought is fueling related. Start simple, change the fuel filter and see if you can find a handheld so you can check fuel pump duty cycle. May sound dumb, but pay particular attention to the direction the fuel filter needs to go by the arrow.

Do you still have your old plugs? If so, please post up a pick of them including a close up of the ground strap. It will be very apparent if you are running too rich.
 

rubior

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Well that is scary. Hate to say it but starting to sound like you're spending way more money into throwing random parts at it vs bringing to a reputable Mustang shop. Not from my area area but I doubt there aren't a few in Tx.
i bought the car from some older gentleman who let it sit for like 8 years, it needed the battery & alternator wasnt charging, spark plugs were the oem ones, & 2 coil on plugs werent working, but i did panic & bought the frps honestly lol
 

rubior

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My first thought is fueling related. Start simple, change the fuel filter and see if you can find a handheld so you can check fuel pump duty cycle. May sound dumb, but pay particular attention to the direction the fuel filter needs to go by the arrow.

Do you still have your old plugs? If so, please post up a pick of them including a close up of the ground strap. It will be very apparent if you are running too rich.
for sure, ill be doing that today, i might go buy a harbor freight scanner just so i can read live data, ill look for the plugs, they honestly didnt look bad, once i get home ill take some pics
 

slow98cobra

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You will probably need a SCT x3 or x4 to read the actual parameters most of us would be reviewing. That’s outside of my areas of expertise but would hate for you to spend money on just a code scanner. It would be better off to invest in the SCT x4 so you can read codes and datalog.
 

Black02GT

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if the pulley is 2.8 or 2.9 you are probably getting spark plug blowout (gap too big)

This plus, definitely can gap IR plugs. Just a lot more tricky to not mess up. If you were running NGK stock gap is pretty wide. Think around 35 at you're boost level and assuming run 93 vs E. Should work, but honestly. This is like Telehealth when you need a CT scan.
 

rubior

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This plus, definitely can gap IR plugs. Just a lot more tricky to not mess up. If you were running NGK stock gap is pretty wide. Think around 35 at you're boost level and assuming run 93 vs E. Should work, but honestly. This is like Telehealth when you need a CT scan.
yeah, it feels like that lol, im on 93 still, the car is still pretty stock, im trying to get a handheld tuner so i can diagnose better but the only issue is $$$ lol, im still new to this & honestly every opinion is helping me, i dont know no one yet who could help me locally, im 18 & i most of the people i know dont even own a car lol
 

rubior

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You will probably need a SCT x3 or x4 to read the actual parameters most of us would be reviewing. That’s outside of my areas of expertise but would hate for you to spend money on just a code scanner. It would be better off to invest in the SCT x4 so you can read codes and datalog.
yeah im probably going to invest in one of those
Post up a pic of your engine bay when you have some time as well. Just curious what else is on it.
 

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