03 Cobra hesistates/ backfires under wot or above 4000 rpms

slow98cobra

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I see several mods there in addition to what you mentioned including a firewall adjuster, caster/camber plates, and I think you have an aftermarket smaller pulley. Might be worth measuring your pulley to see how big it is. Measure the diameter at the ribs.
 

slow98cobra

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Here is a cool way to measure pulley size.

C38E4DC7-65FC-4A76-A874-1ADF98262D7F.png
 

rubior

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Post up a pic of your engine bay when you have some time as well. Just curious what else is on it.
I see several mods there in addition to what you mentioned including a firewall adjuster, caster/camber plates, and I think you have an aftermarket smaller pulley. Might be worth measuring your pulley to see how big it is. Measure the diameter at the ribs.
yeah, nothing major, the clutch cable snapped on me last week & that was a shit show lol, ill for sure mesure the pulley, i honestly thought it was the oem one
 

DSG2003Mach1

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So to clarify - you just bought this car and this is how it’s running? Is it on a full tank of fresh gas at this point?

Definitely some logging in order as mentioned using fuel pressure and battery voltage.

I’d try hitting that MAF with MAF cleaner while you’re at it (ONLY use MAF cleaner, other electrical cleaners can leave a film that will cause issues)

I’d be tempted to either close the gap on the stock plugs are throw in some tr6s gapped down. You had to replace 2 coils, might be worth just doing all 8 (stick to ford/motorcraft/denso). Gapping iridium plugs like traditional ones can damage the electrode.

Fuel filter is good to do but I’ve never really seen it fix much
 

rubior

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So to clarify - you just bought this car and this is how it’s running? Is it on a full tank of fresh gas at this point?

Definitely some logging in order as mentioned using fuel pressure and battery voltage.

I’d try hitting that MAF with MAF cleaner while you’re at it (ONLY use MAF cleaner, other electrical cleaners can leave a film that will cause issues)

I’d be tempted to either close the gap on the stock plugs are throw in some tr6s gapped down. You had to replace 2 coils, might be worth just doing all 8 (stick to ford/motorcraft/denso). Gapping iridium plugs like traditional ones can damage the electrode.

Fuel filter is good to do but I’ve never really seen it fix much
yeah, i just bought the car like a month ago, i put new fluids in the motor obviously, supercharger, & trans, did coolant flushes, replaced all 8 spark plugs with ngk tr6ix (i believe) & all 8 coil on plugs with motorcraft ones(sorry i didnt specify), its been through plenty full of fresh gasoline & fuel additives,(i always try to keep it full) it runs really good, drives smooth, ive been driving it to college & work & its been pretty reliable, only issue i’ve had was the clutch cable snapping on me, im going to give cleaning the mar a try, when i unplug it when its running it dies, idk if its normal or not but ill buy some maf cleaner right now & give it a shot, only issue is the hesitation, ill see if i can post a video & show you guys
 

DSG2003Mach1

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yeah, i just bought the car like a month ago, i put new fluids in the motor obviously, supercharger, & trans, did coolant flushes, replaced all 8 spark plugs with ngk tr6ix (i believe) & all 8 coil on plugs with motorcraft ones(sorry i didnt specify), its been through plenty full of fresh gasoline & fuel additives,(i always try to keep it full) it runs really good, drives smooth, ive been driving it to college & work & its been pretty reliable, only issue i’ve had was the clutch cable snapping on me, im going to give cleaning the mar a try, when i unplug it when its running it dies, idk if its normal or not but ill buy some maf cleaner right now & give it a shot, only issue is the hesitation, ill see if i can post a video & show you guys

Probably woulda been good to start with all that lol

So has it always had a misfire or is that new?
 

rubior

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Probably woulda been good to start with all that lol

So has it always had a misfire or is that new?
it had a small misfire when i bought it, it got fixed when i replaced the spark plugs & cop, but its been doing this where it hesitates & backfires ever since i got it, i thought the spark plugs & coil on plugs would fix it but it didnt, but it does misfire super rarely, it smells like just pure unburned gas & sounds bubbly, but then goes back to normal after like a minute or two. i just bought the maf cleaner & ill give it a shot & update
 

TerminatorCobraJP

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it had a small misfire when i bought it, it got fixed when i replaced the spark plugs & cop, but its been doing this where it hesitates & backfires ever since i got it, i thought the spark plugs & coil on plugs would fix it but it didnt, but it does misfire super rarely, it smells like just pure unburned gas & sounds bubbly, but then goes back to normal after like a minute or two. i just bought the maf cleaner & ill give it a shot & update

This sounds similar to some stuff I've been experiencing with my car. I haven't noticed a hesitation or lack of power or anything like that but my car sounds very bubbly at idle, it backfires on decel a lot, and has a strong gasoline smell. I figured the bubbly idle was just a normal 4V thing with stock exhaust manifolds and that the decel popping would be normal too but it is odd. The idle sounds so strange to me but I don't know if its normal or not. I'd need to hear clips of your car to see if it's what I'm talking about.

Sent from my SM-S536DL using the svtperformance.com mobile app
 

03' White Snake

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What’s the power wire for? Amp? Pumps? BAP? Definitely has a smaller pulley. If the car has a BAP, that could be the issue. Need to look how it is wired. Pre-FPDM or post FPDM. KB directions say to wire post but most cars do exactly what your describing, mine did it too. Changed wiring method and issue went away.

Pull the computer in passenger floor area, look if it has a piggy back chip on it. If it does, good news is you can remove it and switch to a SCT X3/4. If not, you might need to have the computer flash at ford if the previous owner did not give you the handheld. The computer is basically locked.

These cars are getting old. Could be the fuel pump socks deteriorating in the tank and clogging the pumps. Seen this happening a few times recently.

Check the maf connector is good, no damage to the wires. Check the MAF is facing the correct direction. Should have an arrow on it.
 

rubior

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What’s the power wire for? Amp? Pumps? BAP? Definitely has a smaller pulley. If the car has a BAP, that could be the issue. Need to look how it is wired. Pre-FPDM or post FPDM. KB directions say to wire post but most cars do exactly what your describing, mine did it too. Changed wiring method and issue went away.

Pull the computer in passenger floor area, look if it has a piggy back chip on it. If it does, good news is you can remove it and switch to a SCT X3/4. If not, you might need to have the computer flash at ford if the previous owner did not give you the handheld. The computer is basically locked.

These cars are getting old. Could be the fuel pump socks deteriorating in the tank and clogging the pumps. Seen this happening a few times recently.

Check the maf connector is good, no damage to the wires. Check the MAF is facing the correct direction. Should have an arrow on it.
the power wire is for amps that i havent installed yet, its not connected to nothing. i checked the fuel pump cutoff switch location (i believe thats where people wire the bap) & there wasn’t nothing, but where else should i look forin case im wrong? ill check on the computer, how exactly should the chip look?, i didnt get no handheld tuner from the previous owner, but ill check the computer right now
 

03' White Snake

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the power wire is for amps that i havent installed yet, its not connected to nothing. i checked the fuel pump cutoff switch location (i believe thats where people wire the bap) & there wasn’t nothing, but where else should i look forin case im wrong? ill check on the computer, how exactly should the chip look?, i didnt get no handheld tuner from the previous owner, but ill check the computer right now
Pull back the panel in the trunk on drivers side. You will find the FPDM module look for any wires that look out of place. Same with the inertia switch.

When you take the computer out of the body of the car, the chip will plug in on the top. You cannot see it without unbolting the computer. You do not need to unplug it to get it out to check.

Will look like this hanging out of the computer…
 
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DSG2003Mach1

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A29020DF-C619-4DBB-88E5-C6DD63C69BFD.png
the power wire is for amps that i havent installed yet, its not connected to nothing. i checked the fuel pump cutoff switch location (i believe thats where people wire the bap) & there wasn’t nothing, but where else should i look forin case im wrong? ill check on the computer, how exactly should the chip look?, i didnt get no handheld tuner from the previous owner, but ill check the computer right now
See above for chip location
Probably would look Kinda like this below


At this point I’d stop throwing parts at it. Even if you buy some blue tooth shit and use the trowel app to log voltage, fuel pressure etc someone might be able to help. I’d hesitate to jump right to a x4 because you don’t what mods you have to get a fresh tune
 

rubior

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See above for chip location
Probably would look Kinda like this below


At this point I’d stop throwing parts at it. Even if you buy some blue tooth shit and use the trowel app to log voltage, fuel pressure etc someone might be able to help. I’d hesitate to jump right to a x4 because you don’t what mods you have to get a fresh tune
i just unclipped the side kick panel & nothing looks off, ill tke the computer off in a bit, & see how it looks. but heres how it looks without disconnecting it. the blue wires are rcas, & the red & black wires are for the rear speakers, it looks like they took off the black bracket next to the ground. but i dont see the
 

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rubior

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Pull back the panel in the trunk on drivers side. You will find the FPDM module look for any wires that look out of place. Same with the inertia switch.

When you take the computer out of the body of the car, the chip will plug in on the top. You cannot see it without unbolting the computer. You do not need to unplug it to get it out to check.

Will look like this hanging out of the computer…
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thers nothing behind the carpet either, so no bap right?
 

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DSG2003Mach1

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There are two loose connector ends in that photo but I know nothing about them.

If the chip goes in the top of the computer you wouldn’t see it there - have to take it out of the bracket and should be able to see. I don’t think you have to disconnect any wires
 

03' White Snake

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Correct, no BAP. So that’s clear now. Like DSG said, the chip plugs in the top of the computer, you cannot see it without removing the computer. Nothing should need to be unplugged. Undo the 1 or 2 8mm screws and it will rotate down and out. Look if anything looks plugged into the computer on the top side.
 

03cobra#694

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LS WUT

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As stated above that appears to be a 2.93 or even a 2.8 pulley. My initial concern was fuel cut out. Mine did this when I first got it due to my twin GT40 fuel pumps connecting wire being loose. However as has been stated above gap those plugs to .28 and retry that. Regardless of fuel and such I’d do my best to make sure no moisture is getting into the cap. Buddy had that issue on his mach1. He went thru so many tanks drops just to find out his cap had a crack in it. Report back when you’ve gapped the plugs and such
 

hotcobra03

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Fuel filter is my guess,

Hard to change,,very tight spot

Has these symptoms

I also had this issue to say just filter can cause this,

Coils have been known to get weak and not give codes,
Ford racing sold a set of 8 which some of us have gotten .

Here you will find our service manual,,full PC version has this side of repair,
Very helpful
 

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