i just bought this 2003 cobra with 50k miles on it. it looks simi stock i can see the fuel injectors are blue which could mean they are after market but im not sure. i have never owned a ford befor. its got a CAI and Basani exhaust. the car runs good but the service engine light came on. i hooked it up to a diagnostic tool and it spit out 2 codes. it said something about rear exhaust 02 sensors are bad bank 1 and bank 2. when i coast the car on the freeway and or anywhere almost its idel will bog from 1000rpms to 500rpms and it will flucuate up and down when out or gear or in idel. last night i mashed the car up to 100mph on a backroad and when i took it out of gear to slow down the car bogged out and turned off and i had to turn it back on while rolling down the road. can this problem be related to my O2 sensors going bad? the car does smell like it rusn alittle rich. how much are the 02 sensors and can i install them myself. again i have never owned a ford until this week and id like for my new ford family to help me with solving this mistery so i dont have to take it into a dealership. thanks guys

Welcome to the forum!

You're having a lot of things going on at once with your car. It's hard to say what it could be. Sounds like you may have the stall problem. There is a TSB on it, and a dealer will be able to take care of that for you.

But as far as your CEL light goes, I have no clue as to what that could be. Someone here might be able to help you.

But since you are new to your Cobra,you should join svtperformance.com. There is a lot more information available on our cars over there than here.There'sA LOT of things youneedto learn about your car, and svtperformance.com is a good place to start.Also, If no one here can chime in and help you out better than I can, If you post this in the engine/tuning section (after you search), you'll for sure find the solution to your problems.

BTW, the blue injectors are the stock ones.

Any chance the car has an aftermarket mid-pipe without catalytic converters (aka off-road pipe)?

im not sure about the off road h pipe. i got this read out from autozone.

Here are the codes the PCM spit out
P0420(Bank 1) and P0430 (Bank 2)

TROUBLESHOOTING P0420

The PCM has determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions. (Bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)

Definition
Catalyst efficiency low-bank 1
Explanation
The oxygen sensors monitor the catalytic converters ability to store oxygen.

Probable Causes:

1.-catalytic converter defective (failure possibly due to #2, 3, or 4)
2.-Engine misfire or running condition
3.-Large vacuum leak
4.-Engine oil leakage into exhaust-valve guide seals, piston rings


I wish i knew what exactly was wrong with it. i baot some seafoam fuel system cleaner to help clean stuff up in the motor. i gotta take this car back to san fran from chicago. i hope it can make it. sow hat do you guys think it could be or i should do. im scared of taking it to some random mechanic because in my expierence with muscle cars i get f*cked everytime and right now with all my legal stuff i cant afford to many extra costs. my DD has a flat tire so im stuff driving the cobra which is killing me since i gotta drive it 60 miles a day.

Try here, there are 45 threads with the 420 code in it.

http://www.svtperformance.com/forums/search.php?searchid=2012478

specifically this might be a good one.

http://www.svtperformance.com/forums/showthread.php?t=340995&highlight=P0420

ill research it. thanks for your guys help in this matter.

do you guys think this issue could be the reason my cobra is getting worse gas mileage then expected lol i gotta take it back to CA from chicago can i drive it with bad 02 sensors? or is that a bad idea???

02 sensors are easy to replace and they are about $60. All you gotta do is look at your exhaust and you will see it sticking out of the pipe ( kind of looks like a spark plug sticking out of the exhaust pipe). you get the right sized wrench unscrew the old one unplug it then plug up the new one and screw it in. Very easy job todo I did mine my self when i was 16 so..... a bad 02 sensor can very well cause bad gas mileage but i dont know if that is your stalling prob.

Could you be running rich? Did the previous owner have the car tuned correct?

it does seem to be running rich. i dont know if the previous owner had it tuned at all. i got this car from a dealership. today im gonna replace the o2 sensors on bank 1 and bank 2 and see if that fixes all these problems i got currently. i hope it does. my exhaust rattles kinda badly sometimes in lower rpms like around the 2000 rpm range im gonna see if any of the exhaust brackets are loose or missing, causing it to make those sounds when im accelerating or downshifting sometimes.

my room mates dad who works on fords at a dealership said its def a vacum leak. so im gonna try to fix that today. wish me luck!

ORIGINAL: 1sicls1
my exhaust rattles kinda badly sometimes in lower rpms like around the 2000 rpm range im gonna see if any of the exhaust brackets are loose or missing, causing it to make those sounds when im accelerating or downshifting sometimes.


If it always happens right around 2000-2200 it is probably just "drone". The aftermarket exhaust hits a point where it begins to resonate loudly and many seem to get that right around 2K rpms.

i took it to a shop they replaced my fuel pressure sensor on the fuel rail. my cars fuel pressure was running at 28psi insted of 40 psi. they cant figure out why its having trouble finding idle. if u leave it on for awhile the car will just die... if i had more money if send it back to the shop to have it fixed further.

What kind of CAI does it have? I had the stall after power issue you have when I was running a MAC CAI. Changed to JLT issue went away.

i dont know the CAI has no markings. the mechanic took the K&N filter off and ran the car and it still had issues, then he cleaned the MAF and it still had issues. he said the way it runs it might have been tuned but he cant tell...

if you install a stock mid pipe and reset the battery the code will go away. or you can a set of MIL eleminators and install them that will also take care of the problem

could that be causing my car to turn off after it idels for a bit? or when i put it in nutral coasting it turns off too.... what can be causing that?

Congratulations on buying your 2003 Cobra! You're gonna love it. Since you're new to the 2003 Cobra, the FAQ page on my website will provide you some very useful info. http://www.stangshiftergaskets.com/2003_2004faqs.htm

thanks but i have already read that. do you guys think honestly this car is gonna be able to drive from chicago back to california in its current state. i drive it daily right now and it runs fine... should i be periniod of taking it cross country???

Do you know if anyone has put a tune on it? Sounds like they did and didn't turn off the rear O2 sensors, which is what every tuner does. How did this shop determine your fuel pressure was running low? Did they put it on a dyno and ramp it up? I mean your pressure is going to be low while at idle. Just because you have 39psi fuel injectors doesn't mean it runs at 39psi all the time. You really need to go over to www.m (http://www.m) o d u l a r f o r d s . c o m. Remove the spaces of course. The knowledge power is there, this board doesn't have the know how to help you with your problems, no offense to anyone here. Stay away from svtperf too. All you have over there are dyno number happy people.

ORIGINAL: AllVenom
Stay away from svtperf too. All you have over there are dyno number happy people.


Oh I don't know about that, both the MACA and Motor City forums on svtperf have some very nice and knowledgable folks. ModularFords is also a great place so I would try both.

ORIGINAL: TeddyKGB

ORIGINAL: AllVenom
Stay away from svtperf too. All you have over there are dyno number happy people.


Oh I don't know about that, both the MACA and Motor City forums on svtperf have some very nice and knowledgable folks. ModularFords is also a great place so I would try both.


Your right, I should have clarified. However, its hard to discern who knows their stuff and who doesn't. Its a little easier on the other site.