is this a fuel issue? or an air issue? how should i diagnose

[P49Y-CY]

driving to work on the highway the other day and the car sort of died after wot. felt dead while coasting down but then started up again by itself, and drove perfectly normal for the rest of day.

next day it drove perfectly fine all the way to work, but then died on the way home. it will start, struggle to idle, but then stall. after waiting about 15 minutes though, it starts up and runs, but then eventually stalls again (esp if i give it wot).

my first thought was that it's not getting air because it almost felt like the throttle body was just not letting air into the engine.

but the more i research this, the more i'm thinking it sounds like it could be not getting enough fuel.

so where is best place for me to start? maf? iac? fprs? egr valve? fuel filter? any thoughts much appreciated!

very stock-ish 2004 mustang cobra with 126k miles: stock eaton, 2.8 upper, 91 octane tune, stock maf and tb, php air intake. i'm able to swap just about any part over from my other terminator to see if it works.

 

[hotcobra03]

Being it can be anything.

Fuel filter has caused this twice on mine.

The pcv elbows
With smaller pulley your blower may over sound that. Being it’s a whistle

 

[P49Y-CY]

pcv valve? thanks i will check that out

 

[01yellercobra]

I've heard those symptoms before and it ended up being the fuel pump. Can you datalog?

 

[P49Y-CY]

I've heard those symptoms before and it ended up being the fuel pump. Can you datalog?

no bob, i have no way of doing that. i do have my sct handheld tuner that i can check for codes, but i am not getting a check engine light.

fuel pump eh? that does sound like a reasonable culprit since it is hit and miss - i will see what i can find out about that, thanks

 

[DSG2003Mach1]

you should be able to monitor fuel pressure using the hand held, might need to hook it to a laptop to verify (X4 you can do it on device). You could also buy a cheap OBD 2 blue tooth and use a free app.

Is it only dying when your foot is off the throttle? If so it might be the IAC, I dont see the MAF being on again/off again. I would suspect the IAC, FPDM or fuel pump.

 

[01yellercobra]

no bob, i have no way of doing that. i do have my sct handheld tuner that i can check for codes, but i am not getting a check engine light.

fuel pump eh? that does sound like a reasonable culprit since it is hit and miss - i will see what i can find out about that, thanks

Which handheld is it? If it's an X3 or newer I think you can datalog on the device. Which should be enough to watch the pressure drop across the injectors and FPDC. Or get a Bluetooth adapter like DSG mentioned. I have one of those as well and it's pretty handy.

 

[P49Y-CY]

yeah it's an x3 - i will def look into that!

 

[01yellercobra]

Actually, do you own a laptop?

 

[hotcobra03]

You said you have a 2nd cobra

You can use as parts to test ?

This car with issues. Does it sit or more the used 1 ?

Weak coils will also cause this without any codes

 

[P49Y-CY]

Actually, do you own a laptop?

yes i have a laptop. am i able to hook it up somehow to the sct? i probably still have the software (if it came with it when new)

You said you have a 2nd cobra

You can use as parts to test ?

This car with issues. Does it sit or more the used 1 ?

Weak coils will also cause this without any codes

i alternate between the two pretty much everyday and this one gets driven all the time and doesn't just sit. the engine generally runs just as strong or stronger than the other one. it has a lot more miles that the other one though because i bought it new

so as far as a coil, wouldn't that only affect that one cylinder where the engine would keep running (except with a miss)?

and yeah, i figure if i want to test out a part i can just take it off of the other one, so that is cool, you know, without having to just throw parts at it

 

[P49Y-CY]

Actually, do you own a laptop?

i will say though that i am really bad with computers. it all passed me by lol

 

[01yellercobra]

yes i have a laptop. am i able to hook it up somehow to the sct? i probably still have the software (if it came with it when new)

i alternate between the two pretty much everyday and this one gets driven all the time and doesn't just sit. the engine generally runs just as strong or stronger than the other one. it has a lot more miles that the other one though because i bought it new

so as far as a coil, wouldn't that only affect that one cylinder where the engine would keep running (except with a miss)?

and yeah, i figure if i want to test out a part i can just take it off of the other one, so that is cool, you know, without having to just throw parts at it

You can download the Livelink Software from SCT's website. Then you can connect the X3 to the laptop with a USB cable and datalog that way. 3

FWIW, I had a weak coil or two when I first got my 04. It showed up as a miss under boost. It slowly got worse and finally I ended up swapping all 8 COPs with a spare set I have. I never did try to locate the weak one. It never threw a code.

 

[01yellercobra]

i will say though that i am really bad with computers. it all passed me by lol

Lol. I know how it goes. It took me a bit to figure things out. If you were a little further south I'd give you a hand setting it up.

 

[P49Y-CY]

You can download the Livelink Software from SCT's website. Then you can connect the X3 to the laptop with a USB cable and datalog that way. 3

FWIW, I had a weak coil or two when I first got my 04. It showed up as a miss under boost. It slowly got worse and finally I ended up swapping all 8 COPs with a spare set I have. I never did try to locate the weak one. It never threw a code.

Lol. I know how it goes. It took me a bit to figure things out. If you were a little further south I'd give you a hand setting it up.

okay i am going to check that out! thanks alot. i can set it up on my running car and see how it goes, and then do it on my vert and try to read it as it stalls

 

[hotcobra03]

yes i have a laptop. am i able to hook it up somehow to the sct? i probably still have the software (if it came with it when new)



i alternate between the two pretty much everyday and this one gets driven all the time and doesn't just sit. the engine generally runs just as strong or stronger than the other one. it has a lot more miles that the other one though because i bought it new

so as far as a coil, wouldn't that only affect that one cylinder where the engine would keep running (except with a miss)?

and yeah, i figure if i want to test out a part i can just take it off of the other one, so that is cool, you know, without having to just throw parts at it

yes i have a laptop. am i able to hook it up somehow to the sct? i probably still have the software (if it came with it when new)



i alternate between the two pretty much everyday and this one gets driven all the time and doesn't just sit. the engine generally runs just as strong or stronger than the other one. it has a lot more miles that the other one though because i bought it new

so as far as a coil, wouldn't that only affect that one cylinder where the engine would keep running (except with a miss)?

and yeah, i figure if i want to test out a part i can just take it off of the other one, so that is cool, you know, without having to just throw parts at it

I had the coil issue.
It started with with an every now and than miss/jerk.

It got to where car was almost undriveable
But never a code.

I had found a member with a good set of 8. Just for testing.

Both coil issue and fuel filter had that sound at wot. That you have

 

[P49Y-CY]

I had the coil issue.
It started with with an every now and than miss/jerk.

It got to where car was almost undriveable
But never a code.

I had found a member with a good set of 8. Just for testing.

Both coil issue and fuel filter had that sound at wot. That you have

okay thanks for the info! i will definitely not rule out the coils. and i probably should be doing a fuel filter anyway, i think it has been over 30k since i last changed it out on this car

 

[hotcobra03]

okay thanks for the info! i will definitely not rule out the coils. and i probably should be doing a fuel filter anyway, i think it has been over 30k since i last changed it out on this car

Also. Don’t rule out ugly step 1.

A basic compression test.

This also has these symptoms and may not set a code.

Been burned by this the first time mine ran like crap after warranty ran out.

Car runs ok on 7 cylinders.

 

[hotcobra03]

The rubber at air inlet th throttle body.

This I had blow off under boost.

It was soft from oil buildup.

Just loose is enough to also cause issue

And sound that matches

 

[ccq8le]

I had a similar issue to this 2 summers ago. I thought I had bought bad gas and I couldn't get good power out of the engine.

Finally I got it to pop a code and when I ran the code it showed a miss fire on one of the cylinders.

It was a bad coil

Good luck with it. Hope this helps.

If not hope you find a resolution quickly!

keep us posted!