Cutting out During Heavy Acceleration and Stalling When Clutch is Pressed

04RedfireGT

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Alright so I have a 2004 Mustang GT with 248k miles. I’ve had it since February of last year with no issues. No leaks or anything and all of the sudden it started dying whenever I press the clutch in coming from high RPMs or coming to a stop. Caused me to have a fender bender during a sharp curve because of it. It now has the same issue but has added that it’ll cut out around 3k-higher RPMs and then come back. I’ve replaced the IAC, throttle body and plenum, TPS, EGR valve and o2 sensors. I need help with what could be causing this.
 
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04RedfireGT

04RedfireGT

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Also I have had the timing chains and guides replaced already.
 
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04RedfireGT

04RedfireGT

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No, the maf seems to be working fine as when I unplug it when the car is running it’ll kill it.
 

cryptospook

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No, the maf seems to be working fine as when I unplug it when the car is running it’ll kill it.
You appear to be doing shade tree troubleshooting. May I suggest you search my previous post. Get an online library card and login to the free Chilton's website there.

One you do, you'll be able to access their diagnostics through the repair tab.

The diagnostic chart steps you from symptoms and etc codes through actual trouble shooting steps and pinpoint diagnosis. So you'll be able to test the parts you're replacing and know they're bad instead of throwing parts at the problem.




All that said, it certainly seems to point at your fuel and spark.
 

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Have you looked at the condition of the Capacitors (two of them) in your Computer?
 
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04RedfireGT

04RedfireGT

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No, how would I determine wether they are fine or not? I’ve typically never tried to mess with car computers as I don’t want to mess up something big and cause it not to crank again.
 

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No, how would I determine whether they are fine or not? I’ve typically never tried to mess with car computers as I don’t want to mess up something big and cause it not to crank again.
You pull your Pass kick panel and take the computer out; open the computer up. If they look at all fanny - leaking, connections are corroded (greenish) you can farm it out and replace the capacitors, or buy a new unit for your car.

I replaced mine (the capacitors) and prolly the best decision I made early on in my build.
 
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ttocs

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there are probably a few steps to go over before we pull the ecu and inspect/swap caps. Cleaning the maf is a great way to start if you have never done it before even if it dies when you unplug it. If you don't start simple you end up feeling stupid. It would also be helpful to tell us what has been done to the car as far as aftermarket parts. I had problems like this for a while after I put in a pro products throttle body.
 
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04RedfireGT

04RedfireGT

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there are probably a few steps to go over before we pull the ecu and inspect/swap caps. Cleaning the maf is a great way to start if you have never done it before even if it dies when you unplug it. If you don't start simple you end up feeling stupid. It would also be helpful to tell us what has been done to the car as far as aftermarket parts. I had problems like this for a while after I put in a pro products throttle body.
It has a BBK 73mm throttle body/plenum and a x-pipe exhaust but that’s all of the aftermarket parts. It’s stock otherwise. Haven’t really bought anything aftermarket since I’m planning on during a coyote swap down the road.
 
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04RedfireGT

04RedfireGT

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However it started dying and cutting out before I added the BBK throttle body but since I’ve changed out throttle body’s the cutting out has gotten significantly better but it still dies right after heavy acceleration and idling back down
 

RAU03MACH

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Check your vacuum lines dry rotted rubber hoses for emissions up under passenger fender all
 
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Like RAUO3MACH said check for vacuum leaks. What I always find on 94-04 Mustangs is on the pass side in the rear corner by the firewall is the vacuum line that runs to the back of the car for emissions stuff. That hose deteriorates bad and pretty quickly from all the others. I hooks directory to the elbow, You will know when you find it because if you mess with it your fingers will be black. I always change that line with the appropriate hose to avoid the issue again. Do not use just any vac hose it will just do the same thing. If you have a way of dataloging just pick things like timing fuelrail pressure MAF fuel pump anything like that. If you don't have anyway to datalog anyone tha has a SCT X3 or X4 they can datalog it for you it doesn't matter there handheld is married to another car or truck just has to be a X3-X4 for Ford. You can do the same with HP Tuners because there datalog is basically separate so you can datalog Ford,Chevy and Dodge. Long winded reply but I just like to be through. If u have any questions just pm/dm me. Thanks
 
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04RedfireGT

04RedfireGT

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Like RAUO3MACH said check for vacuum leaks. What I always find on 94-04 Mustangs is on the pass side in the rear corner by the firewall is the vacuum line that runs to the back of the car for emissions stuff. That hose deteriorates bad and pretty quickly from all the others. I hooks directory to the elbow, You will know when you find it because if you mess with it your fingers will be black. I always change that line with the appropriate hose to avoid the issue again. Do not use just any vac hose it will just do the same thing. If you have a way of dataloging just pick things like timing fuelrail pressure MAF fuel pump anything like that. If you don't have anyway to datalog anyone tha has a SCT X3 or X4 they can datalog it for you it doesn't matter there handheld is married to another car or truck just has to be a X3-X4 for Ford. You can do the same with HP Tuners because there datalog is basically separate so you can datalog Ford,Chevy and Dodge. Long winded reply but I just like to be through. If u have any questions just pm/dm me. Thanks
Alright thanks for the info, I’ll check the vacuum lines. I was gonna go get a loaner tool from the parts store as well to check fuel pressure. However at idle the car runs fine it’s only when giving it gas and idling down is when it has issues. I’ve been told I might need to change intake manifolds as they are prone to be bad at cracking or creating a vacuum leak, if so is there a intake that yall would recommend for me to get? I’m planning in painting the car and getting a different exhaust setup with long tubes and camels down the road.
 
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04RedfireGT

04RedfireGT

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So I’ve gotten brake cleaner and sprayed it on all vacuum lines, around the throttle body, and the intake that I could see or hit with the cleaner and it didn’t rev higher.
 

ttocs

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that method can work but really isn't the best way to look for leaks. Get a cigar and just pull the hose off the brake booster and blow it into the hose and see if it comes out anywhere.

Any chance it runs different when its cold than when the motor is hot?
 
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04RedfireGT

04RedfireGT

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that method can work but really isn't the best way to look for leaks. Get a cigar and just pull the hose off the brake booster and blow it into the hose and see if it comes out anywhere.

Any chance it runs different when its cold than when the motor is hot?
No it runs the same when it’s hot or cold besides it backfiring a little when first crunk up.
 

ttocs

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ever check the fuel pressure? Cutting out at high rpm's makes me wonder assuming all the electrical connections are still good. If you have any sensors that the harness has 2 clips and one is broken, trust me replace that harness.
 
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04RedfireGT

04RedfireGT

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ever check the fuel pressure? Cutting out at high rpm's makes me wonder assuming all the electrical connections are still good. If you have any sensors that the harness has 2 clips and one is broken, trust me replace that harness.
I’ve considered fuel pressure but been told several times it’s not fuel related. I’m gonna check the IAC and TP sensors along with the MAF sensor to see if I may have gotten faulty ones. I’m getting to my wits end with it and want to do a full coyote swap with a 6 speed but can’t afford it right now.
 

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