Fuel Slight jerking ?? HELP

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Noobz347

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Depending on the size of the leak, pulling in a little bit of brake cleaner may not make it stumble.

Do you have access to a vacuum gauge by chance?

Additionally, have you attempted to pull codes? At a minimum, you should be getting an O2 sensor out of range code.
 

CrazyChick08

Member
Jun 11, 2020
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You need to find the hiss because if there is a hissing vac leak. Thats probably it. Mustangs wont run right with

Depending on the size of the leak, pulling in a little bit of brake cleaner may not make it stumble.

Do you have access to a vacuum gauge by chance?

Additionally, have you attempted to pull codes? At a minimum, you should be getting an O2 sensor out of range code.
No codes at all. Which I don't understand cause this has been doing this for about a month now
 

racerraj

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Dec 17, 2001
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Vacuum gauge - My Torque app (Android, but I am sure iPhone's have something similar) with a BlueTooth OBDII adapter lets me see the vacuum. Not sure it responds as fast as a true vacuum gauge though. It also lets me see the fuel pressure, which "may" be causing this (I lean towards vacuum though). And once I added the Ford PIDs I can see misfire count too.
 

7991LXnSHO

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Yes, she needs to find a vac leak, but she’s already reported it shows a misfire, and someone posted how to check the ignition components. Don’t get the owner chasing squirrels when there are two elephants to address that are not going anywhere.
 

CrazyChick08

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Jun 11, 2020
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Yes, she needs to find a vac leak, but she’s already reported it shows a misfire, and someone posted how to check the ignition components. Don’t get the owner chasing squirrels when there are two elephants to address that are not going anywhere.
I have a small suggestion on what it could be. I never heard a hissing noise, just engine noises. But I think it has something to do with the intake manifold cause there is oil sitting at the bottom of it from the pcv valve.
 

Bullitt95

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Jun 13, 2007
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I already did a vacuum leak test and couldn't find any. There is a hissing now that comes from the engine

1. Make sure that the intake pipe has an airtight fit to the air filter assembly at one end, and to the throttle body at the other.

2. If you haven't already cleaned the MAF sensor, do it.

3. Remove the throttle body and clean it inside out until it looks like new.

4. The 4.6 3V engine doesn't have a PCV valve, and a little oil inside the intake manifold is normal. I recommend that you install a driver's side air oil separator. A cheap $25 Chinese ebay item like the ones I have will do the job nicely. I installed one on the passenger side as well but that stays bone dry.

5. It does sound like you have a vacuum leak and it could be one that's difficult to diagnose, especially if it's from an intake manifold gasket or from the CMCV shaft at the rear of the manifold. It's a good excuse to delete the CMCVs altogether.
 

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