Issue with 17 GT Vacuum.

[kms0567]

Good evening guys, I need some desperate help with my new 17 Mustang GT.

I have driven this car about 150 miles currently and just today, I was installing Mishimoto oil separator.

After installing I went for a test drive and realized that something was not right or something I believe it never happened before.

I did not feel any issue when I was driving, but when the car is on idle, I started to hear and feel some bumps and sounds like doom from the engine bay.

And I figured out that those sounds and feel comes when the Vacuum changes. I think the normal is number 17inhg on display but it rises up to 19~ish every 8 to 10 seconds and that

is when the sound and feel comes at.

The only thing I touched was a PCV valve to install Mishimoto and currently, I removed the oil separator and it is replaced as factory condition.

However, the sound and noise with vacuum change are still occurring.

Is this something normal or something actual issue that I need to fix?

thank you!

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[Kong76]

Do you have your air conditioner running when this happens? My idle with air off is 19 -20. A good way to check for a vacuum leak is to turn off air go for a drive and stomp it and let off the gas. A good engine with no leaks you should see your gauge jump up to 21-23 in before settling back down to the 19 range depending on elevation.

 

[kms0567]

Yes, the AC was running!

 

[kms0567]

Thank you for the information.

I just came back from a drive and for some reason, the bump and noise are not happening anymore.
When idling with AC on, vacuum is steady 19. Without AC, it is going 17.4 to 17.8
I tried as you told me and vacuum gives about 4-5 most of times during acceleration 2000 to 3000
and raises about 20.1-3 and goes back to 19. Sometimes it drops to 15 or 17ish.
I will have to try again tomorrow to make sure, but Would you consider this normal?

 

[seth21w]

Maybe its the engine telling you that it likes breathing a little oil mist...or it could be a vaccum leak around the separator.

 

[Kong76]

Thank you for the information.

I just came back from a drive and for some reason, the bump and noise are not happening anymore.
When idling with AC on, vacuum is steady 19. Without AC, it is going 17.4 to 17.8
I tried as you told me and vacuum gives about 4-5 most of times during acceleration 2000 to 3000
and raises about 20.1-3 and goes back to 19. Sometimes it drops to 15 or 17ish.
I will have to try again tomorrow to make sure, but Would you consider this normal?

With the AC on it should fluctuate every time the compressor kicks on. It should stay steady around 19 with AC off. Yours seems to be backwards which is strange. Your acceleration test seems normal for that rpm test. For me if I stomp it for a few seconds my vacuum actually hits zero for a second and then snaps back to around 5ish until i let off but im north of 5k rpm.

 

[kms0567]

Maybe its the engine telling you that it likes breathing a little oil mist...or it could be a vaccum leak around the separator.

Thank you. Even it is restored as stock would it breathe an oil mist? and where is the separator is located? if it is leaking, how can I fix it?

 

[kms0567]

With the AC on it should fluctuate every time the compressor kicks on. It should stay steady around 19 with AC off. Yours seems to be backwards which is strange. Your acceleration test seems normal for that rpm test. For me if I stomp it for a few seconds my vacuum actually hits zero for a second and then snaps back to around 5ish until i let off but im north of 5k rpm.

Thank you for the reply.
I just tried it once again just on idle and it gave me 17.6 to 8 with AC on and 19 1-2 with AC off. I must got confused.
Result right now gave me this. The car was on idle for about 7 minutes and vacuum was steady 17.5-8 with AC on for first 3 minutes and it started to bounce around between 17 to 19 every 10 seconds and also gave me a boom sound and feels whenever it changed back and forth. And when AC was off, it was making steady 19ish. Would this be considered as a normal thing?
Thank you.

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