Engine vacuum at idle

[2006GT]

What vacuum reading is normal at idle? The reason for the question is that I'm wondering if I damaged my engine the other day when I stayed in first gear too long and the engine began to misfire at high rpm. If the valves began to float, the engine would misfire similarly to what I experienced. If I bent an intake valve(s), intake manifold pressure would increase at idle. The engine still runs smoothly, but I cannot tell if its down on power. Presently the engine produces about 20 in. Hg, but I can't remember if the idle vacuum was greater before my carelessness the other day. Also, one should be able to spike engine vacuum by snapping the throttle closed in first gear. About 21-22 in. Hg is the largest vacuum the engine can achieve. Again, I never paid much attention if previously my engine produced greater vacuum under such conditions.

Thanks in advance for any responses. Just a little research before the possibility of a compression check.

 

[Not 4N]

Are you sure what you felt wasn't the rev limiter kicking in? From my experience if you bent a valve you would know it at all rpms and it wouldn't run smooth at any speed.

 

[2006GT]

It may have been the rev limiter. I have never had an engine with an electronic limiter, only mechanical versions like the valvetrain. How does the engine behave when the limiter operates?

 

[Not 4N]

From my understanding the ecu will retard the fuel input resulting in a "running rough" feeling and not allow the engine rpm to climb.
Maybe one of the GT techs can chime in with a better explaination.

:cheers
Trent

 

[nota4re]

2006GT,

Please rest easy as I really doubt you caused anything bad to happen with your engine. For certain what you experienced was your rev limiter. It will shut down ignition momentarily as redline is hit. It feels weird/bad but it is really there to PREVENT damage. The only chance you have to hurt the engine is if you mechanically induce over-revving. Imagine if you were to accidentally downshift from 5th to 2nd instead of 5th to 4th. In this scenario, the momentum and energy of the moving car can cause your car to exceed redline and the rev-limiter is powerless to prevent it.

In your case, it sounds like your mishap was on acceleration so that was just the rev-limiter doing its job. Rest easy, your car is perfectly fine!

 

[Shadowman]

What vacuum reading is normal at idle? The reason for the question is that I'm wondering if I damaged my engine the other day when I stayed in first gear too long and the engine began to misfire at high rpm. If the valves began to float, the engine would misfire similarly to what I experienced. If I bent an intake valve(s), intake manifold pressure would increase at idle. The engine still runs smoothly, but I cannot tell if its down on power. Presently the engine produces about 20 in. Hg, but I can't remember if the idle vacuum was greater before my carelessness the other day. Also, one should be able to spike engine vacuum by snapping the throttle closed in first gear. About 21-22 in. Hg is the largest vacuum the engine can achieve. Again, I never paid much attention if previously my engine produced greater vacuum under such conditions.

Thanks in advance for any responses. Just a little research before the possibility of a compression check.

For your "Peace of Mind" the vacuum numbers are spot on; no worries.

Then as others have said; long before you cause a valve train issue the engine management system will shut you down.

I am confident in saying; you and your gal are fine

Takes care

Shadowman

 

[2006GT]

Thank you very much for the responses. Very helpful.