need help with vacuum gauge

[Patrick5oh]

i just bought a 2017 mustang GT performance pack, and when starting up the car, the vacuum gauge does not move. Any idea on what the issue may be? The oil pressure needle moves, but the vacuum one doesnt.

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[Skye]

The vacuum gauge does not move. Does it register any reading at all?

The car is new to you. Has the vehicle been modified in any way? Is it 100% stock? Tuned?

From experience, the dual gauge cluster is driven by a single electrical connector on the back of the gauge pod. If one gauge is working, that gives promise proper power is being applied to both. The gauge itself can be bad, but I've not read of that before. Being an electrical circuit board, I'd think the pod would either work or not work.

Setting the dash aside, how does the car run? Well? Idle and performance are what one would expect? Have you studied under hood, to see if there are any loose or disconnected electrical or vacuum lines?

I wanted to learn how the car registers that reading on the gauge, where it gets that measurement from. Reads there is a MAP (Manifold Air Pressure) sensor in the intake system which measures the difference between intake and atmospheric pressure. Along with providing a measurement to the gauge, it also helps the car determine the proper air/fuel measurement. If the gauge wasn't registering anything, moving at all, and assuming the gauge itself is good, I'd think the engine would be operating poorly. The sensor can become dirty over time; they can be cleaned and/or replaced. Statement above regarding the MAP sensor is wrong. See details in the following posts.

So, some questions for more detail, along with some initial, general insight.

 

[K4fxd]

Coyote mustangs do not have MAP sensors. Vacuum is inferred.

 

[Skye]

Coyote mustangs do not have MAP sensors. Vacuum is inferred.

Thanks for the insight.

What I'm trying to figure out now is, is the inferred vacuum reading derived from the Throttle Position Sensor (TPS)? Mass Airflow Flow (MAF) sensor? Both?

 

[K4fxd]

MAF mostly. @engineermike would know.

I'd like to know if it is tweakable. My VooDoo manifold reads low on the dash compared to an actual vacuum gauge.

 

[engineermike]

Inferred map is a function of maf, rpm, cam timing, and possibly exhaust pressure (emap). The problem is that it’s a quadratic equation with coefficients for each term, and the coefficients are different for every rpm and set of cam timings. It’s not very intuitive or easy to manipulate, to say the least.

 

[Proshop]

i just bought a 2017 mustang GT performance pack, and when starting up the car, the vacuum gauge does not move. Any idea on what the issue may be? The oil pressure needle moves, but the vacuum one doesnt.

You might just have a bad half of a gauge since oil pressure is working and not vacuum. If you end up needing a new one I have a one collecting dust since I have all digital gauges.

Edit: I have a 2021 and an all digital dash… do 2017’s show a vacuum reading on the dash between the Speedo and rpm gauges?

 

[Cory S]

do 2017’s show a vacuum reading on the dash between the Speedo and rpm gauges?

Yep.

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