Kansas broke my Autometer vacuum gauge

[Joe Dozzo]

I'm thinking my car is cursed...

Speedhut speedometer died years ago (2010) and I replaced the Speedhut's with a full set of the replacement Autometer gauges, stock speedometer and tach.

This last weekend on a trip to a car show in Liberal KS, the vacuum gauge started reading close to 30 inch vacuum while cruising at ~70. Seems to read correctly under boost. It's gotten worse in that while cruising, the gauge reads close to 12.5 psi BOOST.

Gauge is electric so there must be a sensor somewhere but since the car continues to run phenomenally, I'm guessing the gauge is toast.

All other gauges functioning correctly, new battery, fully grounded - all the usual stuff checks out OK.

Any thoughts or similar experience?

Thanks,

Joe

 

[nota4re]

Hey Joe! I too suspect that the issue may be the gauge itself but you could try replacing the TMAP sensor. It is on the passenger side of the engine up near the snout of the supercharger. The TMAP sensor is about $60 if you want to try replacing that first.

 

[PeteK]

Yes, that’s where I plumbed in the sensor for my Speedhut boost gauge. I had to install a different sensor because my Speedhut boost gauge reads to 20 psi.

 

[DanielJ]

Had my '05 out today and noticed the vac/boost gauge was showing ~22" vac at about 2200 RPM. On rapid acceleration, could make the gauge swing past zero and up to about 10 or so of boost. Engine off, gauge snaps to zero and restart, back to around 15 - 20 of vac.

Sender/gauge issues is my guess.

Wondering if I can drive the car several hundred miles without any damage to engine?

Thanks everyone.

DanielJ

 

[PeteK]

Max boost on a stock engine is about 12.5 psi. You can drive it without a functioning boost gauge as the ECM controls the boost, not the gauge,

 

[DanielJ]

Max boost on a stock engine is about 12.5 psi. You can drive it without a functioning boost gauge as the ECM controls the boost, not the gauge,

Excellent! Thank you ever-so-much!

DanielJ.

 

[nota4re]

The ECU has no control over boost. Unlike a turbo where wastegates can be controlled to divert exhaust flow driving the turbo(s), a supercharged engine is purely mechanical... more pulley speed = more boost.

 

[extrap]

The ECU has no control over boost. Unlike a turbo where wastegates can be controlled to divert exhaust flow driving the turbo(s), a supercharged engine is purely mechanical... more pulley speed = more boost.

= more pulley speed ?

 

[PeteK]

Kendall, thanks for the correction--I'm getting too spoiled by more modern vehicles that do have ECM control over boost and everything else! In any case, the boost gauge has no effect on boost, it simply tells you how much you have.

Extrap: Yes, that's how the "pulley and tune" works. A smaller diameter pulley on the SC makes it turn faster for a given engine RPM and produce more boost. Even so, the practical limit for the stock SC appears to be about 15psi. In principle, you could keep spinning it faster, but in reality there is a tradeoff point between supercharger efficiency and additional boost. To go higher than 15, you should go to a larger SC, like the Whipples.