I have a '94 Touring with no problems (at least not many) except today driving down the road I get a boost guage reading of a almost constant 20 lbs. vacuum even with constant speed on flat roads. It seems like the 20 lb vacuum reading has taken the place of a zero, normal reading. Whe I turn the car off it does return to normal. Any ideas, as it was reading okay yesterday?

 

At idle, 750 rpms, what vacuum is it pulling?

Tim

 

a vacuum reading of zero is a bad thing.....

 

First of all let's clarify something: You do not have '20 pounds of vacuum', you are pulling 20 inches of mercury. Vacuum readings are not in pounds. Boost is, not vacuum.

Now, having said that I wonder if you simply have a defective gauge? A healthy car should pull around 16 inches of mercury at idle. Do you have an alternate vacuum gauge of any sort to calibrate against?

 

bajaman said it better than i could have lol..... vaccum when out of boost = good. buy a new guage

 

The only time the gauge should be reading that much vacuum is during a downshift, it should idle at 16-17. Like said before, sounds like a faulty gauge.

 

Definatly not wrong but not exactly right either, ive seen a bunch of stock port FDs pull 20 inhg at a 800rpm idle. On high deceleration you should be seeing more then 20. But yeah, I would guess like everyone else its a faulty gauge. I would be willing to bet the farm that its a autometer.

 

I don't understand! My boost guage has always read "0' unless accelerating it goes to max of about 12 lbs boost. When downshifting, or decelerating it usually goes to around 16-18 in of mercury (thanks for correcting me), but otherwise when crusing it read '0' -- now it is reading 18" mercury at idle.

So does this mean my guage has just started operating correctly on it's own!? There seems to be no performance change that I can tell, nothing to point to a problem except the guage reading. BUT, it seems to be operating correctly NOW if the idle at 18" is how it's supposed to be. Any thoughts? Thanks in advance.

 

Everything seems good except for the cruising part. It should not "sit" at 0. It should move around with throttle position. Idle at 18 is great, boost and decel seem fine.

 

Exactly

I thought the same thing when my gauge would leap down to like 21-23 in of mercury off deceleration but found out that thats normal when you're in gear. When you pop it in neutral, the vacuum should even out to normal.

 

If your in gear and off the gas your are still decelerating even though it may or may not be noticible to you, so that would still make sense to me. Regardless, cruising off boost the gauge should be ultra sensitive to throttle changes.

 

I don't think you have any problems but here's mine as a reference.

Mine:

Idle= 18
Downshift= 19-21
Hard Downshift= 22
Cruising= All over the damn place depending on rpm, but at a constant steady pace of about 55mph it will sometimes be at a vacuum 5, 2 or 0.
I have the Pettit Racing boost gauge mounted on my steering column.

 

Mechanical boost/vacuum gauges work by the pressure/vacuum deflecting a "Bourdon" tube. This is connected to a rack that turns a pinion gear connected to the pointer. Often these gears wear out due to constantly vibrating in one small range and stick. Sounds like what you have.

This is not limited to boost gauges - most mechanical pressure gauges eventually develop similar problems.

 

Thanks everyone for the time and info. I love this car, and have had it since '96 (it's a 94') but it is, all in all, the most confusing 'thing' I've ever had -- excluding my wife (she's New York Italian)
It's running like 'hus' has described his, so I guess I don't have a problem, but DID have a problem for the past 10 years when it was more or less sitting on '0" at idle, instead of now at 18. (I'd still like to know how and why all of a sudden after so my years the guage reading suddently changed foe no apparent reason -- maybe a hose somewhere has come loose??!!) But anyway now I guess I'm happy!

 

Glad you're happy now..

On a side note, i would LOVE to have an italian girl that was born and raised here. Its just to bad that italian families still have their tradition of their daughters ONLY interacting with another italian.