Does this indicate an EXHAUST RESTRICTION?

It might indicate a restricted exhaust system -if- there is no other device engaging that would account for a change (rise) in manifold pressure, i.e., the EGR valve.

I consider manifold vacuum a very unreliable method for diagnosing a restricted exhaust. If the gauge you bought is a compound gauge (measures both vacuum -and- pressure) you'd be better off using it to measure exhaust back-pressure directly. The easiest way to do this is to get a sparkplug that fits a Ford 300 cubic inch inline six cylinder (F9Y?) and gut it out, braze a fitting on the end to match the hose size of your compound vacuum gauge, second tool source is to use you 18mm compression gauge hose adaptor assuming it comes separate from the compresion gauge. Install you newly built back-pressure tester in place of the oxygen sensor (both use the same 18mm thread) and give the throttle of the running engine a good healthy snap to WOT, short and quick like. Back-pressure should not exceed 3 PSI.

Most driveability training manuals have a conversion chart in them. be advised, the sensor output voltage is dependant on the feed voltage -to- the sensor, the voltage regulator inside the ECM rarely puts out exactly 5.00 volts and it is not uncommon to see them vary by 1/2 volt, i.e., 4.75-5.25 volts. 1.7-1.8 volts is a bit high for 18" of vacuum.

Either statement could be true. Vacuum leaks are the result of unintended mechanical failures of a given sort, they can manifest themselves in many different ways.

I think he was shinin' you on....

Thanks again Neil!:)

You've opened-up a few more questions I have now!:)

What other "devices" could cause this? When you refer to the EGR Valve, are you saying it could be stuck OPEN, or CLOSED?

So are you saying that if the sensor was getting exactly 5.0 volts, it should show "x volts" for "y hg", but if it was only getting 4.75 volts, it should be exactly 0.25 volts less than "x" for the above "y"??

I actually hooked my Vacuum Gauge up-to the vacuum source that connects to the MAP Sensor, so maybe there's a crack in the line/hose going to the sensor itself?

If you go to this page:

You'll see the 4 hoses coming out of the top of the throttle body, the one positioned lowest(in the pic) leads to the Fuel Pressure Regulator and tees off to the MAP Sensor(a seperate hose). I am replacing this hose tomorrow(I had to order it from the dealer) because it had 2 small cracks in it. If the MAP voltage is still as high as it is now, maybe I'll have to look at the hose/line that connects to the MAP itself...

Anything else to add?

THANKS AGAIN!:)

The only other part that comes to mind that could effect manifold vacuum during the BP test would maybe be the canister purge.

I mean it could be opening as it is supposed to do. When checking for exhaust backpressure via manifold vacuum, you do -not- want the EGR or any other device that can artificially effect the true reading to be operating lest you get a false reading.

Here's the scale from the book for 18" of vacuum on the MAP sensor for different reference voltage:

Reference voltage> 4.75 5.00

18" vacuum>>>> 1.250 1.493

So, it appears that the output voltage is not totally linear to the input reference voltage, pretty close though.

Cracked lines are a very strong possibility. One additional procedure recommended would be to supply your own vacuum at the MAP sensor with a mity-vac hand vacuum pump and see if the voltage tracks the vacuum under controlled conditions, tee in your new vacuum gauge and average between the two vacuum gauges if accuracy of the gauges is in doubt.

You know that you'll be pulling the upper plenum off to replace these vacuum lines don't you?

You're welcome.

which was not very difficult.

Well, not as hard as it was for you to TRY and be funny...but good attempt!