Why would my MPG plummet?

[Hypoid]

What do you sugest I check with a vac guage? Do you know how to test O2 probes?

I don't know much of anything about the 2000 model year electronic engine management. I have seen older/other brand systems with scanners hooked up, sensors being monitered in real time. It still takes someone who understands what they are looking at. A simple check with a DVOM may or may not provide usefull information, someone else will have to answer that one.

A vacuum gauge is the bomb! All you need is a manifold vacuum port to monitor physical engine conditions-without lifting a wrench. Although these articles were directed toward carbed engines, much of the mechanical wear diagnostic applies to EFI engines as well.

http://www.centuryperformance.com/vacuum.asp

http://projects.mergecomputer.com/ford%20tractors/Service%20Specifications/vacuum%20gauge%20diagnostic%20chart.jpg

All that aside, I'm starting to get a real bad feeling. Has the tranny ever been serviced? I kid I know picked up 2 seconds on the 1/4 mile at Bandimere with his full size Ford 4X. He didn't realize he was slipping that much until he rebuilt the tranny.

 

[Ecomike]

Some O2 sensor testing details:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/15/22/f9/0900823d801522f9.jsp

and for the 1991 and new Jeeps:

http://www.autozone.com/servlet/UiB..._us/0900823d/80/15/23/99/0900823d80152399.jsp

 

[Powerman]

Guys, thanks. Thats cool. My friend at work has a vac guage. I'm sure they wouldn't be too much to buy either. I'll see what I can do to test my O2 probe. Even If I am just imagining this, it would still be good to check my stuff out and see that things are running right. I have a 331 head and have worried a bit about it. Figured if it wasn't cracked by now I'm good. But who knows. Thanks for the info.