There is this gauge mounted on my intake that used to register a steady 40-45 psi under idle...I still have yet to figure out what it is. Anyway, one night I wanted to liquidize the rear tires a bit, so I go to gun it and the car sounded like shyt and started spitting out smoke. A few days later, I found that my cat totally clogged...after that, this little gauge has done nothing but go crazy- fluctuating from 0 to 60 something psi totally at random....any ideas?

 

Is the guage located at the rear passenger side of the intake, where the brass tube is in this picture? http://rain.prohosting.com/imwhom/junk/sender.jpg

If so, thats a fuel pressure guage, and if it's jumping all over the place thats agood sign that the fuel pump is on it's way out. Also, this would explain the missing/running poorly as the fuel pump isn't keeping up woth demand, thus letting you run way lean in spots. As for the clogged cat, i really doubt the fuel pump would cause that though.

If the guage is coming from the back drivers side of the intake it's an oil pressure guage, and erratic OP would be due to spun bearings or maybe something goofy with the pressure spring in the oil pump. This would have absolutely nothing to do with your driveability problems or clogged cat. It could have been caused by overrevving the engine while liquidizing tires though
...ed

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.8 @ 93.1
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die