Smog Pump? 75 Eldo

[Jeff Wilk]

Anybody have information on what might cause my smog/air pump to suddenly stop working?  Turning fine..... Turned off car to dow work on engine....started car up and pump is frozen solid and wont turn at all. Got a replacement located already but what the heck happened?

[Hankk17]

I've had smog pumps lock up on me that way as well.  the bushings wear out and the spindle inside can get out of alignment and then jam against the casing. 

this is a Jag site, but they've got nice shots of GM pumps that sort of illustrate the problem. 

http://www.jag-lovers.org/xj-s/book/AirPump.html

-Hank

[TJ Hopland]

What usually kills them is the check valve(s) go bad and let the hot / corrosive exhaust gases back flow into the pump.  Usually the first victim is the diverter valve.  Then the next is pump. 

Easy way to test the check valves especially on the big cad is to remove the rubber hose where it connects to the cross over tube and check valve and start the engine.   If you get exhaust out there the valve is bad.   The check valve is a fairly universal part, just the thread size has to be correct so they should not be hard to find.

To test the diverter valve you either need a hand operated vacuum pump to operate the valve or with the hose to the check valve disconnected rev the engine.  With the throttle open you should get air flow from the pump.  Let the throttle close.  The air flow should stop momentarily.    On deceleration there tends to be a rich condition and adding the extra air into the exhaust tends to make it 'pop' in the exhaust so under that deceleration condition the diverter valve diverts or bleeds off the smog pumps air to the outside which in this case is just that screen on the valve assembly.  In later years it went to a hose and into the air cleaner assembly.  THey also added a line to the cat converter in some cases, talk about an expensive valve assembly and a lot of hose.