Smog Pump Delete Fuel Milage

[777-300ER]

Hey guys/gals,

I rerouted the belt on my '89 CS as the smog pump was rattling pretty bad. Before I did this I was getting 17-18 in the city and 24 on the highway. Afterwards I'm lucky if I get 14 city and 17 highway. Do I still have to plug off the air pipes on the back of the heads or is this just the nature of the beast? Any help is appreciated.

[Tiggie]

Is your smog pump and system still in place? You should be okay as far as air pipes go if this is the case. If not, you should plug them because there would be an exhaust leak.

I have experienced similar MPG in my 88 after smog removal, although in theory it should it should have minimal, if any effect as long as the cats stay free flowing. I have no answer for you there.

[BigT]

That is odd. When I removed my air pump, my mpg increased slightly. The old pump was putting a drag on the system I guess.

I wonder if the exhaust gas is building up somewhere in the system and putting an extra drain the engine?

[777-300ER]

Could be a set of bad cats. Thing stinks like hell when you put the pedal down. Only has 55k miles on it so I wouldn't think that would be the issue. I'll also check the exhaust system for any dents, who knows what I may have done while I was hooning.

[gadget73]

bad smell sounds like rich fuel mix. If the ports are open on the back of the heads and its sucking air, it will screw with what the oxygen sensor sees. Extra air will cause the ECM to richen the fuel mix. Might be worth unhooking the rubber hose going to that pipe and putting a cap over it just as a test.