my 90 keeps setting off a code 44 i replaced the o2 sensor but it keeps coming up also im only geting about 9 mpg. Anyone know what it could be. Thanks

 

Code 44 indicates "O2 circuit, lean exhaust indicated", but does not necessarily mean there is any problem with the O2 sensor itself. In fact the GM service manual lists replacing the O2 sensor only after all other possible causes have been eliminated. Briefly, here's how to troubleshoot:

If you have access to a "scan tool" such as the Snap-On type this will be very helpful as you can use it to display the "block learn cells". When the code sets, the block learn values should be around 150.

Check:
* O2 sensor wire, to be sure it is not grounding on the exhaust manifold; would close the circuit and give a false "full lean" reading.
* MAP sensor (top rear of intake plenum). Disconnect the MAP and if the lean condition is gone, replace the MAP.
* Water contamination (even small amounts) in fuel can set a code 44.
* Fuel pressure may be too low. Attach a fuel pressure gauge and monitor the fuel pressure while driving under varying speed and load conditions.
* Exhaust leaks ahead of the O2 sensor -- even small. Will pull air into the exhaust stream and give a false lean reading.
* AIR system directing air into the exhaust during Closed Loop. (You willl need a Scan Tool to monitor this though.)
* Lean (out of balance) injectors.
* When all above checks out OK, then the service manual says to replace the O2 sensor.

There are more specifics in the SM which I can email to you if you want.

Good luck.

 

Hope this helps I had same problem on my 95, turns out that there are check valves in the egr system that return exhaust from the exhaust manifolds to the egr system. When one of these goes out instead of only returning unburnt fuel exhaust to the egr , it allows ALL of the unburnt fuel to be dumped out into the exhaust system. Symptoms include as you stated LOW mpg, reduced temperatures as the exhaust gas has higher temps so it raises the operating temp as it is recycled, A miss will develope as the carbon build up increases due to rich enviroment,. and Black smoke on hard acceleration once enough carbon builds up.... As I said I bought my car w/ this problem after a local mechanic said I could probably fix it for under $500 The check valves are under $50 apiece I ended up spending over a grand here in hicksville because noone here could properly diagnose the problem.. Ended up taking it to Jeff at Corvettes of Dallas ,, Great service . Fixed in no time . MPG went from 13 to 26 on the highway GOOD LUCK

 

thanks for all the advise ill start working on it this weekend