3TAS4ME

Not sure where to look for the problem on this one. First a little background. I have a 1993 LT1 six speed car. I bought it when it was three years old. Used to get 26-27 mpg on the hwy and 21-22 normal driving. Sold the car to my brother in law several years ago. Engine had a fire. I bought the salvage and repaired the car. Damage was minimal but enough to total the car. I replaced the eight fuel injectors with used ones out of another LT1 manifold. I also replaced the engine wiring harness, spark plugs, wires, some of the sensors, ignition coil, optispark and various vacuum lines. The spark plugs were not AC Delco plugs, the only non oem parts installed during the repair. The car is not modified and has only 48k miles on it. I can only now get 22-23 mpg on the highway and 19 with normal driving. Where did my lost fuel economy go? All sensor readings look normal, no SES light. I am running 93 octane all the time.

bombebomb

I know you said all sensor readings looked ok, but did you put 93 lt1 injectors in, or 94+ injectors in? Cause 94+ are 24lb while 93 is a little lower. Just a guess.

3TAS4ME

The intake was supposed to be from another '93 if I remember right. I bought the wiring harness from the same guy and the harness is '93 only. I guess that doesn't mean the injectors couldn't have been changed. Is there an easy way to tell?

Injuneer

Put a scanner on it, and look at the long term fuel corrections (BLM's). If they are significantly above 128, there's a good chance you have a "false" lean condition that is causing the ECM to add fuel the engine doesn't need. This can be caused by faulty O2 sensors or O2 sensor wiring problems, exhaust leaks before the O2 sensors or misfires.

Also look for a clogged air filter, excessive fuel pressure, incorrect fuel injectors, engine running too cool, clogged cat, excessive drag on the brakes, etc.