Hey fellas,I'm having a consistant problem.
I have a 92 shortbed 4x4,with a 5 speed,3.42 gears and 33" tires.
It originally had a 4.3,I later installed a 305 w/ a Mellings MTC1 cam and flowtech headers,and now it has a stone stock 350,still with the headers.The exhaust is a 3" single,no cat,single in/dual out flowmaster.Every engine has had the ECM/distributor that it left GM with,the 350 is out of a 91 Suburban.I have gotten 9-11 MPG from EVERY engine.I'm not getting any trouble codes,and all tune up stuff(plugs,wires,cap+rotor,fuel filter,etc.) are fresh.

I've had 2 other pickups very similar to this one,one was a 92 with an automatic and identical gears/tires,it averaged 15mpg.The other was a 91 w/ a 5 speed,and 3.73 gears,same tires,it also averaged 15mpg,with a best of 18mpg.so why does this truck use so much fuel?It runs great,just the MPG sucks!
Any thoughts or advice are apreciated!

 

Have you used the appropriate ECM/Knock sensor/ESC module/Injector size with every engine?

 

Every engine has had it's original ECM,sensors,throttle body and distributor.The only consistant piece is the wiring harness,but I can't think of anything there that could be blamed.