1989 chevy 2500 horrible gas mileage?
 

Hey everyone, first time poster here.


I've got a completely stock 2500, with the 350TBI, 4x4, 3 speed auto. I've done the usual stuff to help mpg, oil change, plugs etc with no luck. Right now I average 6 mpg. I'm not expecting miracles but others are complaining about 12mpg so it leads me to believe something is wrong. I can keep my foot out of it and it doesn't make a lick of difference. Figured id see if anyone had any input.


thanks in advance.

Brakes dragging, stuck in 4x4, fuel pump going out, engine running lean, clogged fuel filter, oversized tires, plugged exhaust? Any of those things can cause poor mileage. My truck is the same way and I haven't been able to figure it out either. I average 9 MPG in the winter and mine is a 1500 truck with a 5.0L vortec engine. So ...

If I were you, Id' also try putting in a new fresh oxygen sensor.

Already checked the other stuff minus the o2 sensor and exhaust. Might start with those two, have a feeling it could be exhaust related. Truck sounds and runs excellent but my exhaust looks like Swiss cheese from the axel back. Muffler and cat look ok but from there on its pretty shreaded. Not to say either of them couldn't be messed up in some way. Thanks for the response.

Try checking the distributor shaft bearings. Those do wear-out and as in my case caused the plugs to fire as much as 10 degrees off!! A shop put it on a scope and found the problem. I guess one could just remove the cap and see if the rotor wiggles.
Good luck.