OK what could cause bad fuel milage ? on my 89 4.0l limited ?

Could it be bad or worn sparx plugs ?

If i change to a cone air filter won it burn more fuel ?

what can i do ?

OK what could cause bad fuel milage ? on my 89 4.0l limited ?

Could it be bad or worn sparx plugs ?

If i change to a cone air filter won it burn more fuel ?

what can i do ?

TRY A GOOD TUNEUP, PLUGS, WIRES, CAP, AND ROTOR. CHECK AIR FILTER IF DIRTY CHANGE. ALSO CLEANING THE THROTTLEBODY COMPLETELY WILL HELP. CONE AIR WILL HELP TUNEUP WILL HELP MORE THAN ANYTHING. CHECK THE CVC LINES. DALE :nono:

The easiest and most obvious, air filter.
Also, dumb but woth checking, tire pressure, and e-brake dragging.

After that, the usual tune-up stuff. though *usually* but not always, if your ignition system has issues, it would be running rough, and lack power.

What mileage are you getting? Does the engine run smoothly (at speed and at idle)?

As the others have suggested, a good "tune up" to start. Then check vacuum lines.

I had a recent increase in mileage after installing an aftermarket keyless remote. Of course, the remote had nothing to do with it, but I suspect that when I disconnected and reconnected the ECU when I pulled the lower dash out, it improved a connection somewhere. So, also check the connections to the sensors. Disconnect, check for corrosion and reconnect.