Ford F150 - 91 ranger with HUGE increase in fuel consumption

I've got a 91 ranger 4.0 5 spd with a huge increase in fuel consumption. Now the history on this truck.. Replaced the tranny, the engine burns oil but not that much. But lately we noticed that its burning black, burning more oil and a massive amount of fuel consumption.

So another thing on my list to change is spark plugs(will do it tomorrow) but we replaced the oxygen sensor hoping that maybe it would be the problem. There is no block in the intake and the air filter is brand new. I don't have much money and well me being a girl I'm not the best at mechanics so trying to figure this out without taking it to a shop... Any advice would be greatly appreciated..

Oil usually burns blue, black smoke usually indicates your fuel mixture is too rich, which is why you are burning so much fuel. If your check engine light is on, I would take it to Autozone or something and get the code read. If not.........anything after is just a WAG without actually seeing the truck. Maybe it's a failed fuel pressure regulator or something?

check engine light flickers on and off, and well i don't notice anything else changing with it. Ie, any gauges or anything like that, I live in Saskatoon, Sk. Canada. I think tomorrow I'm going to run it into a shop. I'm not sure where to take it but I'm gonna look around and see what different shops have to offer.

I love this truck. A ranger was my dream truck and hate to part with it, but it's not worth a lot. It's 91 with 256,000 km on it.. so hoping for a cheap fix...

Check the thermostat. Sometimes older wax pellet thermostats open prematurely when antifreeze leaks around the O ring that seals the plunger. When the thermostat opens too soon, the engine runs cold and the control module puts the engine into cold enrichment.

It could be the oxygen sensor, i had that issue with a toyota i had. I also had the check engine light flicker every once and a while. But i wouldn't discount the possibility of if being the thermostat like BoatNut said.

Goodluck with the fix.

Try replacing the fuel filter you might have too much carbon build up inside the filter and the clean fuel is sendin more and more carbon to the combustion chambers, it is an easy fix and should run you No MORE than $20..

Guys im rackin my brain here with this one, anyone else think or had the idea that it might be a dead/failing/clogged injector???

Good luck and keep me posted!


Justin