Performance and MPG 4.0 Ranger

[wmayo]

So here it is

I have a 1998 4x4 4.0 Ranger.

Started to see performance problems about six months ago. I just move to
San Diego and had to get it smog. It passed which suprised me for as bad as it was running.

Afterwards I had some time to do some maintenance on it. Changed the plugs, plug wires and air filter.

plugs 1 and 4 were broken in half and had been for some time. Needless to say the truck ran better afterwards. Still the gas mileage was really bad, 12 mpg. I notice the engine temp was not ever getting higher than 1/4 on the gage and it took forever for it to get there. Changed the thermostat. Temp now goes up 1/2 the way and does so in 10 mintues. also runs better with more power. Still it seems to be lacking pwr and after 120 miles I have already gone though 1/2 a tank.

Question: is there something to do next? there are no codes or engine lights. I had engine check light before the work but when I changed the plugs and wires I reset the ecu.

I was wondering if since the thermostat was stuck open the engine would have been running rich. Could this have cause problems for my o2 sensors, foul them up enough to cause mpg and performance problems but not enough to throw a code?

Also since the #1 and #4 were not firing for whatever amount of time would this have caused o2 sensors problems.

I have also run injector cleaner, gumout, for the last three tanks. How would you know if they was a clogged or partuially clogged injector? Best way to clean them?

Like I said it is getting better but still going through alot of gas and still a little weak when going up hills.

In closing it is a testament to the 4.0 and its ecu for the truck to pass a dyno smog with two broken plugs and a thermostat stuck open. That or the smog station really sucked.

Thanks for the help

[85e150six4mtod]

Look at your printout and see what numbers it posted. You may have been at the high end of the scale.

Misfires are not good for cats. Yours are working, but I wonder if they started to melt from the extra heat of burning up the gas from the two dead cylinders. Not easy to check them...but someone mentioned a pressure test at the oxygen sensor port. Maybe you could research that test to see if you have a partially pluged cat.

Good luck.

[TheHandyman]

I sorta agree about the 'cats'. I've seen partly clogged ones that really killed an engine's power yet it continued to run for years! They'd cause extra back pressure if partly clogged. If no other way to test them, they could be cut off, visually inspected and replaced.