how do i check...

[Cyrus2000]

id like to check to see if my car is going into closed loop. truck runs great, drives as well as its driven since i got it 15000 miles ago. total miles 178k, just recently changed out fuel filter, replaced exhaust from the collector back, cone air filter in stock housing, cleaned maf, replaced all 4 tires.

only getting 18-20 mpg and most of my driving is on the highway at ~65mph. truck had a leaky fuel filler neck which i fixed by replacing the filler neck. before this, the truck got ~24-26mpg. some time after this repair is when i first noticed i was only getting 18-20.

also, the temperature needle never gets much above 1/3rd of the way and is often at 1/5th of the way up the gauge.

anyway, im thinking the truck is running rich because its staying in open loop. i drove 150 miles on the freeway and then around the same in the city and got the same gas mileage (7-8 gallons to fill up after each 150 miles).

planning on changing the plugs wires and forward o2 sensor. which sensor controls open and closed loop function? the water temp sensor?

 

[HardcoreKeith]

Sounds like your thermostat's stuck open. I'd check that first.

 

[Spowerback]

termostat ....fuel filter.... oil filter ...change oil battery ...tcheak wire ....gray spot contact... tire ....150.000 miles cat convector....tcheak 02 sensor ohm multimeter ...clean MAF sensor wiht spray carb.....fixe a replace bolt joint and upper, lower ...tie rod loose. changed coolant water....

 

[Cyrus2000]

the heater works like a champ, though it makes an odd noise sometimes when i turn it off. if the tstat was stuck open, would the heater still work this well?

 

[dhendrix]

If you're thermostat was stuck open you probably wouldn't have heat. Also if it is stuck it could cas the truck to run a lil rought due to overcooling. Im with the guys on this one, check or replace the thermostat. It is an easy repair an could prevent very costly repairs. Good luck, hope this helps.