morning, I need info from some of you auto gurus. I have ford f150 4x4 1994 with 5.8 automatic.
questions have are when warming up the vehicle is in open loop. this is running richer mode correct? this is changed to closed loop when warmed up by engine temp correct?
Does the o2 sensor have anything to do with determining when the vehicle is warm enough to close the loop? Or only operating when it is changed to closed loop?
I run the scanner on this engine and only have a open loop no matter what I just bought this vehicle a while back so my theory from some drips is since the engine never gets warm the thermostat has been changed to a really cold temp to keep the engine from getting hot and causing more pressure to help with leaking to get the vehicle sold? or completely removed to keep it from getting pressure.
I know I have to make needed repairs and get the temp range correct im wondering how much is this strange condition have on mpg. im doing good at getting 9mpg and I drive very conservatively .
I think the iac has some major effect also as the idol is to fast but I think the temp is a priority since it does not get to op temp.
thanks for any input it gets confusing when your chasing four dogs tails at the same time all going different directions.
grumpy

 

My first suggestion would be to remove the thermostat housing and make sure there is a thermostat in there. It could be stuck open. What does your temp gauge on the dash show?
Believe it is better if we take things one at a time.

 

As soon as the O2 sensors start responding the engine should be in closed loop, sounds like you have a O2 sensor problem.

 

update;; I changed the thermostat the temp gage read between the n and the o in normal and as stated above the loop would not shift. when I change the thermostat the temp after running and driving was actually even cooler than before. Could the temp sending unit be bad? or another issue.?? I actually think the water is getting hot enough I will check with thermometer tomorrow but can the a temp sensor reading to low actually cause the loop not to change and stay in open loop even when warmed up??
Thanks Grumpy

 

The computer does not look at the engine temp sensor to determine when to go in closed loop.

 

amesgang; if the engine does not look at engine temp sensors what does it use to determine the open closed loop ? the o2 sensor??
THanks grumpy

 

Yes, as soon as the O2 sensor starts working it goes into closed loop. It usually only takes a few minutes.

 

Thanks very much
Grumpy

 

Something you might want to try,
With your vehicle in closed loop, Watch your readings and unplug the ECT (coolant temp sensor) and see how long it stays in closed loop..