Cleared a pile of misfire codes and that pesky downstream O2 sensor.
Drive to work, temp peaks out around 180F and stays right around there. Apparently this Murray thermostat that I've been running for the past year didn't pass the water pot test as well I thought it did.
Also, it is staying in closed loop, except when it says "Open Loop - Driving"
Perhaps THIS is why I've only been getting 14 MPG since I replaced radiator and thermostat?

 

If it's closed loop, then running cooler shouldn't make a huge difference. It will drop to open loop on acceleration. You sure the upstream O2 sensor is good?

 

No problems reported with the upstream O2 sensor. I've been getting CAT efficiency codes for years, which is what I was referring to.

It starts in closed loop and never makes it to true open loop, but this thing is the first reference to "OL-Running" that I've noticed anyplace. Have only been aware of CL and OL prior to this AM.

 

So cruising down the road with low tps voltages the ecu is going into open loop fueling?

 

A quick search for "Open Loop - Drive" says that is a fuel enrichment condition. I have no idea what the Throttle Position Sensor voltages were, but I only get up to about 2,000 RPM during my commute with top speed around 45 MPH.

And the highest engine temp the whole time was 185F, which came down to below 180 in short order.

Expanding on this: "Also, it is staying in closed loop, except when it says "Open Loop - Driving"" (should be Drive)

The status on the streaming data says CL, unless I am moving then it goes to "OL-Drive" then back to CL when I stop and idle at a light or something.

 

Closed loop is what you want for normal driving. It means the feedback loop from MAF/MAP through ECU to O2 sensor is closed and fueling is being corrected in real time.
Open loop is for startup when the O2 sensor isn't hot enough to work yet so the computer has to guess how much fuel from learned data.
Open loop - drive is for when you are pushing the pedal down making enough power that the narrow band O2 sensor is not able to accurately sense so the computer estimates fueling based on learned data. This is designed to come out on the rich side for engine safety and increased power. No one likes burned valves.

If it is staying in closed loop it is working correctly. Open loop startup is somewhere between non-existent and seconds long on modern cars. Mainly it was a thing in the first years of EFI. New cars are often using wideband O2 sensors that read accurately at all power levels so the computer can be in closed loop all the time.


I wouldn't describe winter temps of 185 as broken unless you are getting other symptoms.

 

Here is what 180f looks like on this style gauge.

 

How is your cabin heat?

 

Fine. Can feel it warm when gauge is barely off the peg.

 

I just buzzed the 1997 FSM, and it references normal operating temperature as 180* so yes I believe being below 180 would cause open loop.

 

I thought the thermostat was supposed to be 195F and normal operating around 205? Was that another wild change between 1995/96 and 1997?
Then again, I got the 205 from here somewhere.

 

Ill start my 96 from a cold soak tomorrow and tell you when it goes closed loop.

 

I think the fsm meant >180 is normal and that's when it goes closed and some of the evap stuff kicks in.

 

In the photo, the FUELSYS1 reading is CL. The OL-D with half the D cut off, is a bad screen refresh this gadget does.
Going to the next screen and back corrects it.

 

If you are in open loop the stft should switch to 0.0v