pwb

Hi, how could i tell if my 1993 4.0L is running in cold or hot mode? Is there som signal or pulse width i can meassure?

djb383

Hot/cold (ambient or coolant temp) have little effect on a modern computerized EFI motor. If it's well tuned, sensors functioning correctly, they start/run flawlessly cold or hot. Generally, a EFI motor operates in open loop (cold) until the O2 sensor(s) get hot enough to signal the ECU (closed loop). Heated O2 sensors can reach operating temp within seconds of a cold start-up.

opake

I know on other vehicles the car will run in open loop to warm up till the coolant hits 160 degrees F, then will go into normal closed loop mode. Not sure if theres a way to probe the front O2 sensor to tell this though, and its not OBDII so I'm not sure if theres any way to hook up a scanner to see what fuel table its running off of. What kind of problem are you having with the truck?

Doobie97

What seems to be the issue with your rig?

djb383

That's why most O2 sensors are electrically heated, so the system can enter closed loop well before coolant temp reaches 160.

pwb

Litle low mpg, maybe. The problem is also that temperatur sensor (the one in front at the thermostate) has different values if ordered from jeep4x4 or rockauto, so since that is one of the sensors that tell the ECU to run in hot or cold mode i want to see what mode it runs in.

89Laredo

Guys... He has a ZJ
Wrong section

pwb

Sorry for posting in the wrong section, but i thought that it was the same engine, that a 4.0L in a 1993 GC is the same as any other 4.0L 1993 in any other jeep. Since i didnt got any answer in the GC section and other peopel has this question too, i tok a shot to place the question here. But since i cant find or get any answer i think its not possible to get an answer on this question.

Another thing, it should have been possible to cross-post on things that is the same on the different models. There must be many thing that a ZJ have that a XJ have, or?

djb383

The sensor in the exhaust pipe (O2) has the most to do with determining fuel economy. The sensor in the t-stat cover mainly senses if the electric fan needs to be on. A scan tool will show when the system enters closed loop (max efficiency). It will also show the system switching from closed to open loop when accelerating and flip flop back and forth. Has little, if anything to do with hot or cold mode. Hot or cold is just a temporary state the motor is in.