Hello

My problem is that car is all time open loop. I have tuner pro so i can see all data.

Car starts and works fine, but wont rev over 3500-4000rpm (cuts) and fuel mileage is little bit higher than it should. I think both problems are caused by open loop.


No fault codes. I have tried two new maf sensors 02 sensor, new icm, coil pack, plugs and wires, ect, injectors are cleaned and fuel preassure is good, egr is also tested and fine, all vacuum hoses new.


Maf, ect and o2 sensor can cause open loop, is there other things?

Engine temp can.

Engine temp sensor is good and so is engine temp and thermostat.

When car reaches 40degree celcius and it should go to closed loop, it stays on open. Even if you drive 100miles and look again.

40 degrees Celsius is only 104 degrees Fahrenheit. 104 may not be hot enough for closed loop.

On another note, It being a 1989 and you are using aftermarket scanner to watch data, I'm wondering if you are seeing false data. Too many probabilities to ponder here.

104 or 105f is typically temp to switch loop at my knowledge, tbi chevy has same temp. But no matter is my car 105 or 195f it wont go closed loop.

Tunerpro is pc software and very usable and better than winaldl, i dont think its problem. And i have correct baud cable with it too.

Then I have no idea.

To cold. Don't look for CL with less than 140* F. See if the O2 switches. If so it'* in closed loop. If your scan tool says different it'* wrong.

02 wont switch and int bml are also locked to 128.

The O2 should switch when the engine reaches temperature. Is it stuck high, low or at .45V?

BLM is at rest at 128. I assume the integrator is the same since it'* not in closed loop?