Ok.. Bare with me, this is kinda long.

Awhile back I scanned my car and noticed that my air intake temp sensor was not working. It was reading -40 degrees F. So, I replaced it.

My car instantly started running rich as hell from 0 to 8 pounds of boost. We are talking like 10 flat on the AFR. Which doesn't make sense, because you would think that the car would richen up when it sees -40 degrees, not when its a normal temp.

So, Ive been doing something thinking... Maybe my coolant has something to do with it. I run a fluidyne radiator and a 160 degree thermostat. Im thinking that now all the sensors are functioning properly the car is trying to adjust itself for what they are reading. Unlike before it probably wasn't making any corrections because the air intake temp sensor wasn't working.

My theory is.. is that since my coolant is very cold and my intake air temp is colder than normal, that the car doesn't have a chance to fully warm up.

When our cars are cold, the engine tends to dump more fuel until its warm. Well, if the car never gets fully warm (according to the ECU) then it will run rich as shit.

Does any of this make sense?

Called Mitsu.

They say that you should not run a colder thermostat because the car will run like shit and stay in an open loop mode and be too rich at all times.

Originally posted by siueclipse
Called Mitsu. They say that you should not run a colder thermostat because the car will run like shit and stay in an open loop mode and be too rich at all times.

...and the closed loop cutoff is 150*. Even at near-freezing temps the last winter the car ran, at 70+mph on the freeway with a 16-* tstat, i never saw colder than 175* coolant temps.

Fuck Mitsu and what they think.

Originally posted by siueclipse
Called Mitsu. They say that you should not run a colder thermostat because the car will run like shit and stay in an open loop mode and be too rich at all times.

You're engine isn't exactly stock either. Fuck Mitsu... they don't know what they're talking about. As far as the ECU is concerned, anything over 150 degrees is fully "warmed up".

Open Loop = good, close loop = bad. Closed loop is the destroyer of engines.

I understand that my motor isn't stock. Mitsu says the stock temp is 195 degrees. They say that using a 180 degree thermostat would be ok, but not recommended. They certianly do not recommend a 160 degree stat.

I bought a 195 degree from Autozone. Im going to change it out in the next day or two and I will report and see if it made a change in my system.

It will be worth the $10 in parts just to check out the theory.

Originally posted by WickedESi
Open Loop = good, close loop = bad. Closed loop is the destroyer of engines.

sorry, i had my open and closed loops mixed up.

Originally posted by siueclipse

Originally posted by WickedESi Open Loop = good, close loop = bad. Closed loop is the destroyer of engines.

sorry, i had my open and closed loops mixed up.

No you didn't.

Originally posted by WickedESi
Open Loop = good, close loop = bad. Closed loop is the destroyer of engines.

Depends on the application. If the stock ECU is in closed loop mode it will seak 14.7, not good when you add more than a pound or two of boost pressure. With a MS many people run closed loop under all conditions with the aid of a wideband.

Originally posted by ner947

Originally posted by WickedESi Open Loop = good, close loop = bad. Closed loop is the destroyer of engines.

Depends on the application. If the stock ECU is in closed loop mode it will seak 14.7, not good when you add more than a pound or two of boost pressure. With a MS many people run closed loop under all conditions with the aid of a wideband.

Isn't close loop on a aftermarket ECU essentially what they call "auto tune".

yeah, cept your target AFR isnt 14.7 its whatever you want, thus not blowing up your motor

Yeah it does. When the temps are below 170-180 the ECU richens up the motor to get it up to operating temp faster. You can put a 10k 5W POT in series with the coolant temp sensor and set the right temp by using the data logger.I would post a diagram but I don't know how.

Originally posted by tim96rs
Yeah it does. When the temps are below 170-180 the ECU richens up the motor to get it up to operating temp faster.

No. it doesn't. Open loop cutoff, as stated above, is 150*.

Sorry I was baseing that off the logger and STFT and coolent temp

Well, today I replaced the cold thermostat with a stock one.

Let me just say, my car is no longer rich, doesn't stumble when I cross the 0 pressure mark, and is running better in every way.