closed loop/open loop, explanations ?

[easterwabbit]

anyone know somewhere that i could read up on how open and closed loop emissions systems worked on the early EST and ESC systems on these cars

my 84 has NB1 closed loop system and im trying ot figure out why it runs crappy wont idle when its cold but as soon as the thermostat opens it speeds right up and runs fine

thanks for anything

[GreyGoose006]

basically, closed loop is where the computer is actually reading the inputs from the various sensors on the engine and adjusts the engines performance based on what it is reading. in open loop the computer just completely ignores the inputs from the sensors and the engine runs mechanically. my 84, for example, runs rich all the time, but the check engine light only comes on after the computer has let the car run in closed loop mode. i can get it to go back to open loop for a while if a want to by turning the car off and back on again.

as for your problem, it seems that something may need to be adjusted in the carburettor. what model carb do you have? there are lots of mixture control solenoids that adjust things to even out the mixture when the car is in closed loop mode, but untill the car is in closed loop mode, they dont get adjusted.

i dont know too much about carbs, but i have a haynes repair manual on early model car computers that i use to get trouble codes and other info on these cars.

p.s. if your check engine light is coming on, pull the codes and i can let you know what they mean

[silicon212]

To clarify the above, closed loop occurs when all sensors are working and feeding data to the computer. The engine will not enter closed loop operation until the EGO sensor (that's Oxygen Sensor) is warmed up - generally between 1-2 minutes of operation. In open loop, the computer discards data from certain sensors and runs a program with pre-determined levels for various conditions - generally this is not optimal and is often referred to as "limp mode". If your SES light is on, you're generally in open loop operation.

[cozmo_d]

Sir what is SES light ?


Also i have some questions for you because you sound very competent.

How hard is it too fix the fuel gauge & the parking brake on an 84 caprice?

The fuel gauge has never worked right since I bought the car, the parking break did work but now it wont, when you step on it it just pops right back up it wont stay set.

Also Im curiouse if your in Missouri I dont trust alot of the mechanics in my town
Ive been burned so many times now I feal like a match head. How can I find a good fair & honest mechanic in my home town.

[silicon212]

I'm in Arizona. Mesa, to be exact.

The brake issue is probably a broken or missing spring on the pedal assembly. The fuel gauge could be the sending unit in the tank (likely), the wire between the sending unit and the gauge (less likely) or the gauge itself (not very likely). If other gauges don't work, check the fuse under the dash.

SES = Service Engine Soon - on a 1984 it might be simply "Check Engine".

[easterwabbit]

great info thanks guys, i know that i have researched this loop info in the past but its been so long that i had forgotten

i should ahve said O2 sensor rather than the thermostat

it is a CC Q jet, stock factory original NB1 and NA5 emissions

federal
EST

normal stuff on a typical non-cali '84 305 in low altitude


it seems to be getting quite better though, especially after i increased cold fast idle speed


i think its just because it was sitting for a long while not run

but im still going to swap on a non CC carb and non CC HEI in a couple weeks or so

i tried to check/set the timing today but it just wont run with the HEI 4-wire harness unplugged, just impossible no matter what i did i could not get the dampner timing mark anywhere near the timing tab, at all

i gave up on it, it runs great and strong and drives awesome so i dont really car right now til i swap the carb and hei out soon




thanks