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Need to know more about OEM closed/open loop modes

D

decathect

NAXJA Forum User
Location
Minnesota
The car is a 93 XJ with the 4.0HO. Relatively stock, other than a 2000 intake, 2000 injectors and an adjustable FPR with the pressure set at 49.5 Psi with the vacuum source disconnected.

What are the requirements for Closed loop? I understand that you have to be at a steady speed, not giving it too much throttle, etc. However, I'm wondering what the other requirements are. I heard there was a coolant temperature requirement. Anyone know exactly what that is? Are there other requirements? Does intake air temp have to be in a certain range?

Is there any way I can electrically tell when my car is in closed loop? Perhaps an ecu output that changes when this happens? If I could hook up a light or something, that would be perfect.

Does anyone know how to test my MAP sensor? I'm getting bad gas mileage, and while I usually do during my cold MN winter, I'd like to really boil down the issue.

Sorry about all the questions, but I'm trying to really dig down into this issue.
 
In the Renix XJs there are eight modes of operation effecting open-closed loop mode.

You need to get your hands on an FSM for 91-95 OBDI systems, the info should be under Fuel System/Modes of Operation.

Maybe you need to reconsider your setup. The PCM still OBDI? Other sensors OBDI? Everything married up and working Ok? If so, how about a write up with some photos in the Mod forum.
 
Crap, I dont have my FSM here with me. Can anyone look these 8 modes of operation up and tell me?

Everything is married up and should be working fine. Still OBD1, haven't changed any sensors, swapped everything over from my old manifold (IAT, throttle body with all sensors).
 
You can tap into the output of the o2 sensor. When it hovers around .45 volts(14.7:1 afr=stoich), it is in closed loop. Come 3K+ rpms or earlier with pedal to the floor, it should be in open loop.
 
gradon said:
You can tap into the output of the o2 sensor. When it hovers around .45 volts(14.7:1 afr=stoich), it is in closed loop. Come 3K+ rpms or earlier with pedal to the floor, it should be in open loop.
Click to expand...

that really only verifies that the O2 sensor is working properly though, right? Not that the car is in closed loop, there are more variables to that.
 
Hallo.
There are only 6 open loop modes and 2 closed loop modes imo.

Open: #1 Ignition switch
#2 Engine start up
#3 Engine warm up
Closed : #4 Idle mode
#5 cruise mode
Open : #6 Acceleration
#7 decelaration
#8 wide open trottle..

wim
 
I thought all OBD I cars had to have a check engine light and a means of checking for stored codes.
A quick Google search found this: http://www.jedi.com/obiwan/jeep/dtc.html
For sure, an engine that doesn't go into "closed loop" within a predetermined time, will set a code, and turn on the check engine light.
 
A half way decent code reader that also scans realtime data will usually tell you if your in open or closed loop...mine does...it is an autoxray 4000...picked it up (used) on Ebay for around $75.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warm-up,
the PCM receives inputs from:
† Battery voltage
† Crankshaft position sensor
† Engine coolant temperature sensor
† Intake manifold air temperature sensor
† Manifold absolute pressure (MAP) sensor
† Throttle position sensor (TPS)
† Camshaft position sensor signal (in the distributor)
† Park/neutral switch (gear indicator signal—auto.trans. only)
† Air conditioning select signal (if equipped)
† Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
† Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
† The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
† The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches.
† When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The system will then leave the warm-up modeand go into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the PCM receives inputs from:
† Air conditioning select signal (if equipped)
† Air conditioning request signal (if equipped)
† Battery voltage
† Crankshaft position sensor
† Engine coolant temperature sensor
† Extended idle switch (4.0L engine with police package only)
† Intake manifold air temperature sensor
† Manifold absolute pressure (MAP) sensor
† Throttle position sensor (TPS)
† Camshaft position sensor signal (in the distributor)
† Battery voltage
† Park/neutral switch (gear indicator signal—auto.trans. only)
† Oxygen sensors
Based on these inputs, the following occurs:
† Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
† The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width.It also adjusts engine idle speed through the idle air control (IAC) motor.
† The PCM adjusts ignition timing by increasing and decreasing spark advance.
† The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches.
 
decathect said:
The car is a 93 XJ with the 4.0HO. Relatively stock, other than a 2000 intake, 2000 injectors and an adjustable FPR with the pressure set at 49.5 Psi with the vacuum source disconnected.

What are the requirements for Closed loop? I understand that you have to be at a steady speed, not giving it too much throttle, etc. However, I'm wondering what the other requirements are. I heard there was a coolant temperature requirement. Anyone know exactly what that is? Are there other requirements? Does intake air temp have to be in a certain range?

Is there any way I can electrically tell when my car is in closed loop? Perhaps an ecu output that changes when this happens? If I could hook up a light or something, that would be perfect.

Does anyone know how to test my MAP sensor? I'm getting bad gas mileage, and while I usually do during my cold MN winter, I'd like to really boil down the issue.

Sorry about all the questions, but I'm trying to really dig down into this issue.
Click to expand...

If you go by the flow rates being proportional to the pressure squared, (http://www.jeep4.0performance.4mg.com/tech_specs.html) then you should have the FPR at 42.7 psi. Otherwise, you're dumping in 7% too much fuel in open loop.
 
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