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Open loop/ Closed loop?

D

Dcoy1283

NAXJA Forum User
Location
Apollo, PA
What tells my 2000 XJ to go from open loop to closed loop? I have been chasing down an odd and expensive misfire in my cherokee and had a buddy with a fancy scanner tell me that what ever is telling ( or not telling ) my jeep to switch loops is my problem. Thanks
 
Dcoy1283 said:
What tells my 2000 XJ to go from open loop to closed loop? I have been chasing down an odd and expensive misfire in my cherokee and had a buddy with a fancy scanner tell me that what ever is telling ( or not telling ) my jeep to switch loops is my problem. Thanks
Click to expand...

The ECM controls what mode it is in based upon the input from the various sensors and its built-in performance maps.
It doesn't take a fancy scanner to see what mode it's in, A ScanGauge, or a similar device, shows it, along with the rest of the information that is available on the OBDII bus feed. This can be handy for detecting faults.
Did his scanner provide any codes or a potential place to start looking or did it just say the engine isn't running right. If it is misfiring, the ECM should turn on the CEL and set a code(s).
What have you done up to this point to correct the misfire?
Does your XJ have two coil packs and no distributor?
 
lazyxj said:
The ECM controls what mode it is in based upon the input from the various sensors and its built-in performance maps.
It doesn't take a fancy scanner to see what mode it's in, A ScanGauge, or a similar device, shows it, along with the rest of the information that is available on the OBDII bus feed. This can be handy for detecting faults.
Did his scanner provide any codes or a potential place to start looking or did it just say the engine isn't running right. If it is misfiring, the ECM should turn on the CEL and set a code(s).
What have you done up to this point to correct the misfire?
Does your XJ have two coil packs and no distributor?
Click to expand...

It has the rail with 3 coil packs on it and im getting a cyl 4 misfire. when the engine is cold ill drive it and it will run alittle rough and always within a mile or so the cel will flash and it will run bad, and the scanner says its in open loop, then I shut it off and restart it and it will say its in closed and the jeep will run fine. I replaced just about every sensor under the hood and still acting up
 
Did you try another ignition cassette? Also you can try swapping the #4 injector with a different one and see if the issue moves to that cylinder.

Blinking CEL and OPEN loop means the ECU sees a major miss fire and goes open loop/limp mode to help prevent you from flooding the cats with fuel and over heating them.
 
sidewaysstarion said:
Did you try another ignition cassette? Also you can try swapping the #4 injector with a different one and see if the issue moves to that cylinder.

Blinking CEL and OPEN loop means the ECU sees a major miss fire and goes open loop/limp mode to help prevent you from flooding the cats with fuel and over heating them.
Click to expand...

yes I swapped the #4 injector and the misfire stayed at #4, and I have no idea what and ignition cassette is..... can you explain?
 
What code do you get? P0304(Cylinder #4 Misfire)? If so, I would try to find someone with a late model XJ and borrow its coil pack for a test drive. Might throw in a new plug, if you have not already done so.
If you are getting a misfire code, most likely there is a misfire and it is either an electrical problem or fuel. A leaky or sticking #4 injector might cause this.

The switch from open to close, during the test, could have been the result of the engine warming up enough to go into close-loop mode. The problem may not be related to the open-close issue at all.
Let us know what you find.
 
lazyxj said:
What code do you get? P0304(Cylinder #4 Misfire)? If so, I would try to find someone with a late model XJ and borrow its coil pack for a test drive. Might throw in a new plug, if you have not already done so.
If you are getting a misfire code, most likely there is a misfire and it is either an electrical problem or fuel. A leaky or sticking #4 injector might cause this.

The switch from open to close, during the test, could have been the result of the engine warming up enough to go into close-loop mode. The problem may not be related to the open-close issue at all.
Let us know what you find.
Click to expand...

Just getting the P0304 code. I had a year old coil rail on the jeep and replaced it with a new one, and replaced the plugs with new champions, then swapped them around a few times to double check, also swapped injectors around, along with replaceing the TPS, both upstream o2's, crank and cam sensor, coolant temp sensor, checked index on the cam sensor, and the ECU..... just going crazy

I have a buddy with an 01 xj and used his computer and it seamed to fix it but later relised that if I disconect the battery it wont misfire for a day or so, and when I swapped computers I unhooked the battery so that turned out to be a dead end to.
 
Definitions for Open/Closed Loop Operation:

POWERTRAIN CONTROL MODULE (PCM)​
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is referred to as
JTEC (Jeep/Truck Engine Controller).
The PCM is a pre -programmed, triple microprocessor digital computer. The PCM operates the fuel system,
regulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission
features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt
its programming to meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM
regulates various engine and vehicle operations through different system components. These components
are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs
to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm,
manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection
(automatic transmission), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle
speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air
conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator
charge rate through control of the generator field and provides speed control operation.​
PCM Inputs:​
A/C request (if equipped with factory A/C)
A/C select (if equipped with factory A/C)
Auto shutdown (ASD) sense
Battery temperature
Battery voltage
Brake switch
CCD bus (+) circuits / CCD bus (-) circuits
Camshaft position sensor signal
Crankshaft position sensor
Data link connection for DRB scan tool
Engine coolant temperature sensor
Fuel level
Generator (battery voltage) output
Ignition circuit sense (ignition switch in on/of/ crank/run position)
Intake manifold air temperature sensor
Leak detection pump (switch) sense (if equipped)
Manifold absolute pressure (MAP) sensor
Oil pressure
Output shaft speed sensor
Overdrive/override switch
Oxygen sensors
Park/neutral switch (auto. trans. only)
Power ground / Sensor return / Signal ground
Speed control multiplexed single wire input
Throttle position sensor
Transmission governor pressure sensor
Transmission temperature sensor
Vehicle speed inputs from ABS or RWAL system​
PCM Outputs:​
A/C clutch relay
Auto shutdown (ASD) relay
CCD bus (+A) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp.
gauge and speed control warn. lamp
Data link connection for DRB scan tool
EGR valve control solenoid (if equipped)
EVAP canister purge solenoid
5 volt sensor supply (primary)
5 volt sensor supply (secondary) Fuel injectors
Fuel pump relay
Generator field driver (-) / Generator field driver (+)
Generator lamp (if equipped)
Idle air control (IAC) motor
Ignition coil
Leak detection pump (if equipped)
Malfunction indicator lamp (Check engine lamp). Driven through CCD circuits.
Overdrive indicator lamp (if equipped)
Radiator cooling fan (2.5L engine only)
Speed control vacuum solenoid
Speed control vent solenoid
Tachometer (if equipped). Driven through CCD circuits.
Transmission converter clutch circuit
Transmission 3-4 shift solenoid
Transmission relay
Transmission temperature lamp (if equipped)
Transmission variable force solenoid​
MODES OF OPERATION​
As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to the
output devices. For example, the PCM must calculate different injector pulse width and ignition timing for
idle than it does for wide open throttle (WOT).
The PCM will operate in two different modes: Open Loop and Closed Loop.
During Open Loop modes, the PCM receives input signals and responds only according to preset PCM
programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop modes.
During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensors input. This input indicates to
the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is
14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM
can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low
emission engine performance.​
The fuel injection system has the following modes of operation:​
Ignition switch ON​
Engine start-up (crank)
Engine warm-up
Idle
Cruise
Acceleration
Deceleration
Wide open throttle (WOT)
Ignition switch OFF
The ignition switch ON, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open
throttle modes are Open Loop modes. The idle and cruise modes, (with the engine at operating
temperature) are Closed Loop modes.​
Ignition Switch (Key-In) Mode​
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following actions
occur:
The PCM pre-positions the idle air control (IAC) motor.
The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel strategy.
The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy based on
this input.
Intake manifold air temperature sensor input is monitored.
Throttle position sensor (TPS) is monitored.
The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for
approximately three seconds unless the engine is operating or the starter motor is engaged.
The O2S sensor heater element is energized via the ASD relay. The O2S sensor input is not used by the
PCM to calibrate air-fuel ratio during this mode of operation.​
Engine Start-Up Mode​
This is an Open Loop mode. The following actions occur when the starter motor is engaged. The PCM
receives inputs from:
Battery voltage
Engine coolant temperature sensor
Crankshaft position sensor
Intake manifold air temperature sensor
Manifold absolute pressure (MAP) sensor
Throttle position sensor (TPS)
Starter motor relay
Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor
signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay. 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 determines the proper ignition timing according to input received from the crankshaft position
sensor.​
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 clutch relay. This is done if A/C has been
selected by the vehicle operator and requested by the A/C thermostat.
When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The
system will then leave the warm-up mode and 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
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 clutch relay. This happens if A/C has been
selected by the vehicle operator and requested by the A/C thermostat.​
Cruise Mode​
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the PCM
receives inputs from:
Air conditioning select signal (if equipped)
Air conditioning request signal (if equipped)
Battery voltage
Engine coolant temperature sensor
Crankshaft position 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)
Oxygen (O2S) 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 adjust the
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. It also adjusts engine idle speed through
the idle air control (IAC) motor.
The PCM adjusts ignition timing by turning the ground path to the coil ON and OFF.
The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been
selected by the vehicle operator and requested by the A/C thermostat.​
Acceleration Mode​
This is an Open Loop mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure
as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width
in response to increased throttle opening.​
Deceleration Mode​
When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the
PCM receives the following inputs.
Air conditioning select signal (if equipped)
Air conditioning request signal (if equipped)
Battery voltage
Engine coolant temperature sensor
Crankshaft position 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)
Vehicle speed sensor
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will
ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not supply
a ground to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector
pulse width and continue injection.
Based on the above inputs, the PCM will adjust engine idle speed through the idle air control (IAC) motor.
The PCM adjusts ignition timing by turning the ground path to the coil ON and OFF.​
Wide Open Throttle Mode​
This is an Open Loop mode. During wide open throttle operation, the PCM receives the following inputs:
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)
During wide open throttle conditions, 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 ignores the oxygen sensor input signal and provides a predetermined amount of additional
fuel. This is done by adjusting injector pulse width.
The PCM adjusts ignition timing by turning the ground path to the coil ON and OFF.​
Ignition Switch OFF Mode​
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD​
relay and fuel pump relay.
 
o-gauge-steamer said:
Definitions for Open/Closed Loop Operation:

POWERTRAIN CONTROL MODULE (PCM)
The Powertrain Control Module (PCM) is located in the engine compartment. The PCM is referred to as
JTEC (Jeep/Truck Engine Controller).
The PCM is a pre -programmed, triple microprocessor digital computer. The PCM operates the fuel system,
regulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission
features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt
its programming to meet changing operating conditions.
The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM
regulates various engine and vehicle operations through different system components. These components
are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs
to the PCM are considered Powertrain Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm,
manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection
(automatic transmission), vehicle speed and the brake switch.
The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle
speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air
conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator
charge rate through control of the generator field and provides speed control operation.
PCM.....​

Thanks
Click to expand...
 
Now I have a thought about the open loop closed loop. It seams like my jeep runs a little rough apon start up which would be in open loop, and i have been told that if the ecu sees a misfire it will prevent it from going to closed loop. So whats to so I dont have a crack in the intake or a bad valve or something that is making it miss and when I shut it off and resart, it goes straight to closed loop and the sensors are compensating for the root issue of a bad valve or crack somewhere?

All of this misfire issue started the day after I drove it 3.5 hrs in 95 degree weather, it never overheated or went above 210, but thats when it started
 
You are welcome.

You are reporting a cylinder 4 issue and the CEL is flashing. On my 98, that indicates a mixture issue (or, at least it has in the past...) so the injector may be at issue. For experimental purposes, you can swap the injector in the number four position with another. Same thing with the coil pack and the spark plug although I would just toss in a set of new plugs as they are cheap parts.

One caveat on injector swaps and this is my opinion based upon experience. Buy new o-rings. Napa has two different "kits" available. I have found that if you buy the o-rings without the plastic tip protector, they are extremely difficult to install whereas the o-rings in the box with the plastic tip fit up better. The difference is a few thousandths on diameter of the ring material.

Not that NAPA will admit to it...

The idea is to attempt to force the problem to move to another cylinder. If you move the injector and the problem moves with it then, there you go. First rule of troubleshooting: As soon as you can turn the problem off and on at will, you have the solution in hand.

For those wondering, I taught Kepner-Tregoe Problem Solving and Decision Making back in the 80s and 90s...

For a test sequence, I believe I would toss in a set of plugs and test. No change? Swap the injector with another and test. As I am not fully conversant with the coil packs, perhaps someone will chime in that is as to the ability to swap a single coil with another.

Isolate the probelm and get it to move. No guesswork is involved here.
 
o-gauge-steamer said:
You are welcome.

You are reporting a cylinder 4 issue and the CEL is flashing. On my 98, that indicates a mixture issue (or, at least it has in the past...) so the injector may be at issue. For experimental purposes, you can swap the injector in the number four position with another. Same thing with the coil pack and the spark plug although I would just toss in a set of new plugs as they are cheap parts.

One caveat on injector swaps and this is my opinion based upon experience. Buy new o-rings. Napa has two different "kits" available. I have found that if you buy the o-rings without the plastic tip protector, they are extremely difficult to install whereas the o-rings in the box with the plastic tip fit up better. The difference is a few thousandths on diameter of the ring material.

Not that NAPA will admit to it...

The idea is to attempt to force the problem to move to another cylinder. If you move the injector and the problem moves with it then, there you go. First rule of troubleshooting: As soon as you can turn the problem off and on at will, you have the solution in hand.

For those wondering, I taught Kepner-Tregoe Problem Solving and Decision Making back in the 80s and 90s...

For a test sequence, I believe I would toss in a set of plugs and test. No change? Swap the injector with another and test. As I am not fully conversant with the coil packs, perhaps someone will chime in that is as to the ability to swap a single coil with another.

Isolate the probelm and get it to move. No guesswork is involved here.
Click to expand...

I have done everything that you mentioned. first plugs, then swapped injectors with all new o-rings, then a new coil rail, the misfire stayed at #4
 
For S and G's... Take out your MAT(manifold air temp) sensor in the intake and see if it all full of crap. My 89 was not going into closed loop and not reading the O2 sensor right and the MAT sensor was waaaayyy outta spec. So I cleaned the sensor(MAT) as it was full of crap then reinstalled it and low and behold my O2 sensor reads right and guess what...... I enter closed loop now to.. Dam sensors...

The MAT and the O2 sensors are a couple of the sensors that control your air/fuel ratio...
 
can also be called

intake manifold air temp sensor
intake air temp sensor


no matter what you call it it measures the temp of the air coming into your intake from the air cleaner
 
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