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Stuck in open loop

jrowell

NAXJA Forum User
Location
Bakersfield
What would cause my 87xj to stay in open loop? Once in awhile it will work properly and go to closed loop in about 30 seconds. Usually it will stay open. Just started this last Thursday. Before that it went closed loop like clockwork.

87 xj. 4.7 stroker. Bigger injectors and throttle body. O2 sensor is reading showing it's running rich at 4.99.

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The main sensors for it to go into close loop are 02 sensor map sensor and the temp sensor , the engine needs run at 180 to 190 degrees . so you need to check the engine temp and these sensors . if the o2 sensors are more than 3 years old I would change them .
 
87 xj. 4.7 stroker. Bigger injectors and throttle body. O2 sensor is reading showing it's running rich at 4.99.

4.99 AFR ?, surprised the catalytic converter hasn't burned up.

As said before, the temperature sender and O2 sensor determine when it goes into closed loop.
Have you look at the O2 operation on a scanner in real time?
It should change back and forth from around 200, then up to the 700-800s and then back again continuously, as PCM tried to achieve a 14.7 AFR ratio.
You won't see this on a AFR meter
I'm a OBDII guy, don't know if your XJ's O2 sensor can be monitored.

The temperature sender can be tested for proper resistance, at various temperatures. If it checks out, change the O2 sensor.
 
On normal operation it goes closed loop in about 30-45 seconds. It just stopped doing it all of a sudden.
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I'm assuming if you're seeing close to 5v on the o2 this still applies. Some of Chrysler's early stuff had a 5v bias diagnostic check voltage on the o2 sensor circuit. It should go away fairly quickly after starting and the o2 sensor starts working. It was basically there to verify the sensor was working. If you ever see more than 1v the sensor is bad (when driving) . Under normal operation the o2 operate at about 100-900mV.
 
4.99 AFR ?, surprised the catalytic converter hasn't burned up.

As said before, the temperature sender and O2 sensor determine when it goes into closed loop.
Have you look at the O2 operation on a scanner in real time?
It should change back and forth from around 200, then up to the 700-800s and then back again continuously, as PCM tried to achieve a 14.7 AFR ratio.
You won't see this on a AFR meter
I'm a OBDII guy, don't know if your XJ's O2 sensor can be monitored.

The temperature sender can be tested for proper resistance, at various temperatures. If it checks out, change the O2 sensor.
It only just started, do I don't think the cat will be affected. It also does not stay that high. It does range, just not as fast as closed loop. When it goes closed loop, it'll switch from lean to rich pretty quickly. The block temp sender is pretty inline with the reading I get from the head and thermostat. Runs right at 195.

It does seem that it works right the first time I start it, than the rest of the day it's not right.

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Had the same problem on my 88 running 4 hole injectors etc. Turned out to be the 02 sensor. Went through 3 of them before I found a good one. Just make sure u have a good ground and a 12v source for the 02 heater. The heater stays on all the time with these systems.
 
Just to elaborate a little mine would go into closed as long as I was running down the road but as soon as I would come up to a light it would go open loop. The heater elements where not keeping the 02 hot enough to read correctly.
 
It's my understanding that the engine runs in open loop until it reaches normal operating temp. That's why we run rich and get awful gas mileage if running cool.

I don't believe that to be correct. I think It should go into closed loop pretty quickly... around a minute.

However, that is not my issue here. It can be 220 at the block sensor and still be in open loop.
 
Hello from Portugal

I have se same problem my 89 4.0 was always in open loop, ive check all the sensor with REM and its ok. Last week a try to replace the renix ecu and it fix the open loop problem.
Test with other ecu it can fix the problem


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On the early obd 1 systems they did need to run at 180 to go into close loop. but what are your map sensor and your tps sensor doing if they are not working wright then you wont go in close loop

The REM2 Shows the map and TPS... but I'm not sure what values are normal. The TPS reading changes when I press and release the gas. Outside of that... I dunno.
 
Hello from Portugal

I have se same problem my 89 4.0 was always in open loop, ive check all the sensor with REM and its ok. Last week a try to replace the renix ecu and it fix the open loop problem.
Test with other ecu it can fix the problem


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I have a spare in the garage... If the o2 swap doesn't fix it, then i'll give that a shot.
 
New o2 seems to have done the trick. Apparently my trans line and the o2 sensor want to occupy the same space.
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