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Unread 02-19-2013, 08:55 AM   #1
PolkaPower
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Engine temp or 02 temp that causes closed loop?

I was reading on a Cherokee forum and a guy with a 98 was saying that motor temp had nothing to do with the system going to closed loop and it was the temperature of the 02 sensors that determines that.

So even if the motor isn't up to operating temperature and the 02 heats up to spec, does it go into closed loop mode regardless of the motor temp?

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Unread 02-19-2013, 11:28 AM   #2
4Slow9erHybrid
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Quote:
Originally Posted by PolkaPower View Post
I was reading on a Cherokee forum and a guy with a 98 was saying that motor temp had nothing to do with the system going to closed loop and it was the temperature of the 02 sensors that determines that.

So even if the motor isn't up to operating temperature and the 02 heats up to spec, does it go into closed loop mode regardless of the motor temp?
When the engine and the O2 sensor reaches the "operating temperature". The FSM states something similar. I've searched, but have not found any more definite info.

In reality, it's probably a combination of factors that is programmed into the PCM: engine temp above a certain threshold (but not full op temp of ~200F, probably more ~ 130F), O2 sensor output above a certain voltage (there's no separate temp sensor in the O2 sensor), engine vacuum below a certain threshold (under moderate acceleration the PCM stays in closed loop) AND (in my experience) there's also a minimum warm up time programmed into the PCM.
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Unread 02-19-2013, 05:17 PM   #3
ZeeJay1997
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IDK about the 5.9 programming but I can affirm by scanner that the 4.0 goes into closed loop at about 45 seconds from cold start while idling. This was in shirt sleeve weather.
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Unread 02-19-2013, 06:37 PM   #4
Donnyd21
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Closed loop is obtained at about 120deg of coolant temp, then once the engine is above that if you shut it off and restart it it goes into closed loop after about 30 seconds. Throttle above ~80% reverts back to open loop temporarily untill you go below ~80% throttle.
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Unread 02-20-2013, 07:20 AM   #5
ratmonkey
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Believe my fsm states 160* engine temp plus o2 sensors at full heat. I'll look later
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Unread 02-20-2013, 10:48 AM   #6
98GCLimited
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I was doing some data logging recently to figure out an issue.

It was going into closed loop at around 160-180ish I think (dont know exactly but it was a good bit before full operating coolant temp).

But I agree it probably goes off coolant temp and o2 sensor voltage when deciding when to switch over to closed loop. Once the coolant temp is high enough and the o2 sensor is hot enough it will create enough voltage to trigger the pcm to go into closed loop basically is what I think happens. I think it may be a combination of things the pcm monitors when deciding to switch over.
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