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Old 02-09-2006, 10:04 AM   #1
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Open loop, closed loop

I'm still learning about EFI. As I understand it, the system can either operate in open loop or closed loop. In open loop, the injector duration comes straight from the ECU table, without any modification. In closed loop, the O2 sensor readings can cause a modification to the values in the table. So I guess that open loop is like a failsafe mode and as such, the engine will run rich.

So my question is, what are the conditions for running in closed loop and what would cause a change back to open loop.

Another related question. My shop manual says that the O2 sensor heater acts to stabilize the sensor's output. I dont understand how that would work. I assumed it preheated the unit so it could go into closed loop faster. If that is the case, does it make sense to turn on the ignition a minute or two before actually starting the engine, giving the O2 sensor time to heat up?

I have a feeling that I am out in left field in my reasoning. I'm sure someone here can set me straight.
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Old 02-09-2006, 10:28 AM   #2
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Honda Loops

From my understanding, Hondas will run in "open loop" under a few conditions: wide-open throttle, when the coolant temperature hasn't reached a certain level, and when there's a fault in the emissions system. The rationale is two-fold: one to reduce startup emissions and to save the engine from running too lean if faulty 02 signals are noted.

After getting up to normal operating temperature, you should be in "closed-loop" unless you floor it, then it runs in "open-loop" until the throttle position is reduced. Depending on if you have 2 O2 sensors, one before the catalytic converter and one "downstream" will determine if these come into play in the loop decision. If a fault is determined that the CAT is not operating properly (as in my case with the TL), the sensor after the CAT notices that the O2 levels aren't changed, so I'm in open loop all the time, running rich and getting crummy mileage. The CEL comes on and trips the system.

I'm sure there's much more to it and how all the scenarios factor into the ECUs decision

To warm up the 02 sensors, that's an interesting idea. My guess is that they get up to temp within seconds. I turn the key to "on" for a second or two before starting to get the fuel-pump going and to check for any CEL faults (the ECU runs a quick diagnostic check).

RH77
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Old 02-09-2006, 10:42 AM   #3
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If you're really interested

If you're really interested in learning about EFI, I have some PDF's I can send you on "OBD training for Hondas." It's 37 chapters of excellent reading!
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Old 02-09-2006, 11:12 AM   #4
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Re: If you're really interested

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If you're really interested in learning about EFI, I have some PDF's I can send you on "OBD training for Hondas." It's 37 chapters of excellent reading!
Yes please!

danielbkroushl@eaton.com
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Old 02-09-2006, 11:17 AM   #5
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Re: Honda Loops

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Originally Posted by rh77
From my understanding, Hondas will run in "open loop" under a few conditions: wide-open throttle, when the coolant temperature hasn't reached a certain level, and when there's a fault in the emissions system. The rationale is two-fold: one to reduce startup emissions and to save the engine from running too lean if faulty 02 signals are noted.

After getting up to normal operating temperature, you should be in "closed-loop" unless you floor it, then it runs in "open-loop" until the throttle position is reduced.
I thought that coolant temp had something to do with it. Which begs the question, what temp, or WT sensor resistance level would enable closed loop?
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Old 02-09-2006, 12:00 PM   #6
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If you notice my thread

If you notice my thread about the engine coolant temps you will notice that the ecu actually controls the fuel compensation based on ECT, so yeah it has a lot to do with it. With chipping we can acutally change that. Those graphs I post are the same for your car as for the one I posted.
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Old 02-09-2006, 12:32 PM   #7
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O2 sensors

O2 sensors only produce a usable signal when hot. So, until the sensor heats up, it doesn't report anything to the computer.

When you start the car, the computer doesn't get fed O2 levels right away, and it controls the fuel open loop, from a map. When the O2 sensor gets warm, it starts producing signals, and the computer shifts to closed loop.
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Old 02-09-2006, 01:01 PM   #8
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Re: If you notice my thread

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Originally Posted by SVOboy
If you notice my thread about the engine coolant temps you will notice that the ecu actually controls the fuel compensation based on ECT, so yeah it has a lot to do with it. With chipping we can acutally change that. Those graphs I post are the same for your car as for the one I posted.
WoW! Now I understand that graph! This could be huge for me. Over the last few tanks, the ambient temps have been 25-30F. It usually takes 6 miles to get the temp gauge up the the 1/2 way point. I assume that this is equal to the thermostat temp because that is as high as it gets.

During that first 6 miles, I have some pretty wicked hills to climb, which would undoubtedly be considered high load. The bad news is that according to the graph, I am running at a 1.1 to 1.3 multiplier. The good news is that after climbing those hills, I am up to the thermostat temp.

Now more bad news. At this point I start my long 6 mile down hill coast with the engine off 80% of the time. By the time I get to the bottom of the hill, the temp gauge is back down to a few notches above C. And more bad news. At this point I have a 6 mile uphill climb, possibly steep enough to be considered high load again with a 1.1 to 1.3 multiplier. About halfway up I am back to full temp. In the last seven miles I have another long downhill followed by a steep uphill, another potential for a multiplier. On the way home from work, due to the reverse route, the engine gets warmed up fairly quickly under low load conditions and stays warm for the remainder of the trip.

So what I think that means is that, one, a 195 thermostat might be helpful, and two, a circilating EBH should also help. Another idea would be to use an inverter to run the ebh off of the 12V battery, turning it on maybe 15 minutes before I leave work.

I expect that I could see a measureable improvement in the winter, and possibly even some improvement in the summer.

One question about the recirculating ebh. IIRC, they go into the top radiator hose. How would the coolent be able to circulate if the thermostat is closed?












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Old 02-09-2006, 02:04 PM   #9
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dan, are you not running a

dan, are you not running a grille block? that would fix the problem pronto, plus contribute to improved aerodynamics.
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Old 02-09-2006, 02:19 PM   #10
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Re: dan, are you not running a

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dan, are you not running a grille block? that would fix the problem pronto, plus contribute to improved aerodynamics.
I havent gotten around to that yet. Next on my list. But from previous expenience with the Prius, the grille block didn't help that much. Nor did the warm air intake mod.
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