Open loop, closed loop - Gas Savers

krousdb · 02-09-2006, 11:04 AM

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.

rh77 · 02-09-2006, 11:28 AM

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

DaX · 02-09-2006, 11:42 AM

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!

krousdb · 02-09-2006, 12:12 PM

Quote:

Originally Posted by DaX

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

krousdb · 02-09-2006, 12:17 PM

Quote:

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?

SVOboy · 02-09-2006, 01:00 PM

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.

Sludgy · 02-09-2006, 01:32 PM

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.

krousdb · 02-09-2006, 02:01 PM

Quote:

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?

MetroMPG · 02-09-2006, 03:04 PM

dan, are you not running a grille block? that would fix the problem pronto, plus contribute to improved aerodynamics.

krousdb · 02-09-2006, 03:19 PM

Quote:

Originally Posted by MetroMPG

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.

MetroMPG · 02-09-2006, 04:17 PM

my WAI didn't do anything either (though it also didn't hurt, so it's still on the car).

but blocking my car's grille made a small (2-3%) but instantly observable improvement (aero effect), plus it helps build/retain engine/transaxle heat. (FYI there's a page on my site about the test.)

however, my car's grille openings appear to cover a much larger area than the del sol, so the benefit may not be as great for you.

krousdb · 02-09-2006, 04:50 PM

Quote:

Originally Posted by MetroMPG

dan, are you not running a grille block? that would fix the problem pronto, plus contribute to improved aerodynamics.

OK, grille block is installed. Two layers of cardboard covered in duct tape and even painted milano red. Held on by wire ties. I also installed my 200W magnetic heater to the oil pan. Probably wont help the coolant temp much but at least the oil will be warm. Next will be a recirculating ebh.

rh77 · 02-09-2006, 07:54 PM

Quote:

Originally Posted by krousdb

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.

I had the exact same problem -- turns out the thermostat was sticking open, so the radiator was doing it's job with the coolant cycling through. The rad-block might help a little, but replacing the 'stat would probably do the trick, and negate the need for a block (even though I run a cheesy piece of cardboard over mine -- you have to look close to see it. ;-)

Definitely go with a hotter 'stat -- I assume 170 is stock, and 192 is available (which is what I went to). It made a world of difference.

RH77

SVOboy · 02-09-2006, 07:59 PM

I think our puny 100hp d15s use 175 stock with 195 available.

You need to boost that b18 of yours, 300 whp on a stock block...

rh77 · 02-09-2006, 08:15 PM

Quote:

Originally Posted by SVOboy

I think our puny 100hp d15s use 175 stock with 195 available.

You need to boost that b18 of yours, 300 whp on a stock block...

Wait a minute, what site is this? ;-)

RH77

krousdb · 02-10-2006, 07:21 AM

Quote:

Originally Posted by MetroMPG

dan, are you not running a grille block? that would fix the problem pronto, plus contribute to improved aerodynamics.

The grille block made a huge difference on the way to work today. The coolant got up to temp faster and stayed there the whole trip.

This mod is a keeper. I had the stuff lying around, so it was free.

rh77 · 02-10-2006, 07:38 AM

Quote:

Originally Posted by krousdb

The grille block made a huge difference on the way to work today. The coolant got up to temp faster and stayed there the whole trip.

This mod is a keeper. I had the stuff lying around, so it was free.

What did you use as a grille block? It looks like we have similar bumper designs, and I'm looking to improve aerodynamics. Also, glad to hear that it worked out for you to keep the temps up. Our cooling systems are just really efficient.

RH77

MetroMPG · 02-10-2006, 08:35 AM

a couple of thoughts on grille blocking. some people equate it with radiator blocking, but they have different effects.

- rad-blocking is the easiest approach: usually involves placing a piece of cardboard in front (usually in contact) with the radiator. this works for keeping temperature up, but it also makes the cooling fan less effective when/if it comes on, as it can't draw air thru the block. also, this approach does little to improve aerodynamics because air still enters the engine compartment (though maybe less, since the pressure likely rises somewhat in front of the blocked radiator).

- the best route is to block/reduce air from entering the engine compartment in the first place. better aero effects, but trickier to do if you're concerned about aesthetics. also, doesn't hinder the cooling fan's ability to pull air through the radiator should it need to (ie if there's too much blocking for the ambient temp).

- i've been informed by someone who knows about aerodynamics that it matters little whether you block grille openings from behind (more difficult, less conspicuous) or outside (easier, more conspicuous)

krousdb · 02-10-2006, 09:12 AM

Quote:

Originally Posted by rh77

Quote:

Originally Posted by krousdb

The grille block made a huge difference on the way to work today. The coolant got up to temp faster and stayed there the whole trip.

This mod is a keeper. I had the stuff lying around, so it was free.

What did you use as a grille block? It looks like we have similar bumper designs, and I'm looking to improve aerodynamics. Also, glad to hear that it worked out for you to keep the temps up. Our cooling systems are just really efficient.

RH77

What is noce about the del Dol is that there is only one grille opening and it is recessed. I just cut 2 pieces of cardboard into 34" x 6" rectangles, arrenged them sid by side to double the thickness and covered them in duct tape for waterproofing purposes. I spray painted it red to match the car and used wire ties to connect it in front of the grille. Since it is recessed, you really don't know that it is cardboard unless you look closely.

DaX · 02-10-2006, 09:35 AM

Quote:

Originally Posted by rh77

Quote:

Originally Posted by SVOboy

I think our puny 100hp d15s use 175 stock with 195 available.

You need to boost that b18 of yours, 300 whp on a stock block...

Wait a minute, what site is this? ;-)

RH77

I was a Honda-Tech'er before I was a Gassaver.

SVOboy · 02-10-2006, 02:39 PM

Quote:

Originally Posted by DaX

Quote:

Originally Posted by rh77

Wait a minute, what site is this? ;-)

RH77

I was a Honda-Tech'er before I was a Gassaver.

Honda-tech in the hizzouse. W00t.

Xenocron on there is running his stock b18 bottom to 300whp, pretty nice. Clever guy too.

rh77 · 02-10-2006, 03:19 PM

Quote:

Originally Posted by SVOboy

Quote:

Originally Posted by DaX

Quote:

Originally Posted by rh77

Wait a minute, what site is this? ;-)

RH77

I was a Honda-Tech'er before I was a Gassaver.

Honda-tech in the hizzouse. W00t.

Xenocron on there is running his stock b18 bottom to 300whp, pretty nice. Clever guy too.

Man I missed the boat on H-T back in the day when I was trying to get the Integra to a "go-fast" state. Buggah. The limitation always was the auto-trans (turbo, top-end mod, etc).

I might stop by and check it out...

RH77

SVOboy · 02-10-2006, 03:31 PM

h-t is worthless these days unless you already know everything and/or you like getting yelled at (especially when you're right).

rh77 · 02-10-2006, 03:39 PM

Well then, sounds like a great place to do a "search".

RH77