ECU Logic for HX Civic?

[brucepick]

Originally Posted by rkcarguy

-I thought the VX O2 was a five wire and therefore heated?
also this will depend if you have a VX or HX. The HX searches for the "edge" via the knock sensor not the O2 reading.

^^ Quote is from http://ecomodder.com/forum/showthrea...cars-8111.html

rkcarguy, can you tell us more about the HX ECU's logic??
Anybody else have some background on this?

I've been using my ScanGauge displays, grill blocks and warm air intake to keep my '97 HX in lean burn as much as possible. HOWEVER I have to work mostly on assumptions and hunches as I don't know the ECU's logic.

So far I've been able to do better with a thorough grill block on the cat side of the grill. However it still goes out of LB for reasons I can't fathom.

[theunchosen]

wow, good thread Bruce!

I had been wondering this myself but never got around to asking.

RK I'm sure knows more than I do as he is/was in the engine import business, but the grill block on cat side causes the lean burn to last longer because its making sure the cat stays at high enough temperature. During lean burn you are not emitting hydrocarbons at anywhere near the rate of stoich. So the cat is not really burning anything and is therefore cooling.

I would gamble that before the grill block your lean burn cycled on and off somewhat consistently?

The reason for this would be Honda had to make sure the vehicle would pass EPA under all driving conditions in all modes so if it starts getting too cool for the cat to function properly it kicks back over to heat it back up. The Grill block allows for more heat soak to the cat.

I'm not completely solid on its emissions scrubbing for NOx and SOx under lean burn so I can't say whether or not it needs the heat for those processes or whether its just keeping it toasty should you all of a sudden need to gas it and drop out of lean burn and emit HC's.

update: After searching I was unable to locate anyone actually talking about how the cat scrubs NOx and SOx or if it does that effectively. Everyone else just wants to know how to switch to standard cat so they can put performance headers on. I could have searched for the wrong tags, but the threads I hit all involved that issue even if they wer mistitled to describe how it worked. If anyone has an owners manual it may be in there and that would definitely be the easiest place to look as it has a table of contents and isn't as misguided as most forums.

[brucepick]

Thanks, theunchosen.
I'll have to double check my owners manual. I've done some reading there but found precious little on that topic. I'll post here again after I get another serious look at it.

[rkcarguy]

Thats interesting that lean burn stays in longer when grille blocked. Like unchosen said, it's likely that for some emissions reason it's possible the ecu may drop out of lean burn to keep the cat or 02 sensors at operating temperature, but I thought that lean burn ran hotter which was why NOx is produced because of the higher combustion temperature.
OBD-2 honda's aren't as good with efficiency as OBD-1 versions, so it wouldn't surprise me if lean burn was kicking out for some emissions reason. I've found/seen increases in mileage and performance in every EK series civic that I've converted to OBD-1 or that my tuning buddy did. Stunning example was my turbocharged 1996 Civic HB. In completely stock trim the car got 28mpg in mixed driving conditions. I turbocharged it, converted it to OBD-1, added 2-1/2" exhaust, and front mount intercooler.
On our tuning runs, we dialed in the 'under boost" map, and then did a highway cruising run and were able to run the AFR to 16.0:1 before it started lean surging. Result was 31 mpg average from there on, requiring premium unleaded however. The converter, evap, and pvc system are all functional and still in place.
My bosses son bought the car and it's going on two years under his ownership just with regular maintenance.
It's obvious to me that OBD-2 sacrificed mileage and performance for something else, but I have no idea what. If you can find a crome pro tuner in your area that really knows their stuff it may be beneficial to convert. The adjustments and changes they can make are amazing, turn things off and on, rpm switches and map changes for nitrous, vtec, propane or water injection...wideband o2 sensor reading etc.
I put my tuned ecu to the test coming home from work one day. I blew a heater hose(different car) and lost ALL of my coolant. I didn't notice until I got home that the temp guage was pinned. The tuned ecu's maps were extended out so far that it had pulled back timing and was DUMPING in fuel to try to keep the motor cool, and I never heard a single "ping" of detonation. I let it cool overnight, fixed the hose and filled it up, and it ran like nothing happened.

[theunchosen]

Originally Posted by rkcarguy

Thats interesting that lean burn stays in longer when grille blocked. Like unchosen said, it's likely that for some emissions reason it's possible the ecu may drop out of lean burn to keep the cat or 02 sensors at operating temperature, but I thought that lean burn ran hotter which was why NOx is produced because of the higher combustion temperature.
OBD-2 honda's aren't as good with efficiency as OBD-1 versions, so it wouldn't surprise me if lean burn was kicking out for some emissions reason. I've found/seen increases in mileage and performance in every EK series civic that I've converted to OBD-1 or that my tuning buddy did. Stunning example was my turbocharged 1996 Civic HB. In completely stock trim the car got 28mpg in mixed driving conditions. I turbocharged it, converted it to OBD-1, added 2-1/2" exhaust, and front mount intercooler.
On our tuning runs, we dialed in the 'under boost" map, and then did a highway cruising run and were able to run the AFR to 16.0:1 before it started lean surging. Result was 31 mpg average from there on, requiring premium unleaded however. The converter, evap, and pvc system are all functional and still in place.
My bosses son bought the car and it's going on two years under his ownership just with regular maintenance.
It's obvious to me that OBD-2 sacrificed mileage and performance for something else, but I have no idea what. If you can find a crome pro tuner in your area that really knows their stuff it may be beneficial to convert. The adjustments and changes they can make are amazing, turn things off and on, rpm switches and map changes for nitrous, vtec, propane or water injection...wideband o2 sensor reading etc.
I put my tuned ecu to the test coming home from work one day. I blew a heater hose(different car) and lost ALL of my coolant. I didn't notice until I got home that the temp guage was pinned. The tuned ecu's maps were extended out so far that it had pulled back timing and was DUMPING in fuel to try to keep the motor cool, and I never heard a single "ping" of detonation. I let it cool overnight, fixed the hose and filled it up, and it ran like nothing happened.

I'm pretty sure lean does run hotter(hence the pre-det worries). . .but the cat is not burning any stray HCs anymore. If its not burning HCs it can only possible be as hot as the exhaust(maybe a little warmer because its creating some backpressure). So RK you are right(at least I am pretty sure you are) that lean burn does go hotter, but that cat itself is no longer burning fuel onsite so its temperature will just be the exhaust temp(400 odd C).

The downside of keeping the cat ambiently that hot(without it burning HCs in regular stoich burn) is its going to be that hot when you are running in regular and its going to burn out sensors and unnecessarily heat the engine. My only beef with a hot engine is they don't usually last as long(something gets hot its elastic deformation range shrinks and you get close to plastic deformation and something messing up).

IF I am correct your radiator is on the other side of the car and your ac lines are in front of the engine? If you really wanted to keep the cat warm without having to block off flow and get it too hot you could move the radiator onto the refrigerant mounts, block off the other side of the engine bay(where your AI is to get WAI) and this would pre-heat air that would otherwise slightly cool that cat. At least that would lessen the pulse function so you spend less time in regular heating the cat back up and more time in lean.

[brucepick]

Originally Posted by theunchosen

...So RK you are right(at least I am pretty sure you are) that lean burn does go hotter, but that cat itself is no longer burning fuel onsite so its temperature will just be the exhaust temp(400 odd C).

The downside of keeping the cat ambiently that hot (without it burning HCs in regular stoich burn) is its going to be that hot when you are running in regular and its going to burn out sensors and unnecessarily heat the engine. My only beef with a hot engine is they don't usually last as long (something gets hot its elastic deformation range shrinks and you get close to plastic deformation and something messing up)...

theunchosen, I follow your reasoning but there's a piece that I want to question.

First I have to say I don't have the background I should as far as typical temps for combustion, exhaust and cat operation. I tried doing some quick research but I'm not finding the data easily.

Anyway, normal stoich EGT at part throttle will be x but in lean burn it will be 1.5 x or 2 x, I suppose? This hotter lean burn exhaust is likely not hotter than normal stoich cat operation??

If so, the hotter lean burn exhaust wouldn't damage the cat or oxy sensors BUT -
As you wrote it probably heats up the head more than usual. Would watching the ECT display on ScanGauge reflect this? - or would the high temps be local to the cylinder walls and not be reflected in the ECT data from the ECU?

[theunchosen]

Originally Posted by brucepick

theunchosen, I follow your reasoning but there's a piece that I want to question.

First I have to say I don't have the background I should as far as typical temps for combustion, exhaust and cat operation. I tried doing some quick research but I'm not finding the data easily.

Anyway, normal stoich EGT at part throttle will be x but in lean burn it will be 1.5 x or 2 x, I suppose? This hotter lean burn exhaust is likely not hotter than normal stoich cat operation??

If so, the hotter lean burn exhaust wouldn't damage the cat or oxy sensors BUT -
As you wrote it probably heats up the head more than usual. Would watching the ECT display on ScanGauge reflect this? - or would the high temps be local to the cylinder walls and not be reflected in the ECT data from the ECU?

The temps in the cylinder will be greater and the exhaust temps will be greater, but they are going to dissipate heat fairly quickly in the exhaust pipe. Even over just a few inches heat exchange between 1660 Rankine and 500-600 rankine have the potential to be rather large. That said your cat usually runs as hot as the exhaust gas because its burning excess fuel. if the exhaust gases are the only thing thats reaching the cat and heating it they are going to be cooler than they were when they left. Your o2 sensor should be just above the cat so it should reflect the temps as they enter the cat. I would gamble the emissions software in the ECU mandates that the cat stays around 1100-1200 degrees F. I would expect that the gases could cool below that before they reach the cat(since Lean burn is only going to engage under low load(for you that probably means low rpm and low flow)).