96 HX owner with a scanguage 2 sg2 questions
Im a new member, 96 hx, sg2
i drive 35miles one way to work 3 days a week 210 total my first tank was 546 on 10.6 gal. without sg2 after installing a sg2 I drove home and back into work. these are my observations and questions. This site has been a wealth of info and i find my self reading searching and wondering (aka not what im sposta be doing.) 1. i noticed when I let off the gas in gear i get 9999 this is fuel cutout correct? 2. is any fuel going to the motor? or is cutout the wrong term? 3. i have noticed that acceleration in a gear too high is bad for fe is this correct? any other sg2 tips or observations would be great I still have a egr fault and some other issues im working with on the car. its been babied for that tank due to a possible clutch issue. when i hammer the gas it tends to slip i dont have time to do a clutch right now so ive been easy on it. Tires are inflated to 40 (checked every 4 days) new front clip was installed in the middle of the tank along with new wheels and tires. cv joints are new new right bearing installed I'm reading more about lean burn. and the vtec e synloid. thinking of installing some indicators or monitoring it in some way. kb |
Yes, that is fuel cut you're seeing. My civic holds fuel cut down to about 1200 rpm. It's using no fuel during that time. :D
Note that the scangauge will be inaccurate for the time it's running in lean burn. It reads air flow and calculates fuel used from that, assuming a standard fuel-air ratio. Lean burn changes this ratio, but doesn't tell the SG about it. You'll get the best mileage by accelerating at low-ish rpm and high load/throttle. Not quite to full throttle - there are diminishing returns above about 3/4. Then, when you're at speed, you can cruise gently and use lean-burn. |
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If you're accelerating efficiently (which means low rpm and heavy throttle), your instantaneous mpg could be low, even though you're doing the right thing. What's going on is the SG is not taking into account the value of the acceleration, which means the value of the kinetic energy that's being added to the vehicle (and potential energy, if you're climbing a grade). This energy will pay you back a few moments later, when you're gliding. And then the SG will report very high mpg. What you're trying to do is operate the engine efficiently. Sometimes this means using extra fuel now, in order to save fuel later. The SG can help you do this, but you'll be misled if you overly focus on instantaneous readings, which tend to swing all over the map. |
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So I suspect that on a wideband-sensor car (e.g., VX or HX), the SG will be inaccurate on both sides (lean and rich), not just on the lean side. But maybe the two errors tend to cancel out! Quote:
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I would P&G, but I haven't had the chance to explore what a lean-burn HX will do.
I tested my fuel-cut just last week. I monitored the SG open/closed loop, and there was a simultaneous "surge" from the engine when it started feeding fuel again. It's consistent at 1200 rpm. Yours may be different, though. You may be right about WOT in your case. I don't know. But there's not much to be gained between 75% and 100% either. Try it and see. |
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Sorting out the results is further complicated by the fact that the car is changing in various ways. For example, I've switched from CA to Federal (ECU and O2), adjusted the valves, and taken care of various tuneup items. Those all happened at different times, so it's hard to disentangle the various factors. |
Ah, I hadn't see that test you did. It looks pretty conclusive for choosing P&G over lean-burn. Thanks for testing that.
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Even so, closed loop alone doesn't give you an indication of what AFR the ECU is running. The O2 target could very well be 12:1 for everything above a load that coincides with 75% throttle. That would be in line with every other car on the road. It would be extremely valuable to see the factory calibration of the CA P07, federal P07, and the HX ECU. I'd pay good money to see the calibration on the P2J in it's entirety. |
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Anyway, I'm going to try to devise some instrumentation to do a better job of calculating fuel use. I find it very frustrating that I have to wait until the next fill, in order to get feedback. I don't drive that many miles, so I have to wait a long time. One consequence is that I usually fill when the tank reaches half, instead of waiting longer. But this means I'm dragging a lot of extra fuel around, on average. I recall your statistics, on this factor. |
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I didn't start monitoring AFR until after I did the CA-to-Federal conversion (I swapped O2 sensor and ECU). I have no idea what the meter would have shown, prior to that. When I use a DMM to monitor AFR, I see readings from roughly -0.8v to +0.8v. The amount of time it spends close to zero is very low. I think I would have a hard to time keeping it there, if I decided to try (for whatever reason). When you ask for moderate acceleration, it swings to roughly -0.3v. It will move smoothly to even more richness, as you open the throttle further. If you back off to a light setting and let it cruise, it swings the other way, to +0.3, or higher, if the throttle is very light. Quote:
But my naive understanding of open loop is that I would see a fairly abrupt transition to a much richer mixture, as I approached WOT. But this is definitely not what I see. I see a very smooth increase in richness, generally proportional to throttle setting. Also, I discussed this issue over at ecomodder, and a commenter who seemed very knowledgeable was quite sure that a wideband-sensor system generally avoids open loop. Except when cold, or when there's some kind of a sensor failure. Quote:
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