CRX HF lean burn - Page 2 - Fuelly Forums

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Old 02-27-2008, 02:36 PM   #11
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Originally Posted by Brian D. View Post
lol, or I suppos I could do just a little bit of research first, to prevent me from looking like an entire ***.

I guess I should omit the "lean-burn" phrase, since that is apparently reserved for an engine that keeps 4 intake valves at bay, while using just one intake valve per cylinder during times when only minimal power is required. Instead what I would like to propose is the feature of the VX that allows the engine to shut fuel to the cylinders off when the car is just coasting, since some of us don't like shutting the car off every time we coast. I think every car on the planet should have a way of shutting fuel off when coasting for significant periods of time.
As for the VX, shutting off the fuel to the engine: That only happens in deceleration, not coast. If you are in neutral and the fuel is shut off to the engine the engine would no longer be turning. (And that would be true for all engines.)
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Old 02-27-2008, 10:26 PM   #12
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Originally Posted by MatHadder View Post
If I was going to try it, I would buy an Innovate Motorsports Wideband O2 sensor and controller. These controllers usually come with two sets of analog outputs, that can be programmed to simulate a narrowband O2 sensor
I was thinking the same thing as I was reading through the thread. An ideal setup would be a controller you could adjust on the fly. That way you could adjust the mixture based on current conditions. You should be able to run a leaner mixture in the cool months than the heat of summer. Moisture in the atmosphere can also play a role. An easily adjustable setup would let you tweak things as you go rather than being forced to dial the mixture back to a single safe-for-all-conditions level.

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It is possible this would just confuse the ECU, and cause a CEL, though.
Nah.
The O2 sensor error code gets set when the throttle is closed and the engine RPMs stay up but the O2 signal doesn't swing lean. What significance does that have? Those conditions occur when you're coasting down in gear - foot off the gas, but the car's momentum keeps the engine RPMs up. In that situation, the ECU cuts off fuel flow (as was discussed) by not opening the injectors. In that case, there should be no combustion occurring in the engine and only pure air being pumped through. The O2 sensor would normally swing over to a full lean reading... If it doesn't, the ECU knows something is wrong, sets the error code and triggers the CEL.
So, as long as the wideband controller flips the simulated output over to full lean when the sensor reads air, it should work fine.
Further, the HF ECU doesn't use any adaptive fuel maps like newer cars. Its fuel tweaking is limited to the flip-flop action when in closed loop operation.
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Old 02-28-2008, 09:38 AM   #13
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[QUOTE=bobski;92293]
Nah.
The O2 sensor error code gets set when the throttle is closed and the engine RPMs stay up but the O2 signal doesn't swing lean. QUOTE]

Yeah, I haven't looked into how the ECU determines that the O2 sensor is bad. Generally, it seems like closed loop systems only allow a certain percentage change from their stored fuel curves. I was theorizing that the ECU might trigger the O2 sensor code if it was reading rich, and the closed loop was unable to adjust enough to make it lean (which is what could possibly happen in the setup I described above). However, if the O2 sensor code is only triggered like you describe, this should not be an issue.

I am kind of interested in trying this setup out, since I already have the wideband sensor, but since I also have a VX with the stock lean burn, I am not all that motivated. Oh well, maybe it can be a future project on the Fit...
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Old 02-28-2008, 11:28 AM   #14
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Originally Posted by MatHadder View Post
I was theorizing that the ECU might trigger the O2 sensor code if it was reading rich, and the closed loop was unable to adjust enough to make it lean
Good point... I don't know how far it will alter the injector duty cycle to satisfy the closed loop code. I imagine it would have a fair amount of wiggle-room to account for variations in manufacture and the effects of component wear. The ECU doesn't have any means of measuring the exact fuel pressure or accounting for partially clogged injectors... It only has the O2 sensor reading.
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Old 02-28-2008, 09:43 PM   #15
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Originally Posted by Ryland View Post
does anyone know if a vx ecu would work in a 2nd generation crx? are they simaler enough that it would plug in?
The fact that the plugs are different is the least of your concerns. After all, LOTS of people modify their 1988-1991 Hondas to use 1992-1995 ECUs. Rather, the BIG problem is the fact that you are going to get check engine lights due to the lack of VTEC on the HF motor. And even if you can somehow rig up a way to bypass this, the fuel maps will be wrong. And reprogramming a P07 is apparently different from reprogramming other OBDI ECUs. Not that it can't be done. But it's not like people generally know how to do it.
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Old 02-28-2008, 10:04 PM   #16
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reprogramming a P07 is apparently different from reprogramming other OBDI ECUs.
Yeah... For one thing the board architecture is completely different. The P07 uses two processors where the other ECUs use one.
I don't think there was enough demand for the P07's additional hardware features to make it worth decompiling and reverse engineering the code.

I just had a thought as far as the O2 sensor tweaking goes.
If closed loop operation turns out to be too limited, you could install a MAP signal scaling device like an SAFC and set it to lean out the mixture. Normally, closed-loop operation would override any tweaking by the AFC, but together with the wide band controller it would work perfectly. Adjusting the AFC would move the closed loop code's window of operation up and down the A/F ratio scale, and the wide band controller would set the actual target point within that window.
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