Another S/C'd member worried about his AFR

[eTiMaGo]

Long, since you are the best equipped (SC + Wideband + Scangauge), I'm thinking of a few tests you could do to assess the functionality of the blitz fuel controller.

We need to answer 2 main questions, I believe:

1) Is the Blitz fuel controller working as expected, trying to force more fuel in the system?
2) If so, why does it not seem to do it at WOT (hence the lean condition)?

If I am not mistaken, the Scangauge should be able to display long term and short term fuel trims, right? I think this is the key to see how it is trying to fight the stock ECU.

As I mentioned in the brainstorming thread, any piggyback that tries to make the mixture richer, will be foiled by the O2 sensors, as these will detect the lower AFR. The way they feed this information back to the ECU is through the aforementioned fuel trims.

So, what I think we should do is set up a baseline fuel trim. Please keep in mind I am saying this out of theory and just a decent understanding of this ECU! Anyway, the first step would be make sure that you can actually get a reading for the fuel trims on your scangauge! If that's the case, the next step would be to clear the ECU's stored information so we can start with a clean slate. You could disconnect the battery, or pull out the EFI fuse which I believe is in the fuse box that's in the engine bay.

As a result fuel trims should be both at 0. Next, you'd need to drive around normally, but with the SC switch to OFF, and if possible with the fuel controller disconnected. This way we can know what is the default trims that your stock engine setup will generate. I am not sure over what period of time the long term fuel trim is calculated, but it is essentially an averaging of the short term trim over time. I'd guess a day of normal driving should be enough. Also, during this time, you can use your wideband to verify that the AF ratio will be pretty steady around 14.7 as this is what the ECU strives to achieve.

So once we have this data, it would be time to see how the Blitz fuel controller reacts when the car is in closed loop, SC activated and car driven in a normal fashion. So, reset the ECU, reconnect the fuel controller, set the SC to LOW, and drive! Try to avoid mashing the pedal and going over 4000RPM too as these would trigger open loop mode and we want to keep that out of the equation.
If the fuel controller is working as expected, it will try to force a rich mixture, which the ECU will then counteract. You will *probably* see a rich mixture on your wideband at first, until the ECU calculates the correct fuel trim to counter that. So, after a day of driving around like this, we would need to compare the fuel trim values to our baseline. If we see pretty big negative fuel trim values, this means the fuel controller has worked as expected, and the ECU has responded as expected.

If the fuel trim is unchanged from stock, then there are two possible explanations: The fuel controller is not working, or it is smart enough to know to leave the ECU alone when in closed loop mode (not likely)

Now for Part 2, WOT diagnostics, unfortunately I can find very little information about open loop operation in the manuals, so it'd be quite hard to test anything properly.

Only thing I can think of, is to compare your wideband readings at WOT with the fuel controller unplugged, and then again with it plugged in, under the same conditions (reset ECU before each test) and see if there is any difference in the readings.

I know we can't really compare readings between our cars which are modified quite differently, plus the USDM and Thai ECUs are different, but I have a basic narrowband AFR gauge, and I can see, when I push the car into open loop, the needle jumps up to 12:1, even as rich as 11:1 sometimes...

So... do you feel like giving that a try?

Oh and on the subject of the stock injectors reaching their limit, those work using PWM, I think the only way to see their duty cycle would be to connect an oscilloscope or similar? And, even if you were to put in bigger injectors, I think you'd hit the same hurdle, the ECU will detect too much fuel and trim it back. Although, under open loop, it may just work... hmmmmmm

[LtNoogie]

Originally Posted by eTiMaGo

If I am not mistaken, the Scangauge should be able to display long term and short term fuel trims, right? I think this is the key to see how it is trying to fight the stock ECU.

I did not think the ScanGauge could display fuel trim. I'll have to look it up in the manual. If anyone knows how to program it to do so, you can save me the research.

What kind of units would it be displayed as?