a73camaro

Two question here, just a little related to prom burning / tuning.

A narrow band O2 sensor is best around 14.7:1 AF ratio. Lets say that at 3000 RPMs, at 50% throttle or 5 in HG in the intake, we have 5.0 milliseconds of pulsewidth. The O2 sensor has 0.50 volts. If I were richen the pulsewidth to 5.5 milliseconds (10% increase fuel flow since the injector is operating in the linear range), the AR ratio should goto 14.7:1.1 or 13.4:1. I know it is extrapolating, but it seems to make sense.

Now on to philosophy of tuning -- What does one exactly tune to? I know WOT you want best power without ANY detonation, but what about part throttle? I assume you'll want 14.7:1 AF ratio.

When does part throttle turn into WOT, i.e., when do you switch from a 14.7 AF ratio to a 12.5 AF ratio??

This is for an older EFI system, so I'm looks for general guideline. BLM's and VE won't help.

Thanks

Grumpy

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A narrow band O2 sensor is best around 14.7:1 AF ratio.

It switches from rich to lean at 14.7, no more no less/

Lets say that at 3000 RPMs, at 50% throttle or 5 in HG in the intake, we have 5.0 milliseconds of pulsewidth. The O2 sensor has 0.50 volts. If I were richen the pulsewidth to 5.5 milliseconds (10% increase fuel flow since the injector is operating in the linear range), the AR ratio should goto 14.7:1.1 or 13.4:1. I know it is extrapolating, but it seems to make sense.

It only makes sense if you assume things are linear through out their range, which it isn't.

Now on to philosophy of tuning -- What does one exactly tune to? I know WOT you want best power without ANY detonation, but what about part throttle? I assume you'll want 14.7:1 AF ratio.

14.7 is to keep catalytic converters happy. 13.5 makes for a nice idle usually, 15.5 for cruise, and something around 12.5 for N/A WOT.

When does part throttle turn into WOT, i.e., when do you switch from a 14.7 AF ratio to a 12.5 AF ratio??

You transistion, from one to another, you don't switch from one to the other, and if your efi is not sophisticated enough to do that you're going to have troubles.

I have personally recorded an 820 millivolt O2 output and had it read 12.5 to 11.8 AFR.

Plug reading is a million times better then depending on just an O2

a73camaro

My question was about the O2 sensor operating in the "linear" range, that is around 0.5 volts. Your example is in the nonlinear range.

Plug reading has its limitations, just like an O2 sensor. Today's gas just does not leave its mark on the plugs unless you're pig rich, super lean or detonating. If you are not keeping your engine at one throttle position, constant load and at the same RPM for 20 minutes to an hour you will be putting the fingerprints of various positions of the fuel map onto the plug.

I'm trying to tune a SD fuel map with a Procharger on a SBC. The EFI unit is a Haltech F3. A bit on the simple side, but it works. So far I've tuned idle and part throttle using the O2 sensor and looking at plugs.

My thoughts are to tune the engine to a 14.7:1 AF ratio at idle and part throttle. Then transition into 12-13:1 at the higher boost/RPM numbers. Since this is on a boat, I'll have to use the butt dyno to verify results.

hectorsn

Generally speaking, you have a can of worms. A boat even under a cruise is under a load. A boat with a blower under a cruise and you have 5" of vacuum? That doesn't make sense to me. I'm not saying it isn't happening but that from my knowledge that doesn't make sense which might mean I know a whole lot of nothing. Now, you want to rely on the O2 and as stated before a narrow band is only good at stoich. Me personally, I wouldn't think running stoich on a boat is a good idea (going back to the always under a load thing), so a narrow band O2 is useless. I'm not trying to argue with you here just telling you what I think I know. You also stated that you can't get a good fingerprint on a plug unless you run it at the same throttle angle under the same load and rpm for twenty minutes but that's what boats do a lot of. I wish I had an answer for you but I don't. I think EFI tuning needs to be done with a lot of reliable data on hand and without it, it can be rather difficult but it seems to me you're doing pretty well. Just keep on tuning with your butt and away from knock and you should be OK. And for WOT you might need more than 12:1 since it's blown and in a boat to make best power but that's just a guess.

a73camaro

hectorsn - A centricifal supercharger doesn't make boost until a higher RPM, maybe 4000+ RPMs. Plus I just threw an example of numbers, not real live data from a running engine.

I'm running at stoic under light to medium loads. As Grumpy stated, I may want to run a touch richer to smoothen the idle.

Here is a pic of what I'm talking about. From 200 millivolts to 800 millivolts the O2 sensor operates in the linear range. The hysteresis makes it more "interesting", but only varies the AF ratio from 1% to 3%. I can live with ~2% error.

Pic is from the DIY-EFI site.

91L98Z28

even assuming that the O2 sensor does have a linear operational range (which from everything I've read - it doesn't), the linear range usefullness is just about null as pictured by the graph.

Worst case scenario as depicted by the graph: anywhere between ~800mV and ~200mV could represent ~14.7:1. Best case scenario as depicted by the graph: ~800mV = ~14.7:1, ~200mV = ~ 15.2:1. So under normal operational characteristics, the ONLY characterization you can make of the O2 voltage reading between 200mV and 800mV is that the air fuel ratio is somewhere between 14.7:1 and 15.2:1.

O2 sensor just isn't designed to be a linear device. It sounds like you might have a bit of EE knowledge, so think of the O2 sensor kind of like a diode used as a regulation device. A diode will have a V drop of ~ 0.7v for a VERY wide range of current (mA) flowing through it. Anything below 0.7v and current is 0, anything above 0.7v and diode go POP. O2 sensor is roughly anagolous: anything below 14.7:1 is high volts, anything above 14.7:1 is low volts. The diode has a VERY small V range where it can flow a wide range of current, the O2 sensor has a VERY small A/F range where it can indicate a wide range of V.

That's why the ECm only reports the A/F ratio as LEAN or RICH in scandata. it's just a toggle. The A/F ratio you get back from the ECM is just what the computer thinks it is spraying - it has nothing to do with the O2 sensor at all.

hope that's not too cofusing

a73camaro

91L98Z28 - You nailed it about my EE background (although I thought I had a little more than a bit since I'm an electrical engineer, ).

The diode was a very good example. I also have a WB that is work in progress. I'll tune with the narrow band to get in the ball park and fine tune with the WB...and look at plugs.

What is your background? Sounds like you have a bit of EE in ya too.

BTW, for small x WRT e^x, 1 + x is linear.....

91L98Z28

Oh, I have a bit of EE myself. I'm now a programmer by trade so don't remember so much of it anymore. But when i was in school, I did both AC and DC fundamentals type classes, which formed the groundwork for stuff more in my major - computing hardware/digital equipment (micros, PLD's, VHDL, etc. etc.)

Getting back on topic - I've got a WB02 board myself, haven't bought any of the parts for it yet. I've got a 406 I'm building up (406ci, cam 232/240 @ 0.050, the zz430 fast burn heads, yada yada yada) that I want to throw a '730 and miniram on, so I'll be needing it! And for everyone out there who took part in the WB02 project to bring this to life for people like me, THANK YOU!

a73camaro

YES A BIG THANKS!