I finally have the truck running again, with all of my opted sensor views working in my datastream. I am now having issues figuring out how to tune for the VAFPR.

I am using Dimented's $OD_MAF code which has a table for injector flow rate vs MAP. I set this table using my shop FP guage and a vacuum pump. At first I thought everything was ok, but now that I am starting to abuse the truck a little, I am noticing that it is way off.

I started fresh with the LS1 MAF calibration table and made some minor adjustments.

When I am driving, with light load, the wb is showing that I am way rich (10.5 actual, 13.1 commanded) but if I have the pedal to the floor I am near dead on ( +/- .3 of desired) I have sorted the log data along with an added sensor value of actual injector flow rate to see if I could find a trend using map/injector flow rate vs AFR but it doesn't seem to be linear. ( I could not find a pattern )

The only thing that I can see causing the issue is the variable fuel rate. I may try to do without it and see what happens when it hits boost (only reason why I'm running it) Maybe I can run enough fuel pressure to make up for the atmospheric pressure change :think:

once again, I'm open to any ideas..... in the meantime I'll go for another couple of drives

 

Are you running 2 O2's, NB and WB?

Different locations will read different. Placement in the exhaust pipe has an effect, closer to head unburnt/still burning fuel will show (more O2), then farther down the pipe, after time for burning (less O2). Read high EGT and glowing pipes.

Fuel burning in the headers from a blower and cam overlap will change the AF reading. You are wanting to read the cylinder burn not the exhaust burn.

Some members here have reported better results and longer WB life buy moving the WB 16 inches down the pipe to the exhaust pipe not having it in the header at all. This gives time for all the burning to get done. The EGT sensor will tell weather the burn is in or out/past the cylinder. The O2 can't.

My car, with OEM shorty type header (stock location no cats), gets a cold NB O2 (low volts/lean output), even at 50 mph cruise (1500 rpm) or any time the engine idles. It is better (hotter) at 70 mph (2000 rpm). MPG is 15 city 20 trip. Needs a heated NB or WB O2.

 

I have a heated NB just below the pass side collector and the WB on the drivers side.

I can understand the difference in the readings per placement but don't understand the change in readings from one drive to the next. If the readings were due to the placement/air flow/egt then shouldn't it be consistent? ie I should show either lean or rich at low flows all the time.

how about a different question: how can you ensure accurate AFR readings?

I was just asking this question at a different forum but thought it might be interesting enough to bring it up here as well.

 

How is it working with boost, the vafpr that is? is it rising in pressure for you? I wish I could help, but I have the EBL, and I am not using a MAF sensor. I would know how to add it if I wanted too, lol.

 

The readings are always accurate at the point of reading. How that relates to what is going on in the cylinder is a different matter. How much burning occurred between the cylinder and the sensor?

Put a WB in each header pipe, one in each collector, one before the cat, and one after. At each location they will be accurate as to that specific location.
They will even read the difference between idle pulses, at the header pipes. So you factor in the averaging effect (of pulses), the revision effect (dilution), and then calibrate that to a known good reading. Somewhere that result will be accurate. Direct measurement in the cylinder is the best but not cheap or easy.

There is also a lag factor from the O2 back to the injector. The AFR, (actually just the O2 content) when read by the O2, is not the charge that will be in the cylinder after the computer makes it's change, always a day late and a dollar short.

 

It is rising in pressure as per the boost and the only reason I have it installed. I am going to experiment with it without the vafpr and see if it still works well in boost.

here's a vid of me abusing the truck, the afr is targetted a little rich right now but you will notice a point where I let off the throttle a little bit and the afr will jump a little.

 

Damn, now you're making me even more confused

Everything you have said actually makes sense, however how do we relate the WB readings to our tune?

Let's say for instance, I am targetting stoich for ethanol 14.13, how do I know if I am actually at stoich or not if the placement of the sensor changes the readings?

 

The sensor is always reading the correct AFR, but only right at the sensor.

This question gets answered at the test stand, with all the fancy computer inputs, reading everything, including cylinder pressure, temp, color of flame, and anything else that can be read. The more the better.

With just a WB sensor, all it will tell you is, how much oxygen is in the exhaust, at that exact point and time of the reading.

This reading has to be calibrated/corrected, to allow for the amount of oxygen consumed, from the time the charge left the cylinder and arrived at the sensor.

On a stock/OEM set up there is little overlap and no blower. So the oxygen is almost all consumed in the cylinder. Save the bit that is burned in the cat. You can do a test pre and post cat to see the difference in what the cat burns.

This can happen just in the exhaust pipe, when you add a blower with a large overlap cam. All the exhaust and part of the fresh air fuel charge is pushed down the exhaust pipe.

Good for HP, every compression stroke burns a 100 % new fuel air mix with little exhaust residue.

Bad for MPG and the O2 sensors. They read only the oxygen in the mix, but with all that extra fuel and oxygen in the exhaust pipe, the burn will continue till either all the fuel or oxygen is gone. If the sensor is near the head, it will read leaner because of extra oxygen, farther down the pipe after the burn stops, richer because of less oxygen.

You can actually have a rich cylinder and a lean O2 reading, depending on how much is burned in between.

When a EGT probe is used, it can show this blow out into the exhaust with a high temp rise.

There are special cams for blowers, that close the exhaust valve early, to build pressure from the boost. These cams cut down on the blow down the exhaust. They will also present a different O2 readout because of the different burn down the exhaust.