Chassis Dyno Wideband o2 sensors?
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what they do is put a wide band sensor in your tail pipe. then when on the dyno the wide band will tell you what your air fuel ratio is and hence tell you if your motor is running lean, rich, or just right. Contrary to some peoples opinions, this is the only way to get an "Acurate" a/f reading.. the autometer gauges aren't worth the metal they are made out of and will not give you a dead on reading like a wide band. Basically the wideband is an essential piece of tuning IMO. I've heard that Paul's Automotive Engineering in Cincy is pretty good.. I've never dealt with them personally but I've seen others post that were happy.
Michael Yount
Mustang Master
The O2 sensors that come from the factory in our cars are designed to provide a varying voltage proportional with changing levels of oxygen in the exhaust stream. They feed that signal to the computer, which uses it in closed loop mode to adjust the amount of fuel injected thus trying to optimize fuel mileage and reduce emissions. However, they only 'read' oxygen levels within a very thin band right around stoichiometric air/fuel ratios. So, if your a/f ratio strays very far from 14.7 to 1, they can't measure it. They can only tell the computer if you're above or below it, but not how much. That's why they don't work very well to send a signal to an a/f ratio meter. They make other sensors - called "wide band" sensors, that offer the same varying voltage, but over a much wider spread of air fuel ratios - from anywhere around 9:1 to 18:1. So, with a sensor like that, you're able to know exactly what your a/f ratio is over a much wider range of operating conditions. That's why dynos use them. That's why good a/f ratio gauges use them. However, your computer isn't designed to use them. So if you want to add one permanently, you have to weld in another bung in the exhaust head pipe where you can add the wide band sensor. The prices on the wide band sensors have come down - Bosch now makes one that is around $50 -- about the same price as replacing our narrow-band factory sensors.
When you dyno with a wide band, they shove a pipe up one of your tailpipes, and it samples and measures air fuel ratio with a wide band sensor. The printout of your run will have your torque and HP vs. rpm curves, and also an air/fuel ratio vs rpm curve. By seeing when you're lean/rich vs. the power/torque levels, you know what you have to do the mixture to increase power/efficiency. Usually we're too rich and need to lean things out to make more power. But you don't want to go too lean - this causes heat, detonation, etc. - bad joo joo.
When you dyno with a wide band, they shove a pipe up one of your tailpipes, and it samples and measures air fuel ratio with a wide band sensor. The printout of your run will have your torque and HP vs. rpm curves, and also an air/fuel ratio vs rpm curve. By seeing when you're lean/rich vs. the power/torque levels, you know what you have to do the mixture to increase power/efficiency. Usually we're too rich and need to lean things out to make more power. But you don't want to go too lean - this causes heat, detonation, etc. - bad joo joo.
Michael Yount
Mustang Master
"When you dyno with a wide band, they shove a pipe up one of your tailpipes"
That would be a wand in the tailpipe...
That would be a wand in the tailpipe...
makarov
New Member
As an add-on, as I recall, that's why people have a chip burned or a piggy-back added to match their setup when they dyno. The eec will not effectively read sensor supplied air/fuel ratios in the open loop, above 2500 rpm. It uses pre-programmed look up tables. The potential supplied by high hp h/c/i, s/c, maf, injectors means the ability of the computer to satisfy the increased fuel/air flow will be exceeded. Not necessarily damaging in an n/a motor (which won't live up to it's potential), but suicide with boost.
Michael Yount
Mustang Master
Not sure I see it quite the same way makarov. Open loop doesn't occur above 2500 rpm. Open loop happens on cold start up (til the O2's warm enough to work), and happens when the computer sees w.o.t. from the tps sensor. So if you floor it at 1500 rpm, when the computer sees the tps at w.o.t., it begins it's shift to open loop. If you're cruising along at 4000 rpm in 4th gear (about 80 mph in mine), the throttle's not open much -- you're still in closed loop using O2 feedback to adjust mixture. As long as the maf is calibrated properly, the computer will supply fuel to match the air flowing across it -- it will supply fairly accurately to HP levels that exceed the 19's ability to support. And above that, with larger injectors, the maf calibration "tricks" it to provide the fuel needed. The chips are used to do things like turn off emissions functions, recurve w.o.t. dist. curves, change idle speed, and make fine tuning adjustments of the fuel curve so that a/f ratio is closer to stoich - for more power. The computer even coming off the the open loop tables will tend to keep things a bit rich (safety); the chips allow adjustments to lean things up a bit. Or, in the case of boosted engines, to pull back timing/richen the mixture at high rpm to avoid destructive detonation. At least, that's my understanding of it.
makarov
New Member
Geez Michael, am I getting the wrong info somewhere? I see where the computer (in this explanation in closed loop), tries to keep the stoichiometric at 14.7:1 and can vary as low as 10:1 and as high as 17:1. The info I have has the computer looking at water temp, throttle blade angle at cold strart in closed loop, then referring to the program that's already there, injector size, etc. The air fuel ratio in this supposed closed loop condition uses the maf and 02 sensors to keep the air/fuel mixture within the stoich at below 2500rpm.
Open loop, happening at above 2500rpm and below 10" of vacum, the computer does not actively attempt to adjust the air/fuel ratio after consulting sensors, but relies on the lookup tables to determine fuel and spark settings. Am I losing the w.o.t. function here? Does it refer back to sensor readings for the info? Also, it was my belief that the computer will do everything it can to circumvent tuning changes, such as increasing base fuel pressure with a regulator, or injector pulse width with a "piggy back system". I'm somewhat confused, as is obvious. I know the sn95's consult at all rpm's, but I thought I had the eec-Iv handled. I have a hunch it might have something to do with the "below 10" of vacum.
Thanks, Steve
Open loop, happening at above 2500rpm and below 10" of vacum, the computer does not actively attempt to adjust the air/fuel ratio after consulting sensors, but relies on the lookup tables to determine fuel and spark settings. Am I losing the w.o.t. function here? Does it refer back to sensor readings for the info? Also, it was my belief that the computer will do everything it can to circumvent tuning changes, such as increasing base fuel pressure with a regulator, or injector pulse width with a "piggy back system". I'm somewhat confused, as is obvious. I know the sn95's consult at all rpm's, but I thought I had the eec-Iv handled. I have a hunch it might have something to do with the "below 10" of vacum.
Thanks, Steve
Michael Yount
Mustang Master
The computer on the Fox bodies with mass air has no idea what the vacuum level is - speed density does - it uses the Map (manifold absolute pressure) sensor for that. But in a mass air car, it uses that sensor (Bap) simply to measure barometric pressure. It does use data from temp. sensors to determine which strategy it's gonna operate under, and many strategy's are open loop; but they all try to get to closed loop as soon as possible as control is better under closed loop operation - real time feedback is available. Probst covers 8 or 9 different ecu operating strategies - crank strategy, cold start strategy, part throttle acceleration warm, part throttle acceleration cold, etc. - the list goes on and on. However, with mass air it tries to get to closed loop just as quickly as it can as the system control is better in closed loop. The ceramic material on the sensor has to get to at least 570F before it can start generating a voltage that's proportional to the O2 level in the exhaust stream (it's actually based on the differential between the oxygen content of the exhaust gas and the oxygen content of ambient air). It usually takes between 90 and 120 seconds for the non-heated O2 sensor to reach those temps. A heated sensor may reach operating temps that support closed loop operation in only 10-15 seconds. During this warm up period the car operates in open loop. To quote Probst "The sooner the oxygen sensor becomes hot enough to send proper signals, the sooner the engine can operate in closed loop for better control." The computer will simply try to return operating conditions to those it was programmed for. So, on a completely stock car, lets say we put on an adjustable fuel pressure regulator and crank pressure up from 40 to 45. That will richen the mixture. The computer will adjust pulsewidth to lean things back out, and it will "learn" about the change over time so that it stores the data needed to continue that running strategy - effectively 'undoing' that pressure change with reduced pulsewidth - if that's what's required to return the engine to the programmed operating conditions. Alternatively, over time the injector may clog a bit, so less fuel is being injected. Sensing this gradual leaning over time the computer will learn to increase pulsewidth to make up for that, and it will remember what it learned.
Again from Probst "Adaptive strategy continually shifts the base calibration to compensate for changes in barometric pressure, intake air temp, fuel composition, small drifts in sensors or actuators......the strategies stored in the ROM are based on how the TEST engine responded to sensor inputs. Adaptive strategy looks at how THIS engine is currently responding - and further, how this engine is responding to how this driver drives." So not only will it try to learn about mods or gradual operating failures (valves not sealing as well, injectors being dirty, miles piling up/degradation of cylinder seal, etc.), it will pay attention to how the car is driven and try to optimize mileage and emissions in that regard.
You can look at all the different operating strategies - but the engine tries to get to closed loop as quickly as it can in all of them. The exception is when it sees w.o.t. from the tps - it then assumes that performance matters more than emissions or economy and goes to it's look up tables for the proper data. That's why so many chip burners only mess with fuel in the w.o.t. area. The computer can usually do a better job controlling mixture using closed loop real time O2 data in all other conditions. But, it's looking at the tps for it's signal of w.o.t., not rpm.
Again from Probst "Adaptive strategy continually shifts the base calibration to compensate for changes in barometric pressure, intake air temp, fuel composition, small drifts in sensors or actuators......the strategies stored in the ROM are based on how the TEST engine responded to sensor inputs. Adaptive strategy looks at how THIS engine is currently responding - and further, how this engine is responding to how this driver drives." So not only will it try to learn about mods or gradual operating failures (valves not sealing as well, injectors being dirty, miles piling up/degradation of cylinder seal, etc.), it will pay attention to how the car is driven and try to optimize mileage and emissions in that regard.
You can look at all the different operating strategies - but the engine tries to get to closed loop as quickly as it can in all of them. The exception is when it sees w.o.t. from the tps - it then assumes that performance matters more than emissions or economy and goes to it's look up tables for the proper data. That's why so many chip burners only mess with fuel in the w.o.t. area. The computer can usually do a better job controlling mixture using closed loop real time O2 data in all other conditions. But, it's looking at the tps for it's signal of w.o.t., not rpm.
Michael Yount
Mustang Master
At our local dyno they usually charge $50 for 3 pulls - no tuning. Usually takes about 20-25 minutes from roll in to roll out - and tieing the car down takes more of the time than anything else. That assumes that the car doesn't puke parts/fluids during the run. 
If you want wide band a/f data the charge is $70.
For tuning they charge at rates of anywhere from $100/hr to $200 hr. Just depends on how long you're gonna be on there. The longer you're on, the more the hourly rate drops to the lower end of the range listed above. And, it's somewhat negotiable. But you'll have to see what they're charging in your area. One thing's for sure. Be certain your car is good operating order (it'll survive the pulls) and that your tuner has a clear, well organized plan for what's gonna be changed in what order - one change at a time or you don't know what's helping/hurting.
If you want wide band a/f data the charge is $70.For tuning they charge at rates of anywhere from $100/hr to $200 hr. Just depends on how long you're gonna be on there. The longer you're on, the more the hourly rate drops to the lower end of the range listed above. And, it's somewhat negotiable. But you'll have to see what they're charging in your area. One thing's for sure. Be certain your car is good operating order (it'll survive the pulls) and that your tuner has a clear, well organized plan for what's gonna be changed in what order - one change at a time or you don't know what's helping/hurting.
Thinks Michael, you answered a question or two I have been wondering about for a while. I feel more "in the know", Thanks again.
I guess that's what I need to get, a wideband. I had my autometer hooked to my left bank o2, and the sensor went bad as well as the meter. Now I don't know if they were related but I think I'll exchange my autometer one and get the wideband and hook have it welded to another part of the exaust, proball in the crossover tube and have it only run to the meter. When it was hooked to the factory o2, it read real lean at low throttle, and really rich at open throttle.
I guess that's what I need to get, a wideband. I had my autometer hooked to my left bank o2, and the sensor went bad as well as the meter. Now I don't know if they were related but I think I'll exchange my autometer one and get the wideband and hook have it welded to another part of the exaust, proball in the crossover tube and have it only run to the meter. When it was hooked to the factory o2, it read real lean at low throttle, and really rich at open throttle.
Michael Yount
Mustang Master
90 - I wouldn't put it that far back in the system. Remember, it wants/needs heat to operate properly; the further back you go the cooler things are. Second, chemical reactions - further oxidation - occurs in the exhaust stream. Most sensors want the reading as close the chamber as you can get it; the dyno set ups are designed to sense at the end of the tailpipe. I'd put the wideband in close to the stock ones. Also, your meter is probably calibrated for a certain type of sensor - if it was calibrated to work with a standard O2 sensor, it probably won't read the wide band data correctly. Just a thought.
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