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Old 07-04-2005, 08:06 PM   #1
twilightprotege
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idea for the technically minded

well those hos email "chips" have got me thinking.

if anyone is unsure about what i'm talking about with the famous ebay chips, basically they are a resistor. they go in between the positive and the output wires on the air temp sensor to fool the car into thinking it has colder air coming in. why is this bad for us? well for most cars when you modify them they tend to be a little lean at high rpm. having the ecu think it's getting colder air means more fuel injected into the engine. for most modified cars with stock ecu, small power boost.

now the problem we have, esp in the BJ's, is that the cars run flippen rich at high rpm. so doing this "chip" would make less power than before. anyway, using the idea of resistors, we could do a test (on dyno with true a/f ratio readings ofcourse) and put a resistor inline on the output from the MAF sensor to fool the car into thinking it's getting air than what it really is and therefore, less fuel.

but wouldnt this make the low rpm even leaner than what it already is? well no. at low rpm, known as open loop, the engine uses all sensors to determine the best amount of fuel to inject into the engine. but this is where our cars are good. the ecu will trust the o2 sensor over the maf to work out the ratios. so changing the maf by a little bit wont hurt. at high rpm when the ecu goes into closed loop, it only uses the air temp and maf sensor to work out the amount of fuel to use. that's right, not even rpm. rpm is used to fire the injectors and that's it. the ecu has a predetermined "safe" amount of fuel to inject for the amount of air sucked in. when it's an injectors turn to fire, it fires blindly so to speak.

so, if with testing on a dyno and reducing the amount of air the ecu thinks it's getting, i could have a winner a very very cheap mod which should yield decent results.

but there is a downside, and this is where i dont have electronics knowledge so correct me if i'm wrong.

there are several types of resistors right? ones that take out percentage of voltage, ones that take out a fixed voltage, and ones that limit voltage. is that right?

anyway, where do i start to work this out? who can help moi?
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Old 07-04-2005, 09:16 PM   #2
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I've gone through this before twinkles, but never followed through. I used to have the list of resistors and how much the temp change reading is on the IAT sensor for them. Oops, I don't have that information anymore, give me a few days and I will get around to finding it again...

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Old 07-04-2005, 09:28 PM   #3
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oky doky
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Old 08-04-2005, 05:14 AM   #4
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If I can find the damn thing I bought one in November to satisfy my curiosity with my famous low rpm pinging. I never had the time to fully investigate once purchased but now may be a good time to investigate further.
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Old 08-04-2005, 07:36 AM   #5
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I have to dissagree about the O2 sensor, it needs to be at a high temp (about 300 degrees C) to work. This temp isn't reached at idle and low rpm but is at medium to high rpm. Changing the way the AFM relates to the ECU will only effect low rpm fuling IE batmans low rpm pinging.
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Old 08-04-2005, 07:51 AM   #6
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but in my engine that temp is reached at idle. my a/f ratio at idle is around 16:1 - aka very hot - that's why my hp coating is flaking off
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Old 08-04-2005, 08:17 AM   #7
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I'll breakout the OCR later and scan some stuff from the EFI books I have. If I'm wrong then I'll post it anyway.
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Old 08-04-2005, 08:24 AM   #8
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cool, thanks
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Old 08-04-2005, 09:21 AM   #9
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Quote:
Originally Posted by Bosch Fuel Injection & Management by Charles O. Probst,SAE
PULSED INJECTION—THEORY
Lambda Control
You’ll remember from chapter 2 the discussion of the ideal air-fuel ratio (lambda) and its relation to emissions. On most systems, the air-fuel ratio for best emission control is achieved by sensing the oxygen content of the exhaust gas with a lambda sensor, shown in Fig. 2-45. The lambda sensor’s signal is monitored by the control unit, which then adjusts pulse time to maintain the ideal air-fuel ratio. The system operates closed-loop.
Fig. 2-45. Lambda sensor looks something like a spark plug installed in exhaust pipe or exhaust manifold to sense oxygen content of exhaust gas. The closer to the exhaust valves, the faster it heats up.
Lambda Sensor Design and Operation. The lambda sensor is essentially a small battery that generates a voltage signal based on the differential between the oxygen content of the exhaust gas, and the oxygen content of the ambient air.
A cutaway view of the lambda sensor is shown in Fig. 2-46. The tip of the sensor that protrudes into the exhaust gas is hollow, so that the interior of the tip can be exposed to the ambient air. Both sides of the ceramic tip of the sensor are covered with metal electrodes that react to create a voltage only if the ambient air has a higher oxygen content than the exhaust and the ceramic material is hotter than 575°F (300°C)
When these conditions are met, voltage is generated between the two sides of the tip. The voltage is usually about 1 volt. But if the engine is running lean, the exhaust gas has about the same amount of oxygen as the ambient air, so the lambda sensor will generate little or no voltage; if the engine is running rich, the oxygen content of the exhaust will be much lower than the ambient air and the sensor voltage will be larger. See Fig. 2-47.
Fig. 2-46. Cutaway view of lambda sensor.
Fig. 2-47. Rich mixture and low content of oxygen in exhaust causes voltage output from oxygen sensor. Re member, rich = voltage.
Some cars have a lambda sensor that has a heating element built-in to speed warming of the sensor to improve the drivability and reduce the emissions of a cold engine. On a cold engine, it may take 90 to 120 seconds for an unheated lambda sensor to get warm enough to start generating voltage, while a heated sensor may be warm enough after 10 to 15 seconds.
Lambda Closed-Loop Control. Recall the discussion o open-loop/closed-loop systems in chapter 2. The lambda sensor and the control unit form a closed-loop system that continually adjusts the air-fuel ratio by means of the fuel-injector pulse time. For example, the sensor generates a high voltage be cause the mixture is rich, so the control unit reduces pulse time to lean the mixture. Sensor voltage falls, so the control unit increases pulse time to enrich the mixture. Sensor voltage increases, etc....
Fig. 2-48. Since about 1980, fuel-injected engines operate closed-loop most of the time.
The lambda sensor voltage is always fluctuating as shown in 2-49, so it is hard to maintain the exact point at which the air-fuel ratio is ideal. Instead, the ratio tends to oscillate to either side of the ideal ratio, but the oscillation is so fine (about 0.1% change in the air-fuel ratio) that it is not noticeable in engine performance. The rate of the air-fuel ratio oscillation is related to the quantity of exhaust passing the sensor. At idle, the cycle from lean to rich and back again may take 1 to 2 seconds. At cruising speed, the cycle may happen several times a second.
Rich Lean Rich Lean
Fig. 2-49. Closed-loop lambda sensor voltage cycles back and forth from slightly rich to slightly lean. In chapter 4, you’ll measure the effects of this cycling.
This closed-loop system can compensate to some degree changes in the engine over time. For example, if a valve is leaking slightly, or if there is an intake air leak, the lambda sensor senses the change in combustion and brings the system back within its design limits. This has been described as having a skilled technician under the hood, continuously tuning the mixture for best operation under all conditions. Changes beyond the system’s range, though, can still lead to drivability problems.
When the oxygen sensor is cold and not generating a voltage signal, the control unit is programmed to operate open loop at a programmed injection rate. The same thing happens if you disconnect or cut the lambda sensor wire, or if the sensor is fouled by leaded gasoline. This becomes important when you are trying to make closed-loop adjustments at idle, but the sensor cools off because not enough exhaust is passing it. Many service procedures depend on closed-loop operation, so remember that the sensor has to be warm enough.
As you’ll see in the service chapters, the lambda control system is properly adjusted when engine-out CO is the same whether the system is closed-loop or open-loop. This adjust- point allows the system its full range of compensation for operating conditions.
L-Jetronics have been used since 1974. Engines adapt easily to L-Jetronic. In 1980, when tighter U.S. emission limits were mandated, virtually every European car imported to the U.S. which had used carburetors in 1979 switched to L-Jetronic. Those that did not, switched to K-Jetronic.
3.1 Air-Mass Sensor
The air-mass sensor is completely electronic. It depends on the measurement of current flowing through heated wires to measure air flow. It is also known as the hot-wire sensor because of its heated-wire design, hence the H” in LH. It has several advantages over the vane-type air-flow sensors of L Jetronic.
1. It measures air mass, or weight, so it requires no correction for changes in density due to temperature or altitude. The air-fuel mixture ratio depends on mass: so much weight of fuel mixed with so much weight of air. Measuring mass eliminates the need for compensation sensors: air temperature, and altitude. It also reduces correcting computations in the control unit.
2. It has no moving parts. That means mechanical simplification. It responds even faster than the moving vane of the air-flow sensor. Measurements follow changes in air-mass in 1—3 milliseconds.
3. It offers insignificant resistance to the passage of air. Even at maximum air flow, drag force on the wire is measured in milligrams.
Air-mass measurement by hot-wire improves drivability, stability, and reliability. It is used in racing. In my opinion, air-mass sensing will probably supplant the measurement of air flow by vane-type sensors.
Air-Mass Sensor Design and Operation
Under hood, between the air cleaner and the manifold, you’ll see a simple black plastic cylinder with an electronic box, as shown in Fig. 3-1. If you remove it and look inside the protective screens, you may be able to see the small platinum resistance, or hot wires, that are suspended inside the cylinder so that the intake air can flow over them. See Fig. 3-2. How fine are these wires? The diameter is 70 micrometers—that’s less than 1/io millimeter, finer than a human hair. By careful design of the sensor and its mounting, the fine wires survive automobile vibration. In the unlikely event a wire should break, the warm engine runs, though without fuel compensation, in a limp-home mode. You can simulate limp-home mode by driving the car after pulling the air-mass sensor connector of a warm engine.
Fig. 3-1. Look for air-mass sensor between air cleaner and intake manifold.
The hot-wire system depends on measurement of the cooling effect of the intake air moving across the heated wires. Suppose you had a fan blowing across an electric heater. With a small movement of air past the heated wires, the cooling effect is small. With more air moving past the heated wires, the cooling effect is greater.
LH control circuits use this effect to measure how much air passes the LH hot wire. The hot wire is heated to a specific temperature differential 180°F (100°C) above the incoming air when the ignition is turned on. As soon as air flows over the wire, the wire is cooled. The control circuits then apply voltage to keep the wire at the original temperature differential. This creates a voltage signal which the control unit monitors: the greater the air flow (and wire cooling) the greater the signal.
Fig. 3-2. Air-mass sensor includes hot-wire assembly and control circuits.
Control Circuits. The LH control circuits use a Wheatstone bridge, as shown in Fig. 3-3. The hot wire is one leg of a bridge circuit whose output voltage is held to zero by regulating the heating current. The hot wire, known as Rh, changes resistance with temperature. Incoming air passes over the hot-wire. Rh, and also over another resistance wire, Rk. The same voltage is applied to both wires. In series with Rk are two fixed resistances, R1 and R2; in series with our hot wire, Rh, is fixed resistance R3.
Fig. 3-3. Wheatstone bridge principle explains maintenance of hot-wire temperature.
The Rh wire is controlled to be 180°F (100°C) hotter than the intake air flowing through. For example, if the air is at freezing, 32°F (0°C), the wire will be heated to 212°F (100°C). On a hot day, if the air is at 86°F (30°C), the control circuits heat the wire to the same 180°F (100°C) difference, to 266°F (130°C).
The air mass changes when the driver changes the throttle opening:
1. more air passes over both resistance wires in the air-mass meter;
2. both Rh and Rk are cooled by the increased air mass;
3. Rh decreases its resistance, because of its Positive Temperature Coefficient;
4. current flowing through Rh increases more than the current through Rk;
5. that unbalances the bridge circuit;
6. comparator increases its output;
7. amplifier increases current (Jh) to bring Rh back to its original resistance, and thus its original temperature back to 180°F (100°C) above ambient temperature of the intake air;
8 the heating current is measured as a voltage drop (Um) across the fixed resistance R3;
9 this voltage drop is a measure the air mass and is used as the output signal to the control unit.
All this happens is 1—3 milliseconds.
The air mass can also change because air temperature or altitude changed its density.
Some lite reading.
NB:
The text refers to a Lambda sensor, that's an O2 sensor.
Almost all EFI systems have their origins in Bosch Jetronic/Motronic land. Mazda may use slightly different values but definatly the same theory.
I didn't include the pics but I can scan and e-mail the original pages if anyone is interested.
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Old 08-04-2005, 09:43 AM   #10
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A resistor in series will provide a voltage drop in relation to the rest of the load. I'll try to explain (this is where a whiteboard in a lecture theatre would be handy).
If you have 12 volts and an AFM which has a resistance of 1000Ω then the AFM carries all 12 volts;
If you add a 200Ω resistor into the curcuit then the AFM will carry 10 volts and the resirtor 2 volts;
Now if the AFM changes resistance to 800Ω and your resistor maintains its 200Ω then the AFM carries 9.6 volts and the resistor 2.4 volts.
This is where it becomes tricky as this is how the whole thing works, The AFM appears to the ECU as a resistance and for the ECU to measure this resistance it must have its own resistance in the curcuit and read the voltage from that. So to change the ECUs reading of the AFM you're adding a third resistor into the curcuit. To raise the resistance you add in series but to lower the resistance you need to add in paralell.
Resistors are about 2 cents each and their are thousands to choose from so you could give your self a hobby and start trial and error ($5 gives you thousands of possable combinations) or find the pinouts and start taking voltage readings, either way a spreadsheet will be your friend.
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Old 08-04-2005, 09:57 AM   #11
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notes : i think our o2's have an inbuild heater

so in theory, the best design will be to have a resistor between the output and the ground wire then? to allow some current to go from the output back to ground (and not kill any fuses/electronics)???
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Old 08-04-2005, 12:07 PM   #12
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You need to identify if the voltage goes up with the increase of oxygen (resistance increases) or goes down (resistance decreases).
For up you would add a low value resistor in series between the AFM and ECU to simulate more O2 by increasing cicruit resistance.
For down you would add a high value resistor in parallel between the AFM and ground to simulate more O2 by decreasing the circuit resistance.
If you had a programable ECU then you would just alter the mapping. Many tuners don't use closed loop claiming it's too difficult and that the maps have been set correctly by them anyway.

Heated O2 sensors have multiple wires going to them. I'd guess that if you're running lean at idle (16:1 air/fuel) that your ECU isn't using the O2 sensor at that stage.

For those who arn't confused yet:
12.6:1 should be maximum Power (any richer and you're blowing unburnt fuel out your exhaust for no good reason)
15.4:1 should be maximum Economy (any leaner and you are loosing power and may be damaging your engine)
14.7:1 (as Goldilox said) is just right
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Old 08-04-2005, 03:42 PM   #13
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I would not do this mod! as it will effect one part of the afm's operation and stuff up the other! This is all related to open and closed loop operation of the o2 sensor! If u lean out the system in wide open throttle mode (yeah it sounds like a good idea) when it goes back to operating in closed loop the ecu will notice the afm is running out of its pre-programed operation level (this should take about 5 min of operation) cuasing the check engine light to light up and the afm to log a code in the ecu. This is alll part of the air/fuel correction program thats constantly running while in closed loop operation, older ecu's dont apply.
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Old 08-04-2005, 04:24 PM   #14
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there was a good article on this in autospeed.com using pentiometers ( variable resistors )
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Old 03-07-2006, 07:36 PM   #15
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Any idea about where the IAT sensor is for a 2000 Astina Protege Shade (1.6 lt engine). I am trying to put a intake mod chip in to see the effects on performance gains..... Thanks.
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Old 03-07-2006, 08:07 PM   #16
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IAT sensor is in the same unit as the AFM (MAF... same same) on the 1.6
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Old 03-07-2006, 09:09 PM   #17
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Thanks but where is the MAF thing located???
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Old 04-07-2006, 07:55 AM   #18
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in the intake piping... just nearby the battery....

plug has 5 leads going into it
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Old 04-07-2006, 05:21 PM   #19
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Thanks mate. I spotted the MAF thing with five leads going into it. Ummmmm five leads - last one is in red .. which two are for the IAT sensor ?? I feel really dumbbbb now.........

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