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07-04-2005, 08:06 PM | #1 |
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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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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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07-04-2005, 09:28 PM | #3 |
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oky doky
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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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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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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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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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08-04-2005, 08:24 AM | #8 |
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cool, thanks
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08-04-2005, 09:21 AM | #9 | |
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Quote:
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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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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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)??? |
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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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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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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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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03-07-2006, 08:07 PM | #16 |
living in the past man
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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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03-07-2006, 09:09 PM | #17 |
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Thanks but where is the MAF thing located???
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04-07-2006, 07:55 AM | #18 |
living in the past man
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in the intake piping... just nearby the battery....
plug has 5 leads going into it
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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.........
Last edited by bluesky_astina; 04-07-2006 at 06:07 PM. |
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