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Old 08-14-2009, 08:59 PM
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S10 computer

I have 2 questions, 1. what is the range of self adjustment that the computer can do to the AFR without throwing a error code? 2. What AFR does the computer try to maintain under WOT conditions?

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Old 08-15-2009, 10:36 AM
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Air fuel ratio? I believe the ecm will only set a code if the problem exits for a certian amount of time. Do you travel long distances at wide open throttle? That sounds fun. No, even in this case no code should set except maybe a max RPM code. If you have a scanner, check the O2 sensor voltage both manifold sides should constantly jump from .1 volts to.9 volts. If a sensor stays low it is reading lean and will try to richen the mixture until the engine is flooding itself, replace the sensor.
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Old 08-15-2009, 10:40 AM
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I think around 14 to 1, Doesnt really come into play with regular repairs.
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Old 08-15-2009, 12:51 PM
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S10 computer

Thanks for the insights. I am trying to get a bypass around the MAF sensor to work. I have built a damper controlled bypass that will flow up to 40 % more air and a bias circuit that corrects the MAF sensor output to reflect the increased air flow. My problem is when to switch the bias circuit in and how much bias do I really need, I know the computer will correct for some increase in air flow but I don't know how much and how fast it will do this. I am pretty sure it will do at least 5% change based on experiments to date.
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Old 08-15-2009, 01:07 PM
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Narrowing or widening the opening to the mass airflow, the configuration of the "neck" to the mass air flow sensor totally reflects its response, I had a car with a leaf and some fuze on the screen,"Some have some don't", it somehow blasted air right at the sensor and made the car run too lean, Its kind of *** backword, like a bad o2 sensors reading lean and dumping gas to compansate. I may be wrong but then again.......
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Old 08-15-2009, 03:14 PM
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S10 computer

Hi SAITEC yea I have noticed similar behavior. This time I stayed away from the MAF itself and built a separate duct that comes out of the filter box and goes into the "pot" that sets over the throttle body. The damper in the bypass is driven by throttle position so more air is bypassed as throttle is opened.
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Old 08-16-2009, 12:47 AM
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I think that the whole thing depends on how the airflow acts over the MAF.

The computer wants the engine A/F to be at 14.7 to 1 during normal driving. The fuel table is set up to give that.The O2 sensor tells the computer if it is doing OK.

If you increase the airflow, a MAF system should be OK -- if this shows up as increased air velocity over the MAF sensor. If you've made everything bigger and the velocity is the same, the MAF won't sense it. They work by basically measuring wind chill (what's the temp of the heated resistor in the flow vs the temp of a heated resistor in still air).

However, the computer might still complain because the throttle setting shouldn't produce that much airflow.

Bypassing the MAF and biasing it up shouldn't work any differently. The computer SHOULD increase the injector on time to compensate.

Problems come from 2 sources.
1. The computer can only adjust the fuel trim so far -- possibly 10%
- this is done first as a short term adjustment, and -- if it continues -- a long term adjustment. However, it will ***** if these adjustments are too high
2. The injectors can only deliver so much fuel. Increased airflow may require bigger injectors.

MAF systems are supposed to allow for easier modification because they measure actual airflow. Speed density systems (MAP) are calibrated for a stock engine.

Note: These are mostly comments based on what I've read in a lot of various forums/tech articles. -- I have not tried these mods.
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Old 08-16-2009, 09:52 AM
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S10 computer

Thanks Ford2go: Very good insights, I agree with your points. So far I have verified that the computer will correctly vary injector timing for at least 5% increase in air flow. Also that the computer will **** if MAF signal and the computer's ESTIMATE of what the MAF should be reading disagree for 40 sec. I tripped this code when I bypassed a lot of air (like 20%) and did not turn on the bias and deliberately ran the motor at an rpm where it was bogging, computer got real unhappy. I am going to try 10% air bypass with bias turned off and see what I get. I doubt that the computer can crank in 20% more fuel on its own without getting unhappy.
The bypass is sized to reflect injector capacity (duty cycle limit) less 10% to be safe. I am pushing 145 hp at rear wheels (chassis dyno) vs 133 hp stock. This is with me playing around (manually) with the bias and damper opening timing to get best results. So far I haven't been able to do this automatically on the road.
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Old 08-22-2009, 09:26 PM
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S10 computer

I have picked up a little more insight into the AFR behavior of the computer. I tried a bypass of 10% with no bias and initially, to my surprise, it worked fine. Engine was cold and AC was running. But, after driving around for a while, freeway and street, I stopped the S10 and restarted it, letting it idle while I made some notes. It immediately threw a lean code. I cut the bypass to 7% and got the same behavior. It appears that the computer can handle up to 10% bypass except at idle when engine is warmed up. More to chew on, as I refine my design.
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Old 04-17-2010, 09:54 AM
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S10 MAF Bypass

I am developing a MAF Bypass for the S10 4.3 (2002 model). This design adds a damper controlled bypass duct around the MAF and a electronic bias box to bias up the MAF signal when the bypass is open. Lots of weird computer error codes but making progress. It is a 2 mode system. In economy mode I can bypass up to 15% mass flow over stock. On a 2000 mile road trip Albuquerque to LA and back I got a 1.4 mpg improvement. I make this trip a couple of times per year so had lots of data. Currently working to debug the performance mode where I can bypass up to 40% mass flow over stock. this is about the practical limit (set by fuel injectors). Have solved all the various computer error codes that have shown up and getting ready to dyno test. A crude version of this system increased power on "shoulders" of the dyno curve by 30~40 hp and peak by 10 hp, the shoulder improvement blew my socks off. Truck feels like the current design is really helping, hope to get dyno numbers next week.
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