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Старый 15.03.2021, 14:49   #1
Регистрация: 26.12.2020
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ALFAMAF на пути к лучшему

Hello Pin,

I believe you need to clarify an issue.
In your connection diagram for generation of the ECU VAF reference voltage, the voltage divider R1/R2 is depicted as connected to +12v. If users interpret this as battery voltage source this is incorrect. Reference voltages must be generated from stable sources. If the diagram actually means connection to the VAF supply sourced from the ECU, then all is good as this voltage is actually a regulated voltage from the ECU. In my case measured at 12.5V when battery volts are 13.6V. Use of non regulated VAF reference will cause all sorts of issues and the sky may fall in ?

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Старый 15.03.2021, 17:21   #2
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Регистрация: 08.09.2009
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Pin на пути к лучшему
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Hi Doug
In your case you should connect the top point of the divider to ECU's stable output.
The schematic on the website is for general purposes. Some mazda's AFMs takes voltage from battery as supply. Thats made for compensaing injection time during cranking at cold winter - the lower the voltage , the longer pulse width of the injector.

By the way on L-jetronic, when you will install new maf, you can get lean mixture at high load, even if the output of the converter will be at 255 points. In this case you will need to decrease resistance of the bottom resistor to reduce ref voltage, and retune the conversion table.
On L-jetronic reducing of the ref voltage , will enrich the mixture.

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Старый 17.03.2021, 07:57   #3
Регистрация: 26.12.2020
Сообщений: 5
ALFAMAF на пути к лучшему


Yes\ - I have used the supply which is the top of the VAF resistor divider chain.
To get the car going I have initially used a 1K potentiometer so I can adjust the reference voltage easily. Also this is useful in easily enriching the car for a cold start until it is all sorted. My guess is that the L Jetronic looks at the difference between the reference voltage and the VAF output, the greater the difference is the leaner it will be - ie at full air flow VAF = Ref voltage and thid is the richest it can deliver. So I can then understand how decreasing the Ref voltage will enable the ECU to deliver more fuel.

I have done some other measurements that may be of interest. Basically I have plotted the ECU injector pulse width at various RPM V's VAF voltage.This was done with a 220ohm resistor in the ECU temp sense circuit to simulate a warm engine. The measurements are a bit fluffy but the general relationship can be seen

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