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I am in the process of completing the Lex AFM/550 modification and decided to monitor the Vf signal before and after the modification. I'm not sure if this will be helpful in making adjustments but at least I'll have the data. Has anyone made these measurements on their car? For the limited driving I have done while monitoring Vf the signal starts at 0 at start up and after a few minutes it reads between 1.0 volts and 3.5 volts but seems to be at 2.2 volts most of the time. My understanding is you don't want a 5 volt signal because that would indicate the computer wants maximum fuel. I would like to hear from anyone that has knowledge on this subject or the adjustment process for the Lex AFM/550 modification.
 

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Back in the day JeffM made VF Monitors. They had a series of 5 LEDs showing what the computer was reading. Very cool.
 

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You'll find info on the Vf signal here: http://www.mkiiitech.com/forums/viewtopic.php?t=593

A Vf gauge is easy to make if you have basic electronics knowledge. There are a couple ways to make them. Here's the schematics for one of them: http://www.mkiiitech.com/forums/viewtopic.php?t=54

When monitoring your Vf signal it's important to realize that the voltage may not be dead on. There may be fluctuations or each step may be off by a specific amount. Just remember that there are only 5 steps to the signal and it's easy to figure out what you're seeing.
 

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A few years ago,after doing some small mods to my car, I drove about 200 miles watching VF and fuel pressure. It was mostly what you had seen. Slight to moderate load on the engine and it would go to the upper normal limits and less load or decel at lower speeds was equally opposite. Average was about 2.5 volts at no load cruise. This was just what I wanted to see.
 
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