86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Adjusting MAF

Old 06-04-2009, 08:46 AM
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Has anyone leaned out the AFM to see what effect that has on MPG? My 22re's always smell rich. I wonder if it is just because of the crappy head design or if they are set rich from the factory. I don't think the ECU for the 22re's are very advanced in that I don't think they run "maps" per say, they just trim the AFM reading against the O2 and TPS signal to set a injection duration.
So by leaning the AFM you set the fuel "map" to the lean side but the O2 and TPS will just shift it back up.

Any thoughts?
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Old 06-10-2009, 08:23 AM
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I have a dumb/simple question. I was replacing my VAFM the other day and I noticed on the connector (harness side) there is a pin missing. IIRC, it's the 3rd one from the left. I remember reading somewhere on here that there is no readout for that so it may not matter? I just wanted to confirm this and if I am supposed to have a pin in all of the plugs for the ECU harness.

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Old 06-10-2009, 08:28 AM
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If you're messing with your VAFM (it isn't a MAF) to correct a perceived rich syndrome, you're masking another problem. IMHO, unless you've done some pretty significant performance mods to your engine, changing the VAFM settings is just asking for trouble. $.02...
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Old 04-10-2019, 11:34 AM
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Talking The springs on older sensors lose their tension over time.

Originally Posted by seanmearse View Post
This might be a dumb question, but why do this? I mean if you have headers, custom intake, things of that nature, i understand. But what would be the cause to make this adjustment on a stock engine? What benefits are there? What are the cons?
You asked why change it if there haven't been any modifications? These are old vehicles, parts wear out, springs lose their tension. There is a potentiometer attached to the sensor that depending on how far the sensor door is opened, it tells the computer how much fuel to supply the engine. The door is opened by intake vacuum. If the door opens too easily the computer adds too much fuel causing the engine to run rich. If the door has too much resistance, the computer doesn't recognize the increased demand for fuel and causes it to run lean, starving the engine for fuel, burning up valves, etc. Too rich makes it waste fuel and causes it to run sluggish, fouling plugs and causing a rough or low idle. For maximum performance these old, but beloved trucks, occasionally need a tweek.
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