1994 VAF question

[mcmlxxxv]

So i've been chasing issues with this truck since I bought it and as usual MUD was really helpful.

The truck is a stock 1994 fzj80 with roughly 235k miles had issues accelerating and I get round 7mpg ignition was bad when I bought it so everything was replaced (coil,Spark plugs , wires ,capand rotor).
Fuel filter is also new ,TPS readings are good, coolant sensor replaced but nothin changed much UNTIL I played with the VAF gear.

At first I leaned it out a little (3 cog) the problem was the same but a lot more present, so I turned it the other way , 3 cog richer than the original setting and the truck is running MUCH better. The thing I dont really get is how that reading richen up mixture. Does it change fuel pump voltage by the resistor ? change injector pulse or else ?

Because I know im not supposed to mess with that part so I wonder if my fuel pump is just not getting the voltage it should or if its going out.

I seriously begin to miss my 60.....

No check engine either, still feel very underpowered. I know it can push more as sometime it doe it !

 

[sogafarm]

Got any pics of how your adjusting the VAF? Did you pull out the two screws that are near the plug?

 

[mcmlxxxv]

Got any pics of how your adjusting the VAF? Did you pull out the two screws that are near the plug?

No only top cover

 

[sogafarm]

That little leg to the lower left that hits the tab reads the idle. Im assuming that if you adjusted the clocking the it would read differently since the timing of the off idle would change. I wouldn’t think it would adjust rich or lean settings while running.

 

[sogafarm]

Check for any air leaks in the rubber plenum, that would affect lean/rich while running. The only other factor would be the oxygen sensor.

 

[jonheld]

The thing I dont really get is how that reading richen up mixture. Does it change fuel pump voltage by the resistor ? change injector pulse or else ?

What you're doing is changing the tension on the spring which is altering the reading that the ECU "sees" to know how much air is entering the system. This will alter the A/F ratio across the RPM range.
Folks usually do this in conjunction with a higher octane fuel to prevent pre-ignition.

 

[mcmlxxxv]

That little leg to the lower left that hits the tab reads the idle. Im assuming that if you adjusted the clocking the it would read differently since the timing of the off idle would change. I wouldn’t think it would adjust rich or lean settings.

Yeah this is indeed the ilde switch , changing the adjustment I did only change the spring load on the flap . So the resistor on the board changes reading position at different engine speed.

@jonheld you are right , the thing I wonder is how . Does it change voltage to the fuel pump ? or did I fixed my issue by putting more fuel in the engine from the signal to the injectors?

if so , that would just be a ''band-aid'' on the fuel pump issue.

 

[jpoole]

I can't tell if this VAF has both adjustments from the pic but these VAFs often have two primary adjustments to support factory setup.

• One allows you to move the head without changing the spring tension. For instance you might loosen a screw that allows rotation of that black plastic center body so that the metal swipers move to a different point on the board, without rotating the center shaft or changing spring tension at all.
• The other is where you add or remove spring tension, which sounds like is the adjustment you made.

If you are confused about what these adjustments are doing one way to think about it is that the vane inside the VAF opens as more air is sucked into the engine. If you lower the spring pressure or move the swipers further along their sweep (counter clock wise) then that's the same as the Vane opening for more air. If the VAF says more air is inbound the computer will add more fuel to keep the ratio where it needs to be. Depending on the system logic there may be O2 sensor inputs, temp sensor inputs, etc. that are also factored in but the VAF basically monitors how much air so that the computer knows how much fuel to spray. Counter Clock Wise movement of the swipers = more fuel signal to computer.

When you change VAF tuning you may simply be compensating for some other problem in the system. For instance, if loosening the spring and richening the mixture makes it run better then you may have intake air leaks between the VAF and the combustion chambers. Unmetered/unmeasured air is going to lean the air/fuel ratio so richening things up will help offset that.

Back to the two adjustments above. The first adjustment makes the mixture richer, or leaner, across all RPMs. The second changes the curve of fuel being added. If you are lean at all rpms you would use the first adjustment until the air fuel ratio was correct across the full rpm range. If you are rich at higher rpms you could tighten the spring a few clicks to get the curve right then go back to adjustment one to set the air fuel ratio at all rpms.

You need a real time air fuel ratio reading to tune the VAF in my experience.

I suggest you make sure everything else is dialed in before you move the VAF from stock tuning. Smoke test the intake, confirm that timing is perfect (Across the rpm range), confirm all injectors are up to snuff, etc. then setup a real time air fuel monitoring system and tune the VAF under load/driving conditions if still necessary.

 

[mcmlxxxv]

I can't tell if this VAF has both adjustments from the pic but these VAFs often have two primary adjustments to support factory setup.

• One allows you to move the head without changing the spring tension. For instance you might loosen a screw that allows rotation of that black plastic center body so that the metal swipers move to a different point on the board, without rotating the center shaft or changing spring tension at all.
• The other is where you add or remove spring tension, which sounds like is the adjustment you made.

If you are confused about what these adjustments are doing one way to think about it is that the vane inside the VAF opens as more air is sucked into the engine. If you lower the spring pressure or move the swipers further along their sweep (counter clock wise) then that's the same as the Vane opening for more air. If the VAF says more air is inbound the computer will add more fuel to keep the ratio where it needs to be. Depending on the system logic there may be O2 sensor inputs, temp sensor inputs, etc. that are also factored in but the VAF basically monitors how much air so that the computer knows how much fuel to spray. Counter Clock Wise movement of the swipers = more fuel signal to computer.

When you change VAF tuning you may simply be compensating for some other problem in the system. For instance, if loosening the spring and richening the mixture makes it run better then you may have intake air leaks between the VAF and the combustion chambers. Unmetered/unmeasured air is going to lean the air/fuel ratio so richening things up will help offset that.

Back to the two adjustments above. The first adjustment makes the mixture richer, or leaner, across all RPMs. The second changes the curve of fuel being added. If you are lean at all rpms you would use the first adjustment until the air fuel ratio was correct across the full rpm range. If you are rich at higher rpms you could tighten the spring a few clicks to get the curve right then go back to adjustment one to set the air fuel ratio at all rpms.

You need a real time air fuel ratio reading to tune the VAF in my experience.

I suggest you make sure everything else is dialed in before you move the VAF from stock tuning. Smoke test the intake, confirm that timing is perfect (Across the rpm range), confirm all injectors are up to snuff, etc. then setup a real time air fuel monitoring system and tune the VAF under load/driving conditions if still necessary.

Pretty much all of that was done already that's why I went in there .Smoke test is negative ,everything is tight and air hose is also new. did replace all the vacuum hoses also and timing was on point !

Deleted the PAIR system and EGR . can it have effect on it ? All that stuff was vacuum controlled....

Anyway I will continue the search , the truck runs acceptably, still have to see if fuel consumption is better ...I know its probably a band-aid for another issue that's what I'm searching.

need to check fuel pressure ... fuel pump voltage (maybe?)

 

[jonheld]

Yeah this is indeed the ilde switch ,

Negative. Please refer to the Toyota EWD.
The switch in the AFM is what fires the secondary coil in the circuit opening relay to keep the fuel pump running after releasing the ignition key from the START position. It is part of the fuel pump logic circuit.
This is one of the differences between the OBD1 and OBD2 1FZFE.
The idle switch is in the TPS.

 

[mcmlxxxv]

Negative. Please refer to the Toyota EWD.
The switch in the AFM is what fires the secondary coil in the circuit opening relay to keep the fuel pump running after releasing the ignition key from the START position. It is part of the fuel pump logic circuit.
This is one of the differences between the OBD1 and OBD2 1FZFE.
The idle switch is in the TPS.

Hum I've been misinformed then, thx for clarifying. Will look it up even if it does it's job , i want to make sure everything is set as it should

 

[jonheld]

Hum I've been misinformed then, thx for clarifying. Will look it up even if it does it's job , i want to make sure everything is set as it should

The FSM has tests and specifications for all the sensors. Always refer to the Toyota manuals.

 

[petegangies]

I wouldn't have personally gone messing with the VAF internally at the cog. You can also add a screw to the airby-pass to adjust mixtures slightly, but never recommended unless you run a wideband sensor in the exhaust to check your air /fuel rations. Unfortunately, once you've disrupted the cog internally they are a nightmare to calibrate correctly again.