Changing to a larger Air Flow Meter (AFM) and installing a hi-flow, boxless air filter.

Every modifications you do to your engine increases the airflow through it... Header, big cams, porting, turbo, supercharger, etc... You need to be sure that your ECU can measure that all that air, so that it can calculate how much fuel it needs to add, and you need fuel injectors big enough to supply the proper ratio of fuel to all that air. The 4age engine came with 185cc/min fuel injectors and an AFM that can measure the corresponding amount of air. According to my rough calculations, 130-140 hp is about all that can be expected from the stock fuel system. If your mods bring you to that level, you may want to add bigger fuel injectors and a larger capacity AFM. A Fuel injector monitor is a handy device to have and can tell you if you are reaching the maximum capacity of your fuel injectors. Larger fuel injectors and a larger AFM will NOT add any horsepower to your car! They will only allow the proper amount of fuel to be added to the extra air that your other engine mods allow, like a turbo, or a supercharger. Since I added both a turbo and a supercharger, I knew I needed more than stock 4age parts could deliver, so I upgraded to 4AGZE (320cc/min) injectors and the AFM from a Supra/Cressida. I also went with an open-element filter at the same time.


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The first thing to do is to remove the stock air filter box and airflow meter.



Go and get one from a 82-86 Supra or 85-87 Cressida.





As you can see, the Supra's AFM is a little larger on the outside, but MUCH LARGER on the inside (where it counts).




The pin configuration, resistance ranges and THA (the air temperature sensor) are the same, between the supra/cressida and 4AGE, not 4AGZE. The electrical plug is the same too. :) You also need to install larger fuel injectors while doing this AFM swap, or else you'll run lean at any speed above idle and possibly damage your engine.



Take apart the Supra's air filter box.



Find a suitable air filter... Just look around in the garage.



This is where I found mine... A new Kawasaki (or UNI) air filter goes for about $35 US.



Get these pieces together....Outer filter, inner filter, plastic filter frame, air filter outlet.



Use a suitable implement of destruction to cut out the six inch round intake funnel from the filter box.



Assemble the plastic frame of the air filter onto the funnel you just cut out.



Oil the air filter with a suitable air filter oil (PJ-1) or put the filter in a plastic bag with an ounce of engine oil and squish it around a while. Assemble the air filter, then install in car.

Don't forget to install larger fuel injectors too! The stock fuel injectors on 84-87 corollas are the peak/hold variety (3.5 ohm), the same as the 4agze. This means that the ECU can drive these injectors without frying the ECU. If your car has saturated injectors (14 ohm) then you'll need to use 10 ohm 10 watt series dropping resistors to keep from overloading your ECU if you change to the 4agze peak/hold style. There are large saturated injectors out there too, On my Links page, there's a link to Autospeed.com's injector chart. That will show what car you can find bigger injectors on. If you have the 84-87 corolla wiring harness, you'll soon see that the electrical plug for the 4age injectors won't fit the 4agze injector. Newer Corollas have the correct plug, so a trip to the junkyard can get you the connectors that fit. Just cut the fuel injector connectors out of the newer corolla, don't attempt to refit the entire harness, that's quite a hassle. Since the supra AFM is about double the capacity of the 4age and the 4agZe injectors are about double the capacity of the stock 4age injectors, I figured that the air/fuel ratio would be about right. The injectors are physically the same size and shape, so they fit between the fuel rail and intake manifold nicely. Once you get this far, you may want to upgrade your in-tank fuel pump. I'm told that a 7mge or 7mgte fuel pump is an easy swap, I'm looking forward to performing that swap soon....

The car did not run well after the swap, it would start and idle, but right off idle, it would stall. Cruising, half throttle and full throttle were fine. A/F (Air/Fuel) ratios were bouncing between 13:1 and 15:1, and stayed right at 13:1 at full throttle. I'd like to see the mixture richer under boost, but my ecu doesn't sense boost. (yet....) Lots of adjusting of the AFM and the TPS has almost eliminated the off-idle bog. I now have enough fuel for the power levels I hope to reach.

Any questions? Mail me. Twincharger@hotmail.com

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