general afm ?'s

[diy guy]

first let me give a quick intro. im not new to cars or turbos. I've built and tuned a turbo gsr, and was in the process of turboing a s14 but lefts face it, a stock turbo motor is a much better platform.

I came across a 88 turbo supra with a freshly installed jdm 7mgte, figured its a good base. As you wouldve guessed by the sn, i dont like spending money on anything i don't have to, not that i have much money to spend anyways so i'd liek to make this as fast as possible with simple/cheap mods.

well... guess that wasnt so quick

onto my questions. i think it was here i read that a stock afm measures about 2.5v at idle. does that sound right? thats pretty high so i'll assume max voltage is at least 5v. since its already halfway at idle, could voltage be dropped at the signal to ecu, then the fuel corrected by afc? that would allow more airflow before fc while still being metered, right? unlike a fcd, bcc, safc, etc. which tricks your ecu into thinking theres less airflow, therefore less fuel will be injected. anyone tried it

btw, is there a voltage to rpm table for fuel cut or is it a certain voltage no matter what rpm?

 

[BlackDevilSupra]

What you're referring to is the Toyota's standard Vf signal, which is an indicator of how the ECU is trimming / adjusting the fuel delivery, and NOT a measurement of the incoming air. Also, the 7MGTE is a Karman Vortex system, therefore, the ECU measures and records air frequency, not voltage .

FC depends on many factors, not just simply RPM. Few are RPM, load, ambient air temp., air frequency, coolant temps, ATM pressure, etc...
The Supe aint a Mitsu bud.

 

[diy guy]

thanks for the quick reply

actually i meant integra gsr, honduh not dsm... map...even easier than maf

i figured afm=load so that'd be load vs rpm. same way fuel/timing maps are drawn out. coolant temp/iat/throttle/etc tables adjust, but generally the difference in negligible, and as far as I know, theres no pressure sensor.

i guess its not as simple as a resistor though. what frequency then does it happen at? how does a fcd know when to clamp the signal?

 

[jetjock]

AFM output on a stock 7MGTE is a 5 volt square wave with the frequency varying with airflow. It's around 20-30 hz at 700 rpm, 90-100 hz at 2500 rpm and 160-180 hz at 4000 rpm. Exact setting depends on how the AFM was calibrated to that engine using the bleed screw. Look for a two digit code stamped nearby.

 

[diy guy]

anyone have datalogs hitting fc with at least parameters load and rpm. i know i cant base it off just that but it'll help me understand.

 

[IJ.]

JJ: You are such a geek!

Thanks for the explanation!

 

[jetjock]

JJ: You are such a geek!

Thanks for the explanation!

Geek? Look who's talking

My geekness just goes beyond cars. Before becoming a professional pilot I spent years as a machine design engineer so I know enough to be dangerous about lots of things, from electronics to hydraulics and everything in between. Since both are very technical occupations I suppose I'm guilty as charged. Plus I'm a "just the facts 'Mam" kinda guy. The devil is in the details you know

 

[IJ.]

LOL I've never owned or even played with the stock GTE electronics but often see them discussed here and it was nice to have an explanation!

I went Stock NA> Full standalone.
(the easy way out)

 

[diy guy]

yes, thanks for the explanation. sounds a lot more complicated than i though

how about this. greddys emanage has a boost cut eliminator, but unlike the other fuel controllers, it can also control the injectors independently from the stock ecu. what if i clamp afm to the ecu and add fuel on the additional injection table to compensate for the extra, unmetered air? anyone tried that? i was going to get a piggyback controller anyways, probably safc, for about $100 more for a emanage blue and options, i get to keep the stock injectors/afm (440s ought to be good for something in the high 300 low 400whp range right?), timing control, 16x16 3d maps, ability to control 2 additional injectors independently, option to MAP based load, an aux output with airflow adjustment (i'm thinking water/alky injection), wb input, and datalogging. im surprised there arent more people using it.