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September 07, 2010, 01:23:29 PM
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Pages: [1]
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Author
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Topic: Supra afm and injectors (Read 659 times)
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worgamer@aol.com
Newbie
Posts: 1
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So my turbo truck has those two mods done along with a t3 and intercooler. I am currently at 8psi of boost looking to turn it up. The truck has trouble keeping an idle below 1200. Has anyone else ran into this. I also have the spring in the afm adjusted too far for it to function right with the idle control setup . Im thinking the injectors are too big. also what psi do u think I can run with stock insides with my set up? 
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« Last Edit: February 07, 2010, 01:15:40 AM by worgamer@aol.com »
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mosk
Pooh Bah
Administrator
Three cylinders
Posts: 707
Been there, done that
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So my turbo truck has those two mods done along with a t3 and intercooler. I am currently at 8psi of boost looking to turn it up. The truck has trouble keeping an idle below 1200. Has anyone else ran into this. I also have the spring in the afm adjusted too far for it to function right with the idle control setup . Im thinking the injectors are too big. also what psi do u think I can run with stock insides with my set up?
OK, let's break this down a bit.
When I ran a Supra AFM and Denso 460 cc/min injectors (from a normally aspirated gen. II RX-7), I had to tighten the AFM adjustment gear 21 teeth tighter than stock to get it to idle correctly (I was also running more boost and had a rising rate fuel pressure regulator; more on that later). Why did I need to tighten it so much?
On the stock AFM, each tooth on the gear translates to roughly a 2% change in fuel flow. Stock 22RTE injectors flow 295 cc/min. As I said, the injectors I ran flowed 460 cc/min, which is probably a little more than your unspecified Supra injectors, which are either 440 or 415, IIRC. So if you were to just swap in the Supra injectors and retain the stock AFM, you'd immediately be flowing 56% more fuel than stock at idle (460 - 295 = 165. 165/295 = .56). However, that's not the only change you made; you also increased the size of the AFM, which means the AFM is flowing more air at every position, from idle to WOT. So at idle it is flowing more air AND more fuel. I can't find the measurements for the AFM size difference at the moment, but I believe it was pretty big, something like a 40% increase? You have to account for this, as the motor won't need that much fuel or air at idle, so to get the AFM to flow less air at idle, you tighten the AFM spring.
Another thing you might need to do is drill out/expose the secondary air bypass adjustment near the rear of the AFM, which you can use to "hide" some of this air from the ECU at idle (you can also use this to give the engine additional unmetered air at idle). As with any AFM adjustment, ALWAYS begin by carefully bottoming out the adjustment screw and counting how many half turns that takes, so you know its starting position. Write this down!!! Once you move it away from its stock setting, that's the only way to return it to stock. Also, IIRC, I think this secondary bypass works opposite of the way you imagine: tightening it = more air bypassed, loosening it = less air. I'd need to find my notes, which I don't have here with me at work.
Finally, if you are the sort of person who likes to read up on this stuff, A. Graham Bell's Modern Engine Tuning has an outstanding discussion of how to tune an AFM. Hmmm...just noticed that the book I linked to is out of print and going for over $100 used. His newer book, Four-Stroke Performance Tuning may have the same material, and it's only $23. I found his stuff to be exceptionally clear and easy to follow, so I don't think you'd go wrong to add it to your library, but his stuff is not Toyota specific; he's English, and his examples tend to use European motors, with the odd Chevy reference thrown in for US audiences.
One of the real benefits of this swap is that it lets you skirt the fuel cut parameter a bit. Fuel cut is triggered, in part, by how quickly the AFM vane swings open. More tension obviously slows this down a bit, but that's OK because you are flowing more air at every position, and with the larger injectors, you are also flowing more fuel at every position. The downside is that it can be very hard to tune, as you only have a few ways to adjust the fuel flow, and an increase in boost requires a different fuel curve than what you are going to get with this setup. One option is to also use a rising rate fuel pressure regulator (RRFPR). Something like a MSD 6BTM, which will retard your timing under boost, can also be helpful. But now you have a real house of cards that isn't coordinated and can be impossible to tune, or at least very difficult.
At about this point, most of us get so frustrated trying to tune the motor that we ditch the stock ECU and move to a standalone 
Jeff
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« Last Edit: February 12, 2010, 12:01:49 PM by mosk »
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Jeff's 22R-TE PageThe vintage HTML ain't pretty(!), but the articles are still worth reading if you are new to the motor
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rupertyotauser
One cylinder
Posts: 49
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im swapping in a t3 AR.42/.48 with intercooler,bov. i have a maf outta a 83 supra naturally asperated. would this be better to run than the stock 22rte maf
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86xtracab,22rte,Sas,53''rears,5.29s,35s,intercooler,T3swap...
85regcab,22r,sas,5.29,37boggers,aluminum-fueltank/crawlerbox
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rupertyotauser
One cylinder
Posts: 49
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any links for how to soider and do this i need to find out how to swap these into the 83 sensor
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86xtracab,22rte,Sas,53''rears,5.29s,35s,intercooler,T3swap...
85regcab,22r,sas,5.29,37boggers,aluminum-fueltank/crawlerbox
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mosk
Pooh Bah
Administrator
Three cylinders
Posts: 707
Been there, done that
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>any links for how to solder...
Google it. Seriously.
>i need to find out how to swap these into the 83 sensor
The parts look identical except that the Supra's has a larger body, and its output signal swings from high to low as the AFM door swings open. On the stock 22RTE AFM, the signal swings from low to high. THAT'S why you need to swap circuit boards. If you don't, wide open throttle will cause the signal to go full lean, which will make your motor very unhappy very quickly.
If you've never soldered before, don't learn on the AFM -- the contacts are too delicate, and the solder is 24 years old, so it will likely need a lot of heat to loosen up. Learn and practice elsewhere, or find someone else to do this for you. Or find a 1982 5MGE Supra AFM, which doesn't require any soldering.
The basic steps to do this (from memory, so forgive me if I skip a detail or two, but you'll see what you need to do once you get into it):
1. Cut the seal on the blast plastic lid the Supra AFM and remove it without destroying it.
2. Remove the armature that rides on the resistor board, exposing the resistor board. Put it off to the side gently, you'll need to reinstall it later.
3. Remove the screws that hold the connector plug to the AFM body.
4. Unplug the two thermistor leads from the back/top of the connector
5. Carefully unsolder the resistor board from the connector.
6. Remove the co nector form the AFM body.
7. Remove the screws that hold the resistor board to the interior of the AFM body and lift it out.
Repeat the above steps in the 22RTE AFM, then mark it with a Sharpie so you don't mix them up.
Now, install the resistor board from the 22RTE AFM into the Supra AFM and reassemble the Supra AFM, reversing steps 1 - 7. When you have it all together, tighten the spring and install it in the truck. It may take considerable trial and error to get the spring tension right, especially if you are also swapping in larger injectors at the same time. Once you have it dialed in to your satisfaction, seal up the parts you exposed with silicone.
There is probably a much simpler and more clever way to invert the stock Supra AFM's output signal so the swap I describe isn't needed, but that's beyond what I know. The above method will work.
Final note: Give yourself enough time to do this, as you won't be driving anywhere without a working AFM. If you have never soldered and this is all new to you, it could easily take you several hours or more the first time you do this swap. Again, if this seems over your ability level, get someone to help you who knows how to solder. Too much heat will ruin the resistor board!
-Jeff
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Jeff's 22R-TE PageThe vintage HTML ain't pretty(!), but the articles are still worth reading if you are new to the motor
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