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Just to confirm, you cannot run different sized injectors with the stock ECU. The only exception would be a rom tune by ats. Last time I looked they did 550cc injectors only. You need to make whole new injector tables. The ats rail is a stock bored out rail for more flow. The stock rail is very restrictive. It is side feed, some sard 800cc injectors would be a good match.
 

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How does a stock ECU control a bigger injector?
When it has the proper ROM tune to do so. I don't know why it didn't spread to the Toyota community, but back ~20 years ago I was tuning stock ECUs for SR20DETs and Z32 VG30DETTs. I've run 740 cc injectors (Nismo sidefeeds) on a stock SR ECU, which was a similar vintage to an SW20 ECU. It ran fine overall, but I got the feeling I was at the limits of what it could do for idle stability with that size injector. It definitely didn't have as tight of control on the injectors as a modern standalone with way more processing power and a wideband input.

I'm definitely not advocating plugging a bone stock SW20 ECU with a tune for 440cc injectors into some 1000 cc injectors, that's ludicrous.
 

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When it has the proper ROM tune to do so. I don't know why it didn't spread to the Toyota community, but back ~20 years ago I was tuning stock ECUs for SR20DETs and Z32 VG30DETTs. I've run 740 cc injectors (Nismo sidefeeds) on a stock SR ECU, which was a similar vintage to an SW20 ECU. It ran fine overall, but I got the feeling I was at the limits of what it could do for idle stability with that size injector. It definitely didn't have as tight of control on the injectors as a modern standalone with way more processing power and a wideband input.

I'm definitely not advocating plugging a bone stock SW20 ECU with a tune for 440cc injectors into some 1000 cc injectors, that's ludicrous.
It seems tuning the Toyota ECUs form the 80s and 90s was not able to be done or it was extremely difficult.

I have heard from someone that the fuel map on a GEN2 3SGTE is controlled up until around 4000rpm then the duty cycle is 100% from there on up.
 

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ATS does it, and lots of JDM companies offered tunes back in the day. It’s just hexadecimal tables after all... the hard part is deciphering the tables and putting in a flashable chip. Nissan ECUs actually have a 2x20 pin header you can solder a daughter board to, then moving a resistor on the board uses this diagnostic port for the tune info on the chip. It’s surely a holdover on how they initially developed the tunes for the engines at the factory. Each ecu design has its quirks. Hondas of the era are pretty easy to socket off come socketed.

On stock IDC, there’s no way stock IDC is 100% at 4000 rpm, as it follows the HP curve very closely. So you’d be pig rich there and lean at higher rpm if that were the case.
 

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At stockish boost the a 3S-GTE with bolt-ons should peak VE in the ~5000-5500 RPM range (makes sense given peak HP occurs just after that). All corked up it might peak down as low at 4000-4500 RPM, so maybe that control scheme could "work," but it sounds pretty scary to me!

Honestly, modding stock ECUs made sense back in the early-mid 2000's, as the OEM stuff from the early-mid 90's wasn't that far off most standalones on capability. You typically just lost built-in boost control capability. But given how much more powerful standalones have gotten, and how many features they've included, it makes absolutely no sense to keep a stock ECU on a modded early-mid 90's car these days unless it's almost completely stock (even then, the standalone will likely drive better). The ease of troubleshooting engine issues alone makes a standalone really invaluable IMO.
 
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