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I have another beginner question:

I read that the stock Mk3 turbo fuel system runs out of juice somewhere above 300bhp. I was wondering what modifications are required to make bigger injectors and pumps work on a stock ECU?

I assume the ECU controls the duty cycle of the injectors and pumps based mostly on the MAF signal, but there's no way to tell it there's now a larger flowing capacity, so it will decided on a duty cycle based on the stock fuel system performance.

Wouldn't this cause the engine to run really rich? How do you tune the AFR on a stock ECU?
 

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I was wondering what modifications are required to make bigger injectors and pumps work on a stock ECU?
Only option without resorting to a piggyback fuel tuner is a Lexus V8 air flow meter housing and 550cc injectors. Search the forum for the Lex/550 mod and there will be many threads discussing it in detail. You'll also need a higher flowing fuel pump and a fuel pressure regulator.

Wouldn't this cause the engine to run really rich?
If you just throw bigger injectors in yes.

How do you tune the AFR on a stock ECU?
In short, you don't. Aftermarket engine management is the only option with these Toyota ECUs.
 

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Discussion Starter · #3 ·
In short, you don't. Aftermarket engine management is the only option with these Toyota ECUs.
Thanks for the info!

This seems like something that you could reasonably tackle with a very simple homebrew microcontroller to translate the MAF sensor input and fuel injector output. I was wondering if there was an easier way. Looks like the Lexus MAF is easier but more expensive and less tunable?

With regards to fuel pumps, what kind of flow rate would be required to feed 550cc injectors? I assume the flow rate is in cc/m, so 6x550cc is approximately 200 litres per hour? So something like a 255 Walbro or equivalent would be fine?
 

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This seems like something that you could reasonably tackle with a very simple homebrew microcontroller to translate the MAF sensor input and fuel injector output. I was wondering if there was an easier way.
There are aftermarket piggyback ECUs that do that same thing with a fair bit more computing power than a homebrew microcontroller and they still don't do a very good job of tuning it. Getting the Vf signal to match what the OEM ECU is happy with and getting the motor running well is a difficult process with lots of trial and error. It's why pretty much everyone has abandoned the idea and skipped straight to a full standalone engine management system

Looks like the Lexus MAF is easier but more expensive and less tunable?
Much easier, cheaper, and less tunable. But the increase in fuel flow from going to the 550cc injectors is very close to the increase in airflow from going to the Lexus AFM housing over stock. It's simple and really only intended to be a gap filler between simple boltons and full engine management system upgrades.

With either method of piggyback ECU and Lex/550s you still can't adjust the ignition timing which is the Achilles heel of the 7M EMS.

With regards to fuel pumps, what kind of flow rate would be required to feed 550cc injectors? I assume the flow rate is in cc/m, so 6x550cc is approximately 200 litres per hour? So something like a 255 Walbro or equivalent would be fine?
The Walbro 255 is the standard upgrade as it fits in the stock hangar easily and doesn't flow too much for the stock fuel lines. You do need to bypass the fuel pump resistor so the pump gets a full 12v at all times though.
 

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You can adjust trim using fuel pressure if you go with the Lexus AFM/550 injectors, or use an SAFC to trim the fuel by spoofing the AFM signal. The ECU has only two pump modes, low and hi, which is triggered by the internal load calculation. Many just force the pump to run hi all the time (so called 12V mode) but its not ideal.
I have a long thread on Supramania (currently down sadly :cry:) on the internal workings of the ECU if you need more detail and that site ever comes back up🙏 🍀.
 

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You can adjust trim using fuel pressure if you go with the Lexus AFM/550 injectors, or use an SAFC to trim the fuel by spoofing the AFM signal. The ECU has only two pump modes, low and hi, which is triggered by the internal load calculation. Many just force the pump to run hi all the time (so called 12V mode) but its not ideal.
I have a long thread on Supramania (currently down sadly :cry:) on the internal workings of the ECU if you need more detail and that site ever comes back up🙏 🍀.
RIP Supramania :(
 
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