DanielleAlek

Hey all
I've been fervently searching through the entire internet, reading decades of forums and such, and there seems to be absolutely no consensus on this.
I have aftermarket headers. Runs around 8-12% lean now. I wanna be able to go WOT without frying piston rings. I'm not looking for a crazy optimum high-performance tune, I'm just looking to make it safe to drive hard with the new headers. This isn't my track car, this is the car I want to get to a million miles in. What's the best way to tune these?

The name I hear a lot for full-ECU tuning is VFTuning, which does seem to have Toyota/Lexus tunes, but doesn't seem to support any 2JZ platforms. Seems to be most popular with Tacoma owners. Loooot of money to spend just to find out if something works or not.
The other is Apexi, although there doesn't seem to be a consensus on which unit works best. Can I just buy an Apexi S-AFC second-hand, tell it how I want the A/F ratio to be, and send it? I've heard of E-Manage, and most people say it's miserable to use, and Dezod is impossible to get and seems to be more geared towards the IS300.
From where I'm standing, it kind of looks like the Apexi is the only unit that both works for 2GS and is actually possible to purchase at the moment. Found one for around $200 near me that came out of a Mitsubishi. Worth it? Also found an Apexi AFC Neo, is that better?

If not that, what's the best bypass unit for these? Or better yet, does anyone know of any actual proper OBD2 port tuners that work for these?
I also wanna use this as an on-ramp to learning how to tune altogether. Generally, my philosophy is anything I don't know how to do yet is another skill I can learn, so I'm not looking to take it to a professional. I have a beater I can test things on so I can get a handle on how the software works without blowing up my darling. I also could get a spare ECU, as well, although that's assuming I actually am able to find a way to tune through the OBD2 port instead of using a normal bypass. Bypass seems to be the safer, cheaper, and actually currently available option. The pros have to be using SOMETHING to do the tunes on these, though, I just can't seem to figure out what it is.
I also found this forum post, from literally 15 years ago, claiming that tunes are literally stored in editable .dat files, but there never seemed to be any followup since then on how to actually do this and make it stick, since apparently the ECU is programmed to reset after any tampering.
Whaddu ya'll think? Should I keep trying to find the full-ECU tuning setup, or should I jus save myself the time and money, buy an Apexi and send it? Should I give up on my tuner dreams before they begin? If we pretend professional tuners don't exist, what're my options?
Thanks!

Scigheras

There's almost infinite options, and it all depends on what you want to be able to do and how much you want to spend. This is something you need to decide for yourself.

Note you will need a wideband o2 sensor and controller for any method of tuning so that you can actually see what the AFR is after making your tuning changes.

I will give you some very rough guidelines of the options:

Mechanical AFR tuning with an adjustable fuel pressure regulator, $xx

Piggyback AFR tuning with stuff like the Apexi you mentioned, with this you will be able dial in more specific AFRs per load/rpm value, as opposed to with the FPR which will just give you a single global offset, $xxx

Full standalone ECU, with this you will be able to fully tune every single aspect of your car's engine management, good options are Haltech, Link, ECUmaster and many more, $xxxx

McPierson

iTrader: (3)

I gotta say, headers don’t usually NEED a tune. Are you confident everything else is sorted?

firelizard

iTrader: (1)

https://www.youtube.com/@ForwardMomentum

This guy is also on these forums, I think.
One of the few people to have documented the use of an AFC on the 2GS recently.

Typically though, when modifications reach the point of needing more than very minor changes, most people will integrate a standalone ECU using a custom harness like a Boomslang harness. This allows far greater control than an AFC, while retaining most factory functions.

GReddy e-Manage is antiquated at this point, I can't think of a use case for it where a modern standalone wouldn't be better.

DanielleAlek

Why can't I use a scantool or the Apexi itself to monitor AFR? Even if I'm using a tune to change the AFR, I don't see why stock oxygen sensors won't be able to read it accurately. I'm not looking to do crazy rich tunes to get flames in my exhaust or anything, I jus wanna get back to the stoichiometric ratio so I can send it without worrying about burning a piston.
Nice Aphex Twin pfp, btw

DanielleAlek

It has a VVT system code even though I've already replaced the filter and solenoid and changed the oil a couple times. Thinking there's a clog in the high pressure oil line, gonna try putting compressed air into that and seeing if anything comes out.
Those shouldn't affect fuel trims, though. Headers pull the exhaust gasses out faster, which allows for better air flow, thus the computer will read more oxygen in the fuel mixture and adjust the trims accordingly. I'm planning on pairing this with a resonator box delete (no idea why the original owner didn't do that in the first place) for a bit better airflow, but the stock intake is honestly pretty good besides the resonator box.
Long story short, yeah, I'm like 90% sure it's the headers. I already fixed a vacuum leak it used to have, and tried to track down if the slight lean condition is another leak of some sort, and I have every reason to believe it's just that it needs a tune to pair with the headers.

DanielleAlek

Yeah, I've seen that guy.
I'm not planning on doing more than very minor changes at this stage. Maybe an air resonator box delete, I'm not looking to put turbos and go super rich or anything, I jus wanna take the car back to the stoichiometric ratio and don't wanna be relying entirely on the ECU fuel trims to do it lol
This is the car I wanna take to a million miles. If I get a second one, that'll get GTE pistons, turbos, huge exhaust, new harness, custom ECU, all that good jazz, but this one gets very minor adjustments and stays 90% stock.

DundukovEM

The original 2JZ ECU is not programmable. It was possible to upload only small patches (calibration updates, *.cuw files) to engine / transmission maps released in the early years of production through the OBD port and Toyota TIS to eliminate identified problems. For something serious - only aftermarket solutions. Unfortunately, the stock ECU also controls the automatic transmission. Therefore, any aftermarket 2JZ ECUs will only work with a manual transmission. And it's a popular option in the SUPRA community. For example, with a swap to a manual transmission and the installation of a Link / Haltech / Syvecs ECUs.
Lots of $$$$ and hassle to install / setup / tune ---> not worth it for the current Lexus GS.

Scigheras

The Apexi SAFC has no capability to monitor AFRs. The OBDII system has, but it will rely on the stock o2 sensors, which are narrowband sensors. They can only tell you if your AFR is above/below/at stochiometric. Without a wideband o2 sensor you won't be able to tell what your AFR is at wide open throttle.

I disagree

DanielleAlek

I'm not sure if I completely understand this still. Could you direct me to some resources that have more information on the subject? I'm not sure I fully understand the relationship between air-fuel ratio and WOT, since I was under the impression that stock performance is still trying to maintain the stoichiometric mixture at WOT.
So basically without wideband O2 sensors, I'm running into the same issue as before the tune, which is that I can't safely push it to WOT without worrying?
Wouldn't this only be true if the engine was tuned to run fairly rich at WOT? I could still see whether or not it was running around the stoichiometric mixture, is it not supposed to run around there at full throttle?
Thank you for your time!

firelizard

iTrader: (1)

The stock "narrow-band" sensors will not provide enough information to an aftermarket gauge or ECU. They are just made to tell the factory ECU if things are nominal, lean, or rich. If the factory system sees a lean condition that is outside of normal operating parameters, it doesn't go "cool, more power" and keep adding fuel, it just doesn't have that ability.

DanielleAlek

Yeah, but my goal is to stay within normal operating parameters. I wanna use the tuner to get the car back to the normal AFR after the mods I've installed.

Scigheras

You are asking the right questions and already starting to understand what you didn't know before. Stoichiometric (14.7 for gasoline cars) is only targeted during cruise, constant rpm / low load. At WOT richer fuel mixtures are required to keep the combustion chambers cool and supply adequate amounts of fuel. Typical values are between 11 and 13, depending on the type of engine and its specific power output.

Example of AFR targets over different engine conditions (higher manifold pressure = throttle opened more)


Given that WOT conditions are the most dangerous for an engine, this is the critical part you want to make sure you have correct AFRs on, so yes you need a wideband to measure that since the narrowband only measures stochiometry

Wideband vs narrowband voltage output graph

DanielleAlek

Ahh, thank you very much, this is the answer I was looking for! That also gives me a better idea of why going WOT is dangerous when you have headers but no tune. I just heard something vague about running rich and melting cylinders, didn't fully understand why that happens.
The chart also helps me understand what's safe to do until I can get the tune done. I've been going granny on the throttle the entire time I've had it 'cause I knew it needed a tune and it's kinda cool to see the chart actually laid out objectively. I'm very interested in the relationship between throttle response and manifold pressure now, that's something I hadn't actually thought too hard about on a naturally aspirated engine.
This must be what people mean when they say tuning seems simple at first, but quickly becomes an inescapable rabbit hole lol it's exactly the level of geek I was looking for
Where do you learn this stuff?

Scigheras

Note that while all of this stuff is really interesting to learn more about and experiment with, and you WILL improve engine safety and performance, you are not gonna hurt your car at all if all you did is swap the header. The amount of flow optimization such a change realises is simply not enough to push an engine into "engine component damage levels of dangerous" lean territory. Especially on a n/a engine with relatively low heat production. You'll be fine.

Anyways, manifold pressure is pretty simple. The cylinders are constantly sucking in air. When the throttle body is only partially open (cruising) you are essentially choking the engine, you limit the amount of air it can suck in. This creates a vacuum in the manifold since the engine is trying to suck in more air than is being supplied. Now when you are WOT, a properly designed engine should be able to provide equal or more air than is needed to the engine, hence there will be no vacuum, the intake will be at atmospheric pressure. And ofcourse on forced induction applications positive pressure levels can be reached.

I guess I learned this just by being bored and curious at the same time, for many many years now, LOL
The internet has the answers to almost everything, it's your job to start googling away with any questions you have and make up your own mind from everything there is out there to read