08 Yaris 'S' Turbo Build

[06YarisRS]

Originally Posted by scarsofcarma

Anything that modifies fuel flow and allows the stock ECU to see the results will create issues when it goes into closed loop. I am not aware of any piggyback which can dynamically compensate for the stock ECU adjusting fuel trim in closed loop.

What you suggest with taking fuel control away from the stock ECU entirely will probably be safer but that will certainly not allow for closed loop operation. You can't deny (or dump fuel on top of) fuel control to the stock ECU and expect it to be happy enough to run in closed loop consistently.

One trick people used to do (on older vehicles) is to try and force the stock ECU into open loop whenever you dip hard into the throttle to apply boost by cutting out the 02 sensor on command.

However not every ECU goes into open loop based on O2 readings. It's essentially dependent upon load and which emissions criteria and/or functions may or may not be in play. Older cars (which I am more familiar with) switched to open loop at a certain RPMor at WOT because they had simpler emissions regs. Newer cars are in closed loop more often by design.

Regardless of whichever conditions are in play any time you try to run richer than the stock ECU wants you to, it will compensate when in closed loop operation. What matters most is how much boost is made while the ECU is still in closed loop operation. The bigger the boost the bigger the risk.

There are a few options on the market that do modify the O2 signal or somehow force a stock ECU back into open loop. (Piggyback kits for Miata's can do this) but even they work with varying degrees of effectiveness. The only ones that work well are developed specifically for a particular car.

I am not aware of any such piggybacks that were developed specifically for a Yaris. Maybe it's possible, maybe not. What you are hoping to achieve without a full standalone, I'm afraid, is just not very likely mainly because the Yaris was not offered with boost to begin with. (At least not in the US)

If it was, a piggyback controller in the league of a COBB Access Port could be used to adjust the tune relatively easily.




It wasn't that hard to convert the stock pump assembly to accept the Aeromotive Stealth 340 pump. I don't remember what I did exactly but I believe all I had to do was wire in the connector pigtail for the wiring connector, strap the pump to the 'frame' with some zip ties and maybe use a length of fuel hose. The 340 pump is actually quite compact for what it is.

I could pull the pump out again to refresh my memory and take a picture for you.

Yes my Yaris is no longer a return style fuel system it is a dead-head.

Thanks for the detailed info! I think my car does go into open loop mode when the throttle is fully depressed, or nearly fully depressed. I get a nice fat AFR when floored, somewhere in the vicinity of 11.5:1 and the car's ECU doesn't seem to be pulling any fuel under these conditions. It's partial throttle and transitioning into boost that it may hesitate. If I increase throttle input linearly, it will sail right through the rpm range smoothly. If I have cruise control engage and the car is running up a steep hill, for example, and hits around 2 - 3 psi, the AFR gauge will start to fluctuate and it may cause a hesitation. Even a slight tap on the throttle will smooth this out. I did play with the 02 spoofing capabilities of the F/IC by inputting various 'experimental' voltages into the 02 map. At around 3 psi, it will send a voltage of something like 2.6v to the ECU and it enriches the mixture. My problem is that I haven't yet been able to put in incremental voltages that result in a smooth AFR through the various boost levels. I want to be able to say, for example, I want 12.5:1 from 1 - 2 psi, 12.0:1 from 3 - 5 psi, 11.5:1 from 5 - 8 psi etc, and have that happen. I am not sure if the DET-3 "Transplant Fuel" mode can do this.

I tried following the procedures in the video linked below, but every time I entered even the sightest decimal vlotage, my fuel trims went something like -20, regardless of how large or small the voltage input was. As perviously mentioned, I did manage to trick the ECU into delivering a rich AFR with ~2.6v in a section of the 02 map, but couldn't achieve a smooth and consistent richness as psia, rpms increased.

https://www.youtube.com/watch?v=SCeMaLC0Dqo

Maybe I will ultimately have to go with a standalone, but I'm hesitant at this point as I think it would be a nightmare figuring out how to control all the peripherals (DBW, A/C, cruise control etc, etc). I expect I'd be looking at many, many shop hours to get it working and then tuned.

Fuel pump - So you're returnless? Isn't the Yaris returnless to begin with? Is it as simple as the wiring and strapping the pump to the assembly? No need for a fuel pressure regulator or anything else? I don't think I'm fuel starved even at full boost/rpm, though if I hold on the throttle through 6000 rpm, it will slowly start to lean a bit. I don't worry about this a lot currently, as I rarely stay in boost for long at high rpm and I have a decent amount of water being injected above 3 - 4 psi. I've seen an AFR of as lean as high 12s at 7 - 8 psi and 6000 rpm. Again, my intake temps were low (in the 70s F), high rpm, so less cylinder pressure and close to 180cc of distilled water being injected into the throttle body.

If it is not a big job to yank your pump for a shot, that would be fantastic. However, please don't go to the trouble if it is an inconvenience.

Thanks again. Great stuff!