Simplyscion

highly doubt it

aarontrini85

hahaha i figured that

matty-tC

i doubt they'll change out the fuel pump or use a black box.

some guys on here are running 6 psi on the stock fuel system so i can see just an injector bump handling 5-7psi of the blower.

Simplyscion

true...i guess we will find out sooner or later...probly later

lo_bux_racer

It is possible to reflash the computers. You need a tool that starts at $8k just to get access.

I have one difficult question I have not been able to solve with the whole injection problem. On a conventional injection set up, the fuel pressure regulator has a vacuum/pressure line from the manifold to maintain a constant pressure in the fuel rail relative to manifold pressure. This keeps the injector's maximum fuel flow constant regardless of manifold vacuum or pressure. The tC (and many other new cars) use a returnless system that does not have this feedback mechanism to adjust fuel pressure, so the rail pressure is constant. It's no big deal to compensate for this in the fuel maps until you hit boost. As manifold pressure rises, the pressure drop across the injector pintle decreases, so maximum flow drops. This means when you need WAY more fuel, your flow rate is dropping. How are the turbo kit guys getting around this basic issue without converting the fuel system to a return-type system?

I know Jotech just threw all the returnless stuff in the trash and built a return system with a conventional FPR. How is Scionspeed, ZPI, Dezod, and everybody else dealing with this fuel delivery issue? Call me old school, but I've learned a great deal about Toyota boosted engines from the Supra I've had for the better part of 12 years. I know alot about TCCS and Toyco's long and short term fuel correction factors and how to use Vf to really see what's going on. I'm just a little confused about how you can make the injection work when the regulator is in the gas tank and not provided any feedback about what the engine needs. Sure, it would be easy (sort of) to do this electronically, but I haven't seen anything in the New Car Features or the Factory Service Manuals (yes, I bought them all) to tell me how this system compensates for boost or vacuum. Even the fuel pressure test doesn't seem to show any hint of variability for vacuum compensation. Does anyone here know and is willing to tell?

James_GSC

awesome question, never thought about it that much - curious as well

for any race type application first thing anyone does is ditch the returnless system to make high hp #'s

matty-tC

You are correct in your theory but I don't believe that anyone has been hitting enough boost to warrant the return based fuel system (other than the stated Jotech)

Simplyscion

I converted to a return line setup in my xB and it still didnt help cause the in tank regulator limits you to 45-50 psi and w/out that in tank regulator, it wont pump gas out. Thats where the extra injectors come in and compensate for the MAF adjusting constantly because of the added boost.

matty-tC

you need a 1:1 fpr

Simplyscion

I got one and even w/ that it still limits it to 50 psi cause of the in tank reg...its the aeromotive fpr

lo_bux_racer

You need to ditch the in-tank regulator and get the fuel pump to work without it, or figure out a way to disable the in-tank regulator so it no longer regulates.

Simplyscion

its still not gonna help cause my MAF sensor is still gonna regulate how much fuel is gettin dumped in when under boost.

lo_bux_racer

Not exactly. The MAF tells the ECM about the air density flowing through it based on the amount of current required to keep a thermal device in the airstream at a constant temperature.. The ECM uses that data along with rpm and load and determines what the best amount of time to open the injector is. That pulse width is a result of a lookup table and two correction factors called long and short term fuel trim that are calculated by feedback from the engine sensors, primarily the O2 sensor. So, the thing that's relatively fixed is the injector pulse width.

The amount of fuel that gets sprayed in the amount of time the injector is open depends on the fuel pressure relative to the manifold pressure. The MAF does not directly control the amount of fuel, only the length of time the injector can spray. If the pressure is greater than design spec, more fuel gets sprayed, if it is less, less fuel gets sprayed. If the injector inherently flows more than the one originally used by Toyco, more fuel ends up in the engine. So, there are a number of things you can fiddle with to change the actual amount of fuel. That's why piggybacks work. They intentionally corrupt sensor data to make the ECM think something different than actual conditions is happening.

-Keith-

Well the ep civics (new si's) and the rsx do the same thing alot of turbo kits out for them... Ill have to look around again I saw a thread about how they were doing it.

matty-tC

it's nice seeing some intelligent discussion on these forums as opposed to "which CAI is better?!?!"

good job fellas

-Keith-

thanks....

as for the topic....

From what I can tell theres a fuel pressure regulator that when the pressure decreases as I take it it puts more in to make sure it doesnt lean out. I was also told that the emange will help solve this problem with the no return lines.

In all honesty im talking to some local companies gonna try build my own turbo kit.

lo_bux_racer

Sure, but that's what any regulator does. The "returnless" system actually has a return, it's just all located in the tank. The FPR is right next to the fuel pump, and the excess fuel is routed back into the tank just like in a return system, except the fuel never goes out to the rail and back (where it heats up and changes both the density of the fuel in the tank and facilitates increased evaporative emissions).

Some guys running exotic setups like dual 255 Walbros on Supras have had problems with extended cruising because the fuel bypassing the rail heated the entire gas tank (especially at less than a half tank) and changed the fuel density enough for the ECM to run the engine too lean (because there's no sensor for fuel temp/density). Some guys went as far as to put coolers on the return line to the tank. The returnless system avoids all this by dumping the fuel right back into the tank before it ever makes the trip to the rail.

If it were feasible to put an electronic pressure sensor on the fuel rail, referenced to manifold pressure, and control the pressure regulator electronically (or just directly control the fuel pump speed), then the whole thing would be a snap, and getting constant pressure across the injector pintle would be no problem at all.

Instead, it appears the accountants at the factory said no to all that control stuff, and asked how it could be done with an absolute minimum of pieces. So the engineers rightly figured out that you could set it up to run with a slightly higher fixed pressure and just use injector pulsewidth to compensate for pressure variations. You can infer manifold pressure from the MAF, rpm, and Ve map for the engine, so figuring out the required pulsewidth isn't too hard. That might also have something to do with the newer style injectors they use; it would seem they can handle very short pulse durations without problems. I just would like to know for sure if that is what is being done, or if it is something else.

Of course Toyco is as tight lipped as ever about their TCCS algorithms, and I doubt that will change any time soon. It really would be great to be able to disassemble the ECM code and see how they are doing it all. I have friends at very high levels in TMUSA, and they all tell me the code is one of the best kept secrets in the company. I did see that Toyco intended to release certain information about Scions in a press release from SEMA a year ago, but I don't know whether that included ECM functionality..

-Keith-

Only time will tell.

I just know that I dont trust running boost with no kind of system managing it.

lo_bux_racer

Agreed!

superbill

umm..yeah..but ive read these posts..like 4 times now and i still dont know what the hell you guys are saying ..emanage..or not too emanage that is still the question.