Fuel system question

[Missing Linc']

Is the LS a return style fuel system? Also where is the fuel pressure regulator on a Gen2? I was looking around today briefly but didnt see anything on the rails or anything. Thanks

 

[Quik LS]

nope - almost all of the modern cars are returnless - and so is the LS.

On the Gen1 the FPR is right on the fuel rail, driver's side where the fuel line connects - not sure about Gen2 but that a good place to look.

 

[Missing Linc']

Is this lil fukker it? It doesnt have any kind of vacuum reference or anything but it seems to be the regulator, the line feeding it looks to be coming from the tank and then it goes through this and into the rail?? This is on the front drivers side rail, on the passenger side front rail there is some kind of sensor type deal that has a vacuum line that goes to the throttle body adapter and also to the EGR. Any info on what the hell is what on this engine?

 

[Quik LS]

here it is on the Gen1 - there is a electrical connection (for the pressure sensor) and a vacuum reference port on the rear end

 

[Missing Linc']

Alright I got that on the opposite side, so Im assuming something is gonna be effed up if I unplug it and put a manual adj fuel pressure regulator on it?

 

[Quik LS]

well - the PCM uses it (along with the vacuum) to keep the fuel pressure at 40 psi at the injector nozzle.

Why would you want to mess with that?

 

[Missing Linc']

In my old Camaro (350TPI) I picked up 14hp at the wheels by upping the pressure

 

[Quik LS]

yeah - those days are gone.

today - the tuning decides how long the injector is open and how often, then using feedback (when not in WOT) from the O2 sensors lean or rich that up. At WOT the PCM uses tables to determine this. The PCM also uses the fuel pressure reading, combines that with the vacuum reading and then decides how to pulse the fuel pump.

Simply trying to force more fuel through the injector while it's open (by increasing the pressure) will not translate into more HP - it's air + fuel + spark. plus the emission go to heck, messing up the spray patterns and stuff.

 

[Missing Linc']

Well I was actually gonna tune it down some, Im running an average of 12.2:1 AFR's right now at WOT

 

[Quik LS]

well - that's normal for the LS

You can improve performance by running closer to MBT (minimum for best torque) spark or LBT (lean best torque) fuelling. The LS already runs LBT fuel (approximately 12:1 air/fuel ratio, compared to the normal stoichiometric 14.6:1) at wide open throttle (or wide open pedal for Gen2). Spark is normally the minimum of MBT and "borderline" (the spark level at which knock begins occurring).

so it's seems that you are spot on.

 

[Frogman]

Simply trying to force more fuel through the injector while it's open (by increasing the pressure) will not translate into more HP - it's air + fuel + spark. plus the emission go to heck, messing up the spray patterns and stuff.

Tell that to the idiot that put oversized injectors in his Mark VII. LOL

 

[Missing Linc']

Umm Im not trying to challenge you or anything but a 12.2:1 AFR average on an N/A application is complete crap, on a boosted app thats like perfect as far as everything Ive learned, if I can get it to mid 13's or even a steady 13:1 Id be a lot happier and Im almost willing to bet Id pick up some power.

 

[Missing Linc']

That or I need to just get some more air into this thing and hopefully that will lean it out some.

 

[absentee]

Tell that to the idiot that put oversized injectors in his Mark VII. LOL

different car, different motor, different reactions to different mods.

see a pattern? there's a lot of differences.

 

[Frogman]

The hell are you talking about?

It's an internal combustion motor! It takes fuel, air and spark, just like the LS motor. They are both ran by ECU's. Granted, the Mark VII is a speed density, and the LS is not, but the principals are the same. You put bigger injectors (to a certain point, as most new ECMs can deal with a couple of points either way in injector size) on the motor and don't tell the computer, it will not make more power.

See a pattern? There's not that much difference between the two.

 

[Quik LS]

Umm Im not trying to challenge you or anything but a 12.2:1 AFR average on an N/A application is complete crap, on a boosted app thats like perfect as far as everything Ive learned, if I can get it to mid 13's or even a steady 13:1 Id be a lot happier and Im almost willing to bet Id pick up some power.

I learned this from Mike Scannell - the Ford engineer responsible for the engine calibration on the LS. Call it crap all you want - he seemed pretty smart to me.

LBT (lean best Torque) is the point of producing most torque. this is way the LS reacts so negatively to port or upsizing the throttlebody. You lean it up and mess of the LBT tuning. now, if you do mods and then retune to LBT then you get the improvement.

 

[Missing Linc']

Alright so let me get this straight, the timing is so far advanced from the factory that running it any leaner than like 12.5:1 AFR will produce knock/pre-det?

 

[absentee]

The hell are you talking about?

It's an internal combustion motor! It takes fuel, air and spark, just like the LS motor. They are both ran by ECU's. Granted, the Mark VII is a speed density, and the LS is not, but the principals are the same. You put bigger injectors (to a certain point, as most new ECMs can deal with a couple of points either way in injector size) on the motor and don't tell the computer, it will not make more power.

See a pattern? There's not that much difference between the two.

and there are a million little differences that make them react differently to changes, the fact that the 3.9 is tuned at 12.1:1 and the mark 7 is tuned to something else says so right there, never mind the fact that they have different redlines, different displacements, different compression ratios, etc.

I do agree with the last statement though, I thought you meant whoever did that WAS making more power in your original post.

 

[Quik LS]

Alright so let me get this straight, the timing is so far advanced from the factory that running it any leaner than like 12.5:1 AFR will produce knock/pre-det?

unless your running better fuel than the 91 it needs. This is why the LS is soooo picky about the 91+ octane rating - the spark attempts to get MBT (minimum best torque) unless knock gets in the way first.

 

[Missing Linc']

I run 93, its either 87, 89 or 93 where Im at so of course I do the 93..

 

[Quik LS]

right - so you have a 'little' room for more spark than guys running only 91.

 

[Missing Linc']

Alright so are there any other options besides the SCT stuff so that I can tune everything myself instead of spending $50 each time I wanna change something? What about the SCT Livewire, is that a user based system? Im about to put my Proform 750 on this thing and say fuk the luxury part hahah.. Never gonna happen..

 

[Quik LS]

nope - this is a PCM-based system - and SCT are the only ones I know who reversed engineered it. The LS is unique in that it was the first of the new generation PCM, but the ones that followed (F150, Mustang, ...etc) are slightly different - meaning that those PCMs have more aftermarket options, vendors, ...etc.

And no - the Livewire, XCal, .... are all the same when it comes to tunes - the devices have more/less features but the tune/delivery is the same.

 

[Missing Linc']

So theres absolutely no way for me to do my own tuning unless I drop like thousands on the SCT dealer software correct?

 

[Quik LS]

the only way I know to tune the car properly - is to use the SCT tools. The base models XCal2/XCal3 is about $400 with 3 tunes. If you use a local SCT dealer with an inhouse dnyo, then that's about the best you can get.

Can you rig up something else? sure. Before SCT we had to use extra injectors and control them externally off of WOT switches - very crude and prone to big mistakes.