WaachBack

iTrader: (21)

Straight to the battery.

WaachBack

iTrader: (21)

If its true that the negative lag skews numbers then it makes complete sense. Going from 0 to -0.20 takes a huge amount of fuel out of the map. And I can see how that would relate to incorrect injector duty cycle numbers on the PFC. What were your lag settings like?

Someone needs to confirm:

1. How much is the injector duty cycle skewed by using negative lag.

2. Does using negative lag effectively turn an 850cc injector into something like a 750cc injector.

2a+RoN

In short your reported duty cycles *should* reflect actual pulse width sent to the injector, not "effective" like some other ECU's. Assuming this, duty cycle reflects how much fuel the injectors are flowing and will not be skewed by lag times even though using negative or wrong lags are a bad thing to do no matter who says it works or is acceptable. Here's why...


---First off, I highly encourage you all to read this article as it goes pretty in depth into dead times and will probably help you understand fuel injection in general much better.

http://www.injectordynamics.com/dyna...erization.html

However, I will try and simplify it specific to this situation---

Here goes...

Ok, so you have an 850cc injector at static flow. Firstly, the injector never, repeat never goes static on a vehicle. Even if it says its at 100% duty cycle, the ECU needs a specific amount of time to close and re-open the injector.

So on a car where its actually being pulsed, you need to know how much fuel the injector flows for a given pulse width and how much time is wasted flow which is called dead time, lag, latency, etc. The ECU adds this value to the calculated pulse width after all compensations have been made. I don't recall exactly what the stock 850 dead times are, but for ease of math, lets assume its .5ms or 500usec but I think its in the neighborhood.

At 80% duty cylce, the injector does not flow 680cc/min (850cc x .80) because there is an additional .5 ms where the injector does not flow, putting the actual flow at 637.5cc/min at 100hz (6000rpm on a rotary) where math is simple and 10ms is the time per period. That .5ms dead time equals 5% duty cycle of the injector or 42.5cc/min (850 x .05).

By entering a lag that is .6 ms smaller than what should be, you are in effect telling the ECU that the injector flows more, 51cc/min (850 x 0.06) more than it should at a given pulse width and will result in huge errors when the ECU goes to make compensations such as a change in air density, temp, etc.. NOT COOL! However, your car still requires 85% duty cycle worth of fuel to maintain your desired a/f.



End rant..

Given that, I would definitely log fuel pressure. If you don't have logging capabilities, at least do something to be able to see fuel pressure while driving. In cases I've been known to use a 6' hose with a gauge on it connected to the FPR and mounted using the windshield wiper just to diagnose an issue. Cheesy, yes, effective, yes.

WaachBack

iTrader: (21)

Very good info and excellent read. I (and I bet the rest of us who read that) now understand exactly what tuning with negative or incorrect lag does. Having said that, unfortunatly, I still am unable to use the correct lag because the car simply cannot idle without using negative lag. I dont see any other way around this other then raising the engines idle to 2k+ which I wont do.

I dont currently have the capability to log fuel pressure, but I will hook up a line and a gauge to diagnose the issue as suggested.

thewird

iTrader: (8)

You don't necessarily need to log it. Just need a gauge in the car so you can see it. Or if your doing pulls on the dyno, ask someone to watch the gauge in the engine bay during a pull.

Also, thats why I hate 850's. You can't get them to idle nice and lean.

thewird

Trots*88TII-AE*

iTrader: (11)

People have idled on 1000's, even 1600's. The PFC from I understand just doesn't allow bigger injectors to idle. One option is to lower your base pressure and up the size of your secondaries, like the ID2000's

thewird

iTrader: (8)

The PowerFC has an unknown minimum injector ms you have to run. That is why you can't idle lean with the 850's or bigger injectors. It will idle but be in the 11's or lower no matter how much you lower the ms. A way around that (somewhat helps) is by running negative lag but that changes some other things including drivability smoothness.

But I still think there is another issue here if hes getting 85% duty cycle with that fuel setup.

thewird

rx72c

iTrader: (8)

Its not unknown. Its around 2.5ms.

And please people. ITS NOT HIS FUEL LINES.

thewird

iTrader: (8)

It's actually lower then that lol. :P

thewird

WaachBack

iTrader: (21)

Both pumps work fine. What do you suggest it is?

thewird

iTrader: (8)

Check your fuel pressure during a pull and ignore everyone until then :P.

thewird

silverfdturbo6port

iTrader: (26)

After reading the thread so far i agree with the weird. The fuel line size is perfectly fine and u are running two pumps but that also means that those pumps will supply more fuel if you take advantage of that so like the weird said turn the base fuel pressure up it cant hurt anything since you have good fuel supply. So turn the base pressure up to 45 and see what it does before u do anything else. Note* i think factory base pressure is like 43# anyways if i am not mistake

rx72c

iTrader: (8)

Your right i just went and checked on a FD and the lowest it would go is 1.6ms

rx72c

iTrader: (8)

You have to establish if its the pumps or not. DO a pull and see if fuel pressure is dropping once your up it. If it is. GET A REAL FUEL SETUp.

WaachBack

iTrader: (21)

1680cc x2 850cc x2 with dual pumps is more then adequate for my goals of 500whp on pump. I also just bought the stuff and Im not willing to shell out even more money for another fuel system.

But yeah, I will check fuel pressure during a pull.

BluRR

iTrader: (1)

I think he referring to the choice of pumps

WaachBack

iTrader: (21)

Even if he was, 2 Walbros are still more then adequate for my goals. I am not going for 600+ whp. Dudeman is making over 500whp on 2 stock FD pumps...

thewird

iTrader: (8)

Just do the pull while watching fuel pressure already.

thewird

WaachBack

iTrader: (21)

I will this weekend, I havent had time to do it during the week.

Trots*88TII-AE*

iTrader: (11)

J-Rat made 550whp with a single in-tank Walbro on stock FC lines. It was maxed though, and with a lower base pressure.

Dudemaaanownsanrx7

iTrader: (23)

Yeah you must have some sort of fuel pressure problem. The way you T the lines could be a factor as well. Straight T's with 90* turns will force the fuel back into itself and increase restriction, A Y block would allow the fuel to smoothly flow into the line. I'm running 550/1680 with higher base pressure and stock return/feed line, so your 850/1680 dual pump setup should get you there even easier. I agree with everyone here, you need to see what the pressure is doing under a WOT pull. I use an electronic fuel pressure gauge in cabin, it's worth while to have some way to monitor fuel pressure. Helps diagnose issues like this.

rx72c

iTrader: (8)

Lets be careful when we quote powerfigures here people.

No offense to Dudemaaanownsanrx7 hasnt actually dynoed his car has he? he is only estimating.

thewird

iTrader: (8)

I've learned to completely ignore dyno numbers. Try taking your car to multiple dyno's and you'll know why. Line up your cars on a straightaway and see who gets to the end first

thewird

Dudemaaanownsanrx7

iTrader: (23)

http://www.wannaspeed.com/fuelcalculator.html

Here's a fuel calculator in the above link that uses Brake specific fuel consumption as its basis, It gives you an idea of what you can expect from different fuel setups. It also allows you to calculate fuel pump requirements.

When adding a second pump in parallel the head pressure stays the same and the flow is doubled, when adding a pump in series (one flows into the other) the head pressure doubles and the flow stays the same. As this diagram demonstrates.

And yes rx72c is correct I haven't dynoed my car, but that doesn't change the fact that 850/1680 and dual walbros should be beyond enough fuel to support 500 RWHP. My 550/1680 are maxed out at base pressure, which is why I have mine raised.

GoodfellaFD3S

iTrader: (213)

I'm wondering if the resistors somehow are causing you problems.

I've had similar experiences with my FD (2x870cc, 2x1680cc, all top feed, BNR fuel pump, base px 43.5 psi) and my duty cycles are even higher, high 80s % at 16-17 psi IIRC. My FD has been stored for the winter, so no recent seat time.

I've been toying around with trying the FJO injector driver and deep-six'ing my resistors (not sure of the resistance offhand).

I can tell ya that ever since I switched away from 850cc side feed primaries, I've been able to idle in the 14s AFR all day long.