There was a leak a while ago. A line coming from the back of the car was split. I replaced that with a new one.

The other thing I did is remove the relay from the pump that was installed last time the motor popped. I could hear it clicking on and off. Didn't think that was very safe. So the pump is wired back to how it was stock.

Pump is appx 10k miles old.

Would the best way to get accurate fuel pressure be to get a fitting on the sx regulator, and use regular fuel line to run from the engine bay to the cabin and place the gauge at the end of that hose?

 

Interesting. What does the fuel relay do, exactly? Is there a "high" and "low" fuel pump voltage? Even so, I think I just proved that we're not fuel CAPACITY limited.
However, Steve's tune might have expected a higher fuel rail pressure which WOULD affect the fuel delivery.
We might be on to something here....

FYI: relays are supposed to "click" when they turn on or off. That's why your turn signals emit that "click-click-click-click" under the dash every time they turn on and off..

 

The relay was pretty much put in to make the fuel pump run on high voltage all the time. Normally, (someone correct me if I'm wrong) under cruising it'll run on 6v or 7v, but then under hard acceleration (boost) it'll turn up to 12v.

We put the relay to keep it at 12v all the time. But I'd notice just while driving I'd hear it come on and off. I should only hear it switch on and off when the ignition gets turned on or shut off. I'd hear the "click" 3 or 4 times while just sitting at a stoplight. That's why I removed it, because I wasn't sure if it'd be on under boost or if it'd turn off.

 

Nah, because the injectors open up more at higher boost level, the a/f ratio may or may not change as much. If the injectors have the same duty cycle for both high and low boost, you'll see leaner a/f ratio at higher boost. Basically, higher duty cycle on the injectors offset it in a certain way, it seems to me that the fuel pressure drop was consistent enough where the a/f ratio was affected in the same way on both low and high boost.

 

The relay was there to ensure that the fuel pressure stays the same through out the rpm, alot of times, the ECU driver couldn't deliver enough current to drive the fuel pump hard enough at higher rpm to maintain the fuel pressure and will see a slight drop. The fuel pump can draw up to 20amps at WOT and isn't sufficient enough for the factory 16awg wire (17ft long) to maintain the needed current/voltage to keep up the needed fuel pressure at higher boost level. By hard wiring the fuel pump straight to the battery in-line with the relay, it helps maintaining the fuel pressure. I normally see half a point lower in a/f ratio by doing this.

 

So it may be safer to put the relay back on... Just the constant noise of hearing it turning on and off scared me away from keeping it installed on the car.

 

maybe the clicking noise was caused by low voltage trying to activate the relay at idle (8V) vs. (12V). You shouldn't hear it clicking at WOT if the voltage is consistent

 

I understand what you're saying, but for the graphs to be identical, the Injector DC never hit 100%. If it had hit 100%, then the AFR would have quicky gone lean, especially on the high boost setting. If the DC never hit 100%, then you cannot be fuel flow limited. Make sense?

 

If your resistor was left in place then the relay would click on/off as you change from low/high load conditions.
If you left the relay out of play then you should only here the relay click once when you acctivate the circuit.

How did you run the car without the relay?
Did you still have the factory fuel circuit running?

 

I guess it depends on how you interpret fuel flow and fuel capacity. Fuel flow can be interpreted by the size of the injectors going into the engine or at the rate of fuel flowing to the fuel injectors (i.e. fuel line/fuel pump/fuel filter/FPR)

for example, lets say 4000cc/min worth of fuel injectors are good for 600rwhp at 40psi static pressure, if you raise the fuel pressure to say 50psi, it can support 750rwhp. I think cavell's problem is not on the injectors, but rather on the fuel pressure not maintaining its static pressure.

 

Ok, that makes sense... I don't know that the AFR's would still overlap so perfectly, but it sounds like a plausable solution.
Get that fuel pressure guage installed, Cavelle! People are waiting!

 

To reiterate my previous question...

Would the easiest, and safest way be to get a fitting on the regulator, and run regular fuel line from the engine bay under the hood or thru the firewall and put the gauge on the other end? Would a length of line 3 or 4 ft like will be needed affect the pressure reading?

C'mon Dave, you've known me how long and you can't spell my name right? sheesh!

Cavell

 

Actually, the more I think about it, the less I'm convinced... Man, this is getting complicated! (Thanks for the discussion, BTW)

What you're saying is that the fuel pump/FPR/filter cannot supply the required volume fuel at the required pressure, correct? I can believe that- there's only a finite amount of fuel it can pump. No arguement there...

However, that flow limit would be reached SOONER on the high boost situation (because more fuel is required) and the AFR should reflect that. Even if the injector DC% increased as a result of the lower fuel pressure (does the ECU factor that in?), this "enrichment" mode would happen at different RPM's, right? (basically, back to my previous fuel flow graph). Now, if it DID happen at different RPMs, I would think it would appear in the AFR...



Man, I need a beer....

 

Dammit... I always screw that up....

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And to answer your other question- I think an electric guage would be better. Put the sensor on the fuel rail and run the wires to the interior. The idea of running gasoline through the firewall scares me.

 

Yeah, I guess 40+psi of fuel spraying into the cabin would be kinda bad.

Even if its just a temporary thing, maybe run it to outside the windshield.

Cause I already have a little mechanical fuel pressure gauge. Might be worth just to test it out before I spend $100+ for an electronic one. Even if later on I decide to get one.

I understand what you guys are saying. I'll try the gauge first, then put the relay back on to see if that makes a difference.

 

Sounds like the pump is having trouble sustaining flow to me, too.

 

What is the point where 2 pumps would be necessary and/or beneficial? Certainly not at least until 500+ rwhp, right?

 

Their dyno is hosed and your HP/Torques readings are crap. WHY, torque and HP will cross at 5200 rpm not 6500rpm.

 

Chuck, if you look carefully at the scales for torque and HP, you will see they are different. If you look at the torque and hp values at 5250 rpm, they are the same.

 

Or if he had taken the time to read the rest of the thread where that's been pointed out twice already.

 

Haha, well I didn't bitch at any of the guys that were still arguing about the crossover point after I already pointed that out, so why would I yell at Chuck...