I have 315cc injectors with a Vortech S-FMU running idle fuel at 25psi. Even with the fuel presure that low I still get a system rich code. I seam to get it when I am crusing on the highway. I even look at my air/fuel when crusing on the high way, it is rich. It is still only at 30psi while cursing. If I punch it in 4th or 5th gear, at low rpms (3000-3500) I go lean. If I punch it in 3rd gears at the same rpms it gose lean for a second then rich, and bomb (instant power). I don't want to turn my fuel pressure up anymore because I keep getting a code. But it seams like I'm not getting enough fuel in 4th or 5th. Help.

Someone correct me if i'm wrong, but cant that code mean a bad o2 sensor also? I would check into that. Damn, you have the same set up that i will be going with here in the next few weeks. 315cc injects and the SFMU. Keep us posted, I know i'll need some advise for this set up :)

no, usu. when you get a too rich code, it means your car is way too rich the majority of the time.

A.D.P.
"...If you do too much, people become dependant. If you do to little, people loose hope. If you do it right, people won't be sure you've done anything at all."
bring it on............

what disk and spring are you using in your SFMU? your rise rate may not be correct for the 315's..

Well, the absolute best way to diagnose what is happening is to datalog your car. Otherwise, I would say that you may want to use a different disk in your sfmu. It sounds like you need to keep low static pressures but increase the rise rate to give you more fuel at higher boost. Either that or turn in the bleeder screw a bit farther. Post what disk you are using now and how much boost yer running and that might help us figure out how much fuel you are currently dumping in and how much you fuel you actually need.

I am using the 2.72" disk. Boosting at 10psi seeing about 70psi of fuel. I was useing the larger disk at first, but it would really lean out then. You would think the oposite. I think the ecu may have been compensating though, seeing to much fuel and leaning it out. I don't get it. I'm about to try the next smaller disk to see what happens. The only problem is that disk is only a 3:1 disk while the one I'm using now is a 4.4:1.

man, its too bad that i didnt know that you had this problem before the shootout since I had my datalogger with me then. Anyway, if you go with the smaller disk, make sure that you watch yer egt like a hawk. If you see it going in excess of 1600, then you need to stay with a larger disk no matter what the a/f gauge is telling you. I wouldnt think that theres any way that you would get too much fuel with that small of a disk to cause any afterburn at 10 psi of boost. Good luck!

Since you are running the 4.4:1 disk shouldn't you see like ~84psi fuel at 10psi boost? I don't have a FP gauge in my car but that would make sense if you do it mathmatically :/

70 psi is too low for 10 psi of boost. With stock 235cc injectors, at 10 psi, you need at least 110-120 psi of fuel pressure. Since 315's aren't that much larger than stock, i would take a good guess that you will need at least 80-90 psi of fuel pressure at 10 psi of boost. Dont go with a smaller disk. That will lower your rise rate too much, even more thatn it is now. PUt in the largers disk(3.72"), and USE the bleed valve to bleed off boost pressure to fine tune the rise rate. I belive others with the same injects and sfmu have their static pressure set around 44 psi, and full vacum pressure is around 30 psi or so of fuel. You dont have enough fuel when you are at higher boost, so try using the largers disk. The dics sizes have nothing to do really with the static and idle fuel pressure, as you can adjust it the same with any of the disks..Start out rich, then tune down. Good luck man! Sorry we missed you at the shootout too :(

One thing I want to do is have no change in fuel presure until boost. When the car is idle the vacume causes my fuel presure to drop. When I give 50% gas the presure rises, even though I have no boost. Thought I could do this with a one way check valve. That way the S-FMU would not see any vacume. I worked but once I build boost the fuel presure stays high due to the presure still on the other side of the check valve. I need one that will blead that presure off after boost stops. Any help?

Hmmm...why do you want to do that? Even our stock FPR will raise and lower the FP when going from full vacum to 0 hg's. My SFMU does this, but it only goes from about 42 psi of fuel at 20+ hg's to about 55 static pressure at 0 hg's. Then it rises acordingly to boost. You can bleed off vacum if you want to by opening the vacum screw on the top of the sfmu. What this does, is it makes the sfmu see less vacum at idle. Lets say you pull 17 hg's at idle. With the vacum screw opened up some, you can adjust it so the sfmu will only see like 5 hg's or whatever you want really.Remember that by seeing less vacum at idle, the sfmu will raise the fuel pressure also. There are little balls behind that screw to act as a valve so that no boost pressure is bled off when under boost. I still think you should go with the largest disk and dark spring inside the sfmu, then use the bleed valve on the bleed port on the sfmu. This disk is working excellent for me, and it gives the highest rise rate the sfmu can work at. This will prob be too rich for the 315's, but you can use that bleed valve to bleed off boost pressure that the sfmu sees, and it will lower the rise rate to get less fuel pressure. With your T3 setup, running 10 psi on 315's, i would shoot for around 90-100 psi of fuel pressure at WOT. I'd bet it be much better on your o2 voltages. Just fine tune from there. Set you static pressure to about 44 psi(0 hg's), and your vacum pressure should drop to about the right amount. This is what i'm gonna do when i put in my 315's. Again, a datalogger can be your best friend when tuning. Even if it had cost 500 bucks, it would be worth every penny IMO. It will tell you how much fuel is being cut or added when you are just at idle, comparing to stock fuel trims. This is very helpful to set your idle and static fuel pressures. Also, i'm not too sure, but isn't 24 psi at full vacum too low for the 315's to spray fuel corretly? I thougt the 315's need at least 35 psi or around there to function right?.. Good luck man.

420aVenger runs low idle fuel presure as well. He runs the same setup as me. The car will run with the fuel presure down to 15psi or lower. It just idles a little rough. I think the computer is fuel cutting when I first hit boost. Since the fuel presure goes from 25psi at 18psi of vacume to 35psi at 0psi vacume. That is alot of fuel at 0psi of boost. This is why I want to keep the vacume from the S-FMU. The car can run at 30psi all the way up to 0psi. Then, once it gets boost, she gets more fuel.

Hmmm, your static fuel pressure seems very low. Even with a 1:1 FPR and 625cc injectors, I see at least 34-35 psi at idle. Since I don't have an electrical gauge, I don't know what my fuel pressure is under full boost.

Kon Chittavong
HRC: Stage IV | http://laoracer.homestead.com/mainpage.html

Well thats all i can think of for now, so i tried :) But i'm tellin ya, get a datalogger! I can tell you that within 15 minutes or so of dataloggin, that you will know exactly what you fuel problem is, and how much the computer is trimming fuel, or adding fuel, esp in closed loop under boost,and idlle/vacumm. If ya got the cash, get one asap, you will love it. It makes tuning a lot simpler. Good luck man.

I guess I will just deal with it untill I finish my 8 injector setup.

Maybe I have been reading what you are saying wrong, but it sounds to me like you might be confused with your fuel system. I assume that you have a 1997+ car with the stock regulator by the tank. That regulator should be removed and the aftermarket regulator is strictly what you use for fuel pressure adjustment. Hopefully you have already done this. You should have your aftermarket regulator adjusted so that your static pressure is around 42 psi and idle fuel pressure in the 30's with those injectors. You should see at least 90 psi of fuel pressure at 10 pounds of boost.

From vacuum to 0 vac, the fuel pressure is supposed to rise. 42 psi on those injectors at 0 vac is definately not too high. The only one way check valve on your regulator should be on the outlet where the regulator bleeds excess boost to drop the WOT fuel pressure. It is there so that when the car goes into vacuum, air isnt sucked through that opening which would cause a vacuum leak.

If you have any more questions or dont understand what I am attempting to say, post here or hit me up on AIM (name=SleeperEclipse). Definately don't drop your pressures that low and run a smaller disk. I promise you that isn't enough fuel.

Yes, my setup is just the way you say.

I raised the fuel presure back up to 30-32psi idle. I also took the vacume source off of the turbo instead of the manifold. This way the S-FMU dose not see as much vacume, just boost. I like this better because my fuel presure dose not float as much from 18psi vac to 0psi. The car runs strong and no code yet. It seams not to lean out as much now. Time will tell if the system to rich code comes back..

OK, I did some math.

Acording to RC Engineering's Fuel Injector Worksheet:

@ 240 Crank HP
w/4 injectors
brake specific fuel consumption of .52 (acording to Corbin's site)
a injector duty cycle of 75%
w/315cc injectors

The fuel presure should be about 84psi.

This sound right? This means I need about 40psi base fuel presure. I may have to pump the idle presure up to 35 psi.