#104257, "Help Tuning with SFMU" Sep-09-08 02:23 PM by Rondan97
Hey all. Finally after 5 years of boosting I just ditched my FMU for 30lb injectors and a SFMU w/bleed valve. So I'm trying to get A/F in the 11.4 range at WOT. My problem is when I do a 3rd or 4th gear pull @ 6psi, the WB goes lean to 15-16 then slowly goes down about every second (like 15, one one thousand,14,one one thousand, 13, one one thousand, 12 ). It will eventually get to 12ish but it seems to take forever (5+ secs.) I think the A/F will get down to want I if I stayed at WOT longer but that seems waayyy long. My egts just reach 1500* at the end of the pulls. Is this slow reaction normal? I was expecting the SFMU to richen things up a much quicker than that since I rarely boost that long.
I running the largest disc w/no ring (3.63"?) bleed valve open 1 turn dark stiff spring fuel pressure is 22 psi @ idle (@ about 12hg) And I dont have an in-cabin FP gauge. Using a AEM Uego Wideband
95' Avenger - Turbocharged Toy (SOLD) 99' Eclipse - Daily Driver (SOLD) 01' Audi A4 Quattro - Euro Cruiser (TRADED IN)
#104258, "RE: Help Tuning with SFMU" In response to Reply # 0
What is your static pressure set to? Should be around 30psi. 22psi at idle is fine. Close your bleed valve for now, only use the bleed valve if you need to lean the car out a little bit but never start with it open. You may be loosing all the air pressure by having it open to much right now. Also you may want to tune to the low 11s if you still on the stock bottom end. These motors love fuel and run well around 11.2 or so, plus it will help keep your EGTs down.
#104259, "RE: Help Tuning with SFMU" In response to Reply # 1
My static pressure is @ 30 psi. I closed the bleed valve, as you suggested, and did a few more pulls tonight and the A/Fs got down to around 11.2 . But it still seems to take longer than I think it should to get there (about 4-5 scary secs of WOT)
95' Avenger - Turbocharged Toy (SOLD) 99' Eclipse - Daily Driver (SOLD) 01' Audi A4 Quattro - Euro Cruiser (TRADED IN)
#104260, "RE: Help Tuning with SFMU" In response to Reply # 2
That does seem to be taking a little bit to long. I am assuming your saying it take 4-5seconds once boost hits to bring the AF down. Make sure your tapped into a good vac. line. Other than that Im not real sure without actually seeing the car.
#104262, "RE: Help Tuning with SFMU" In response to Reply # 3
That's it...once I hit 6psi, it gradually starts to richen up. What's the normal amount of time it should take? I wasn't thinking it could be the WB sensor but the A/F gauge responds pretty quickly to normal throttle changes, so I'm stumped. The vac line is tapped directly into the manifold. Tonight, I'll remove that metal resistor in the vac line to see if that helps.
95' Avenger - Turbocharged Toy (SOLD) 99' Eclipse - Daily Driver (SOLD) 01' Audi A4 Quattro - Euro Cruiser (TRADED IN)
#104263, "RE: Help Tuning with SFMU" In response to Reply # 3 Sep-10-08 07:30 AM by cs82685
I know many have said idle 22ish psi, static 30ish psi, but I found it was too lean with the largest disc and dark spring. Personally I raised my idle up to around 30psi and found much better a/f ratios at WOT. It does however seem that when cruising under light throttle with zero (or very little) boost, sometimes it will run way rich on me at about 10.5:1.
IDK it made sense to me, stock injectors flow about 75% what 30# injectors flow, so why would you set idle fp to 50% of stock instead of 75% stock. Maybe that's the wrong way to look at it, but I found to be too lean running the lower idle fp everyone suggested. Obviously that just addresses your fuel delivery at idle compared to stock injectors and I haven't really looked into it or thought about it enough to compare fuel delivery under boost. I do think with the higher idle fp though I should switch to a smaller disc but the car hasn't been driven for months, I just don't have the time to mess around with it.
Back to your problem of your AF's slowly coming down. Have you checked for leaks in your vac source to the sfmu? The line could be bleeding off pressure and prevent the sfmu from raising the fuel pressure as efficiently as it should be doing.
I contributed to the Wiki! EVO IX - just a really expensive boost gauge and a K&N air filter 96 Eclipse RS -awaiting registration and inspection 95 Eclipse GS - parts car Mods/Profile - http://www.2gnt.com/index.php?d=cs82685
#104267, "RE: Help Tuning with SFMU" In response to Reply # 5
Originally posted by cs82685 Have you checked for leaks in your vac source to the sfmu? The line could be bleeding off pressure and prevent the sfmu from raising the fuel pressure as efficiently as it should be doing.
It's funny that you asked that, because I did find a small leak in the vac line where it connects to the resistor thing. I put in a new vac line w/o the resistor and I noticed an improvement in the reaction of the AFs @ WOT. Still not the instant response I want but it now takes about 2-3 secs to richen up. The A/Fs settle around 10.3:1. Now I'm gonna play with the bleed valve to try and lean it out a little.
95' Avenger - Turbocharged Toy (SOLD) 99' Eclipse - Daily Driver (SOLD) 01' Audi A4 Quattro - Euro Cruiser (TRADED IN)
#104270, "RE: Help Tuning with SFMU" In response to Reply # 6
Now that I think about it I had a similar situation with my SFMU. The fuel pressure would take a second to build up. When you set the idle screw its suppose to allow air to be sucked in lowering the vac pressure in the unit. But when boost hits there is a ball in there that is suppose to stop air from leaking back out. Well mine wouldn't stop the leak. Take the vac line off the intake manifold and blow hard in it. No pressure should be leaking out and if it is then find out where and thats probably your problem. Make sure the bleed valve is closed also. If your leaking out the idle screw like I was, try setting static to around 28-30psi and close the idle screw all the way and then run the car and see if the fuel is more responsive.
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