When I first start going into boost my Autometer A/F gague reads waaaaaaaaaay into the red and just before I lose my nerve and let up on gas it jumps to at least 3 or 4 lights into the green and everything seems fine...my EGTs stay rock solid at just above 1500 degrees. It's not so bad when I roll into boost but when I mash the throttle is when the lag shows up the worst. I'm going to look at my vac hoses tomarrow but I read in one thread were some one drilled out the restrictor a bit and that helped out alot....if anyone has done that how big did you go? I've also heard people not running the restrictor at all...how dose that work? My pressures are 25-30 at idle 35-40 at static and I have the 2.72 disk and the orginal spring in the S-FMU. I've datalogged this and my Short Term trims are right around 0 to -5 and my Long term is like in the -20's so it seems like I'm running pretty FAT. I just don't like that lag. Also at warm up I'm get a minute or so of knock that I don't like...but after a couple of minutes that clears up....how can I get rid of that? TIA!
#105173, "RE: S-FMU lag....restrictor mod?" In response to Reply # 0
Yeah, ner did it, and I did too, but it basically gets rid of the fuel pressure lag when you go into boost. Before, the fuel pressure would take a half second to go up when i would punch it. Now, its much, much more responsive. I took a drill bit, and enlarged the end of the restrictor that is smaller than the other. I believe I used a 5/64" drill bit. Thats all there is to it.
13.5 @108 MPH-2.2 60ft(stupid FWD!) S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential fuel injection) My webpage: http://eclipsed4evr.home.comcast.net -1998 Mitsubishi Eclipse RS-T- "Toy" -1992 Plymouth Laser Turbo AWD(SOLD) -2000 Honda CR-V(daily)
#105176, "RE: S-FMU lag....restrictor mod?" In response to Reply # 3
well, i didn't drill out the whole thing. here's the deal.
i had the lag problem myself, but everything was fine when i was in boost. around 12 psi of boost i'd need about a turn and a half out of the bleed valve to get the boosted fuel pressure to where it was suppose to be.
at this point i tried the easiest solution, removing the restrictor all together.
the lag problem went away. but, i was running VERY rich in boost. i tried to tune my fuel pressures at 12 psi of boost but no matter how many times i turned that bleed valve i couldn't get the fuel pressures to come down.
so i was stumped for a little while. while on the crapper at work, i thought about the problem and the simple "there must be not enough bandwidth through the restrictor" idea somehow entered my head.
i took the vacuum restrictor, and drilled out the hole a little. i can't remember what size drill i used, but i didn't go nuts. i enlarged the hole by a fraction of a mm around the outside, because i know that a small change in diameter results in a large change in flow, because it's not a linear relationship.
i went back outside, installed it, and everything ran fine. no more lag, and i was able to tune the boosted fuel curve by taking a few more (like 3 or 4 turns out of the bleed valve instead of 1 or 2) turns out of the bleed valve. at this point i called it a day.
#105179, "RE: S-FMU lag....restrictor mod?" In response to Reply # 6
Quote >Any idea on the knock when I'm warming the car up?<check for exhaust leaks. especially at your manifold where it seals to the head.
mmmm...ok...I've retorqued my manifold like 3 times already and some of the studs have been lose and I have had an exhaust leak there I can see carbon on my head. I hope I haven't warped my mani;(but why would an exhaust leak cause knock?
#105180, "RE: S-FMU lag....restrictor mod?" In response to Reply # 7
its not a knock per say, but a small exhuast leak makes a tapping noise that may sound like knock...i know when i blow off my egr solenoid when running 18psi, it always worries me, b/c the eaxhuast leak sounds a lot like my spun bearing sounded before it went completely.
a lot of our cars have noisy lifters as well during warm-up that cause a loud tappin-type noise
#105182, "RE: S-FMU lag....restrictor mod?" In response to Reply # 9
If your exh mani bolts were ever loose to the point you could hear the leak for more than a few days, chances are it's warped. Just go have it resurfaced.
Before I went to threadlocking in RRE's 4g63 manifold stud set I was having problems with the bolts backing out and warping the HRC manifold.
It's been resurfaced twice now, and RRE says I "need a new manifold, otherwise it'll just keep warping." I'll keep running it as long as I can hold boost though...
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