first off, here is his setup: star stage 2, built block, 30lb injectors, Vortech FMU with 8:1 disk, SAFC, Missing link. ok, here is his problem. when you first hitthe gas in his car, it runs lean, almost to the point it feels like fuel cut without the bucking back and forth. you can watch the boost gauge build, but the car doesnt go anywhere, then about 2 seconds later, the A/F gauge smacks .93-.95 and the car ROCKETS forward like it just hit nitrous. when its falling on its face when the gas is first mashed, you can see the lean condition via the digital A/F gauge.its like the car waits,waits,waits, then BAM, fuel to match the boost and it takes off. if you gently "roll" on the throttle, like in 3rd gear, it doesnt fall on its face as bad, but you can see it still runs lean for a few seconds while building boost, then it hits .94 and off we go. can you guys give em some ideas on what to check? he doesnt have a FP gauge, no $$$ right now. i wouldnt think its the fuel pump, id expect it to run out of steam on the top end if anythng, and thats NOT the case, it pulls hard once its past the little lean condition. anyone ever had the regular vortech FMU stick on them or have trouble building fuel pressure? could it be a bad MAP sensor? this problem really has him down cause the car is running great other than this. oh, by the way, he does NOT have the fuel pump rewire done, could this cause it you think? thanks guys for any help/ideas.




www.TeamKLR.com
1997 Silver RS
12.3@118mph,20psi, race gas(drag radials)
Wiseco 10.5 Pistons
Eagle Rods
Started as a manufactured turbo kit, now its a custom one!
Greddy Exhaust
440cc Injectors

Waiting on the EVOlution!

I'd throw a fuel pressure gauge on it and see what it's doing. My guess is something is goofy with the Vortech FMU.

i don't really know much about the S-FMU (because i don't have one), but isn't there some type of crazy thing where you insert a harder spring into the unit to facilitate a faster rising rate? put a mechanical fuel pressure gauge (i've certinly had adventures with my crappy hahn fuel pressure gauge in the cabin with a little fuel hose running up from the engine bay leaking gas EVERYWHERE) in there somewhere, and find out what your fuel pressure is doing. datalogging your short term and long term fuel trims can't hurt either. or even better, get a nice eletrical fuel pressure gauge although they are kind of expensive.

and your friend hasn't done the fuel pump rewire? so he's running an aftermarket high pressure fuel pump on the stock wiring? that's BAD... the stock wiring is designed to support the eletrical needs of our cheesy stock "fish tank" pump until about 47 psi with a little over 190 cc/min fuel rate, so it would never be able to support the eletrical drain of an aftermarket fuel pump needed to run boost.

so to recap:
1. get a fuel pressure gauge (they're like $40 for a nice one, stick it on the FPR) and figure out what your friend's fuel pressure regulator is doing in that time where it's excessively lean
2. datalog to double check things
3. rewire the fuel pump as soon as possible

anyways, good luck with getting it fixed. should be a nice stage 2 beast when you're done!

Ill be re-wiring his fuel pump today or tomorrow...but get this... i got over to his house this morning, and we were talking about the possible causes of this problem. he mentioned to me that it seems the "lean condition" starts when ever the throttle % hits the point that it passes the low-throttle setting, like say you have low set for 35% and Hi set for 55%, the lean condition seems to start when the throttle % gets to 35%, and then it works through it. so knowing this, i went out to the car, took all the low and Hi settings back down to 0, and went for a drive. now of course it runs pig rich now, almost pegging 1.0 on the A/F gauge, but i didnt notice any of the lean condition happening. FP and boost seemed to build accordingly. i didnt hook his SAFC up, and i didnt tune it for him, some other shop did. the settings before were: Lo-throttle-1k= -10%, and went down 1% for every 1k rpm after that. on the Hi-throttle setting, it was leaned down all the way to -20% in the 4500rpm range, and -19% on each side of it...does this seem a little lean for 30lb injectors? in any case, we are going to re-wire the fuel pump when we have time, and try to re-tune it. it the problem persists, ill take the FMU apart and see if anything looks amiss. anymore ideas are welcome.




www.TeamKLR.com
1997 Silver RS
12.3@118mph,20psi, race gas(drag radials)
Wiseco 10.5 Pistons
Eagle Rods
Started as a manufactured turbo kit, now its a custom one!
Vortech FMU
Greddy Exhaust
440cc Injectors

Waiting on the EVOlution!

you need to datalog it, with safc values that crazy your getting timing advance probably which is killing him. The Safc should only be used for minor fuel adjustments. Im guessing the timing advance is your problem.

I used to run a SFMU and I have the same problem. I think the car is runing to rich in closed loop so it adjusts the fuel trim, take fuel away. Making it run lean. Then you punch it and the car goes into open loop, no fuel is adjusted and you get all the fuel you need. This is just my theory. Let me back it up a little. Once I switched out my disk to the 2.75" (lower rate) disk I no longer got the lean spot. The fuel pressure would rise nice and the A/F would stay nice and rich. Now I didn't have a S-AFC, so you can tune a little more with that. I would replace the fuel filter as well. You will be suprised how bad they get.

Another possible scenario is that the High throttle fuel trim is too lean. I think with 30 Lb. injectors, it should be less than -20%. I would try something like -10% right around 3500-4000 rpm's. If that is too rich, then just increase fuel by 1-2% with each WOT run to see egt and O2 readings.

When I used to run the S-AFC setup, I experienced the exact same problem, and it was due to a lean fuel condition at WOT and during the transition into boost (and between shifts). I also set the Lo throttle to zero, and actually richened up the fuel delivery from 2-3000 rpms by something like +5 to +15% (in Lo throttle) Somehow, it helped.

Fly1, you were exactly right. richened it up, and there isnt anymore problems. he is gonna get a SFMU next, and just use the SAFC to fine tune things, probably only as far as -5%. thanks for your help guys.



www.TeamKLR.com
1997 Silver RS
12.3@118mph,20psi, race gas(drag radials)
Wiseco 10.5 Pistons
Eagle Rods
Started as a manufactured turbo kit, now its a custom one!
Greddy Exhaust
440cc Injectors

Waiting on the EVOlution!