camarodave98

iTrader: (2)

I just had my fast 90/90 put on my car last night. Although when doing the tune at the shop my car stops accellerating after 5000rpms and starts dropping. I was told i may need new fuel filter, new injectors and possibly new fuel pump. I have a 98 z28. Is this a common problem after install? All my fuel stuff is stock and never been changed, but Id hate to throw down $800+ for a new fuel system and it not fix the problem.

I took the car out that night and ran it hard, pulled great 1-4 then in 5th the rpms dropped as soon as i got to 5k??

Thanks for your opinions!

David

Redneck Z

iTrader: (3)

You also really need heads and a big cam to utilize that intake. It will probably feel pretty "soggy" until you do heads/cam.

BAIN

iTrader: (5)

Make sure the TB is opening all the way. The cable may be in the wrong hole.

bshell

iTrader: (24)

Did the shop monitor injector duty cycle and fuel pressure? It sounds like they did if all of their suggestions were fuel related. Have the shop give you specific #s for fuel pressure and IDC at wot so you know where to start. Given your mods, I wouldn't say you were maxing out your injectors at 5k. You are probably stressing them beyond what they should be though.

I would also respectfully disagree with the belief that the 90/90 needs heads and a big cam to realize good gains. I've witnessed two cam only cars with identical mods on the same dyno / same day. One had a 224 cam and ls6 intake, the other had a cheatr cam and fast 90 / nw 90. The 90/90 car dyno'd at 401, the other car dyno'd at 375.

camarodave98

iTrader: (2)

AF ratio was MIN:11.8 MAX:19.6

camarodave98

iTrader: (2)

would this be the problem? I was having issues with it sticking open on my way home, but the shop did not even suggest that

Redneck Z

iTrader: (3)

Check this out. This car had a hotcam and longtubes and made better power with the LS6 manifold up till 6300 rpm. You might make better peak power ~6500rpm+ with the fast, but better average and under the curve power with the LS6. It all depends on where you want to spend your time in the rev range. With a stock cam, or even the heads/cam that I have, I don't even see 6500rpm, ever.
http://www.gearchatter.com/viewtopic10974.php

camarodave98

iTrader: (2)

reguardless, i feel a difference from the ls1 i had in it, and i got the 90mm TB(i paid almost the same for my combo as a new ls6 and ported stock TB would run). And will be doing a decent size cam. But thats not the problem today, its why Im not getting fuel up top!?

oange ss

iTrader: (50)

your stock injectors should be om until the cam, i would get a fuel pump tho

SUX2BU

iTrader: (14)

check injector duty cycle and fuel pressure during a run before doing anything else.

bshell

iTrader: (24)

If this is all they used to diagnose a fueling issue, I would go back and ask them to do some runs logging IDC and fuel pressure. If your fuel supply is in working order, I really don't think you are running out of injector just yet. Did the shop do any tuning for the 90/90, or did they notice the fueling issue and stop?

You can put yourself at ease by removing the lid / MAF and having someone push on the go pedal to make sure the blade is opening fully. Does the FAST 90 TB have the dual cable setting like the NW TB (I can't remember)?

MadBill

Err.. am I the only one concered about 19.8:1 AFR? Depending on WHEN it ws so lean, this could be meltdown City! (on second thought, it's too lean to overheat; there's not much fire left at this point) Surely they can say if it was coincident with the power loss at high RPM WOT?

Redneck Z

iTrader: (3)

Your stock fuel pump and 28.6lb injectors are more than enough for your combination. You might want to make sure you don't have an injector/intake leak with that high of an AFR.