Spirit-RE

iTrader: (25)

Hey i did a bunch of research and i couldnt find much for this. My problem is this: In 1st and 2nd gear my car pulls good, but in 3rd around 4-5k it coughs a bit, in 4th it studders at about 4500 or so but then pulls past it and will run fine. and then in 5th gear it will not go past 4000 at all. Im learning alot about the rotorys and from what I know I would guess its running lean but why?
Its a 87 turbo II w/ these engine mods: exhast, intake, series 5 turbo, ported wastegate, street ported, and a SAFC. the SAFC was 'tuned' when i got it and I changed some things in it which helped, and then I had a tuner tune it and it helped a little bit but not much. btw it dynoed at 245hp on 12psi so could this be to much for the stock fuel system? but what I cant figure out is why it only does it in the higher gears. any help would be greatly apreciated

g14novak

iTrader: (1)

Do you have a wideband? What A/F ratios are you showing when your running it at 4k in 5th gear?

Spirit-RE

iTrader: (25)

NO. but we tried adjusting the fuel up at those rpms, which would help in that gear we were tuning on, but then it would either go lean or real rich at those rpms after a minute or so of driving. If I change anything in the SAFC now it will either lean cut or fuel cut

need-a-t2

iTrader: (9)

stupid question, but i have to cover the bases. i'm assuming you have a FCD of some sort if your running 12psi?

did you upgrade your intercooler?

I'm guessing your leaning out. your turbo becomes terribly inefficient over 10psi or so, thus causing your intake temps to sky rocket. your ECU is trying to compensate by dumping more fuel in, but without any fuel upgrades your over running the duty cycle on your injectors, causing your lean condition

this would explane why you are getting power loss when you are. 1st and 2nd gear, you alost never build max boost (beacuse boost is dependent on engine load, not RPMs). however, 3rd and on you easily can. I HIGHLY recommend turning down the boost to 10 psi MAX until you can get access to a wideband or upgrade your fuel system.

since your new to rotaries i'll let you in on the widley known fact that rotaries are prone to seal failure under detonation conditions....which from the sounds of it is exactly what your doing...

RotaryRocket88

iTrader: (7)

SAFC or not, there's no doubt you're running lean. About 5 years ago I blew a motor running 10-11 psi w/ a FCD and stock fuel system. Bad information and being too boost happy will cost you. Bring it down under 10 psi, then get some fuel upgrades.

I can also tell you that I never had the power breakup at all at those pressures. It may just be due to how you have tuned it though.

Spirit-RE

iTrader: (25)

yeah i forgot to mention the fcd. No, its the stock top mount. I always heard that the stock turbos were good for 12psi though. but It makes sense now why it does it in the higher gears. thanks

RotaryRocket88

iTrader: (7)

The turbo is good for 12 psi. It's the fuel system that isn't.

Spirit-RE

iTrader: (25)

Ic. thanks for the help guys

need-a-t2

iTrader: (9)

Im going to disagree. yes, the turbo will output 12psi, but it's way outside of it's efficiency envelope. this is why he's running out of fuel. the turbo is creating more heat at 12psi than anything, superheating the air. the stock intercooler isn't that great, so it can't reduce the temperature to a decent temp, so the ECU is dumping in fuel trying to cool the intake charge down to avoid pre-detonation. the larger air flow in combination with the extra fuel usage to cool the intake charge is overrunning the injector duty cycle causing a lean condition, causing the power surges.

my theory...