Greddy @6psi /w Stumbling issues maybe ?
 

ok heres the info on my car and the problems.

Greddy kit /w starion intercooler.
1.8L injectors ~256cc
Stock fuel pump, /w stock ecu
Begi 2025 FMU, rising rate needle turned all the way out.
TurboXS mbc
FM 2.5" single tip exhaust /w 2" test pipe
-40 psi idle pressure, @0 vaccum/boost 55psi, under full boost @3.3k rpm 74psi.
-capacity of my stock pump = 82psi (did the f/p grd jumper /w clamped return line)
-I talked to corky he said he would be sending me new valves for my fmu and also a couple restrictors for the boost/vaccum signal line.

ok so with all that information heres my situation.

i've been messing with the manuel boost controller and since i just installed an ACT heavy duty clutch with a fidanza flywheel i figured i should b able to push the boost past 6psi with no clutch slipping issues.

So once i begin to turn the mbc up past 6 psi i get nasty boost spikes then it leveling out around 10 psi. but once i reach around 5.5k rpm + my car begins to loose rpms and gain them in rapid succession. maybe stuttering or something ? also i hear alot of popping coming from the exhaust (maybe excess fuel making it out near the hot exhaust tip or something ?)

So without a piggyback or anything what do you guys think the problem is ? maybe malfunctioning mbc that allows for spikes in actuating of the wastegate ?

Thanks again
Scott

it could be the MBC, the spring may not be able to support more tension after 6psi, but definately sounds like fuel cut... i'm not speaking from personal experience but when we were tunning my friends protege we noticed this same problem, our easy fix was to add more fuel delivery to different parameters... it worked for us like a charm, no spikes, no stutters...

i have been planning on installing a walbro soon. what should my target fuel pressure to the rail under boost @8psi be with that set up 256cc injectors and all ?

Scott

74 psi of fuel pressure will not support the boost you are trying to run.

Assuming a base pressure of ~50psi at 0 psi of boost and 6psi of fuel per psi of boost after that (as a general guideline, not hard numbers) you should be somewhere in the ballpark of 86psi of fuel needed (actually a little less since you have slightly bigger injectors) at 6psi but even more if you are getting boost spikes. Also, which boost gauge are you running as sometimes they can be off by 1-2psi so if you are running 7-8psi of boost, you would need even more fuel.

Each setup is slightly different, but I'd imagine that you'd need somewhere in the ballpark of 80psi of fuel pressure with the larger injectors for the 6psi you are currently running and somewhere in the ballpark of 90psi for 8psi.

Also, did you have the 1.8 injectors cleaned before you put them in? A bad injector could do this as well. Injectors that have been sitting outside the car for a period of time tend to get gunked up.

you're running out of fuel. Sounds exactly what Brad's car did when his pump would cause a drop in fuel pressure. It would almost feel like a rev limiter with a muffled "pop pop pop" out of the tailpipe.

yea i think those are very diagnostic conditions the pop pop pop sound, ill keep you guys posted when i get a walbro installed.

i actually didn't get the injectors cleaned up before installing them brgracer. maybe i should when i decided to bet the walbro.

hey i also had another question maybe related but maybe not. how is your fuel economy ? ever since i installed the 1.8L injectors i really havn't been getting good fuel economy. i used to get like 25mi/gallon even driving in the city but no i get like 18/20 mi/gallon although i have been boosting more often since im in LA for a couple weeks....

I still get 25-27 with 305cc injectors. always got the same with the 1.8Ls. Most likely the tune.

tuning with the afm possibly ? i may be picking up a lc1 soon to data log onto my laptop. unfortunately no rpm vs afr available on the lc1 so maybe need to get one of those rpm signal things.

no need.