Right when i get into boost it instantly leans out to the point of detetonation.
ive replaced/checked…
injectors (replaced with known good)
fmu (3x tried: 10:1, 6:1, 12:1)
fuel pump (255 walbro intank)
fuel filter
o2 sensor
fuel pressure good(55psi)
timing is retarded
6 MAP check valves
fmu is plumbed up correctly and no CEL
map sensor
cap/rotor/plugs @ .028
internal coil
Spiral core wires
ive searched and searched and im really lost 
this problem has transcended two complete motors
because its a really shitty fuel management setup, the injectors are maxing out, they can only squirt so much fuel, you need larger injectors, and at least the hack if not a chipped ecu and a free rom program like turboedit or uberdata
i realized an fmu isnt the best route to go, but irregardless, NO injector would max out the SECOND(2psi) it would go into boost. If i cant get enough fuel to the injectors now, why would i rewire for 450’s?
for as little boost as im running, and fmu will do fine.
I agree that you should try bigger injectors.
I have 450cc injectors…No FMU…No Missing Link…Running with CROME tunning. No problem here…Get bigger injectors…And I would toss the FMU.
It may be possible that your Walboro 255 pump is not working as it should…Is it an Inline or In Tank?..If it is an InTank, check connection…If it is an InLine, then you will have to remove the inTank OEM Fuel Pump for better flow.
are you sure you are leaning out? you may have your vacuum lines backwards and the engine is hesitating or bogging, or something odd like that, double check everything in your vacuum system, make sure there are no leaks and everything is connected properly.
Well its really wierd, the second it touches boost it instantly falls flat on its face and starts popping and backfiring. Its almost like all the injectors are shutting off. At 1lb, the crappy a/f gauge jumps from stoich to lean INSTANTLY.Its just like something flips a switch?!
I DO realize that an fmu is a poor way to manage fuel, but it SHOULD NOT lean out to detotation at 1psi! I have good fuel pressure but i cant make the fmu work at an idle for obvious reasons…
First off, ditch that narrowband guage and use a wideband to see if it’s really going lean. Those things are worthless. And are you sure that it’s detonating? Popping and backfiring is different from detonation. What are your plugs gapped at? Is your base timing set properly? It sounds more to me like an ignition problem rather than fuel.
The plugs are gapped to .04 and the timing is retarded 5deg +/-. The car runs perfect all the way to redline AS LONG AS the charge pipe is dissconnected… thats why i think a sensor is reacting boost or something odd that wouldnt throw a CEL.
this problem is at any rpm, irregardless of throttle position(1/4throttle or full), it happens right when it makes the transition from vac to boost.
thanks alot for the help so far!
i think i saw somewhere to gap the plugs to .028
Tune it with a wideband, a narrowband is ueless.
Get some fresh plugs and narrow the gap
Get some fresh stranded plug wires
I had a similar problem when I put mine together and MSD stranded wires did the trick.
i will tune up my ignition when i get home. What i dont understand is why would an ignition problem be boost dependant?
i guarantee it is your map sensor seeing boost. check all of your vacuum lines, when i first bolted up my turbo i had the EXACT same problem, as soon as it hits boost bam… its sputtered and falls flat like there is something holding it back, and it is its the map sensor telling the computer to cut the fuel, my fix was my map sensor vacuum line was swapped for one of the others dont remember exactly which. hope it helps
I never thought about the MAP sensor, but that’s a possibility now that you have me thinking about it.
The reason that it could be your ignition and there’s only problem in boost is because you need a stronger spark when the engine is under boost. On my first tuning run I had the plugs gapped at stock spec still. Although it wasn’t as bad as your problem, as soon as I hit full boost (10psi) above 4500rpm it would misfire real bad. The engine would still rev, but the car would fall flat on it’s face and misfire, sputter, pop, and all sorts of other noises. I put a timing light on it and the distributor was way out of time. I fixed that and I gradually brought the gap down and was finally all set at .028.
ok guys, i changed…
-cap
-rotor
-regapped plugs from .044 to .032
-ignition coil (why not)
the problem has moved to 5psi!!! Im freakin happy! Were finally heading in the right direction. Any more ideas? Close the gap more?
Get some new NGK plugs and plug wires, and gap the new plugs down to .028.
ok new wires and plugs set to .028
no change
Hmm…It’s hard to tell you much more unless you get a wideband on it and see what your AFR is.
i replaced the map sensor with a known good one. No change
Like I said, get a wideband on it and see what your AFR is when you go into boost and when it cuts out on you. There’s nothing else I can really tell you without that.