? about boost cut and z32 maf PLEASE HELP =)

[racemydatsun]

Hi

i have a question for the nico CA18DET guys,

say i had a stock maf on the car and it would boost cut at, lets say 15psi and the airflow reading on my safc said 97%. Its obviously cutting because my airflow signal to the ecu is high right?

now i put a Z32 maf on the car and i changed the whole sensor in and out setting to spec 2in 7out..........NOW at 15 psi im only reading 49% airflow on my safc but still boost cutting?

whats the deal? are there other variables that makes the ecu go into boost cut ?

i know im getting enough fuel (460cc) i have a hks gt2510 turboroad tuned by me just on safc and backed off timing ( of course using a aem wideband) afrs are around 11.2:1

can anyone help?

[r34 gtr]

Does it matter what RPM you are at? Or is it completely engine speed independent?

[float_6969]

Just to clarify, if you turn the boost down to say, 12psi, it won't cut out?

[racemydatsun]

Does it matter what RPM you are at? Or is it completely engine speed independent?

it only happens when it hits 15-16 psi..... I can make it hit the cut at any rpm where its capable of that manifold pressure manifold pressure/ airflow reading

[racemydatsun]

Just to clarify, if you turn the boost down to say, 12psi, it won't cut out?

yep 12-13 psi and all is good, but im aiming for more power

[racemydatsun]

i mean the boost cut is totally airflow dependant right? or am i wrong?

[r34 gtr]

You may have to chip the ecu.... I'm curious though, how does the ecu know the manifold pressure? It uses a hot wire MAF setup, not a pressure sensor. I mean, its dumb as hell, as far as computers go. Do you still have any of that boost control solenoid crap hooked up?

I'm sorry I'm not much help, I've been part of the stand alone crowd for a while now.

[racemydatsun]

You may have to chip the ecu.... I'm curious though, how does the ecu know the manifold pressure? It uses a hot wire MAF setup, not a pressure sensor. I mean, its dumb as hell, as far as computers go. Do you still have any of that boost control solenoid crap hooked up?

I'm sorry I'm not much help, I've been part of the stand alone crowd for a while now.

its ok, thanks for the input though! im so confused . no boost solenoid stuff just straight mbc from turbo to wastegate.

the computer doesnt have any idea of manifold pressure at all. im wondering if its just reading airflow for the boost cut purposes, it always cuts at the same airflow capacity reading of 49% which im guessing is my equivelant of my 15-16psi

[racemydatsun]

any other takers?

[float_6969]

Wait, maybe this isn't a boost cut at all, but an ignition blowout.

How are plugs? Have you looked at them recently? What brand of plugs are they? Coil Packs in good condition? Do you have a spare ignitor you could try? What about grounds? Are you sure they're all hooked up? Do you have the main ground from the battery tray to the intake manifold hooked up? Try adding more grounds.

[racemydatsun]

Wait, maybe this isn't a boost cut at all, but an ignition blowout.

How are plugs? Have you looked at them recently? What brand of plugs are they? Coil Packs in good condition? Do you have a spare ignitor you could try? What about grounds? Are you sure they're all hooked up? Do you have the main ground from the battery tray to the intake manifold hooked up? Try adding more grounds.

brand new bcr8 ngk plugs gapped down to .028this motor is in a datsun 510 so maybe i need more grounds i have the battery ground directly to the engine, then from there a 2 gauge cable grounded to the body, ignitor is grounded also. i will def. add more grounds though

im stumped

i was planning on getting a chipped ecu to remove boost cut, but it doesnt make any sense to purchase it if the ecu is only seeing an airflow of about 50% of capacity. my biggest question on the fuel cut part is if there are any other things that the ecu reads that can cause the cut

[float_6969]

Nope, it's based purely on the signal from the MAFS. IIRC, if the voltage exceeds about 4.5v, the ECU cuts timing/fuel.

[racemydatsun]

ok so since i swapped mafs to a n62......i should theoretically be able to boost up to whatever this thing maxxes out at (or close to it which is what?..... around 500 wheel or so)

so maybe i should factor that part out, and focus more so on the ignition part of this. what else should i be looking for? is there any way to upgrade the coil packs? will one of those MSD ford dis coils work if i figure out the wiring?

i want to thank youo guys for the help also!

[RS12Turbo]

Any updates on this? I'm experiencing the same symptoms....my ca maf was maxing out at 99.6% @13-14psi. Swapped over to a n62 maf today, and the same thing, except now it'll cut at 46% at 13psi....afr's are mid 11's. My next step will be to add dsm 450's and see if that helps, which in your case it sounds like it didn't. My boost control solinoid crap is still hooked up....not the vac lines, but the harness is still hooked up to it....does that matter?I'm wondering if it may be a boost leak...I sprayed some starter fluid around the throttle body coupler, and the idle raised slightly for a few secs. I tightened down the t-bolt clamp, but didn't re-spray it or drive it...so not sure if that was it...i'll find out tomorrow.

[zmannz]

I had a similar issue in my rb20, when the motor isn't warmed up enough I can get this same symptom under WOT at about 5000 rpm. I replaced my coils two a time with known good units and no change. I then changed them all out, still no change. So, I changed ignitor and nothing. .003" closer spark gap on the same plugs fixed it. I think my issue was with the car runing too rich and having deposits while it was cold.

[RS12Turbo]

when it was running rich, what were your afr's at? I lowered my spark gap too....no change

[Ca_Silvia]

brand new bcr8 ngk plugs gapped down to .028

Try some 7's

[RS12Turbo]

just ordered a new set of copper 7's.....damn this is annoying. I thought I might of taken care of it.....I started thinking it might of been a boost leak...I sprayed all of the intercooler couplers with starter fluid....when i sprayed the tb coupler, the idle rpms went up some for a few secs. Re-seated the coupler and took it for a drive.....and did 4 runs...without it cutting out! afm was at 43% and my boost was around 16.5. No problems in all gears for those 4 runs. Then the cut-out came back a little bit later.....so now i'm back to square 1. Hopefully the new plugs gapped down will do it. If not, next step will be throw in the 450's

[zmannz]

I was running between 10.0-10.4 ish at first, had no choice but to cut the fuel pressure til I chipped it so at 35 psi I got it up above 11:1 under wot at 10 psi. It always ran pretty close to 13.8 under cruising conditions in those states. Now I have my cruising afr's right around 14.7 until I hit boost but I also run maf and map via piggybacked megasquirt so I'm special lol. I had knock issues once but no more blowout since I fixed up my fueling with first the chip and now chipped ecu and piggyback. I run 93 octane all the time btw.