Standalone & Z32 MAF in place, but still early cut-off. What gives??

[JDMSIL80]

Here's the deal:

Ive got my Apexi Power FC & Z32 MAF installed & street-tuned using wideband, A/F is relatively stable around 11.5 to 12.

So we dialed in for more boost to 9psi, but the fuel/boost cuts off at around 5000rpm.

Then we tried 10psi, and the cut off came even sooner at 4800.

Basically, the higher boost we go, the lower the cut off becomes. Only at 7psi that I am allow to rev pass 6000.

Im using Blitz EBC to controll boost, not the optional Apexi boost control kit.

According to the Power FC instruction manual, it would work as long as we set the Power FC boost to a level where fuel cut will not occur.

So we followed the instruction and adjusted the boost limit settings on the Power FC up to allow maxium of 18psi.

My MAF voltage peak value is 3V, and injectors duty cycle peaked at only 50%. So Im far from hitting the MAF reading ceiling and max injectors duty.

Now what other causes can you think of that may cause this problem??

FYI, here's my mod list:

Power FC + CommanderZ32 MAF444cc injectorsGT28RBlitz ID-color boost controllerBlitz gauges (pres, EGT, boost)FMICTubular manifold3" turbo backHKS filter

[Florida240sx]

What is your spark plug gap?

[JDMSIL80]

Im running NGK spark plugs PFR6A-11 from the box as is, do I need to have them gapped??

[sdtouge]

i think you should be running some of the 7s or whatever for your setup.

not sure though, and i dont think thatwould cuase the cut out but i dont know too much about tunning and all that.

[c-rad]

Fuel cut happens because of maf overrun. Something is up with your maf, maf settings, or a boost leak...

[JDMSIL80]

I just put in new spark plugs today, there are:

PFR5B-11B (thats from a 1990-1996 300zx twinturbo)

I can boost slightly higher now at 9psi, but boosting any higher and the fuel/boost will cut off.

However, the cut-out seem to happen later now at higher revs (6000 vs 5000), but the problem is still there.

Im certain there is no boost leak, and the MAF settings is fine. What other factors can you guys think of?

[float_6969]

Try gapping the plugs way DOWN. If that cures the problem you are, somehow, overpowering the coilpacks.

[Akihisa]

PFR5B-11's are even hotter than the 6's. I have 7's with .8mm gap in my car.

[JDMSIL80]

Im gonna try putting copper 7's and see if it helps.

Is it necessay to gap the plugs to smaller size? What is the reason to do so because I thought stock was 1.1mm?

[JDMSIL80]

I cant seem to find the colder copper plugs here locally as no shop carries it.

However, they do have the NGK iridium plugs: BCPR7EIX-11, which is the same as this one selling on ebay: http://cgi.ebay.ca/NGK-IRIDIUM...wItem

Now I understand that Iridum plugs do not require gapping, so is it neccesary to gap them down like some of you did? What is the reason behind this? Thanks!

[Akihisa]

You still have to gap them. When you start making more power you need to adjust the gap accordinglly.

[Not_a_sr]

goto your local auto parts store, they sell normal copper plugs.

[JDMSIL80]

I talked to NGK technical support and he recommended me to put in the BCPR7EIX with (032") pregap, these are iridium plugs with heat range -7 & smaller gap than stock plugs. He also assures me these plugs would solve the cut-off problem.

So I bought the plugs and installed them just moments ago, hoping that I could finally turn the boost up.

I just came back ripping around a few blocks. Guess what, it STILL cuts out on me if I turn the boost up pass 9psi!!!

Im really lost at this point, what the heck is wrong with my car????

[float_6969]

Does it cut out at 7psi?

[JDMSIL80]

I can rev all the way to redline up to 9psi after I changed the plugs, but boosting any higher and the fuel/boost would still cut out.

Basically, the higher boost I dialed in, the sooner (lower revs) the cut off becomes.

[JDMSIL80]

The new plugs did made an improvement, I can boost up to 10psi now without cut-off. But higher boost would still cut me out eventually, but at a higher rpm than before. I can see the problem is narrowed down, because with my old plugs the highest boost I could hit was only 8psi. So my local tuner could only tune in the lower portion of the fuel map up to 8psi. We still have not touched the fuel table for higher boost because it was cutting out @4800 with the old plugs. So there might be a possibility that A/F for higher boost is not yet optimized so cut-off would occur. Do you guys think this could be the problem??

[c-rad]

Are you getting fuel cut or is your ignition just breaking up? If it feels like you hit a brick wall, its something MAF related and will have little to nothing to do with the spark plugs. And the fact that when you say you increase the boost and it hits earlier also still leads me to believe that you have a boost leak.

[JDMSIL80]

Im pretty sure there is no boost leak as the boost is stable with no peaks/spikes anywhere.

As for the MAF, Im not totally sure because I bought it from local junkyard. However, it doesn't cut out anywhere under 10psi and drives normal. Only above that boost level, the motor started to cut on me.

The cut out is both fuel/boost related, it feels like it hit a brick wall.

[JDMSIL80]

Would it be possible to have boost leak in the blow off valve??

Im running ARC BOV which has a knob for adjusting the pressure plate.

I had loosened the knob for running low boost, so it might be too loose for running high boost. Could that be the cause of boost leak??

Are you getting fuel cut or is your ignition just breaking up? If it feels like you hit a brick wall, its something MAF related and will have little to nothing to do with the spark plugs. And the fact that when you say you increase the boost and it hits earlier also still leads me to believe that you have a boost leak.

[biosehnsucht]

I never understood it specifically to be for boost levels but to adjust how much preload there is for pressure difference between the vacuum/boost source at the intake and the boost in the intake pipe, when the pressure differential overcomes the preload of the spring it opens up and vents or recircs (depending on how you have it set up) the air.. I suppose you could have a problem if venting it if you set it too loose, then it'll vent sooner, but since this is working on the case where boost in piping >>> intake I wouldn't htink it would be a problem unless you were boosting more than you could consume by a large margin (and making extra "boost" against the throttle plate - since if the boost made it to the intake mani then there'd be no diference and no vent/recirc action) ... ?

I've been having problems when cold with fuel cutouts.. like a brick wall indeed. I'm thinking maybe when its cold air + cold engine + quicker spool than stock + low revs I'm tripping the "boost limit", which Inever bothered to change.. but then I'm only running "stock" boost (i.e. whatever the WG manages w/ all my mods, I have no boost controller)

my car runs fine once warmed up, even when its cold out (in fact it runs GREAT then)

I know of one point of likely vacuum/boost leak however, which can be part of my problem, and it could just be using an old KA24E MAF, maybe when it hasn't been on long its readings are unstable somehow? I still haven't hooked up my RB20 MAF and reprogrammed..

however as I have problems only in the first few minutes after starting cold, its no show stopper..

[JDMSIL80]

After reading your post, I did a few runs with 11psi at around 5000 and actually hear flapping noise coming from the ARC BOV. So I thought maybe it was setup too loose from the beginning. I tried tightening up the tension and did a more few runs, didn't help too much in terms of the cut-off but actually got worse if I tightened it too much. But I find different loads of the BOV definitely affects the driveability of the car, can somebody give me some details in terms of BOV tunning?

Another thing I discovered last night is that if I put on the throttle gradually as boost increase, it actually allows me to run higher boost without cutting. The cut-off seems to be related if I floored the gas pedal from low rpm (2000), then it would cut me off quickly depending on the boost.

[8ggalant]

i know people here love arc jdm tyte bov's but when i was over there 3 out of 4 friends who bought them used ended up chuckin em in the trash becaue they leaked horribly..i think ive read of a few peoples on here doing the same...i dunno man...

[JDMSIL80]

Are u serious that ARC BOV is known for leaking...?!

If this is really whats happening to my BOV, is it quite possibly the cause of my cut-off problem??

Im positive that my MAF is in good shape and am running the best suited spark plugs.

Should I get a HKS SSQ BOV instead? I have only heard good things about them.

i know people here love arc jdm tyte bov's but when i was over there 3 out of 4 friends who bought them used ended up chuckin em in the trash becaue they leaked horribly..i think ive read of a few peoples on here doing the same...i dunno man...

[float_6969]

I'm kinda with 8ggalant on this one. I don't have any personal experience with them, but from hearing people talk on the boards, they seem to have problems with it.

The way to check would be to plug the BOV outlet. Go to a pool store and ask for an expandable rubber plug. Make sure you know what inside diameter of the BOV outlet is before you go. Then tell them what diameter and they should be a able to help.

I used one for MONTHS to plug the recirc opening in my S14 coldpipe. It never blew out.

[slownslurious]

I have an HKS sqv already mounted on a ca18det pipe I'll sell you cheap, it doesn't leak and I need money. Its in good working condition, I'm just not using it anymore cause I switched to an ARC.

[JDMSIL80]

Thanks for the offer! But I want to make sure whether the BOV is really the cause of the cut-off problem.

How much boost are you running and on what turbo? Do you have any leaking problem with ARC BOV?

Ive only heard good things about the HKS SSQV because it is a pull-type BOV that does not leak, why are you switching to ARC instead??

[slownslurious]

its HKS SQV not SS, and sorry I wasn't thinking I switched to a TBO valve, not ARC. TBO is more responsive.

[biosehnsucht]

The way to check would be to plug the BOV outlet. Go to a pool store and ask for an expandable rubber plug. Make sure you know what inside diameter of the BOV outlet is before you go. Then tell them what diameter and they should be a able to help.

I used one for MONTHS to plug the recirc opening in my S14 coldpipe. It never blew out.

thats exactly what I'm using for my S13 SR ARC SMIC, which has the recirc connection on the SMIC just like stock S13 SR SMIC, and is useless to me.

Been stuck in there for almost a year now w/o problems

[NeedCAforS13]

ARC's are ment to be recirculated... if yours isn't, thats a problem! Mine leaked at idle, but never on boost, so I dunno, your diaphram is probably shot. Big rubber seal thats old as hell.

Sean

[JDMSIL80]

I thought it would fine to vent the BOV open-air since I already have standalone computer??

I do not have any idling problems, so do I still NEED to run the BOV recirculated? Please explain~

My ARC does not leak at idle and low boost, thats for sure. Im gonna install a block-off plate to replace the BOV tonight. This way I can find out if it is really the ARC thats making the boost leak.

ARC's are ment to be recirculated... if yours isn't, thats a problem! Mine leaked at idle, but never on boost, so I dunno, your diaphram is probably shot. Big rubber seal thats old as hell.

Sean