rb25 studdering under boost

[perkeset]

my rb25 runs well at idle and will free rev great but under boost the car bucks and losses all power and i cannot figure it out, i have an safc2 and i have tunned it, i have an maf off of a 300zx (no i cannot put it back to stock because i dont have it) anyone who has a suggestion i would greatly apperciate it. thanks -J

[Kansei240sx]

Might also want to check for vacuum/boost leaks.

[Yellow4g63]

could be a bad coil pack too.

[Shocker]

and or fouled plugs.

[perkeset]

well we just replaced the spark pluggs and checked all the connections but if it is a bad coil pack could that acctually cause the problem?

[Kansei240sx]

yes

[BigPar]

Mine does the same thing. And you more than likely don't have a boost leak, as I don't and it still does it. Mine will buck and fall completely on its face at full throttle/boost. You have to let up off the gas, coast, and ease back into it for it to work itself out and drive it normal again. I'm going to put a FPR on it and finish my exhaust and see what it does then. One friend said I'm maxing out my MAF becuase I don't have an exhaust. Other friends says I'm lean spiking, which leads me to putting a FPR on it. But my plugs don't show signs of lean or rich. I'll figure it out one day I guess.

[gomer23]

Ya if you have a upgraded fuel pump and no FPR that is probably it. Thats what was wrong with mine, under any boost it would bog, but would drive fine otherwise. Basically it was just choking itself with fuel. Nismo FPR took care of all that.

[Sandy sx]

Hmm, upgraded fuel pump? Well, mine is doing the same thing... I mean, It WAS working pretty well for a while. But I had trouble getting it to boost over... Say, 8 psi. Anything up to there it would work pretty well.I set the boost controller to 12 psi. It HAS sucessfully made 11.5 psi. However it still seemed like I had a boost leak. The stock rb25det bov seems to be pretty good at leaking boost. Clogged up the hole in the bov, the small one and it seemed to work really well for a while also. However on my way back from georgia it seems to be breaking up real bad if I get on it. Have to moderate the throttle to keep it from falling on its face entirely. Is it possible I have the same problem and need an FPR? I'm really in the dark about this one. My boyfriend thinks it's a boost leak. It almost seems like the waste gate isn't opening, and it's not holding any boost above a certain level, i.e. :8 or 9 psi. Is it fuel starvation? I'm stumped! Help!

[BigPar]

i will let you know how mine turns out. I get my nismo FPR tomorrow.

[perkeset]

well i have found that we capped off the frp line and tuned the car with the afc and it seems to be running well, just using the afc to control the fuel flow. i still dont have an exhaust on my car so i havent driven it much but it does seem to pull very hard now and no longer has the falling on its face problem, i know its not much help but i hope that you can use it. ohh i think it is because the stock rb25 has a rising rate fpr and if you have the wrong maf it will not work well with it. well good luck let me know what you figure out.-J

[BigPar]

Whats the fuel pressure to be adjusted to using the Nismo unit?

[gomer23]

Make sure the vaccuum line is off and set it to 43.5psi.

And yes Sandy if you have a bigger fuel pump in back such as a Walbro then you will need a Nismo FPR trust me haha, I found that out real fast. Solved all my problems....well some anyway ha

[Sandy sx]

Interesting. I think I'm definately going to try that. I have another question for you. In addition to another I will ask after this one... Ehm.

For those of your with fuel gauges... What's your pressure at at full boost WOT? Mine has climbed as high as 60 psi, while ilde at approx. 40. Which seems to be correct. Correct me if I'm wrong, but the rising rate SHOULD in theory be GOOD for my engine, due to more fuel demand at higher rpm and more load, leaning out under such conditions would be pretty bad. So my question is.... How does the nismo FPR function? Does it raise fuel pressure... Slower? Or not peak as high? How does it solve the issue?

Also, I recently reset my boost back down to about 7.5 psi and the damn thing is still giving me shyte. Whats the deal? Argh!

[gomer23]

The Nismo one just handles the volume of fuel that is coming from the bigger pump (as far as I know) and allows you to adjust fuel pressure. yours seems a little high. Mine is 35psi at idle, not sure what WOT is but i dont know if it reaches 60 or not, I dont think so.

It solved my problem because the stock regulator cant handle the amount of fuel from the Walbro so when I would hit any boost it would just run SUPER rich. It bogged the car down, I could feel it boosting but the car wouldnt move any faster haha.

[Kansei240sx]

I have the Walbro 255 HP, i had a fuel pressure regulator in at 44 psi, and it ran like crap, i put the stocker back on and it ran like a dream.

When i raise boost to 12 and octane to 95 ill probably put the FPR back on, another thing is, i hate those nismo regulators unless you have a way to see how much pressure you're actually adding with an inline gauge or something. Or, scratch that, get an Aeromotive, they're awesome as hell. I wish i had one.

[gomer23]

did you have it set to 44 with the vaccum line on or off? And thats what I did I got a cheap gauge from jegs, and t-ed off the fuel line temporarily to get the pressure then took it out.

[Darius]

I'm planning on getting an aeromotive with the tap already in the regulator for a 1/8" NPT gauge fitting. That and a $17 Jeg's gauge is in my near future.

[Sandy sx]

Alright. So it just handles the amount of fuel the upgraded pump pushes through. Alright. Yeah, mine would do that, too. Spike... It spiked to 19.5 psi at one point... But like you said the car didn't move. Hahaha... -.- A shame. Oh well, it's not like the stock turbos can handle that much boost anyway.

But please if you can monitor WOT FP please let me know what you guys are getting, that'd be helpful as well. Thanks!

[gomer23]

Now that I got my pressure set I took my inline gauge out, didnt want to chance getting a leak. I was thinking i read somewhere that for every lb. of boost the fuel pressure rises 1psi....i could be wrong but it was something close to that. and I have my boost at 8psi (aftermarket turbo) so I was thinking my fuel pressure was around 51 at WOT. Like I said I am just trying to go off memory on this one.

[Sandy sx]

Hmm, that's interesting. Well if that statement holds true... Then mine should be nowhere over 50. Uhg.*cracks*I'm just going to go ... do bad stuff. Blow up stuff, kick old ladies, throw large stuff into the road next to my house... Ought to relieve some stress.

[gomer23]

Heres the link that I found that said that 1psi of boost = 1psi of fuel pressure....so your 60 sounds a bit high.

The Nismo FPR was 111 shipped for me, best 111 I have spent since I got teh car running...well more or less ha.

[Sandy sx]

Neat, where'd you get it from. Most places I found want 150 plus shipping.

[gomer23]

http://performancenissanparts.com/

[perkeset]

from that website did you order just the universal or did you get the fpr for a specific car. ohh and yes me car is doing the same thing now makes boost but doesnt go anywhere man that sucks so bad!!

[gomer23]

No you dont get the Universal one you get the other one. If you look the part number is the same on them all (except universal) then one I chose was this one 22670-RR580US NISSAN 180SX (RPS13) 1991-1998 .