RB25: hesitation @ ~5500rpm

[maxgohan]

so, when i go WOT, at around 5500 rpm i get a hesitation and it feels like fuel cut...
almost like the torque curve drops

what could cause this ?
o2 sensor??

mods:
-turbo back straight exhaust
-FMIC
-Neo RB25 turbo

thanks in advance guys!

[godzillarb]

What kind of spark plugs are you running and what is the gap? Sounds like spark blow out to me, assuming the tune is fine.

Did you upgrade the fuel pump? If stock, you could be running out of fuel. Do you have an adjustable fuel pressure regulator?

[EvoVIII808]

+1 on spark plugs.

[maxgohan]

stock ECU so no tune,
i should check my spark plugs, good idea, haven't checked mine yet (recommendations on some? and gap for them?)

i am on stock fuel as well, should i upgrade the pump and FPR?

edit: my car comes stock with rb25 (c34 laurel)

[Sileighty_85]

uhhh yeah guy you need a bigger fuel pump to accommodate a boosted 6 cylinder, why would you think a NA 120hp fuel pump would be enough for a 250hp I-6?

plugs need to be heat range of 7 gapped at .028-.030

[89JDM240sx]

^ agreed.... Cooper plugs are good to... Upgrade your pump and a Z32 fuel filter if you haven't already

[wrgibson]

Are you still running the OEM coilpacks?

I had the exact same problem with my car. It was the coilpacks. They are a known to have problems. I bet if you replace them your problem will go away. I got my SuperSpark coilpacks from Ricky @ Raw Brokerage....he will get you set up.

[Tantwoforty]

my money is on fuel pump. OEM coil packs work just fine unless they are cracked and bad.
Walbro and a z filter and you should be cool.
Be careful making it choke like that, your prolly leaning out and you could very easily damage your engine.

[dubzy]

If it's a hesitation, my money is on the spark plugs.

Now if it feels like a drop off, or a limiter, then its more than likely it's your fuel system. (Fuel pump, FPR, or the lines)

I had a similar problem, but I'm running 550 injectors and an aftermarket fuel pump. However we experienced this on the dyno and could see the gauge on the FPR drop. I ended up having to run dual fuel pumps which was the cheapest fix in my scenario

[Darius]

I will bet all of my money that it is not the spark plugs. It is almost NEVER an issue on RBs in stock form regardless of gap.

The OP said he has a stock KA fuel pump. Obviously, it is going to run out of steam under WOT on an engine that makes 2/3 more power in stock form.

If the issue is still there after you bring the fuel pump up to par, then it is likely the coilpacks that are going bad. You can coat them with silicone, flexane, or replace them. I would put LS2's in if you have an excuse to do so.

I have a supra tt fuel pump for sale if you want it. $150 shipped. PM me. :)

[Tantwoforty]

I have a supra tt fuel pump for sale if you want it. $150 shipped. PM me. :)

but a walbro is like $100 brand new with a install kit
http://www.frsport.com/Walbro-High-Flow-Fuel-Pump-Kit-for-1989-1994-Nissan-240SX-S13_p_1216.html

[maxgohan]

alright guys,

it is the stock fuel pump however my car comes equipped with an rb25 from the factory (c34 laurel)

still think it could be fuel pump?

[Darius]

but a walbro is like $100 brand new with a install kit
Walbro High Flow Fuel Pump Kit for 1989-1994 Nissan 240SX S13 (http://www.frsport.com/Walbro-High-Flow-Fuel-Pump-Kit-for-1989-1994-Nissan-240SX-S13_p_1216.html)

If you want a noisy & sketchy pump, then save the $50 and get a walbro. Personally, I wouldn't choose to run one.

OP, yes. You need to swap out your KA fuel pump regardless if your engine is stock or not. The pressure created by full boost is too great for the pump to produce the flow needed by the RB at WOT. Is the ECU pulling timing because it is likely seeing knock. If you want to keep that motor in one piece, stay out of boost until you can change out the fuel pump.

[maxgohan]

ok let me clarify,

the car comes equipped with an rb25 from the factory, so it has a factory rb25 fuel pump....

[bllabong89]

Lol. The fuel pump should be ok for the time being since it's FACTORY. Lol. I would replace the plugs and check the coil packs and if that doesn't fix it, I would personally install a fpr and check the pressure.

But you should start with the parts that cost pennies at first. No reason to buy a bunch of expensive parts for it to end up being something cheap. Good luck

[Darius]

LOL! I thought you meant the engine came from a laurel! hahahaha The pump should be fine but could be wearing out, but that's doubtful. Usually they just crap out and that's it.

If it breaks up but still keeps intermittently firing at WOT, then I would check coilpacks. They can be reinsulated with silicone or just buy new ones.

If it falls flat on its face at WOT, I'd look at what the fuel pressure is doing. In another recent thread, the vacuum line came off of the FPR.

[Jez]

Had the same problem with my RB20 when I first got my Skyline, close the plug gap down to 0.7mm and I bet you'll be sorted.

[Sileighty_85]

I will bet all of my money that it is not the spark plugs. It is almost NEVER an issue on RBs in stock form regardless of gap.


interesting, my RB25 wold not boost past .5 bar due to the plugs gapped at .040 and having the spark blown out. closed them down to .028 problem went away