Rb25 leaning out over 10psi

[94typem]

I changed my fuel pump to a walbro 255 and ever since then it wont run over 10psi without leaning out really bad (17 on my aem wideband) i have no idea what to do to fix it. Do i get a adjustable fpr and crank up the fuel pressure or run a new ground to the pump or both? I need my car ready for some upcoming events and stck boost just wont cut it.

[nick-nismo]

firstly i would hardwire that fuel pump via relay, there's tons of info floating around on how to do it.

playing with fuel pressure is never a good idea, make sure the vac line is hooked up to the stock FPR, also take it off and run engine and check for fuel comming out of nipple on frp. that would mean its broken

[Voodoo_ChildR32]

X2 on the hardware. My GTR would just stall out dead in traffic until I hard wired. Haven't had an issue in almost a year now. Chalk it up to crappy Nissan wiring and old age.


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[BenOswald]

Stock fuel pump will handle 12-14 psi no problem. Put it back in and see if it fixes it

[amnash]

Stock fuel pump will handle 12-14 psi no problem. Put it back in and see if it fixes it

old pump with old wiring wont fix it, but if hard wired like everyone else mentioned that would probably work fine. would have hardwired the oem pump first before getting a new pump

edit: can use any relay, and if you have one of those green nissan relays laying around they work fine. its what i used

[Skym]

Aftermarket fuel pump needs 13.5 volts vs factory 10-12 volts. It's common for voltage to drop to 10 volts (drops fuel pressure) at higher boost levels and engine to run lean.

If fuel pressure drops enough the boost in intake manifold can make it hard for fuel to exit injectors, so that's why peak fuel pressure (with vacuum hose removed) has to be equal or slightly higher than boost level you are running. At idle the vacuum helps to suck fuel out of injectors, so that's why FPR drops fuel pressure via using vacuum hose to FPR.

If fuel pressure is low, check hoses for leaks, check fuel filter for blockage (check fuel pressure). Also hard wire fuel pump, as mentioned above.

[94typem]

so i got around to hard wiring the fuel pump and now it doesnt lean out under high boost anymore but it still backfires and shoots huge clouds of fuel out the back and surges aswell. if you get into it slowly you can make about 11psi before it starts backfiring and spitting but if you just mash into it right away is backfires and and stuff wuth the a/f staying betweet 10.8 and 11.2 im so confused with this thing. Also the CAS has to be fully advanced for it to even want to boost stock psi of you set the cas in the middle it just start bucking and backfiring. the timing belt is on perfect so i have no idea what to do anymore

[SlidingSideways]

What injectors are you running?

[Skym]

Bigger lph fuelpump + stock FPR (small orifice inside) raises fuel rail pressure that pushes more fuel through stock injectors when they open more at mid to high rpm, which makes engine run richer (into 10's). To solve this you have to close injectors (ECU retune).

Also the stock o2 sensor when clogged (due to engine running rich) can be slower to react thus make engine run richer for longer at lower rpm, pop flames from exhaust. So this sensor will need to be replaced once ECU tune is fixed. Can unplug o2 sensor to stop engine running too rich, but check A/F ratio afterwards to make sure engine is not running lean. ECU goes into open loop which ignores o2 sensor input (closed loop is when o2sensor is looked at) when o2 sensor is unplugged.

Can use a modified Z32 ECU, Z32 MAF, Z32 MAF plug, Nistune to do this on a smaller budget. Link or ViPEC ECU (fits into stock ECU casing) with Mac boost control solenoid if can afford those ECU's. They are MAP ECU's (no MAF).

Stock fuel pump is 135lph (same lph as stock fuel pump on R32 GTS-T) and aftermarket fuelpump can be 255 lph when give it 13.5 volts.

[94typem]

The car has stock injectors. If i only go 3/4 throttle it pulls hard with no problems and gets up to 12.8 psi but if i go WOT it starts backfireing and bucking right away.

[Skym]

ECU would be using the richest part of fuel map. Also check sparkplug gap (stock is 1.1mm, which is the "-11" and should be 0.8mm to stop missing at higher rpm), heat range (should be one heat range colder / PFR7A if A/F ratio is leaned out or stock PFR6A heatrange if engine is running too rich). Stock is NGK PFR6A-11 (I think same sparkplug as used on stock RB26).

[cozmosland]

if your on stock ecu wouldnt this be rich and retard. or basically boost cut. mine does it at 11-12 psi and above 4000rpm just starts bucking due to the afm not like the added air and then return to normal from 6-7k

[Skym]

Knock maps. Ignition timing is retarded to 0 degrees on knock ignition map, so engine should stop accelerating.

Boost cut is when MAF maxes out (stops ECU running off the side of fuel, ignition maps). This can happen with an intake airleak just before MAF due to clamp on to adaptor type of airfilter setup. Bolt on podfilter to MAF solves this problem (Apexi or similar podfilter).

If happening around 4000rpm, could be feeling the VVT switch over (creates a V shape in dyno graph plot for torque, power), boost maps switch over (low to high boost level). If ECU detect's knock it should switch to the knock boost duty maps, knock ignition map, knock fuel map, etc.

Without connecting Nistune to ECU and datalogging ignition timing, etc, hard to say if it's pulling ignition timing.

[Romdoc1]

Did you ever get this issue sorted out?

[94typem]

No im still fighting with it