Nismo FPR = Flooded engine

[MarusGTR]

Okay, so what the hell?

Long story short I wanted to adjust my fuel pressure and bought a Nismo FPR, drove the car into the garage and installed it today. First adjusted with ignition at around 34-36psi, as I thought ignition pressure would be the same as idle I attemped to crank it to see if idle would match. Engine wouldn't start, no ignition spark. I then realized that ignition pressure should be WOT pressure, 43, and turns down to 36 with vacuum during idle (duh).

So I raised the pressure to 44 and tried turning her over. No ignition. After a few ECU resets I took the no.1 plug and its drenched in fuel.

So whats next? Take the plugs off and let the engine vent or try to put a flame in the chamber to burn the excess? Moreover, what caused the flooding in the first place? Was the pressure too low at that first start?

[gtrjon]

when my aem fpr failed it flooded all cylinders. we pulled all the plugs and cranked it with no spark and it shot 3 foot gysers of fuel out of each cylinder. we would crank a few rotations then pause and repeat til most of the fuel was out. then try out cylinder with cloth for excess and put in some new plugs and it should fire right up

[MarusGTR]

Most of the pistons heads were dry, with the exception of very moist no.1 and no.6, and no.3 had unburnt gasses (smokey haze). All plugs were fouled so yeah I'll be grabbing new ones (if I can in this shithole, I had bought 6 of the last 8 at my NAPA) to replace those I put in 3 weeks and drove 15m to park the car waiting for the nismo FPR from Japan which was backordered. And I'll probably need an oilchange.

Anyway thanks for the input, I'll see what I'll be able to do tomorrow.

As for the FPR, like I said its brand new. Took the vacuum line out to check for leaks, its dry, so the FPR diagphram holds -some- pressure and its not dumping into my vacuum lines. I guess being such an idiot the first pressure I set in ignition was too low for proper ignition and all the tries after that was in fact, beating a dead horse. Funny, considering I had put a goddamn reference line on the hat to even check for warping when securing the adjustor screw (people on the internet seem to hulk the thing and spin the hat and rip the diagphram in the process.)

EDIT: So yeah, TL: DR: What caused the flooding? Too low pressure at that first startup?

[MarusGTR]

Tried 44psi on dried up engine, still flooding. I'm at a loss, any ideas?

[Bruizer]

Man, I think my base pressure is like 25psi without vacuum (pretty sure you had to set pressure without vacuum, disconnected hose)... If your plugs are NOT copper, they are garbage after fouling. My car wouldn't start above 35 psi (not running, no vacuum when set)

[MarusGTR]

They're copper, BKRs. I cleaned them with brake cleaner and compressed air before trying them on again, as suggested by NGK.

Basically the FSM calls for 43psi at atmosphere, 36psi under vacuum. So this means (and the FSM confirms) that 43psi is expected to be in the line at ignition-on (no vacuum, lines are at atmosphere). I first was a mongaloid and set 32-34 at ignition on (should have been 43) but because I figured my gauge had a check valve I could only set by increasing pressure. The caveat was that I had left the vacuum line on so pressure probably dropped in the 20s (I think the FPR maxes at 23-25?) as the engine was creating vaccum.

Anyway now I have the FPR with vacuum line on set at 42 psi, still no ignition.

Its maybe worth of note that I had forgotten to plug one of the grounds next to the FPR (the closest, next to the intake temp sensor which I had unplugged too) as I tried my first pressure blip. I noticed pretty rapidly as the fuel pump wouldn't prime with that ground off. Maybe I burnt something? SOL in any case I have no clue what to do.

PS: Should the ignition-on pressure be taken during priming (I see high 50s maybe 60s when set at 42psi) or when static (42psi)?

PPS: I've just realized that if I do have a check valve, how come I can see 42 psi after the initial prime...

[Dakota_gsx]

not exactly helping op but its a funny story.
My 2g dsm had a shitty chinese afpr on it when I bought it, and the rubber lining inside to separate fuel from air had cracked. The vacuum sucked about 10L of gas out of the lines, and into the cylinders, turbo, and intercooler. Fuel shot about 15 feet out of the cylinders when we cranked it over with no plugs in lol.

[collector240sx]

Hi Marc,

I know your scratching your mind wondering what's happening. But lets step back and go back to the basic.

You need fuel and SPARK, you're saying the fuel is getting there ''flooding''. But did you make sure that you're getting any spark.
If you do get spark, is the spark strong enough.

If it's like you said and you're not getting ANY spark, I would check to make sure all your grounds are good and clean.
When you've made sure you got good spark them I would start looking at the fuelling.

Just my 2 cents man. Wish I was closer.
On a side note got the RB25 started in the 240sx (did have to rewire the ECC relay so it would saved the Power FC setting)
Haven't got the time to get the exhaust on it yet, but it's driveable Will let you know if or when I have time to start tuning it.

[MarusGTR]

Cleaned up engine and plugs again, turned down the pressure to around 30psi surge 20 static, still no ignition. BUT the starting changed pace (not the speed) but there's a flat spot where it seems like its trying to start.

EDIT: Faced with another flooding I put the old FPR on and checked the pressure:

50psi surge
36psi static

Basically, here's a little background, I wanted to adjust my 50psi (ding ding) idle fuel pressure (OEM FPR) with the Nismo FPR down to the OEM 43psi, as I surmised it was the cause of my last two years of overfueling. So, for posterity's sake, you have to set the fuel pressure in the 2-5 second surge window, and not the static pressure.

Now that this has been established, what now? Put new plugs in, set the nismo FPR and hope for the best? ...Again?

PS: I think the static pressure of 36psi and the OEM idle (with vacuum) pressure of 36psi is merely a coincidence and of no consequence.

[Skym]

Fuel pressure is lower at idle because engine is helping in sucking fuel (engine is under vacuum) out of injectors.

When engine transistions to boost there's no vacuum, so FPR valve closes and gives the full 42.6psi. Also when engine is under boost the boost / pressure inside intake manifold actually makes it harder for fuel to exit injectors, so fuel pressure has to be equal or slightly higher than boost pressure to make sure fuel exist's the injectors. Stock FPR should be 1:1 (fuel:air) or basically equal amount of air to fuel. That's why you never drop fuel pressure on a boosted injected engine to remove fuel, should take fuel out via ECU tune (proper way).

Before starting engine there's no vacuum to FPR, so you should see similar fuel pressure as to what you would see under boost.

Stock fuel pressure should be around 35.5psi at idle with vacuum hose connected and 7.1psi higher with vacuum hose disconnected.

Also if you have different size injectors, it might affect fuel pressure when injectors open. Someone has posted posted charts on here in the past showing injector size vs fuel pressure. Also I think there's a formula for this (would have to ask a tuner).

Then there's higher boost levels, which might require more fuel pressure to keep the 1:1.

I have heard of some adjustable FPR's not giving enough fuel pressure and removing vacuum hose to FPR makes it work.

[MarusGTR]

Fuel pressure is lower at idle because engine is helping in sucking fuel (engine is under vacuum) out of injectors.

When engine transistions to boost there's no vacuum, so FPR valve closes and gives the full 42.6psi. Also when engine is under boost the boost / pressure inside intake manifold actually makes it harder for fuel to exit injectors, so fuel pressure has to be equal or slightly higher than boost pressure to make sure fuel exist's the injectors. Stock FPR should be 1:1 (fuel:air) or basically equal amount of air to fuel. That's why you never drop fuel pressure on a boosted injected engine to remove fuel, should take fuel out via ECU tune (proper way).

Yes, and I have a tune set at 11.6 AFR, but my walbro 255 paired with my OEM FPR increased the rail pressure from 43psi to 50psi in 1:1, which I surmised caused my richness; my max AFRs to touch 9.6, but usually its around low 10s. Basically the stock FPR diagphram is too narrow to regulate the additional flow of 60L (compared to OEM IIRC?). Each time my injectors open, more fuel is expelled than their duty was set for through the increase in pressure.

This theory is compounded by my closed loop AFRs which are nominal, 11 to 13s or when cruising 14.7, as the computer can cut the trim to compensate, contrarily to when boost kicks in and the ECU goes in open loop where the overfueling occurs (goes to 10s) because it cannot track the mixture appropriately.

I'll have a more winded discussion about this in my build thread.

PS: You basically repeated what I wrote in the tread in the rest of your post huh? :P Guess it'll act as a summary.

[MarusGTR]

GODDAMNIT its not starting with new plugs, I'm out of ideas **** **** **** ****.

Did I burn something by having the ground disconnected that first time I primed the pump?

In the vid you're going to notice the closeup shot of the grounds which were the only electrical-related area to be touched (and which were accidentally left unplugged the first time I primed the pump)

I'm mute in the video because I'm litterally speachless... this is two days of simply ******* the dog for something that should have taken 10 minutes.

Edit: Confirmed, no spark on cyl no.1 (not worth checking the others) What in the holy hell is going on!?

[Skym]

Yes, and I have a tune set at 11.6 AFR, but my walbro 255 paired with my OEM FPR increased the rail pressure from 43psi to 50psi in 1:1, which I surmised caused my richness; my max AFRs to touch 9.6, but usually its around low 10s. Basically the stock FPR diagphram is too narrow to regulate the additional flow of 60L (compared to OEM IIRC?). Each time my injectors open, more fuel is expelled than their duty was set for through the increase in pressure.

Yeap, there's more fuel into engine when injectors open more, when engine is under boost, due to increase in rail pressure (used as a band aid technique vs upgrading injectors). I noticed on one RB20DET, they raised rail pressure by 10psi (300lph Bosch fuel pump, 1.1-1.2bar boost) over stock to make injectors stretch another roughly 100hp from what they are rated to (270cc injectors or I think it actually was up to 276cc when flow tested).

You can drill the FPR out to make it flow more (can even drill stock FPR out to drop fuel pressure). Search for how to's, as it should mention the drill bit to use.

PS: You basically repeated what I wrote in the tread in the rest of your post huh? :P Guess it'll act as a summary.

I guess I did repeat, my bad.

Did I burn something by having the ground disconnected that first time I primed the pump?

Is that the injector loom ground or CAS loom ground????

Have you tried swapping ECU's, checking all fuses under dash, especially ignition fuse???? If there's no ground to ignition module / coilpack loom it can blow the ignition fuse (might if that is the CAS ground, as from memory is connected to ignition module in some way), hence why I'm saying to check ignition fuse under dash.

Edit: Confirmed, no spark on cyl no.1 (not worth checking the others) What in the holy hell is going on!?

That confirms my suspicions of a blown ignition fuse under dash.

Also pull CAS off (make sure you mark CAS, housing behind it with twink to reposition properly when refitting CAS and clear CAS error code on ECU afterwards) with ignition to power up the ECU, dash and turn CAS shaft. Do the injectors click (checking to see if signal gets from CAS to ECU to injectors)???

Engine won't start if CAS is not working (has a donut / electrical part inside), hence why I'm asking to do this test to confirm CAS, ECU is working and signal is going to where it should go.