Fuel Pressure Problem.

[The Dan]

Does anyone know if this car actually runs a dropping resistor for the fuel pump? Not every car has one so I think it would be good to check.

I think what was said before about boost rising and fuel pressure not rising with it is a fair call and I think the problem you will find is the factory FPR is not really up to the task.

When more pressure is present in the manifold, the fuel pressure needs to increase with it. If you keep rail pressure at 52psi when it should be around 65 psi, it's only ever going to do one thing....go lean. The manifold pressure acting against the injector is equal to the equivalent amount of fuel pressure drop.

This means you are basically doing the same thing as reducing the fuel pressure by 13psi

Your injectors probably have enough scope to handle a small increase but I'm guessing at 13psi it's probably a little too much.

Do as suggested with a return style system or find out another way to increase pressure in the system

[Harey]

Does anyone know if this car actually runs a dropping resistor for the fuel pump? Not every car has one so I think it would be good to check.

I think what was said before about boost rising and fuel pressure not rising with it is a fair call and I think the problem you will find is the factory FPR is not really up to the task.

When more pressure is present in the manifold, the fuel pressure needs to increase with it. If you keep rail pressure at 52psi when it should be around 65 psi, it's only ever going to do one thing....go lean. The manifold pressure acting against the injector is equal to the equivalent amount of fuel pressure drop.

This means you are basically doing the same thing as reducing the fuel pressure by 13psi

Your injectors probably have enough scope to handle a small increase but I'm guessing at 13psi it's probably a little too much.

Do as suggested with a return style system or find out another way to increase pressure in the system

Why cant you tune it out? Even if he runs it on 10psi, its still the tune making it run properly. The tune doesnt care if theres 39psi, 52psi or 65psi as long as its the same as when its tuned.

[R31Nismoid]

Tune what out?

Lack of fuel is lack of fuel. No tuning can stop it if you need more.

[Harey]

Not having enough fuel pressure in the rail seems dodgy.

If I wanted to feel comfortable driving the car hard and wanted to know the setup was solid, id do things properly.

440 injectors for 220HP is heaps. I think changing injectors out is masking the real problem of a weak fuel system.

It aint good to run shit on the limit, especially fuel.

Braise a fitting on the end of the rail, run a Sard reg, and run an extra line to the rear for the return. Also hard wire the pump. Ditch the Walbro and go 040. Piss easy.

Who said there is not enough fuel pressure in the rail? We are saying there is less than if it didnt have a turbo on it. 39psi is only a bit less less than 3 bar. Injectors are flow rated at 3 bar of fuel pressure so its hardly a "dodgy" fuel pressure.

I agree with hard wiring the fuel pump, but converting it into a return fuel system is a big job and from the sound of it not something the owner is prepared to do.

2 things to do turbo_xtrail: check the fuel pressure and the fuel pump voltage under load.

Have you read about the kennebell boost a pump? http://www.kennebell.net/accessories/boost.../boostapump.htm

I am not necessarily saying to get one, but it does show you how important the voltage to the fuel pump is.

[Harey]

Tune what out?

Lack of fuel is lack of fuel. No tuning can stop it if you need more.

The way I read Elite Racing's post was that because the fuel pressure was dropping with boost that it couldnt run properly. Yes it is not ideal to have the fuel pressure dropping but when tuning you just add more fuel in to compensate (as long as the fuel system can handle it). Yes there is a fuel supply issue here which tuning cannot replace.

[Harey]

In the 30 odd so of boosted Gen3 and 4 I've tuned I've never had an issue up to 350rwkw and 10Psi of boost using the std 1 one way fuel system - they do however have injector flow scaliing vs injector pressure drop. There is no reason to swap to a return system you have an aftermarket ECU - just tune around its not like the ems has any brains anyway. There should be no reason to assume fueling wont be consistant.

The things I would be checking is whether or there is a fuel pump controller. It maybe PWM if the std ecu is still controlling the fuel pump side of things.

Exactly, this is a perfect example.

[StealthX]

Hold on guys, I'm still not sure whats going on.

Cos theoretically, the injectors aren't maxing out (ive already checked the duty cycle, and they done go over 70% even under 10-12psi of boost.) and the fuel pressure is probably only dipping under 40psi witch is HEAPS to still supply a decent amount of fuel with the appropriate pulse width.

So which brings me to the question, why didn't my tuner Andrew just increase the pulse width of the injectors? (i.e. add more fuel in)

I gotta clear this up before I go searching for any more resolutions, there must've been another problem that he picked up that I didn't understand.

Correct me if I'm wrong, but if there's a good 20% of duty cycle to play with, surely regardless of the pressure (assuming its not ridiculously low), there's room for more fuel to go in right?

[rob82]

Hold on guys, I'm still not sure whats going on.

Cos theoretically, the injectors aren't maxing out (ive already checked the duty cycle, and they done go over 70% even under 10-12psi of boost.) and the fuel pressure is probably only dipping under 40psi witch is HEAPS to still supply a decent amount of fuel with the appropriate pulse width.

So which brings me to the question, why didn't my tuner Andrew just increase the pulse width of the injectors? (i.e. add more fuel in)

I gotta clear this up before I go searching for any more resolutions, there must've been another problem that he picked up that I didn't understand.

Correct me if I'm wrong, but if there's a good 20% of duty cycle to play with, surely regardless of the pressure (assuming its not ridiculously low), there's room for more fuel to go in right?

I would find out how much the fuel pressure is dropping a couple of psi I wouldn't be too concerned. If that's the case just add a bit more injector duty. I don't think anybody has said it but your injector flow rate increases withvacuum and decreases with boost as well.

[zebra]

Lets not forget that the increase in fuel pressure under boost also helps to atomize the fuel.

Im also certain the EMS stinger runs muti-point injection (all injectors at once) so running big duty cycles will probably cause issues with fuel pooling on the port walls, and giving strange AFRs, I think the best bet would be to run as much pressure as you can and minimum injector pulse / duty cycle.

To try and avoid big globs of fuel sitting on the top of the valves

[Harey]

Hold on guys, I'm still not sure whats going on.

Cos theoretically, the injectors aren't maxing out (ive already checked the duty cycle, and they done go over 70% even under 10-12psi of boost.) and the fuel pressure is probably only dipping under 40psi witch is HEAPS to still supply a decent amount of fuel with the appropriate pulse width.

So which brings me to the question, why didn't my tuner Andrew just increase the pulse width of the injectors? (i.e. add more fuel in)

I gotta clear this up before I go searching for any more resolutions, there must've been another problem that he picked up that I didn't understand.

Correct me if I'm wrong, but if there's a good 20% of duty cycle to play with, surely regardless of the pressure (assuming its not ridiculously low), there's room for more fuel to go in right?

Yeah I think this thread has stalled till you find out some more info.

[The Dan]

Hold on guys, I'm still not sure whats going on.

Cos theoretically, the injectors aren't maxing out (ive already checked the duty cycle, and they done go over 70% even under 10-12psi of boost.) and the fuel pressure is probably only dipping under 40psi witch is HEAPS to still supply a decent amount of fuel with the appropriate pulse width.

So which brings me to the question, why didn't my tuner Andrew just increase the pulse width of the injectors? (i.e. add more fuel in)

I gotta clear this up before I go searching for any more resolutions, there must've been another problem that he picked up that I didn't understand.

Correct me if I'm wrong, but if there's a good 20% of duty cycle to play with, surely regardless of the pressure (assuming its not ridiculously low), there's room for more fuel to go in right?

The reason is probably because he added fuel to compensate but because the pressure is dropping, he would have to add the rest of the injector duty and it still wouldn't do anything. The fact is, it doesn't matter how much you tell the injector to open and close, it will only deliver the amount of fuel according to the pressure behind it, and if you reduce that pressure, not only does the injector move below it's opearting pressure (and sometimes cease to even open properly at all) but it also messes up the spray pattern. Don't forget - unburnt fuel will also show up lean in your mixtures

[Harey]

The reason is probably because he added fuel to compensate but because the pressure is dropping, he would have to add the rest of the injector duty and it still wouldn't do anything. The fact is, it doesn't matter how much you tell the injector to open and close, it will only deliver the amount of fuel according to the pressure behind it, and if you reduce that pressure, not only does the injector move below it's opearting pressure (and sometimes cease to even open properly at all) but it also messes up the spray pattern. Don't forget - unburnt fuel will also show up lean in your mixtures

I think turbo_xtrail needs to find out from his tuner if this is the case. I wouldnt have thought a few psi below 3 bar would be this severe.

Would be great to hear what fuel pressure is in the rail under load as well.

[StealthX]

Ok I've had some people on the other forums (in the US) tell me that the tune is very dogey. Yeah it moves around a bit, but never pings and is safe as houses.

Andrew has had years of experience tuning cars in motorsport etc, I doubt his tune would be 'dogey'

Also I doubt he wouldn't have let something slip if it was potentially dangerous, he would've tried to fix up the AFRs if there was something wrong.

with those A:FRs, do I have anything to worry about?

[Harey]

I think the afrs are fine. 12.5 at redline is fine imo.

One way you could have a chat with him without accusing him of a bad tune is just to say "hey just wondering if I wanted to improve my fuel system without going to a return system, what would be the first thing to do?"

Its quite easy to put a fuel pressure guage just before the fuel rail. For a test I used longer fuel lines and poked it out of the bonnet so that I could see the fuel pressure guage around the wipers while I was driving That way I could see the pressure at WOT.

[StealthX]

Yeah i'd still like to clean it up though.

I still can't see why he would've left the tune like that, cos even if the fuel pressure starts to drop, you can still add more fuel and compensate! Thus i would have richer (less lean i should say) A:FRs...

Dunno what the limiting factor was.

In the mean time, the car is savage. I see 150km/h wayy too quickly, haadrly feels a struggle at all. Soo much torque, i rekon its making an easy 500nm of torque!

But its never goo to run things on the edge of their limit...

[StealthX]

Hey guys, After a bit of researching and such, I've figured out that my problem will be the stock pressure regulation system. The only thing I can suggest is that the x-trail's system is different to a sentra's hence why you guys have never had a problem similar to this!

I'm gonna go with a Aeromotive or Tomei FPR I think...

Ok so here's the thing, I've been talking to a guy who has an X-Trail GT. A GT has an SR20VET 206kw (280hp) from stock, and his has 254kw at all four wheels (ahh bout 340awhp) on 18psi with an aftermarket turbo, modified everything...

The stock GT fuel system is the same returnless system as our QRs run. He said to quench his GT's thirst, he converted to a return system, but without touching the fuel rail.

He put an FPR in the feed line, so everything from the line to the rail, is pressurised. So in other words what hes done is put a boost referenced FPR in the position of the stock one, i.e. under the back seat, then ran a return line to the tank... (I don't think it was literally in the place of the stock one, cos the boost line would be laggy as f**k, but its on the FEED side of the system...)

My question is how would i go about installing the FPR? The stock lines are rubbery plastic and don't seam to be very easy to just attach with hose barbs, how have you return guys attached the FPR to the stock lines!?? Do i have to go full braided etc??

Thanks!