Fuel pressure problem

[Doctor G]

Having a fuel pressure issue.

Installed a walbro pump and a gotech. The gotech fires in batch. All 4 injectors simultaneously on every stroke.

Now, the APFR shows that the system isn't holding the fuel pressure when the pump is off. Or after it primes for that matter. The pressure drops back to 0 within about 5 seconds. AFAIK the walbro has a check valve and the pressure is supposed to be held for quite some time. (days even)

I have the AFPR set at 3.7 bar and when just the fuel pump is running, it holds 3.7bar perfectly. But, while the car is running, the gauge jumps around like crazy. More or less around the 2.5-3 bar mark, and gets less as the car revs up. I take it in part it's because the 4 injectors firing constantly depressurise the rail quickly.

Any ideas? I checked and can't see any air leaks in the system.

[Sokar]

Having a fuel pressure issue.

Installed a walbro pump and a gotech. The gotech fires in batch. All 4 injectors simultaneously on every stroke.

Now, the APFR shows that the system isn't holding the fuel pressure when the pump is off. Or after it primes for that matter. The pressure drops back to 0 within about 5 seconds. AFAIK the walbro has a check valve and the pressure is supposed to be held for quite some time. (days even)

I have the AFPR set at 3.7 bar and when just the fuel pump is running, it holds 3.7bar perfectly. But, while the car is running, the gauge jumps around like crazy. More or less around the 2.5-3 bar mark, and gets less as the car revs up. I take it in part it's because the 4 injectors firing constantly depressurise the rail quickly.

Any ideas? I checked and can't see any air leaks in the system.

Why all 4 at once? Why not the 2 "corresponding" cyls like wasted spark, its makes the calculations alot easier?

Unless you have 8 cyls.....

[Doctor G]

Sokar I'm using the Mini-x and need the other injector output for something else.

But I can run it to 1&4 and 2&3, although I don't think that will solve my fuel pressure problem much. My main issue is why the system isn't holding the pressure. Once that's sorted I'll consider changing the injection setup.

I believe it makes no difference to performance whatsoever, and fuel economy wise it can hardly be noticed. A lot of dictators run like this too.

[RAW]

Sokar I'm using the Mini-x and need the other injector output for something else.

But I can run it to 1&4 and 2&3, although I don't think that will solve my fuel pressure problem much. My main issue is why the system isn't holding the pressure. Once that's sorted I'll consider changing the injection setup.

I believe it makes no difference to performance whatsoever, and fuel economy wise it can hardly be noticed. A lot of dictators run like this too.

1. Your regulator is poked, more than likely from the massive reversion in the fuel rail, you would need at least 10mm ID fuel lines and 15 to 20mm ID fuel rail to dampen that form of simultaneous pressure drop.

2. Running single batch injection on a multi cylinder motor is about 1/2 as effective as a carburetor

3. It causes one cylinder to fire on the back of just closed valve, one half way threw, one to early and one at the right time, doesn’t take a rocket scientist to work out this will cause different power levels on different cylinders... this will cause reliability problems, poor fuel economy, reduced performance ectr.

I believe it makes no difference to performance whatsoever, and fuel economy wise it can hardly be noticed. A lot of dictators run like this too.

unfortunatly you were lied to.

[Hennie Marais]

oi, 4 at once. try fitting a large pulse damper on it, it might help a little. That's the main reason I don't like the mini-x.

[Doctor G]

1. Your regulator is poked,

This is what I'm thiking after some research. Where can I buy another AFPR with a gauge on it? I see them at Autostyle but not sure if I can trust them.

more than likely from the massive reversion in the fuel rail,

I think it's just the way it is. Cause it's brand new and wasn't holding the pressure even before I fired up the gotech for the first time.

2. Running single batch injection on a multi cylinder motor is about 1/2 as effective as a carburetor

3. It causes one cylinder to fire on the back of just closed valve, one half way threw, one to early and one at the right time, doesn’t take a rocket scientist to work out this will cause different power levels on different cylinders... this will cause reliability problems, poor fuel economy, reduced performance ectr.

Please explain some more. The way I understand it 4 injectors pulse together, but the spark is only thrown on 1 cylinder at a time. So although the fuel is sprayed behind closed valves on other cylinders etc, only the fuel in the correct cylinder is ignited.


If it's really such a bad idea I can rewire the injector setup to inject on 1&4 and 2&4 together. I must just check up on the TDC reference required for that mode.

[Doctor G]

oi, 4 at once. try fitting a large pulse damper on it, it might help a little. That's the main reason I don't like the mini-x.

Yeah last time round I ran an overcomplicated XMS on my n/a setup and it was a huge waste of money, time and worst of all there was no one to tune it.

So this time I decided to go with the simplest system that can still do the job well. And must have a big tuning fan base.
I didn't need too many outputs, so I opted for the mini-x. Pro-x would have been nice I guess. Cause the features I kinda miss on the mini-x is the fuel pump output, radiator fan output and tachometer output. Nothing that can't be worked around, but it's extra work.

[RAW]

Please explain some more. The way I understand it 4 injectors pulse together, but the spark is only thrown on 1 cylinder at a time. So although the fuel is sprayed behind closed valves on other cylinders etc, only the fuel in the correct cylinder is ignited.

Think of how a motor works, a carburetor'd car draws the air fuel into the chamber, it draws it in as the intake valve opens obviously...

Fuel injection (proper fuel injection) usualy the injector fires about 2-3ms before the intake valve starts to open, that way the fuel front just reaches the valve as its opening to draw the fuel into the combustion chamber.

By doing it batched youll have one cylinder working close to right, the rest will fire at the back of a closed valve, the one that is the furthest away from opening will just puddle on the valve and port walls totaly killing any form of atomization... this is usualy most evident at lower RPM.

This is the reason all new cars are sequential not single batch,,, even dual batch is a massive improvment but still far from running sequential, granted most tuners here probably dont have the ability or will to actualy take the time to tune fuel timing if they used ecu's with this ability.

[Doctor G]

even dual batch is a massive improvment

But is the improvement worth the extra R3k and some additional installation costs?

Even though the Gotech Pro has full sequential, I doubt most people use it like you said. Does the Nissan dizzy have the TDC pickup/reference required by those modes?

I'm using an aluminium crank pulley, so 60-2 isn't really an option for me, unless I bolt the pickup wheel to the pulley, and I don't want to drill/tap into the pulley. Also, I'll need coil packs from say a hunday or a ford. That's another R1.5k at least.

So I cannot justify spending R5k + on the Gotech pro at this stage for my N/A 4 cylinder motor. For the S13 I'd get it in a flash though.

[RAW]

But is the improvement worth the extra R3k and some additional installation costs?

All up to you, I know I personaly want the best performance and fuel economy out of my car not to mention reliability and drivability, thus I use the best ECU's available... ECU makes all the difference in a car, when tuned right.

Even though the Gotech Pro has full sequential, I doubt most people use it like you said. Does the Nissan dizzy have the TDC pickup/reference required by those modes?

Nissan tend to use very hard core trigger wheels

[/quote]

[Doctor G]

But is the improvement worth the extra R3k and some additional installation costs?

All up to you, I know I personaly want the best performance and fuel economy out of my car not to mention reliability and drivability, thus I use the best ECU's available... ECU makes all the difference in a car, when tuned right.

I get that. But are we talking 2% better performance & economy, or 10%?

Even though the Gotech Pro has full sequential, I doubt most people use it like you said. Does the Nissan dizzy have the TDC pickup/reference required by those modes?

Nissan tend to use very hard core trigger wheels

[/quote]

The nissan 8pin dizzy has 2x GND, 2x12v+, 1x1deg or 360deg pickup, 1x180deg pickup, 1xresistor (I presume converted to a tacho output by the ecu?) and 1xcoil trigger. Can any of these pickups be used as a TDC ref? Cause without a TDC ref, they will just wire up the Gotech Pro to fire single batch, or dual batch at best.

[rat]

Sorry for the hi jack but kinda on topic.

should you change the std FPR when you get a new pump?

[Doctor G]

I took the AFPR off my sabre and connected it on the S13, between the Fuel filter and the fuel rail. The S13 still has it's OEM FPR in place.

The AFPR is set to around 50psi. After priming, the pressure drops back to 20psi, and then slooooooowlly drops to around 5-10psi after 30mins or so.

Now, does this mean the OEM FPR on the S13 is holding the pressure, and that the AFPR is in fact stuffed?

[smoothedgp]

hey guys had the same problem,it turned out to be the feed pipe from the pump to the bracket where the feed goes.i instaled a better pipe and the problem was sorted.hope that helps.now my gauge is on crack tho it jumps up and down...huh?

[Doctor G]

hey guys had the same problem,it turned out to be the feed pipe from the pump to the bracket where the feed goes.

You referring to the pipe inside the tank from the fuel pump to the housing? What exactly was wrong with it?

now my gauge is on crack tho it jumps up and down...huh?

You running an AFPR with a guage? What make is it?