Nissan ECU Tuning

cb_drift · Joined: 04 May 2004 Posts: 472 Location: New Zealand

been having a discussion with a friend and we cant figure out the way to set the fuel pressure reg correctly

say you have installed a set of injectors that are 550cc at 2.5bar fuel pressure

do you set the reg to 2.5bar with the vac/boost line connected or not?

eg - to get 550cc at 2.5bar - is that 2.5bar with the air line connected to the reg when the car is idling - or 2.5bar with the air line disconnected from the reg when the car is idling...

seeing as the regulator will drop fuel pressure on vac and add fuel pressure under boost i was thinking set the fuel pressure to the rating needed as a base and let the air line change things as needed after that - but a friend recons its set the other way...

anyone got a definative answer for me please? no guesses - i want to know the most accurate way to set the fuel pressure reg to get the rated flow from the injectors at their suggested fuel pressure....

also - assuming that you have a sufficently flowing regulator - would there be any downside to oversizing the fuel pump specs by lots (eg fitting a 500lph @ 5bar fuel pump to a car that used to have a 200lph @ 3bar fuel pump) ignoring the examples overkill of course Smile

cheers and happy new year Smile

lawrence

luk · Joined: 11 Jun 2004 Posts: 93

oops · Joined: 02 Jul 2004 Posts: 100

Hi as luk says, you need to find out if this 2.5 bar is at a particular intake manifold pressure or the pressure differential.

eg, a stock GTiR has the fuel pressure test @ 2.94 bar without vac'... so one would assume one atmosphere (1000 m bar) so when vac' line connected and engine idle, intake pressure at "roughly" 400-500m bar gives a fuel pressure of 2.5 bar. and a difference of 2

engine idle intake 400-500 m bar @ 2.5 bar fuel pressure = 2 bar difference.
engine WOT ( natuarlly aspirated ) intake 1000 m bar @ 3 bar fuel pressure = 2 bar difference.
engine on boost at (atmosphere + 1 bar) @ 4 bar fuel pressure = 2 bar difference

Fitting an uprated fuel pump (more LPH) just ensures the rail doesn't starve when the injectors try to empty it.

Regards..
_________________
changed my user name

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

I suppose a related topic is variable FPR like the BEGI unit. My bro picked up one cheap online and put it on his vg30 turbo modded car.

According to BEGI, you dial in the fuel pressure with no vacuum or boost first. This actually sets the 'crossover' fuel pressure (when the car goes from no-boost to boost). You can then set the 'ramp-up' rate as boost kicks in, pressure is increased. Reattaching the vacuum brings the car to idle fuel pressure.

This crossover fuel pressure should be stronger than stock. How much stronger depends on the car's technology. If its a turbo-modified car with a throttle position pot, then it should be higher. If its a car like a vg30 that relys mostly on MAF, then not as rich.

What happens with this variable fuel pressure approach is that the ecu goes open-loop and adjusts the PWM on the injectors under the assumption of a 'constant' fuel pressure. What really happens is that the ecu is tricked out and flows much more fuel in relation to the boost signal to the BEGI unit.

The overall effect is that the car will run very nicely closed loop with smallish injectors and becomes a fuel fed turbo car under boost (the extra fuel pressure makes them flow more). There are limitations of course. Fuel pump output and too small injectors, etc.

An interesting thing is that IF the actual running fuel pressure under FULL vacuum is slightly lower than stock, the car's own closed loop ecu O2 feedback will increase the injectors PWM and also set the open-loop values higher. This is from the adaptive control scheme that most ecus use. So this is an added bonus that can be achieved. Of course, you can not set the fuel pressure that low.

datsunboy · Joined: 26 Jul 2005 Posts: 209 Location: New Zealand

I think I would prefer my FPR to rise at a constant rate, so that the injectors are going to flow exactly the same rate the whole time.
this would make it far easier to tune your fuel maps for.
because as the others have said, the ECU assumes a constant rate of supply of the fuel.
one that operates in a fashion that you described, would be good if you werent going to try tune your fuel maps...and only rely on the FPR to give it the extra fuel needed on boost
_________________
1970 Datsun 1600 CA18DET Project

The point of life is not 2 arrive at your grave all preserved & in mint condition, but 2 slide in sideways, scratched & bruised screaming F**K WHAT A RIDE!!

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

datsunboy · Joined: 26 Jul 2005 Posts: 209 Location: New Zealand

ANY adjustable FPR can make smaller injectors flow more.

from your previous post, I thought you were saying that the BEGI FPR would increase fuel pressure to different amounts accross the range unlike a normal FPR that would keep a constant ( raised ) Fuel pressure.

it was this statment
"The overall effect is that the car will run very nicely closed loop with smallish injectors and becomes a fuel fed turbo car under boost (the extra fuel pressure makes them flow more). There are limitations of course. Fuel pump output and too small injectors, etc."

that made me think you were saying it would flow normally in closed loop, and then run heaps more fuel needed for extra boost higher up. ( meaning not constant ).

you should always Tune your fuel and timing maps if you are changing anything like the Fuel pressure, you should at very least adjust your k value to suit the higher fuel rate so the ECU still knows how much fuel it is ACTUALLY putting in.
Using a wideband 02 is the best method
_________________
1970 Datsun 1600 CA18DET Project

The point of life is not 2 arrive at your grave all preserved & in mint condition, but 2 slide in sideways, scratched & bruised screaming F**K WHAT A RIDE!!

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

ANY adjustable FPR can make smaller injectors flow more.

Not for an adaptive ECU under certain conditions.

If you have a adjustable FPR (not a rising rate), and increase the fuel pressure from 30 psi to 33 psi, the adaptive control would sense this.

It senses this by the O2 signal feedback. The O2 signals will 'tell' the ecu it is too rich and it will back off PWM accordingly to bring the stoichio condition around for closed loop conditions.

But the ecu also takes that information and applys it to open loop condition. The gain value is adaptively computated from closed loop conditions.

In other words, the ecu can null out an increase in fuel pressure (within its limits). So the statement that ANY adjustable FPR can make smaller injectors flow more would be for a non-adaptive ecu only.

What the BEGI RRFPR neatly does is NOT mess with the closed loop conditions and ONLY increases fuel pressure during open-loop. It effectively works with the ecu maintaining desirable things like economy and drivability, starting, etc but allows small injectors to really open up under boost conditions. It actually is a closed loop device itself since boost feedback is driving it.

The adaptive ecu is self tuning to a degree. It can adjust itself for things like variations in injector size, fuel pressure, etc. But how much is the main concern.

300zx 84-89 ecus have a built in feedback system for the operator. By reading the LEDs on the ecu, you can tell if the mixture mode is being held closed loop. Anyone with these year cars should know how to read these LED modes. People with earlier Z cars should consider retrofitting the ecus, etc from these cars to their cars. If I had a 280zx for example, I would adapt a 300zx NA ecu.

raddy · Joined: 29 Nov 2005 Posts: 95

For example, in ca18det ECU we succesfully used raised fuel pressure to move out from lean mixtrure, ca18det ECU is not adaptive (at least it is not in closed loop).
This ECU does not sense raised fuel pressure, so you can push more fuel from small injectors at top end and avoid lean mixture. Of course, it will overfuel at lower rpm band than.

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

Most every ecu with O2 sensor feedback and PWM on the injectors is adaptive to some extant. The CA18det would be adaptive. The ecu does not sense fuel pressure but just O2 signals and therefore mixture ratio. It modifies the PWM on the injectors accordingly.

From closed loop operation, it then sets the open loop parameters.

How much did you raise the fuel pressure? If its too much an increase, it may be beyond the ecu's ability to adjust to it.

raddy · Joined: 29 Nov 2005 Posts: 95

It was raised by 3psi in one case, just to make correct AF at top end (out of O2 feedback). you can find more topics about this at www.sxoc.uk.

Can you say what kind of (additive) maps in ECU is responsible for this corrections in open loop?

Thanks

luk · Joined: 11 Jun 2004 Posts: 93

K-value should be adjusted if your fuel pressure is revised.

E.g.

370cc@3bar

if you raise the fuel pressure to 4 bar the injectors will flow more.

_____________RP
Square root----------- x SF
_____________SP

RP= Revised pressure
SP= Standard pressure
SF= static flow

3bar = 43.5 psi
4bar = 58 psi

______________58
square root of ------- = 1.15 x 370 = 425.5
_____________43.5

So the new injector flow will be aprox. 425cc…adjust your k-value for your new flow rate.

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

If you raise the fuel pressure by 3 psi on a 37 psi system, the ecu should be able to adjust the PWM on the injectors so that O2 signals match the expected stoichiometric ratio. This is closed loop control

But this will also have an effect on open loop control. The ecu 'knows' that the injector PWM was changed during closed loop control and will modify open loop PWM accordingly. During open loop, when the ecu is basically just using feed-forward info (the MAF output), it will sense the air and inject the fuel as it has already set by using closed loop control.

luk · Joined: 11 Jun 2004 Posts: 93

whats the point in rasing fuel pressure 3 psi?

Lew_ecu · Joined: 05 Feb 2006 Posts: 17

If someone raised FP from 37 to 40 psi, then that would correspond to SQRT(40/37)=4% enrichment