How important is fuel pressure regulator accuracy.

[68C]

Hi all, just a 'wondering about' question.

 

As I understand it the fuel pump delivers a regulated steady fuel pressure and the ECU opens the injectors for the correct time in each cell of the fuel map to deliver the required quantity of fuel.

This brings me to wonder how accurate the fuel regulator is, does varying temperature, battery/charge voltage affect it. If actual fuel pressute differs between bikes, how does this affect map sharing.

 

This is just for interest, I don't suspect a fault on my bike and don't intend to fit any magic super regulator.

[Kiwi_Roy]

Not very, at least it doesn't have to be super accurate.

Injectors run under what's known as choked flow.

[68C]

Thanks Kiwi Roy,

I know gasses flowing through an orifice 'choke' once the flow goes supersonic and that the flow will remain constant even if the supply pressure increases. Gas turbine enthusiasts will know this idea is used to off load the engine during starting and idle

I did not realise this also applies to fluids, makes sense now that the pressure is not that important.

This should not be confused with Miss Shilling's Orifice.

[fotoguzzi]

[emry]

[docc]

Shoooooot . . . . I saw Emry posted and clicked to see The Answer.

 

Aw, man, I hate it when this is the answer:   

[68C]

Somewhat off topic I know but I did'nt realise until I looked further today how relevant Miss Shilling is to a motorcycle forum. And she only lived twenty miles from me, how we live and learn.

 

http://www3.hants.gov.uk/biographies/shilling.htmy

[Lucky Phil]

Not very, at least it doesn't have to be super accurate.

Injectors run under what's known as choked flow.

Not sure where you get your info from Roy but regulation has to be pretty accurate. A friend of mine was making up new adjustable caps for the regs with a heavier spring and an adjusting screw which cranked up the pressure. I worked one day with him doing assembly and setting the pressures on the rig. He sold a lot of these to Harley guys to richen up the overall mixture so they would run properly. A cheap and effective fix as it turned out instead of remapping. The same unit fitted Ducatis as well. So you can increase the pressure to an extent ( I think from memory we were getting about 4.2 bar max out of a 3bar reg) and get the std injectors to flow more fuel and of course if the std reg is regulating low the bike will run badly as it will with a blocked fuel filter.

So the std injectors are quite capable of flowing more fuel with greater fuel pressure because generally engines arn't produced which are injector flow limited. So the injectors will usually support greater fuel flow than the maximum the engine requires in std form and usually will also be good for a modest power increase as well. When you really want a lot of extra power then you'll need bigger flow injectors or additional injectors.   

The reg has a very important role and it's critical it delivers a consistent output, this is obvious as if it didnt then production bikes would all be running differently and would require different fuel maps depending on what the regs output was. It's totally possible to swap regs between bikes or repalce a reg and the bike will fuel perfectly and thats not because fueling tollerances dont matter.

Ciao

[jchayes]

Depends on whether your bike has an O2 sensor in the exhaust...

 

The oxygen sensor in the exhaust tells the ECU how much unburned oxygen there is in the exhaust and the ECU uses that feedback to vary the amount of time the injectors stay open, i.e., adjust air/fuel ratio for optimal combustion. If the fuel pressure is high or low the ECU knows it and is able to compensate, within limits.

 

With no O2 sensor air/fuel ratio depends entirely on the regulator. (Assuming everything else is working as it should.) Fuel pressure too high, bike runs rich. Fuel pressure too low, bike runs lean. Just that simple.

[68C]

That is rather what I thought, just wondered if we are wasting our time swapping maps on non Cat bikes.

[gstallons]

The fuel pressure is important . The ecm is "mapped" for this pressure for the correct spray pattern , volume , etc. The computer decides the pulse width of the injector(s) .

[Lucky Phil]

Depends on whether your bike has an O2 sensor in the exhaust...

 

The oxygen sensor in the exhaust tells the ECU how much unburned oxygen there is in the exhaust and the ECU uses that feedback to vary the amount of time the injectors stay open, i.e., adjust air/fuel ratio for optimal combustion. If the fuel pressure is high or low the ECU knows it and is able to compensate, within limits.

 

With no O2 sensor air/fuel ratio depends entirely on the regulator. (Assuming everything else is working as it should.) Fuel pressure too high, bike runs rich. Fuel pressure too low, bike runs lean. Just that simple.

The std narrow band O2 sensor only operates in steady state operation, in other words at a constant throttle. It's is a crude device and contributes little in terms of performance, either torque or how well the engine reacts to the throttle. Many actually cause mild surging on steady state throttle. It's all about emissions. It reads the sensor and TRIMS the fuel accordingly for emissions and best ecconomy.

The ECU has absolutley no idea what the fuel pressure is and the O2 sensor isnt there to give the ECU an idea what the reg is doing it's there for the reasons outlined and also to give the ECU information it can act on in STEADY STATE operation to cover the many other variables the engine encounters during operation. It closes the loop between what the fuel map and trim tables are ordering and what the exhaust is indicating.

The important thing to re enforce though is its for steady state operation only and is basically rubbish. For usefull practical closed loop you need a fast response wide band sensor and the software to support it.

Its a long bow to draw to say the O2 sensor is there to compensate for any variation in reg pressures.

Moden systems these days the ecu actually varies the fuel pump speed to get the fuel presssure it wants and the engine needs to support the fueling requirements. These are the systems without a fuel return line. 

 

Ciao   

[emry]

While many automotive system use a pwm fuel pump with a fuel pressure sensor most motorsport products don't (none come to mind at least); even with a return-less fuel system. Instead the regulator is incorporated inside the tank and only fuel maintained at the correct pressure flows to the rail. The intake pressure sensor is used by the ECU to compensate for differences in pressure between idle and WOT by changing the injector on-time. Been standard on many Yamaha's since 2006. 

 

I have yet to see an OEM motorsport or automotive application that operates in a choked flow condition. Maybe a DI unit (haven't really studied them to be honest), but those are still a few years away for mainstream motorsports usage.

 

Modifying fuel pressure at the regulator is a very common method for supplying additional fuel in aftermarket boosted applications, normally the regulator is just referenced to manifold pressure at a 1:1 ratio.    

 

Nice quick summary of narrow band Phil!

[gstallons]

 #1 all fuel systems that are not gravity feed , require pressured fuel to reach the fuel mixing device. The fuel supply requires pressure & volume . All systems have operating specs. for this . a. clogged fuel filters will cause a lowered fuel pressure / volume condition . b. fuel pressure / volume is critical for fuel injected powerplants . c on some fuel injected vehicles a 2 psi below specs will cause a no-start condition .

 #2 the ecm does not (in this case ) know what the actual fuel pressure is. It assumes it is in operating range.  

 #3 I do not know if any factory sensors on the V11 are wide band O2 sensors or not .

#4 most fuel pressure regulators have this port that is open to atmosphere , connected to manifold vacuum . This will lower or raise fuel pressure to work with a change in throttle . I do not know why MG does not use this .

To emry , what is aDI unit ? 

[Lucky Phil]

 

 #1 all fuel systems that are not gravity feed , require pressured fuel to reach the fuel mixing device. The fuel supply requires pressure & volume . All systems have operating specs. for this . a. clogged fuel filters will cause a lowered fuel pressure / volume condition . b. fuel pressure / volume is critical for fuel injected powerplants . c on some fuel injected vehicles a 2 psi below specs will cause a no-start condition .

 #2 the ecm does not (in this case ) know what the actual fuel pressure is. It assumes it is in operating range.  

 #3 I do not know if any factory sensors on the V11 are wide band O2 sensors or not .

#4 most fuel pressure regulators have this port that is open to atmosphere , connected to manifold vacuum . This will lower or raise fuel pressure to work with a change in throttle . I do not know why MG does not use this .

To emry , what is aDI unit ? 

 

The manifold vacuum facility isnt necessary. Ducati used it for a while but found it wasnt needed. Modern in tank regs dont use it either. DI....direct injection like my wifes new 2.3l turbo Kuga has.

 

Ciao