Fuel Injection question

[Rough Edge racing]

 On a 98 Ducati SR2 not a Guzzi but I want to also ask here because I believe they both use similar systems...The Ducati uses a simple speed density port injection, inputs  from throttle position, engine and ambient temperature and RPM...It's a return system, the pump in the tank...On autos/truck port injection they generally have around a 50 PSI system pressure with some sort of pressure regulator...My question, what regulates the fuel pressure? The pump or is there a relief valve on the injector itself?  Nothing is wrong with the bike, just curious

[Kev m]

There is normally a mechanical pressure regulator somewhere inline in the system. It could be anywhere in the circuit and many earlier systems used one somewhere downstream of the fuel pump assembly. Later systems moved the regulator earlier in the circuit mounting it to the fuel pump.

I am not familiar with this particular system though so that's a generalization. But if there is a "return system" meaning a second set of fuel lines from the injectors back to the tank the regulator would likely be found in the return side of the circuit for obvious reasons. If the lines run only to the injectors, then the regulator must be in the tank before them.

[RinkRat II]

  On My 907 it uses a regulator similar to Guzzi and is the last component before the fuel returns to the tank.

       Paul B.

[Rough Edge racing]

 By looking at it ,the fuel flow goes directly from the pump, through the filter to the two injectors in series and then directly returned to the tank.There are no other device ..The injectors themselves look typical except for the device on top of the injectors where the hoses are attached...


                   
     

[Rebochi]

The relief is integral with the fuel pump assembly.

[Kev m]

By looking at it ,the fuel flow goes directly from the pump, through the filter to the two injectors in series and then directly returned to the tank.There are no other device ..The injectors themselves look typical except for the device on top of the injectors where the hoses are attached...


                   
   

Oh wow, I see what you mean, those look like little pressure regulators attached to the injectors. And I assume that's the feed and return fittings on the rail. Yeah that would make sense if it's no where else in the circuit.

I can't think of any reason it would be integral to the pump if there's an extra (return) line.

[jas67]

If the return goes directly back to the tank, then the regulator most be in the tank, on the return line.   The return line can't just go back to the tank w/o the regulator, or the fuel line wouldn't have any pressure.

[Rebochi]

   trace the return line back to the bottom of the fuel pump assembly, it connects to the bottom of the pressure regulator.

[guzzisteve]

They are not regulators, it's a banjo fitting w/screen. Regulator is in the pump plate. Don't believe me? Pull off the circlip retainer and look inside on top of injector.

[Rough Edge racing]

They are not regulators, it's a banjo fitting w/screen. Regulator is in the pump. Don't believe me? Pull off the circlip retainer and look inside on top of injector.

  I don't disbelieve anyone.The device on top is not something I've have not seen before... I'm very familiar with US car/truck injection but not Italian bikes....The whole injection system in on my bench...I'm replacing the in tank pump ,hoses and filter as maintenance...There are many pumps to chose from, none are over 60 bucks...Does this system operate on about 50 PSI?

[RinkRat II]

   The fuel pressure regulator is in the bottom plate assembly . Top side of where the return line enters. Pressure is 3 bar or 44psi .

   Paul B

[guzzisteve]

Should be around 3 bar. I went through a Duc of the same stuff a couple years back. It had been sitting for 15yrs.

[Rough Edge racing]

 Thanks, I'm going to add a pressure check point on the feed so I can check it easily if necessary...

[Rough Edge racing]

   The fuel pressure regulator is in the bottom plate assembly . Top side of where the return line enters. Pressure is 3 bar or 44psi .

   Paul B

  Yes...I pulled out the regulator, it's marked 300 KPA , 44 psi.......Regulator fits in the hole in the 11 oclock position, the regulator itself is at the bottom...it has an unused nipple, may be for intake vacuum when used in other applications

   

[guzzisteve]

Don't plug that nipple it's supposed to go to outside air not vacuum. Good Luck

[Kev m]

Can anyone explain why they'd use a return line if the regulator was in the tank at basically the same position as the fuel pump anyway?

Was there a fear of temperature effects on fuel in the feed line that returning and mixing could minimize or ?!?

[kirb]

Circulating fuel to prevent vapor locking could be possible. Using the fuel tank as a heat sink...

[Rough Edge racing]

 Newer cars/trucks have a mixture of return and non return...might just be an engineering preference..The Ducati system, Maybe same year Guzzi is similar..I's a stand alone system with no O2 or intake vacuum reference...Be somewhat easy to adapt to a carburetor engine

[RinkRat II]

  The fuel pump is capable of providing more flow and pressure than the injectors can use, the more efficient way to control  this is to put a regulator on the downstream side of the injectors to keep pressure and flow constant.

       Paul B

[Rebochi]

   Just a wild guess but it probably easier and cheaper to fabricate if the regulator and return was in the fuel pump assembly instead of adding another perforation in the tank that need to be sealed.

[Tusayan]

The fuel pump is capable of providing more flow and pressure than the injectors can use, the more efficient way to control  this is to put a regulator on the downstream side of the injectors to keep pressure and flow constant.

Yes, keeps injector supply pressure constant as fuel filter slowly introduces additional pressure drop.

[Kev m]

  The fuel pump is capable of providing more flow and pressure than the injectors can use, the more efficient way to control  this is to put a regulator on the downstream side of the injectors to keep pressure and flow constant.

       Paul B

Except that it seems systems with separate return lines and downstream pressure regulators (which were the norm say in the 90's to early 00's depending on whether we're talking auto, marine, or point me industries) went the way of the Dodo in favor of systems that only use a single feed line that regulate pressure upstream at the pump before the fuel reaches the injectors.

It might just be as simple as no one thought of the latter till later, but I'm wondering if there was an initial reason they were all set up with full return circuits.

[RinkRat II]

  Federal emission standards dictated to lower EVAP emissions, most mfgrs. went to a no return line system and installed the regulator in the tank, tha main difference on these systems is in the ECM that controls the pump. On returnless, the ECM varies the speed of the pump with more inputs from more sensors, return type typically only uses a Mass airflow sensor to control the injector signal. Pump stays constant.

       Paul B

[Kev m]

  Federal emission standards dictated to lower EVAP emissions, most mfgrs. went to a no return line system and installed the regulator in the tank, tha main difference on these systems is in the ECM that controls the pump. On returnless, the ECM varies the speed of the pump with more inputs from more sensors, return type typically only uses a Mass airflow sensor to control the injector signal. Pump stays constant.

       Paul B

I'm skeptical of the connection between EVAP systems and returnless. For instance the Guzzi Cali systems used both a return and EVAP at least by 00-0? A few years earlier Harley was already using a returnless version of the same Weber-Marelli system despite not having an EVAP system.

Also how universal so you think a pulsed fuel pump signal was? I'm having problems remembering an example that I know for sure.

[rocker59]

I'm skeptical of the connection between EVAP systems and returnless. For instance the Guzzi Cali systems used both a return and EVAP at least by 00-0? A few years earlier Harley was already using a returnless version of the same Weber-Marelli system despite not having an EVAP system.

Also how universal so you think a pulsed fuel pump signal was? I'm having problems remembering an example that I know for sure.

For model year 1998 all Guzzis in the USA were 50-State compliant, with evap canisters.

 

[RinkRat II]

 
   The connection between EVAP and returnless is due to the fact on the return systems, the fuel returning to the tank was pretty much just dumped back in creating the
 evap emissions, on the returnless, the fuel is returned to the inlet side of the pump not aerating the fuel as much. This all started back in '96 and was fully implemented by 2004 regulations on cars. Motorcycles fall under different aspects of these rules.

       Paul B

[Wayne Orwig]

Can anyone explain why they'd use a return line if the regulator was in the tank at basically the same position as the fuel pump anyway?

Was there a fear of temperature effects on fuel in the feed line that returning and mixing could minimize or ?!?

Since the fuel line is pressurized, vapor lock should not be an issue.
By running the line out to the injectors and back, the system purges any air from the lines quickly. If you run a single line to the injectors it can trap air in that line and it needs to purge it all through the injector. If you get air in the line.

[Rough Edge racing]

Since the fuel line is pressurized, vapor lock should not be an issue.
By running the line out to the injectors and back, the system purges any air from the lines quickly. If you run a single line to the injectors it can trap air in that line and it needs to purge it all through the injector. If you get air in the line.

  As I mentioned, many new cars ,but not direct injection, have no return lines..Air is not a problem when the pump is running. When the engine is not running,  residual check valves hold pressure in the line until the things cool down a bit to prevent air pockets...

[guzzisteve]

All the newer model Guzzi's since 06 have only 1 line, return is off pump plate w/check valve. That's why most can't get the line disconnected.