Pressure regulator questions

[battlecry]

I noticed that the fuel pressure regulator on my M800 is referenced to atmospheric, instead of intake manifold pressure.  Is this true of other Monsters?  Seems to me it might make a difference at idle and engine braking.  Has anybody connected the free port to the airbox?  Anybody using an adjustable regulator? 

[ducpainter]

I've never seen a map sensor on a Duc...at least not on a Marelli equipped bike.

Maybe the Siemens system uses one.

[battlecry]

Not a MAP sensor, Nate.   On some FI systems, the exposed (non-fuel) port of the regulator is connected to the airbox using a hose.  That way the 3 bar fuel pressure is referenced to the intake manifold pressure.  The diaphragm of the fuel pressure regulator on my Monster vents to the atmosphere (no hose).  So it is 3 bar over atmosphere, regardless of the engine operation.  No impact at WOT, but at idle and engine breaking, the FI is metering more fuel because there is a larger pressure differential between the fuel pressure and the manifold vacuum.

[ducpainter]

Not a MAP sensor, Nate.   On some FI systems, the exposed (non-fuel) port of the regulator is connected to the airbox using a hose.  That way the 3 bar fuel pressure is referenced to the intake manifold pressure.  The diaphragm of the fuel pressure regulator on my Monster vents to the atmosphere (no hose).  So it is 3 bar over atmosphere, regardless of the engine operation.  No impact at WOT, but at idle and engine breaking, the FI is metering more fuel because there is a larger pressure differential between the fuel pressure and the manifold vacuum.

The pressure in the airbox is not the same as that of the manifold I don't think.

How would the system take advantage of that configuration without a sensor for manifold pressure?

[battlecry]

Let's say the ECU expects that for x milliseconds of injector opening, the system will dump quantity y of fuel into the intake.

For that to be true, you need the fuel pressure delivered to the injector to be constant.  The fuel pressure is set at 3 bar by the regulator, but it is set at 3 bars over atmospheric.   But the injectors do not dump fuel to atmospheric pressure, they dump in to intake.  If the pressure on the intake varies, and it does from idle to WOT, the pressure difference between the fuel injector and the air outside the injector is no longer the constant that the ECU was calibrated to. 

Connecting the diaphragm port to the intake makes the 3 bar regulation "float" over the intake pressure, and should make fuel delivery more consistent between injector pulses throughout the engine operating range. 

Do other Ducati models do something with the pressure regulator port?  Seems to me it can be hosed to the lower airbox or (better) to the intake fitting for the charcoal canister thingie that fell of the bike when it hit that pothole on Route 50.

[ducpainter]

AFAIK all the pressure regs are vented to atmosphere.

There are some models (SBKs) that the regulator is in the tank, but the open port goes nowhere.

Try it...

Won't you need a different map?

[battlecry]

"Won't you need a different map?"

I'd think so too.   I'm going to try it, just do not know yet whether to hose to the airbox or the intake fitting.  Your swiss cheese airbox cover inspired me to grind off the Helmholz resonator and open up the lumps to either side of the front port.  I want to cover the bottom of the airbox with aluminum heat reflecting tape and do the same to the underside of the tank, then remap.  

[Porsche Monkey]

The pressure in the airbox is not the same as that of the manifold I don't think.

How would the system take advantage of that configuration without a sensor for manifold pressure?

The pressure "vacuum" would only be the same at wide open throttle.  You wouldn't run a fuel pressure regulator to an airbox to begin with, it should be run to manifold vacuum.  My bike isn't FI so I'm not sure what your looking at but some regulators do not use vacuum.

[battlecry]

I think some SBKs have shower injectors in the airbox.  In the case of the Monster, the injectors shoot into the manifold, so you are right it should be manifold pressure.   Thanks.   

[ducpainter]

I think some SBKs have shower injectors in the airbox.  In the case of the Monster, the injectors shoot into the manifold, so you are right it should be manifold pressure.   Thanks.   

Only a few used that AFAIK. I think they were R models...my 996 has injectors in the manifold.

[Speeddog]

I've never seen a Duc with that regulator port hooked to anything.

On the few FI cars I've worked on, they've been different.

My Merkur had the regulator port hooked to the manifold, but it was a turbo, so it pretty much *had* to be that way.
My Dakota has the regulator in the tank, so it doesn't get a manifold signal.

You would need a different map if you hooked it to the manifold.

On the bikes with ram air, like the SBK's, I'm surprised they're not hooked to the airbox.