Reason for two fuel pressure regulators?

[rhinoone]

Currently working on replacing the injectors in my project - a 1991 Q45.

Curious why the car has two fuel pressure regulators?

[tmorgan4]

There is only one pressure regulator which is the one located on the driver's side fuel rail. The similar looking device on the passenger side fuel rail is just a "damper" to help smooth out fuel flow instead of flowing into the rail in pulses. Both are talked out in the EC section of the factory shop manuals if you need a better description.

[Chrispy300]

Is the dampner actually needed? Can I chuck it?

[craigztoyz]

NOOOOOOOOOOOOOOO

You will have fuel injector failure. The fuel pulses from the pump, w/o it there are monents of high pressure, and low. Very important piece to keep. Learned that one a few years back, the hard way.

[Q45tech]

The damper is driven from a hose just after MAF so that it responds to air flow.The pressure drop of atmosphere to after MAF starts around 4,000 rpm WOT [1/10 psi] and maxes out at redline [1/2 psi]....................very sensitive!.

When you change air filter box in front of MAF you play with the pressure drop at the port. Cone filters play havoc with the damper system inthat the damper thinks the air flow is about half reality.

The pressure drop depends on vehicle speed as the oem horn is positioned [tuned] to accept the boost [ from speed air pressure] so that the filter, horn tuning, housing becomes almost transparent by 120 mph leaving only the 7" restriction from MAF. The speed supplies 7" [1/4 psi boost] to overcome the system and filter &' restriction.

Engineers spent a lot of money getting the Q45 intake and fuel flow PERFECT.

http://delphi.com/images/ppd/p...t.gif

[Q45tech]

Find a 15-20" water column [gauge manometer] to read pressure restrictions in front of MAF [drill hole in top of air box [install a tube test port and run rubber hose into cabin] so you can measure different rpms and speeds. Then tee jnto the line going to damper to see the total restriction under speed and rpm.http://cgi.ebay.com/NEW-DWYER-...wItem

Don't confuse inches of water with PSI or inches of mercury

27.7 inches of water is only 1.0 psi1.0 inch Hg is 13.61 inches of water

A typical vacuum gauge is way to inaccurate for these tests!!!!!!!Careful a 20" H2O will be destroyed if connected to plenum vacuum where 18" Hg is 245" H2O.

I have a dozen different manometers from 1" H2O to 15 psi

Can even measure the 0.1" H20 difference in brands of drop in filter at WOT and 4,000 rpm.

[TSL]

Stuff

As fascinating as it is to read about your manometer collection i would like it more if you could explain with some clarity your fuel damper theory.

I have noticed that some nissan engines have a fuel damper on the fuel rail and some do not have it. Even on the same engine it seems to vary, that is to say some rb's have a damper and some do not. This leads me to think that the effect is negligible at best or else it would appear on every engine.

However i do wonder about why there is a vac line on them. All the FSM's simply describe them as fuel pump pulse dampeners but the vac line does indicate a second function.

On the rb engines the damper vac line is connected just in front of the throttle body. This would indicate something to do with differences between manifold and inlet tract pressure. Although at WOT this pressure would be equal, not to mention what boost pressure might do at part throttle openings.

I then have to question how much, if at all this damper effects fuel pressure. It would seem to me that this could cause some potential problems with fuel pressure fluctuations if this is also in fact a 1:1 ratio regulator.

What is this graph you posted representing? Fuel or air pressure somewhere?http://delphi.com/images/ppd/p...t.gif

You talk about 1/2 psi drop but the chart shows a fluctuation of 160kPa which is extreme.

[Q45tech]

Fuel pressure gauges are SO HEAVILY DAMPED that they show JUST the average, like MAF voltages, when you use electronic pressure [or vacuum] sensors you see the sine wave nature of the real flows of air and fuel.

The front rubber interconnecting hose also acts as a damper between the bank rails. If you examine with a microscope I'm sure it changes diameter as the acoustic waves flow back and forth inside the rail.

I'm sure the tri speed fuel pump controller [controlled by rpm and load] and the damper are tuned as a system.

They spent the money for some reason to fix something and each engine family has a different method.

[TSL]

It is not uncommon for the factory fuel pump to be upgraded or replaced particularly considering these engines are frequently transplanted into various different chassis.

What effect could this have and should the damper be removed or modified if the fuel pump is changed?

[Chrispy300]

It is not uncommon for the factory fuel pump to be upgraded or replaced particularly considering these engines are frequently transplanted into various different chassis.

What effect could this have and should the damper be removed or modified if the fuel pump is changed?

That's me all over. No FPCU, big fuel pump, which will be into a surge tank, then big external pumps. Turbosmart regualtor, twin feed fuel rails etc. The standard setup is probably fantastic, but I've diverted from the standard just a touch

Quote of the month

As fascinating as it is to read about your manometer collection

[Carl H]

i suspect it has to do with the tristage fpcm the q is equipped with, the sudden increase in pressure from the pump going from a slower speed to a higher speed (more pressure) it would in theroy cause the map to go rich at that point regardless of what its mapped for simply due to the pressure spike.the dampener is proly there to do just that, dampen the surge and slowly allow for pressure to rise as needed; i use the term slowly lightly here.

[Chrispy300]

I'm guessing the extra vacuum on the damener will allow it to have a bigger dampening effect.