[dbbd1]

So, while troubleshooting a previous issue


http://www.toyotanation.com/forum/6...015/1415210-intermittently-randomly-dies.html


I was checking my fuel pressure regulator (FPR) and discovered that there is no vacuum to it. According to Haynes and Toyota, the pressure should be 40.8 to 41.7, with vacuum. If it is higher, check for vacuum at the FPR. Without vacuum applied to it, pressure will be slightly higher (mine was). Now, the interesting thing is that, where the port is for the vacuum connection to the FPR, you will almost never see vacuum there. Only in extreme cases will you get some due to the venturi effect, caused by very large volumes of air flow through the intake. The few threads that I could find about this note that Toyota is a little loco in the head and the theories usually go that it is hooked up there in case the diaphragm inside the regulator leaks, the excess fuel will go into the intake. Plausible? Perhaps. I really cannot say what was going through the engineer's mind with this design. Some have Tee'd the FPR actually into a vacuum line and blocked off the intake port, to bring the pressure down to specs. Just for grins, I am trying this too. I am curious if my mileage and/or power (with my calibrated butt dyno) will change. Right away, I did notice that the RPM's dropped, immediately, when I hooked up the FPR to vacuum with the engine on. They dropped about 100-200. I would love to hear other theories and thoughts about this. I am most curious.


Stay tuned...

 

[92pickmeup]

Read most of your other thread. Vacuum compensation on FPR is nothing new, been used since the beginning of fuel injection. My '88 Mustang came with one from the factory. Purpose of FPR is to maintain constant pressure at the injectors. At high engine vacuum, you need to compensate by lowering the fuel pressure. At low engine vacuum, no compensation is needed.

Newer vehicles may have eliminated it because the ECU can detect & compensate using the fuel pump, since most are now returnless.

Found a pretty good explanation & it just happens to be Mustang.
http://www.americanmuscle.com/return-and-returnless-fuel-systems-explained.html

Your FPR might be an FPDM.

...
1. I was checking my fuel pressure regulator (FPR) and discovered that there is no vacuum to it.
2. According to Haynes and Toyota, the pressure should be 40.8 to 41.7, with vacuum. If it is higher, check for vacuum at the FPR. Without vacuum applied to it, pressure will be slightly higher (mine was).
3. Now, the interesting thing is that, where the port is for the vacuum connection to the FPR, you will almost never see vacuum there.
4. Only in extreme cases will you get some due to the venturi effect, caused by very large volumes of air flow through the intake.
5. The few threads that I could find about this note that Toyota is a little loco in the head and the theories usually go that it is hooked up there in case the diaphragm inside the regulator leaks, the excess fuel will go into the intake. Plausible?
6. Perhaps. I really cannot say what was going through the engineer's mind with this design.
7. Some have Tee'd the FPR actually into a vacuum line and blocked off the intake port, to bring the pressure down to specs. Just for grins, I am trying this too. I am curious if my mileage and/or power (with my calibrated butt dyno) will change. Right away, I did notice that the RPM's dropped, immediately, when I hooked up the FPR to vacuum with the engine on. They dropped about 100-200. I would love to hear other theories and thoughts about this. I am most curious.


Stay tuned...

1. If the hose is connected to the intake manifold, there must be vacuum (at idle). 40 psi is pretty much the standard for all port fuel injected engines. Directed injection has a much higher pressure.
2. Correct
3. Almost never, meaning not at idle?
4. Sounds like BS to me.
5. Yes to Toyota being loco. No to your question. If the diaphragm tears, you'll flood the intake with fuel. Nothing good can come of it.
6. The design has been used successfully for over 30 years by every manufacturer.
7. Bad move. Vacuum is established at the intake where all vacuum lines emanate from.

 

[dbbd1]

Purpose of FPR is to maintain constant pressure at the injectors. At high engine vacuum, you need to compensate by lowering the fuel pressure. At low engine vacuum, no compensation is needed.


1. If the hose is connected to the intake manifold, there must be vacuum (at idle).
2. Correct
3. Incorrect
4. Sounds like BS to me.
5. Yes to Toyota being loco. No to your question. If the diaphragm tears, you'll flood the intake with unmetered fuel. Nothing good can come of it.
6. The design has been used successfully for over 30 years.
7. Bad move.

I am no stranger to regulators, of all sorts, but why do you want to lower pressure at higher engine vacuum? Because the engine will "pull" in too much fuel, in addition to what is being injected?


You will need to a lot of air through the large air box or cold air intake runner to create any sort of vacuum on that port. The Venturi effect is like when you blow across the top of an open beer bottle. That whistling? It is creating a small amount of vacuum.

 

[92pickmeup]

Am still editing, refresh page.

 

[dbbd1]

The hose for the FPR is connected between the air filter and the TB, not the manifold.

 

[dbbd1]

Yeah, me too...

 

[92pickmeup]

...
1. I am no stranger to regulators, of all sorts, but why do you want to lower pressure at higher engine vacuum? Because the engine will "pull" in too much fuel, in addition to what is being injected?

2. You will need to a lot of air through the large air box or cold air intake runner to create any sort of vacuum on that port. The Venturi effect is like when you blow across the top of an open beer bottle. That whistling? It is creating a small amount of vacuum.

1. In order to maintain constant pressure across injectors. It's difference in pressure, i.e., pressure differential.

High vacuum is about 17 inHg (about negative 8 psi)
If FPR is set to 40 psi, pressure at injector would be 48 psi with no compensation. Too rich at idle.

Here's the key point: FPR maintains constant pressure between the fuel rail and the intake manifold, not between the fuel rail and the outside world, i.e. atmospheric pressure at sea level is 14.7 psi.

2. Forget Venturi effect, it is irrelevant to the vacuum that the engine creates. The engine is an air pump.

No, not unless I hook up my handheld vacuum thingey (harbor freight) to it. It may vary it ever so slightly that my 0-100psi gauge is not seeing it.

A vacuum gauge does not go to 100 psi.
I have same gauge, it's 0-25 inches of mercury (vacuum); 0-10psig (gauge pressure)

 

[92pickmeup]

The hose for the FPR is connected between the air filter and the TB, not the manifold.

Went out to look at my 4cyl it's the same.

UPDATE
Found a description of the Fuel Delivery System in the 05-09 Chiltons.
There are 3 "FPR's": Fuel Pulsation Damper, Fuel Pressure Regulator #1 & #2.
The one you see is FPR #1. I-4 FPD is at the rear, FPR at the front.
Start typing part of it here:
...The fuel pulsation damper, which is located at the connection between the fuel supply line and the fuel rail, dampens the pressure pulses from the fuel pump. The vacuum operated FPR, which is located at the connection between the fuel rail & the fuel return line, maintains a constant fuel pressure to the injectors. When the engine is accelerating or cruising at a steady speed with no load, there is little manifold vacuum, so the pressure regulator is closed, which maintains higher fuel pressure inside the fuel rail & plenty of fuel for the injectors. When the engine is decelerated, intake manifold vacuum is high, which opens the regulator & allows fuel to return to the tank. A smaller supplemental FPR, which is controlled by a spring, is an integral component of the fuel pump/fuel gauge sending unit module; if fuel pressure rises to quickly for the system to handle it, this regulator opens when the pressure hits a specified level & dumps fuel back into the fuel tank.

 

[dbbd1]

1. In order to maintain constant pressure across injectors. It's difference in pressure, i.e., pressure differential.

High vacuum is about 17 inHg (about negative 8 psi)
If FPR is set to 40 psi, pressure at injector would be 48 psi with no compensation. Too rich at idle.

Here's the key point: FPR maintains constant pressure between the fuel rail and the intake manifold, not between the fuel rail and the outside world, i.e. atmospheric pressure at sea level is 14.7 psi.

2. Forget Venturi effect, it is irrelevant to the vacuum that the engine creates. The engine is an air pump.



A vacuum gauge does not go to 100 psi.
I have same gauge, it's 0-25 inches of mercury (vacuum); 0-10psig (gauge pressure)

The 0-100 gauge that I was referring to is my fuel pressure gauge. Again, I am no stranger to regulators, air pressure, vacuum, diaphragms, pressure/vacuum differentials. My whole career was pneumatics and hydraulics.


But, you are still losing me when you say "In order to maintain constant pressure across injectors. It's difference in pressure, i.e., pressure differential." How is it doing that by kind of/sort of using the non-existent vacuum on the regulator?



And, your thinking seems to be wrong about being too rich at idle. The fuel pressure drops with higher vacuum.

You mean tee'd off from there?

No, from the factory, it is before the TB, therefore unrelated to engine vacuum. Strictly related to the amount of air flowing through the intake (filtered air) tube prior to the TB. Totally related to venturi effect, that is the only way that you would ever see vacuum on that port.

 

[dbbd1]

It's not an FPR; too small. Probably a PPRV.

PPRV (Positive Pressure Relief Valve) which is implemented to maintain the pressure in the system when you turn the car off, which allows for easy start-ups and it also relieves excessive pressure in the lines by draining back into the tank

Haynes and Toyota both refer to it as a fuel pressure regulator (V6)

Am trying to ascertain if there is no return line from the fuel rails back to the tank.

I do have a return line.

 

[92pickmeup]

Look at the Update above, it's not a traditional fuel injection system.

 

[92pickmeup]

...
1. How is it doing that by kind of/sort of using the non-existent vacuum on the regulator?
2. And, your thinking seems to be wrong about being too rich at idle. The fuel pressure drops with higher vacuum.
3. No, from the factory, it is before the TB, therefore unrelated to engine vacuum. Strictly related to the amount of air flowing through the intake (filtered air) tube prior to the TB. Totally related to venturi effect, that is the only way that you would ever see vacuum on that port.

1. MAP Sensor
2. If it didn't drop with higher vacuum, the pressure at the injector would be higher. The ECU controls everything.
3. It has no spring & diaphragm is very small. Maybe uses Venturi Effect to sense load & no load. They can call it an FPR but it's not. Seems like extra unnecessary hardware for a Return System.

 

[dbbd1]

UPDATE
Found a description of the Fuel Delivery System in the 05-09 Chiltons.
There are 3 "FPR's": Fuel Pulsation Damper, Fuel Pressure Regulator #1 & #2.
The one you see is FPR #1. I-4 FPD is at the rear, FPR at the front.
Start typing part of it here:
...The fuel pulsation damper, which is located at the connection between the fuel supply line and the fuel rail, dampens the pressure pulses from the fuel pump. The vacuum operated FPR, which is located at the connection between the fuel rail & the fuel return line, maintains a constant fuel pressure to the injectors. When the engine is accelerating or cruising at a steady speed with no load, there is little manifold vacuum, so the pressure regulator is closed, which maintains higher fuel pressure inside the fuel rail & plenty of fuel for the injectors. When the engine is decelerated, intake manifold vacuum is high, which opens the regulator & allows fuel to return to the tank. A smaller supplemental FPR, which is controlled by a spring, is an integral component of the fuel pump/fuel gauge sending unit module; if fuel pressure rises to quickly for the system to handle it, this regulator opens when the pressure hits a specified level & dumps fuel back into the fuel tank.

Chiltons seems to be a bit more informative than Haynes. Yes, I knew about the damper and my damper is on driver's side while the FPR is on the passenger side of the fuel rail. I did not know about the secondary FPR on the pump though. But, I am still confused (go figure). It refers to the vacuum on the manifold but, again, this port is on the filter side of the throttle body. That side doesn't see the vacuum that the manifold does. And, when "intake manifold vacuum is high, which opens the regulator & allows fuel to return to the tank" that is when it drops to Toyota's specs. Are they then saying that anything above spec is fine and when it drops due to vacuum, it should only drop to 41-ish?

 

[92pickmeup]

Chiltons seems to be a bit more informative than Haynes. Yes, I knew about the damper and my damper is on driver's side while the FPR is on the passenger side of the fuel rail. I did not know about the secondary FPR on the pump though. But, I am still confused (go figure). It refers to the vacuum on the manifold but, again, this port is on the filter side of the throttle body. That side doesn't see the vacuum that the manifold does. And, when "intake manifold vacuum is high, which opens the regulator & allows fuel to return to the tank" that is when it drops to Toyota's specs. Are they then saying that anything above spec is fine and when it drops due to vacuum, it should only drop to 41-ish?

I-4, everything is on the driver's side. One fuel line goes to FPR, other fuel line goes to FPD. Can't tell which is supply & which is return.
Chilton's or Toyota may call it vacuum, but it's not. Just like they call it an FPR & it's not. They can give it any name they want, doesn't have to make sense to anyone.

Don't quite understand what you mean: 'Are they then saying that anything above spec is fine and when it drops due to vacuum, it should only drop to 41-ish?
Don't know what the spec is, but that sounds reasonable. For a real FPR it's psi with vacuum line removed & plugged, i.e. FPR port to atmosphere. Since it's a mechanical device, 5 psi span would be normal.

Vacuum compensation may only be 2-3 psi. Looks like it's all for reduced emissions at cold idle, when still in open loop.

Been all through this on the Mustang with Megasquirt ECU & fuel supply issues. All resolved.

Back to your other thread. If you have no codes, it's likely the fuel system because it has no sensors.
Your vehicle is 10 years old with 50k miles. Assume fuel filter is new.

Have you done a Load pressure test? Only way to do a Load test is to connect the fuel pressure gauge to the rail with a long hose & strap it to the hood so can see it while driving.

Your post #1 symptoms indicate a weak fuel pump or a partially clogged fuel sock. Either way, you have to pull the tank.
Went through this on the Mustang (55K miles), took years to figure out. All experts said electrical, spent $1k in parts. Still no fix. It was the stinkin' fuel pump. It would idle all day & pressure was normal. Go down the block & it would cut out like ignition turned off; lift pedal & it would come right back. Keep load low & it would run. Some days were worse than others, not consistent. Tank looked brand new inside. Sock had split open & small pieces were missing, probably sucked inside the pump. A $5 filter sock, killed it. Put new pump in, all okay. Then FPR issues because new pump didn't have anti-drainback feature. Only 1 of my 3 FPR's has this feature.

 

[RTFM]

Hell of a thread here guys. Not understanding it all, but glad you two do.

 

[dbbd1]

Chilton's or Toyota may call it vacuum, but it's not. Just like they call it an FPR & it's not. They can give it any name they want, doesn't have to make sense to anyone.

Don't quite understand what you mean: 'Are they then saying that anything above spec is fine and when it drops due to vacuum, it should only drop to 41-ish?
Don't know what the spec is, but that sounds reasonable. For a real FPR it's psi with vacuum line removed & plugged, i.e. FPR port to atmosphere. Since it's a mechanical device, 5 psi span would be normal.

Vacuum compensation may only be 2-3 psi. Looks like it's all for reduced emissions at cold idle, when still in open loop.

Here is from the Toyota FSM

 

[92pickmeup]

OBDII activates pump without turning engine on.
No load test is 40.8 - 41.7psi; 1 psi span is virtually nothing. Nominal is 41psi
With Ford, I jumper test connector pin to ground OR
The ECU grounds the fuel pump relay to activate the pump.
All vehicles work the same way.

Doesn't help you with a load test.
Either way, you need the gauge connected. OBDII can't read fuel pressure since there is no pressure sensor.

I have OBDII tool that uses any laptop computer.
Megasquirt does pretty much the same with it's own software interface & serial port connector.

OBDII is Federally mandated on all vehicles sold in the US since 1996.

 

[dbbd1]

Hell of a thread here guys. Not understanding it all, but glad you two do.

I am not sure that we are even speaking the same language.

1. MAP Sensor
2. If it didn't drop with higher vacuum, the pressure at the injector would be higher. The ECU controls everything.
3. It has no spring & diaphragm is very small. Maybe uses Venturi Effect to sense load & no load. They can call it an FPR but it's not. Seems like extra unnecessary hardware for a Return System.

1- Okay


2- Uh, yeah. Lower vacuum means higher pressure...


3- Well, if its on the fuel line and it regulates the pressure, doesn't that make it a fuel pressure regulator? That's like saying that someone that makes pies is not a baker because they don't bake bread...








The whole point of this thread is to see:


1- Does anyone seem to have vacuum at the FPR port on the filter housing at idle. (I have an aFE cold air intake, does a stock intake make a difference? Or any other brand?)


2- Get some input on the mysterious conundrum of the Toyota FSM and Haynes manual that states that your fuel pressure should be between 40.8 and 41.7 psi at warm idle. If it is higher than that (see 9a and 9b below) you should check for vacuum signal. If you do not see a vacuum signal, to check for obstruction or leak. I have neither obstruction nor leak, but I sure do not have any vacuum at the port either. I also do not see any way to have any significant vacuum created at that port, as it is in the tube between the filter and the TB, not in the manifold. It would take copious amounts of air to create a vacuum at that port with the venturi effect. So, why do the manuals list that specification range for the FPR, if no one will ever see it (under normal conditions) at idle?

 

[dbbd1]

I guess that I am also curious about actually routing a (real) vacuum line to the FPR. Like I said, the RPM did drop a tad when I did this, but is it good, bad, pure evil, or indifferent? Some others have done this but none have reported back on the outcomes.

 

[tmauldin]

Did you ever figure this out?
I have 96 camry 2.2 federal vin j that has a fuel pressure regulator vacuum hose connected to the throttle body . there are two ports in the throttle body at this connection. ( One port goes to area between intake manifold and throttle body, the other port goes to area between throttle body and air filter)

There is 0 inhg vacuum at all times, except when cold starting as it goes to 1 inhg within five seconds of cold starting but drops back to 0 within five more seconds , and ,at this point, it stays at 0 regardless of throttle position.