After installed AFPR, fuel pressure would down to zero when stop the engine.
#173489
January 22, 2004 02:09 pm UTC
January 22, 2004 02:09 pm UTC
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Taiwan
Chih-hong Chou
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Taiwan
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My car is 1g. I've a 255HP fuel pump, it overrun stock FPR to 44psi. Lately I've installed an AFPR to lower the base fuel pressure to 38psi perfectly. When I shut the car off, the fuel pressure would go straight down to zero, it makes the car hard to start up. Before I change to AFPR, the stock FPR could keep it to 40psi when stop the car. I have checked everything, and nothing is leaking. Is there any problem on my 1g? Please share your experience with me. Thanks in advance.
91 Talon FWD Turbo 5MT
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173490
January 23, 2004 01:40 am UTC
January 23, 2004 01:40 am UTC
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Joined: Jan 1970
Posts: 4,971
Beamsville, Ont, Canada
Steve Kinnaird
Senior Member, with Far TOO Much Time on Their Hands
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Senior Member, with Far TOO Much Time on Their Hands
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Posts: 4,971
Beamsville, Ont, Canada
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If all you've changed is the FPR to an AFPR, then, I would say there HAS to be a leak somewhere around the AFPR.
If the system was fine before, and you change one item which results in a problem, the problem SHOULD be with that item. (The AFPR in your case). If the fuel system isn't holding pressure, that pressure has to go somewhere. ie: you've got a leak. You just can't find it.
Now, I'll have all kinds of time to talk about DSMs, because I won't be busy fixing mine!
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173491
January 23, 2004 02:07 am UTC
January 23, 2004 02:07 am UTC
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Joined: Feb 2003
Posts: 2,369
Regina, Sk
Chris Clark
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Insane Member
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Regina, Sk
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Mabey the new regulator is the problem. If there is no visual leaks, mabey the valve isnt closing completley.
1990 TSi AWD - Parked since I bought it (Jan24/03)
Had it out one day, and busted the trans.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173492
January 23, 2004 02:06 pm UTC
January 23, 2004 02:06 pm UTC
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Joined: Apr 2003
Posts: 10
Taiwan
Chih-hong Chou
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Taiwan
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It's a Sard AFPR. I tried to use another Sard AFPR from my brother's car, and it kept FP after shutting car off. Finally I knew I got the defective AFPR, it's an also brand new one. Thanks for everybody to reply.
91 Talon FWD Turbo 5MT
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173493
January 24, 2004 04:42 am UTC
January 24, 2004 04:42 am UTC
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Joined: Feb 2003
Posts: 2,369
Regina, Sk
Chris Clark
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Regina, Sk
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You posted this on the BR Forum right?
1990 TSi AWD - Parked since I bought it (Jan24/03)
Had it out one day, and busted the trans.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173494
January 24, 2004 03:43 pm UTC
January 24, 2004 03:43 pm UTC
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Joined: Apr 2003
Posts: 10
Taiwan
Chih-hong Chou
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Taiwan
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Yes. Since I've owned my 1g almost 13 years, and I'm from Taiwan. Thanks.
91 Talon FWD Turbo 5MT
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173496
January 25, 2004 06:09 am UTC
January 25, 2004 06:09 am UTC
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SASKATOON
Tyler Hodgson
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The fuel pump should not turn on until there is a Cam Angle sensor signal to the ECU, which will flip the fuel pump solinoid under the dash by the ECU.
There is no reason to keep fuel pressure in the fuel lines after the car is shut off. At least my car doesn't do this and I have no starting issues to speak of.
92 Talon TSI AWD
That's right, that's a banana.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173497
January 25, 2004 06:16 am UTC
January 25, 2004 06:16 am UTC
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Joined: Feb 2003
Posts: 2,369
Regina, Sk
Chris Clark
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Regina, Sk
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The regulator is supposed to hold the pressure in the lines while the car is shut off on most if not all Fuel Injected motors.
1990 TSi AWD - Parked since I bought it (Jan24/03)
Had it out one day, and busted the trans.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173499
January 25, 2004 07:36 am UTC
January 25, 2004 07:36 am UTC
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Joined: Apr 2002
Posts: 2,987
Mississauga, Ont
Jerry Rose
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Mississauga, Ont
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Stealth site re denso pump The stock fuel pump used in 3S cars is a constant- or fixed-displacement electric pump that is submerged in the fuel tank. It is called a "wet type" pump because all of its components, including the internal DC motor and impeller-type pump, are in contact with the fuel. The very-high electrical resistance of gasoline (more than 1 megohm) prevents electrical shorts inside the pump. A fixed volume of fuel is delivered for every revolution of the pump. The amount of fuel discharged into the fuel line is determined by how fast the pump rotates. The pump will rotate faster if the supplied voltage is increased or if the fuel line pressure at the discharge port is reduced. If the pressure at the discharge point exceeds about 70 psi, a relief valve built into the factory 3000GT VR4 pump opens to reduce pressure inside the pump. There is also a spring-loaded check valve in the pump to preserve high pressure in the fuel line when the pump is stopped.
Fuel pumps supply fuel volume; they do not create pressure in the fuel lines. In a return-line system (like in the 3000GT and Stealth), the fuel pressure regulator restricts the return fuel flow in order to create pressure in the supply line. As the fuel supply line pressure increases, such as during boost conditions for forced-induction engines, the pump has to work harder (it actually rotates slower and the current draw increases) and so the volume flow decreases. Pumps also have a ceiling capacity where flow drops off rapidly above a certain line pressure (though this might be higher than the relief valve opening pressure).
Every day I beat my own previous record for number of consecutive days I've stayed alive.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173500
January 25, 2004 07:37 am UTC
January 25, 2004 07:37 am UTC
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Joined: Feb 2003
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Regina, Sk
Chris Clark
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Regina, Sk
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Originally posted by Amin Ahmadi:
The regulator and/or any other device CAN NOT hold the pressure in the line. So what does hold the pressure in the lines? Originally posted by Amin Ahmadi:
when the car is shut off the fuel leaks BACK out. It goes back from the way it came in and there is nothing to prevent it. with the pump off there is a two way line that the fuel can travel through. Two way line? There is a main line and a return line. Fuel is not supposed to drain back to the tank through the main line. Originally posted by Amin Ahmadi:
The Fuel pump comes on right when you turn the key on and then goes off. It comes on again when you switch the car to crank position. While cranking the ECU turns the FP on. I know this almost for fact. Yeah almost, that is fiction. The pump does not recieve power until the ECU sees a sinal from the CAS as stated in Tylers post.
1990 TSi AWD - Parked since I bought it (Jan24/03)
Had it out one day, and busted the trans.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173501
January 25, 2004 04:59 pm UTC
January 25, 2004 04:59 pm UTC
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Tyler Hodgson
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So, the fuel pump has a check valve to stop fuel from running back to the tank. Correct.
But it does not hold pressure in the fuel line. The regulator bleeds that back to the tank.
92 Talon TSI AWD
That's right, that's a banana.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173503
January 25, 2004 07:53 pm UTC
January 25, 2004 07:53 pm UTC
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Joined: Feb 2003
Posts: 2,369
Regina, Sk
Chris Clark
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Regina, Sk
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Yeah that would make sense that the check valve in the pump would hold the pressure. Yeah of course if there is no valve the fuel will drain back.
I know 100% for a fact that my pump does not come on before cranking the car. I thought my pump was messed when I first bought my TSi. It didnt run and the pump wasnt coming on with the key in the on postion, then my dumbass friend hooked up the test circut wrong and I ended up replacing the pump for no reason.
1990 TSi AWD - Parked since I bought it (Jan24/03)
Had it out one day, and busted the trans.
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Re: After installed AFPR, fuel pressure would down to zero when stop the engine.
#173504
January 26, 2004 12:09 am UTC
January 26, 2004 12:09 am UTC
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Joined: Jan 1970
Posts: 4,971
Beamsville, Ont, Canada
Steve Kinnaird
Senior Member, with Far TOO Much Time on Their Hands
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Senior Member, with Far TOO Much Time on Their Hands
Joined: Jan 1970
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Beamsville, Ont, Canada
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the FPR is made for when the pump is on. when off it is a whole different matter.
So, what changes in the mechanical FPR when the pump is on, vs when the pump is off?  The FPR is nothing but a pressure release valve. (At a set pressure it releases the fuel). The FPR has NO idea if the pump is running, or not. All the FPR knows is that until the fuel pressure gets OVER a set amount, it holds the fuel in the rail. (It keeps this 36 psi differential under all conditions. Until you go overrunning it..) This "set amount" will vary acording to manifold pressure. However, when the car is off (manifold pressure 0 ) a stock FPR will keep 36 psi in the fuel rail. Try disconnecting the fuel line at the rail after shutting the car off. (Don't forget to sheild your eyes!) The FP solenoid just vents the vacuum line that goes to the FPR to atmosphere. (ie: the FPR sees "0" manifold pressure instead of vacuum. This raises fuel pressure until the solenoid switches back.)
Now, I'll have all kinds of time to talk about DSMs, because I won't be busy fixing mine!
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