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fuel pressure question

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Old 03-20-2005, 10:15 AM   #1
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Default fuel press only 52 when i stab throttle

when i am looking at my gauge how should it react??

right now at idle the pressure is about 63 psi and little stabs of the throttle go to about 58 or so but if i open it up real fast, and i open it up a lot, the fuel pressure will dip down really low, i just held steady rpm and then jabed the throttle open almost all the way and the rpms went up but the fuel pressure gauge went down to 52, i didnt know if it should always stay at 58 or what? but if i just open the throttle a little bit it reacts fine. is this normal or do i have a problem?
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Old 03-20-2005, 11:42 AM   #2
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I've got a dash mounted gauge and it does not drop when I rev in neutral. 58
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Old 03-20-2005, 11:57 AM   #3
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hmmm so i wonder what that means then, regulator? im having problems starting my car up and was told its the check valve in the fuel pump
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Old 03-21-2005, 12:20 PM   #4
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Under a load your car will pull more fuel but the fuel pressure should stay fairly constant. That is the job of the return style regulator. If the pump pushes 60# of fuel the regulator will bypass the extra until it is needed. If the regulator is not doing it's job you might lose fuel pressure like in your case.
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Old 03-21-2005, 12:49 PM   #5
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i had a loose line on the pump, but the car still wont start right so i guess its a check valve. yea as teh vacuum goes up more fuel is drawn, figured that out trying to properly tune my injectors
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Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-27-2005, 11:47 PM   #6
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If the fuel pressure drops when demand increases, the regulator compensates by bypassing less fuel, up to the capacity of the pump and system (lines). if the regulator can't compensate, then the pump (or lines) can't support the flow requirements. Check your fuel pump capacity or line size. HTH
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Old 03-29-2005, 08:44 AM   #7
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A check valve problem won't prevent your car from starting. All it could do if it was missing is give you occassional hard starts if you don't crank it over shortly after it primes.

It sounds to me like you have a weak pump from your first post. A slight dip is okay (2psi or so), a big dip is not.

If you have a regulator problem, your PSI will likely be consistently higher or lower than what it should be.
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Old 03-29-2005, 09:11 AM   #8
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there was a loose line causing that dip, the check valve isnt keeping pressure in the line when the pump shuts off
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Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-29-2005, 09:35 AM   #9
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Then what kind of starting problems are you having?
Quote:
Originally Posted by WS6FirebirdTA00
i had a loose line on the pump, but the car still wont start right so i guess its a check valve. yea as teh vacuum goes up more fuel is drawn, figured that out trying to properly tune my injectors
Did you change your injectors at the same time you changed your pump?
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Old 03-29-2005, 11:07 AM   #10
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Have you already eliminated a possible leak between the pump and the bulkhead on the tank?
I always use double worm-clamps at each end of any line used in the tank.
If you had a leak inside the tank, that would explain both the starting and the pressure dip problems.
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Old 03-29-2005, 06:25 PM   #11
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Quote:
Originally Posted by SMOKINV8
Then what kind of starting problems are you having?

Did you change your injectors at the same time you changed your pump?

the car will not keep fuel pressure in the system with the key off. injectors werent touched but then i changed them and that did nothing for the problem. the loose line just fixed the erractic fuel pressure when running
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2000 WS6 M6
Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-30-2005, 08:02 AM   #12
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Quote:
Originally Posted by WS6FirebirdTA00
the car will not keep fuel pressure in the system with the key off. injectors werent touched but then i changed them and that did nothing for the problem. the loose line just fixed the erractic fuel pressure when running
Mine doesnt keep pressure either. But mine also starts when its supposed to. If it does happen to have a not so quick start up why worry about it. The more you crank it the more you get around the motor so everything is lubricated before firing up I understand you might have other issues, but after firing my car up for the first time, I cycled the key to prime the system and my pressure bleeds off too. Am I worried about it with my A1000? I want to say its supposed to do that. UNless it gives me a performance issue like yours dropping FP then ill be concerned.

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Old 03-30-2005, 11:33 AM   #13
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im gonna worry about it, i paid 225 for a brand new pump and it better work like its brand new, i dont have money to just **** away on thing that dont work right
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Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
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Old 03-30-2005, 12:02 PM   #14
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Quote:
Originally Posted by WS6FirebirdTA00
im gonna worry about it, i paid 225 for a brand new pump and it better work like its brand new, i dont have money to just **** away on thing that dont work right
Its starting and driving right? Does it drop pressure under a load?

Mike
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Old 03-30-2005, 01:25 PM   #15
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it does but its normal drop, it wont start right unless i prime the pump 2 times and sometimes it still wont fire right
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Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-30-2005, 03:16 PM   #16
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Quote:
Originally Posted by WS6FirebirdTA00
it does but its normal drop, it wont start right unless i prime the pump 2 times and sometimes it still wont fire right
What are you considering a normal drop?

What sock did you put on the pump when you dropped it in the tank? Did you pinch the lines or kink them when you reinstalled the unit itself in the tank and compressed it? Sounds to me it could be an install error or that the pump truly is bad.

Do you have a friend with the same car you can drop his tank and plug it in to see if it starts correctly? Takes about 15 mintues to drop the tanks in my kind of cars. Unless you have traditional exhaust systems then it sucks.

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Old 03-30-2005, 04:01 PM   #17
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the install was not an error i know that much. nothing is pinched, it was all done right. the sock i put on was the correct one for the pump. normal drop is 63-62 at idle and 59 WOT. and all my friends have full cat backs so itll take about 2 hours to drop the tank. ive gone through all the trouble shooting racetronix and everyone on here and thunder racing recommended to rule out everything else
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Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-31-2005, 11:15 AM   #18
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Have you checked your regulator....you can swap rails in no time and see if the problem still persists.

Mike
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Old 03-31-2005, 10:35 PM   #19
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well the thing is the problem didnt start until a did the pump swap, that was all i changed
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2000 WS6 M6
Old Setup: 480 rwhp 437 rwtq with 230/232 cam and a best of 7.17@98.47 w/1.58 60'
New Setup: AFR heads, 11.6:1 CR, 90 mm ported FAST, Exo-Skel, 236/244 cam, QTP HVMC, EWP, GMMG, 9" w/4.11s
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Old 03-31-2005, 11:06 PM   #20
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Quote:
Originally Posted by WS6FirebirdTA00
well the thing is the problem didnt start until a did the pump swap, that was all i changed
Yes but new found pressure could have ruptured the disc in the regulator. Dont leave anything untouched

Mike
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Old 03-31-2005, 11:06 PM
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