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i have the exact same problem and it seems as though my car doesn't get enough fuel at idle. As my car is currently stripped down to the frame, i have no answer at this time, however, i have a list of possible causes, and I hope someone can chime in to help me(us) out

My alternator is on its way out, low voltage from here may cause the pump to underachieve (walbro 255lph)
My fuel pump resistor may be shot

I am going to be cleaning and testing all of the wiring I have pulled out of the car to further eliminate sources of the problem.
 

· Supras are never 'done'
1989 Toyota Supra
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When you start the car, it causes a vacuum on that vacuum hose you hooked to the FPR. That brings the fuel pressure down. Contrapositively, the fuel pressure goes up when the vacuum decreases (and becomes boost if you have a turbo motor). This is done in order to help maintain proper air/fuel mixtures without having to vary the injector pulse width as much.

If you don't follow, read up on fuel injection a bit more. I'm not entirely sure why you installed a FPR if you're not sure how it's supposed to function.
 

· Supras are never 'done'
1989 Toyota Supra
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After seeing Adam's reply I think I better understand what you're trying to ask, which is that if you adjust it to the max, you can't get more than that PSI, correct? In that case, you can try putting a jumper in place of the fuel pump resistor so it runs 12v all the time.
 

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greensupra_87 said:
adam u also have a walbro 255?, if so that may be the problem
I think my pump is toast, it only has maybe 5k on it, but I heard it whine about a month ago on a hot day
yep, i've got the walbro. It whined on me once when i was uber-low on gas, and it hasn't done it again.

From what it seems like, it is not the pump as you are getting the pressure you need with the terminals jumpered (same as me).

I'm perfectly fine driving around however, which makes me think it is a voltage regulator and/or pump resistor problem.

At higher rpm, where the pump switches to 12V / my cars voltage jumps to 14V, there is no problem. As well, my egt's never got into a dangerous range at wot (would signify a loss of FP)
 

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well its not the resistor or relay, I've got two of them here and they both have the same resistance, and are acceptable according to the tsrm specification.

for reference, here are my values:
+B - FP - 0 ohms
+B - FPR - ~78.5 ohms
+B - PR - no continuity

resistor terminals - ~0.8 ohms

From this i deduce that my problem is voltage-related. By jumpering +B and FP at the diagnostic block, the pump is effectively switched to 12V mode. When I let my car idle, my voltage is the shits, often dipping below 12 V (head lights dim considerably, etc), which would result in reduced voltage fed to the pump, causing the fuel pressure to drop. When I put my car back together, I'm gonna go with a new alternator, hopefully this fixes the problem.
 

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Discussion Starter · #11 ·
ok the voltage thing you described is exactly what I have too
it doesn't seem like it's charching at idle, however it's definitly charching above 1.5k rpm

The pump might have pressure, but what about flow?
when the Fp nd B+ are bridged the car is not running,
when it's running you need more flow, pressure
 

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you will have one given flow rate for a set pressure....flowrate at X psi is based upon the size of your fuel lines...if you have pressure, you have flow.

you see, the way the fuel system is set up, there is a resistor limiting power to the pump at times of low load. when you bridge +B and FP with the car not running, you essentially bypass the resistor giving the pump full power (or whatever your battery can put out). With the resistor in place, and your charging system not putting out enough voltage, the pump sees a lower voltage than it is designed to, thus, not providing enough fuel pressure.

i say swap in a good alternator and see if this fixes the problem....as it will solve mine as well :)
 

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I've had votlage issues as well and it was bad battery wires and grounds, NOT my alternator (had battery and alt checked and they where both fine)
 
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