Fuel Pressure ?
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Senior Member
Joined: Jul 2004
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From: Fayetteville, NC
Fuel Pressure ?
Ok, just installed twin 255 fuel pumps. At idle, I am only seeing 27 psi on the guage vs 29-30 with my stockers. Is that normal for you guys that have these? Any way to increase it or just leave it alone. Now at WOT it shoots up to about 50 right away. The old one it would shoot up to 40 at partial throttle, these don't, just sit at around 32 psi. Mods in sig. I installed these for the KB I am getting. Thanks Ronnie
Oh these are 255 Walbro's from LFP.
Oh these are 255 Walbro's from LFP.
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Joined: Jun 2003
Posts: 739
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From: Charleston, SC
Originally Posted by LightningTuner
Yes the issue has been solved. The problem was that the 255s are of a design of pump that doesn't like low voltage. When they have normal voltage (i.e. WOT on the Lightning), they flow to their specified capacity. But when they are at the lower stepped voltage, they actually flow less fuel than the stock pumps. Now this is perfectly fine for a stock truck, as they still supply enough fuel for the regulator to maintain base fuel pressure. The problem comes when you have larger rails. Then the pumps do not move enough fuel under stepped voltage to keep the rails full. That's where the low fuel pressure issue comes from.
The solution? Buy a second fuel pump dropping resistor, and wire it in in parallel with the original. That changes the stepped voltage from 7 volts to about 9 volts, and then the 255s move enough fuel to make it all happy again.
Hope this helps.
The solution? Buy a second fuel pump dropping resistor, and wire it in in parallel with the original. That changes the stepped voltage from 7 volts to about 9 volts, and then the 255s move enough fuel to make it all happy again.
Hope this helps.
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Senior Member
Joined: Jul 2004
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From: Fayetteville, NC
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Joined: Jun 2003
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From: houston, tx
Originally Posted by LightningTuner
Yes the issue has been solved. The problem was that the 255s are of a design of pump that doesn't like low voltage. When they have normal voltage (i.e. WOT on the Lightning), they flow to their specified capacity. But when they are at the lower stepped voltage, they actually flow less fuel than the stock pumps. Now this is perfectly fine for a stock truck, as they still supply enough fuel for the regulator to maintain base fuel pressure. The problem comes when you have larger rails. Then the pumps do not move enough fuel under stepped voltage to keep the rails full. That's where the low fuel pressure issue comes from.
The solution? Buy a second fuel pump dropping resistor, and wire it in in parallel with the original. That changes the stepped voltage from 7 volts to about 9 volts, and then the 255s move enough fuel to make it all happy again.
Hope this helps.
The solution? Buy a second fuel pump dropping resistor, and wire it in in parallel with the original. That changes the stepped voltage from 7 volts to about 9 volts, and then the 255s move enough fuel to make it all happy again.
Hope this helps.
i am having the same problem with my 255's i put in yesterday.
