Calling out to SAL
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Calling out to SAL
Word around the Fourms is that ur the man to ask about fuel pressure problems! So heres my problem almost a year ago i did the hole built motor thing and took my L to get tuned. well about the 6th pull my tuner said to me hey ur starting to run out of fuel all of the sudden.So i was ok i might know what it is. so I took the tank down and check to see if i broke the plastic Y inside. Nope the Y and the stock pumps are fine. so i put it all back in and make another pull, it still going lean all of the sudden. I remembered reading something about the resistor about how u tie it together.So i did and made another pull and it goes to 9.0 A/F. so he carries on and finshes. Well i go back to my shop and put a Fuel pressure guage on it and at idel it sit at 39-40 and goes to 50-50 psi WOT. well i thought to my self no big deal its fine and it got tuned that way.(I was stupid enough not to read the rest of what the post Said about the resistor and how it should got to 55 to 60 psi at all times) Well now my fuel pressure is dropping and i said oh great finally almost after a year they are going dead. well i got a set of GSS 342's and stuck them in and modifed the line. I put 2 -6 bulk heads on top of the fuel pump cage and ran -6 hose in to a Y block to a filter all the way up to the rails.
Well now what my problem is I have 60psi at idle and 80 at WOT. i bought a new resistor from ford and now the pressure sits at 20-22psi and bounches around to 60-80 psi when ever it feels like or when i am WOT.
I check the resistance at the resistor and it is resisting 8.7 then i check the voltage at the pumps and it is 3.6 volts. Now when the resisiter is tied together it see what ever the altronator is putting out like 13.8 to14.0 at the resistor, and at the pumps i see only 10.8. So i am out of ideas and i cant drive my L making 60psi at all times. U can watch the gas guage move and can tell the motor is getting loaded up with fuel. I understand that the walbro pumps require more amps and voltage to run, but why is it the the resisotr is holding back so much to where the pumps only see 3 volts
Well now what my problem is I have 60psi at idle and 80 at WOT. i bought a new resistor from ford and now the pressure sits at 20-22psi and bounches around to 60-80 psi when ever it feels like or when i am WOT.
I check the resistance at the resistor and it is resisting 8.7 then i check the voltage at the pumps and it is 3.6 volts. Now when the resisiter is tied together it see what ever the altronator is putting out like 13.8 to14.0 at the resistor, and at the pumps i see only 10.8. So i am out of ideas and i cant drive my L making 60psi at all times. U can watch the gas guage move and can tell the motor is getting loaded up with fuel. I understand that the walbro pumps require more amps and voltage to run, but why is it the the resisotr is holding back so much to where the pumps only see 3 volts
Last edited by black knight; Feb 28, 2007 at 02:42 AM.
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From: Palm Coast, FL
Sounds like you may have a ground issue. None of your symptoms are typical of any other truck I've seen.
Here is how the fuel system is SUPPOSED to work....
You have two pumps, they run all the time. They get full battery voltage from the positive wire all the time. The ground side gets run through a dropping resistor, and also to a relay.
When you are driving normal, the ground runs through the resistor, which drops the pumps to about 7 volts. When the TPS hits WOT voltage (about 3.2 volts I think), the relay kicks the grounds to full ground, giving the pumps battery voltage.
You should see about 39 psi of fuel pressure at idle with the vacuum line OFF. With it on, it can vary because vacuum is pulling on it, but it should be in the 30-35 psi range, depending on how much vacuum your built motor pulls. When you trip the WOT relay and it goes full voltage, fuel pressure should "jump" up like a switch, to about 50 psi or so, and then it will go a little higher under WOT and full boost.
When you run bigger lines and billet fuel rails, some people have problems with low fuel pressure. That's because the Walbro's don't flow as much fuel as the stock pumps at the reduced voltage. So you have to wire in a second resistor, which will bring the stepped voltage up to about 9 volts.
I have no idea why you are seeing such HIGH fuel pressure with your setup, that's a new one to me. But if you are not seeing the voltage you should at the pumps, and you see that voltage at the source, then it sounds like a ground issue.
Hope this helps.
Here is how the fuel system is SUPPOSED to work....
You have two pumps, they run all the time. They get full battery voltage from the positive wire all the time. The ground side gets run through a dropping resistor, and also to a relay.
When you are driving normal, the ground runs through the resistor, which drops the pumps to about 7 volts. When the TPS hits WOT voltage (about 3.2 volts I think), the relay kicks the grounds to full ground, giving the pumps battery voltage.
You should see about 39 psi of fuel pressure at idle with the vacuum line OFF. With it on, it can vary because vacuum is pulling on it, but it should be in the 30-35 psi range, depending on how much vacuum your built motor pulls. When you trip the WOT relay and it goes full voltage, fuel pressure should "jump" up like a switch, to about 50 psi or so, and then it will go a little higher under WOT and full boost.
When you run bigger lines and billet fuel rails, some people have problems with low fuel pressure. That's because the Walbro's don't flow as much fuel as the stock pumps at the reduced voltage. So you have to wire in a second resistor, which will bring the stepped voltage up to about 9 volts.
I have no idea why you are seeing such HIGH fuel pressure with your setup, that's a new one to me. But if you are not seeing the voltage you should at the pumps, and you see that voltage at the source, then it sounds like a ground issue.
Hope this helps.
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Originally Posted by LightningTuner
Sounds like you may have a ground issue. None of your symptoms are typical of any other truck I've seen.
Here is how the fuel system is SUPPOSED to work....
You have two pumps, they run all the time. They get full battery voltage from the positive wire all the time. The ground side gets run through a dropping resistor, and also to a relay.
When you are driving normal, the ground runs through the resistor, which drops the pumps to about 7 volts. When the TPS hits WOT voltage (about 3.2 volts I think), the relay kicks the grounds to full ground, giving the pumps battery voltage.
You should see about 39 psi of fuel pressure at idle with the vacuum line OFF. With it on, it can vary because vacuum is pulling on it, but it should be in the 30-35 psi range, depending on how much vacuum your built motor pulls. When you trip the WOT relay and it goes full voltage, fuel pressure should "jump" up like a switch, to about 50 psi or so, and then it will go a little higher under WOT and full boost.
When you run bigger lines and billet fuel rails, some people have problems with low fuel pressure. That's because the Walbro's don't flow as much fuel as the stock pumps at the reduced voltage. So you have to wire in a second resistor, which will bring the stepped voltage up to about 9 volts.
I have no idea why you are seeing such HIGH fuel pressure with your setup, that's a new one to me. But if you are not seeing the voltage you should at the pumps, and you see that voltage at the source, then it sounds like a ground issue.
Hope this helps.
Here is how the fuel system is SUPPOSED to work....
You have two pumps, they run all the time. They get full battery voltage from the positive wire all the time. The ground side gets run through a dropping resistor, and also to a relay.
When you are driving normal, the ground runs through the resistor, which drops the pumps to about 7 volts. When the TPS hits WOT voltage (about 3.2 volts I think), the relay kicks the grounds to full ground, giving the pumps battery voltage.
You should see about 39 psi of fuel pressure at idle with the vacuum line OFF. With it on, it can vary because vacuum is pulling on it, but it should be in the 30-35 psi range, depending on how much vacuum your built motor pulls. When you trip the WOT relay and it goes full voltage, fuel pressure should "jump" up like a switch, to about 50 psi or so, and then it will go a little higher under WOT and full boost.
When you run bigger lines and billet fuel rails, some people have problems with low fuel pressure. That's because the Walbro's don't flow as much fuel as the stock pumps at the reduced voltage. So you have to wire in a second resistor, which will bring the stepped voltage up to about 9 volts.
I have no idea why you are seeing such HIGH fuel pressure with your setup, that's a new one to me. But if you are not seeing the voltage you should at the pumps, and you see that voltage at the source, then it sounds like a ground issue.
Hope this helps.