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Old 07-26-2010, 09:13 PM   #1
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Default fuel pump test

I have a 92 F150 4.9L. This morning it would crank but not start. Did this once before. I removed the air in tubes and squirted gasoline in and it would run for a few seconds. I could hear the fuel pump run and then stop each time I would turn on and off the key. I do not know where to check the fuel pump pressure. Thought I might have a clogged fuel pump. Removed the line on the outlet side of the fuel filter. Turned on the key and a very little bit of fuel dribbled out of the filter. Removed the inlet side line and turned on the key. Just a dribble. Should it pump fuel like crazy with thye filter disconected?? A side note, I have duel tanks and stopped using the rear tank because the engine would run very bad on that tank. Any Ideas?
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Old 07-26-2010, 10:13 PM   #2
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I just went through the same thing. I guess that doesn't necessarily mean you have the same problem, but the tests would be the same I guess. Here is a link to the thread:
http://www.f150forum.com/f10/no-fuel...estions-59522/

The dribble is no good. I pulled the line after the fuel filter too and only got a dribble. I followed the high pressure pump line back to the reservoir and disconnected there, and got a good strong stream. So I checked each line before and after the HP pump, both were good, so for me replacing the HP pump did the trick.
If you have a pressure gauge check it at the fuel rail first I suppose. I'm guessing if you only got a dribble, you wont have any. Attach to the out side of the fuel filter, should have like 70 lbs there, if not, check the flow, out of the reservoir where it leads to the HP pump. There wont be enough pressure there to check, but you should get a good stead stream from the low pressure pump as long as the reservoir isn't clogged and the pump is working. If only a dribble there to, try before the reservoir, if still only a dribble, it's probably your in tank low pressure pump. Whatever part is in between the good flow and the no flow will be your culprit. Follow the lines back piece at a time and check flow and you should find it. Good luck!
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Old 07-26-2010, 10:25 PM   #3
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Quote:
Originally Posted by Aredecom View Post
I just went through the same thing. I guess that doesn't necessarily mean you have the same problem, but the tests would be the same I guess. Here is a link to the thread:
http://www.f150forum.com/f10/no-fuel...estions-59522/

The dribble is no good. I pulled the line after the fuel filter too and only got a dribble. I followed the high pressure pump line back to the reservoir and disconnected there, and got a good strong stream. So I checked each line before and after the HP pump, both were good, so for me replacing the HP pump did the trick.
If you have a pressure gauge check it at the fuel rail first I suppose. I'm guessing if you only got a dribble, you wont have any. Attach to the out side of the fuel filter, should have like 70 lbs there, if not, check the flow, out of the reservoir where it leads to the HP pump. There wont be enough pressure there to check, but you should get a good stead stream from the low pressure pump as long as the reservoir isn't clogged and the pump is working. If only a dribble there to, try before the reservoir, if still only a dribble, it's probably your in tank low pressure pump. Whatever part is in between the good flow and the no flow will be your culprit. Follow the lines back piece at a time and check flow and you should find it. Good luck!
You mentioned high pressure and low pressure pump. There are two pumps?
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Old 07-26-2010, 10:41 PM   #4
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I have the single center tank with 2 pumps, a low pressure in tank pump, and a high pressure external pump on the frame rail just behind the fuel filter. You have dual tanks so there is actually 3 pumps, 2 low pressure pumps in the tanks and the high pressure external pump. But since you only use the one tank I guess focus on the lines from that tank. But yes you do have low and high pressure fuel pumps.
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Old 07-26-2010, 10:50 PM   #5
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'90-'96 only have high pressure pumps in each tank. No frame pump.
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Old 07-26-2010, 10:50 PM   #6
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Originally Posted by Aredecom View Post
I have the single center tank with 2 pumps, a low pressure in tank pump, and a high pressure external pump on the frame rail just behind the fuel filter. You have dual tanks so there is actually 3 pumps, 2 low pressure pumps in the tanks and the high pressure external pump. But since you only use the one tank I guess focus on the lines from that tank. But yes you do have low and high pressure fuel pumps.

Just so I understand how this works, the low pressure pump in the tank pumps fuel to a resevour and them the high pressure pump draws fuel from the resevour and feeds it to the engine. Is that about how it works? Is the high pressure pump before the fuel filter? Also, when I turn on the key is it the high pressure or low pressure pump I hear. Wait, I just saw sean's post and according to him, I do not have the frame pump.

Last edited by The57man; 07-26-2010 at 10:54 PM.
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Old 07-26-2010, 11:06 PM   #7
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Sorry, I wasn't paying attention to the year of your truck. Sean is right, you only have the in tank pumps. Didn't mean to confuse you. I guess testing is similar though. See if you have pressure before and after the filter and reservoir and if you don't it is probably the fuel pump. It should definitely be more than a dribble. Being that you have 2 tanks, there are more between tank pieces that I don't have and am not familiar with. I read a lot of post about cross filling, that isn't happening to you is it?
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Old 07-27-2010, 02:18 AM   #8
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Sorry, I wasn't paying attention to the year of your truck. Sean is right, you only have the in tank pumps. Didn't mean to confuse you. I guess testing is similar though. See if you have pressure before and after the filter and reservoir and if you don't it is probably the fuel pump. It should definitely be more than a dribble. Being that you have 2 tanks, there are more between tank pieces that I don't have and am not familiar with. I read a lot of post about cross filling, that isn't happening to you is it?

Thats ok. I have no cross filling and I determined that by switching my tank switch and the tank I do not use reads empty. I definatly have virtually no pressure at the fuel line before the filter and I have a little less that 1/2 a tank. Sounds like a bad fuel pump though I supose its possible there is a blockage at the valve that switches from one tank to the other.
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Old 07-27-2010, 03:55 AM   #9
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There is no switching valve, just a valve on each pump assembly that allows returned fuel to the selected tank. If one is stuck the returned fuel pumps to the wrong tank.
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Old 03-09-2014, 12:20 PM   #10
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I also have a '92 F150, with dual tanks. My front tank stopped working one day out of the blue, but the gauge had been working sporadically off & on since I bought the truck 3 years ago. The tank was full, I had to pump it out with a siphon hose so that I could drop the tank. I have the tank out now, and the pump & sending unit/float mechanism is hanging from the lines. The lines have some weird kind of connectors that look like I need a tricky-tool to disconnect them. I want to test the pump & the sending unit to see if I need to go on ebay and buy a new one, or is there some other problem? I can still run the truck on the back tank.

Last edited by Spirit Bear; 03-09-2014 at 12:22 PM.
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Old 03-09-2014, 12:20 PM
 
 
 
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