Check the ground under the rear seat at the connector.
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| Calling lift-pump experts, no fuel! http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=88931 |
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| Author: | pjigar [ Fri Jun 22, 2018 9:00 pm ] |
| Post subject: | Calling lift-pump experts, no fuel! |
I lost fuel one fine day while driving. I had an in-tank lift pump. I used "air-bleed primer pump" to get me home but I knew fuel was not coming. I dropped the tank and checked the 12 V on the pump pins at the lift pump connector so I thought the lift pump was dead. I ordered a brand new pump and installed it. Still no fuel comes out of the tank pipe when I cycle the key on-off-on. I checked the voltage all the way down to the pump terminal inside the tank and it is showing perfect 11.5-11.9 volts. What gives? Why would a brand new pump would not pump any fuel out of the tank? Please help, I am really bummed! |
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| Author: | WWDiesel [ Fri Jun 22, 2018 9:31 pm ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
Check the ground under the rear seat at the connector.
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| Author: | pjigar [ Fri Jun 22, 2018 9:34 pm ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
What do you mean? The ground for the pump is directly hooked to the body of the car. You mean I should check the connection for the ground? |
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| Author: | APC9199 [ Sat Jun 23, 2018 1:49 am ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
Can you hear the pump running when the key is on with the engine off? Have you replaced the fuel filter lately? It may not be a pump problem, but possibly a restriction somewhere else in the system. |
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| Author: | WWDiesel [ Sat Jun 23, 2018 10:54 am ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
pjigar wrote: What do you mean? The ground for the pump is directly hooked to the body of the car. You mean I should check the connection for the ground? Yes, I was referring to the body ground under the rear seat. You said you had 12v at the pump, but do you have a good ground? As APC9199 said, can you hear the pump running when you have 12v present at the pump connector on top of the fuel tank? If you have both 12v and a good ground circuit at the pump, and you can hear the pump running, I would pull the pump assembly out and check the hose between the pump and the plastic fitting on the bottom side of the housing and make sure the hose has not broken or split or come loose from one of the fittings. There is also two wires between the top housing and the pump itself that if one of them were to come loose, the pump would not run. Shown in picture. Lower hose in picture is pump pressure hose, upper hose is return hose. If pump is running but not pumping, then pump has gone bad and you would need to replace the whole assembly.  
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| Author: | pjigar [ Sat Jun 23, 2018 1:50 pm ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
Thanks for help. So here is the final diagnostics and solution. I measured the voltage on the pin connector at the pump end and it was reading close to 12V but not quite. Encouraged with WWDiesel's comment about the ground. I ran a fresh set of wires directly from the battery to the pump pins and pump was pumping fuel out. It concluded that I had an electrical problem from connector under the seat to the connector to the pump. It turned out that both the ground wire under seat was frizzy AND the wire tap for the 12V was also in a bad shape! Finally I soldered the 12V and ground under the seat. That made the pump run. So moral of the story, good voltage does not necessarily mean good current! You need a solid connection to pull the current through! I am an electrical engineer so I get this but nevertheless amazing. Analogy using fluid dynamics: If you have the same "pressure" (aka voltage) at the head of syringe vs fire hose doesn't mean you will get the same "flow" (aka current) from syringe and fire hose. The pipe diameter size (aka connection quality and conductor size) matter. |
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| Author: | WWDiesel [ Sat Jun 23, 2018 2:30 pm ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
pjigar wrote: Thanks for help. So here is the final diagnostics and solution. I measured the voltage on the pin connector at the pump end and it was reading close to 12V but not quite. Encouraged with WWDiesel's comment about the ground. I ran a fresh set of wires directly from the battery to the pump pins and pump was pumping fuel out. It concluded that I had an electrical problem from connector under the seat to the connector to the pump. It turned out that both the ground wire under seat was frizzy AND the wire tap for the 12V was also in a bad shape! Finally I soldered the 12V and ground under the seat. That made the pump run. So moral of the story, good voltage does not necessarily mean good current! You need a solid connection to pull the current through! I am an electrical engineer so I get this but nevertheless amazing. Analogy using fluid dynamics: If you have the same "pressure" (aka voltage) at the head of syringe vs fire hose doesn't mean you will get the same "flow" (aka current) from spring and fire hose. The pipe diameter size (aka connection quality and conductor size) matter. Bingo!!!  Those grounds will get you every time. On a DC system, 12v (+) means nothing if the current flow cannot get back to the (-) ground side of the world to complete the circuit....  Glad you found it! 
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| Author: | pjigar [ Sat Jun 23, 2018 2:34 pm ] |
| Post subject: | Re: Calling lift-pump experts, no fuel! |
I did had ground at the pump but the connection was weak so not enough current was flowing to turn the pump motor on. |
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