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Old 02-01-2021, 12:11 AM   #1
nissand21newb
 
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Default Fuel pump woes

Hey folks,

A few weeks ago I replaced just the sending unit on my fuel pump assembly on my 1990 D21 2Wd inline-4. I've been driving the car somewhat regularly since then with no problems and I finally have a working fuel gauge now, which is nice.


I was driving down the road yesterday and the car just died. Had it towed home and I've come to the conclusion that I'm not getting any fuel pressure. Car starts right up when you use starter fluid or pour gas down the throttle body. Also, I remove the fuel filter and put in a fuel pressure gauge with a t-junction and I get 0psi.


I'm trying to determine if the pump is bad or there is a wiring issue and would like y'alls help. I'll list below what I've done thus far:


1\ Connect 12v battery charger directly to the fuel pump harness. I connected + to the b/w wire and - to one of the black wires. Fuel pump turned on immediately but was very loud. Maybe because my batter charger runs a bit hotter than 12v.

2\ Bench tested the fuel pump relay. Works fine.

3\ Verified that the ECCS properly grounds the coil on the relay and that the other terminal on the coil receives +12v.

4\ Verified that the other pins on the relay, (3&4) have 12v across them.


Interestingly, when I turn the vehicle, however, the fuel pump does not turn on. Despite the fact that I know the relay is working and all voltages are correct.

Additionally, when I run the pump directly off the battery charger (or connect +12v to the red/white wire from the relay panel the pump turns on but I get 0psi.

so I seem to have two simultaneous problems. One, even with pump running I get 0psi and two the pump doesn't turn on for the standard 5seconds with the key in the run position.

Any thoughts?
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Old 02-01-2021, 01:01 AM   #2
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You may be dealing with a clogged fuel line?

Also, test for 12vdc between the white/blue wire and the black wire at the fuel tank....on the truck side of the connector, not the pump side.
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Old 02-01-2021, 01:11 AM   #3
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Thanks for the reply.

I do indeed have 12vdc on the truck side of the connector. I'm gonna lift the bed this week and I'll blow some compressed air through the line to see if it has a clog. Until then, I think its really odd that the I can get the pump spinning when I directly connect it to 12vdc but I cannot get it to turn on with the key in the RUN position. I'm confident the relay is working properly. Any thoughts on that?
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Old 02-02-2021, 01:44 PM   #4
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Quote:
Originally Posted by nissand21newb View Post
I think its really odd that the I can get the pump spinning when I directly connect it to 12vdc but I cannot get it to turn on with the key in the RUN position. I'm confident the relay is working properly. Any thoughts on that?

I wouldn't be "confident" unless I tested the relay. If the relay is delivering positive voltage to the fuel pump, that isolates your issue between those.
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Old 02-02-2021, 01:58 PM   #5
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Hi, I have indeed tested the relay on my bunch. +12vdc across terminals 1&2 closes the circuit between terminals 3&4.
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Old 02-02-2021, 01:59 PM   #6
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I just ordered a Bosch replacement pump and I'm going to swap out the pump on my assembly when it arrives on Thursday. I'm hoping that'll fix up the problem. Any tips for that process?
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Old 02-02-2021, 03:01 PM   #7
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Before you replace the pump, but after you’ve removed the assembly, try manipulating the wiring to see if the connections are good between the pump and the truck. I had to replace the assembly on my son’s truck due to a flaky connection
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