Mechanics

NO POWER TO FUEL PUMP

1995 Jeep YJ • 150,000 miles

4.0 L motor
Manual transmission
20 gallon tank

Would just crank (it started and stalled after a second a few times making me think a fuel problem was present)
Fuel relay clicked, fuel pump fuse is good, battery was good
Swapped relay with starter relay and no change, swapped with the relay that's in the fuel circuit (automatic shut off? No change either)
Checked fuel pressure at rail, there was none
Fuel filter was not very old, and there were no obvious leaks
Fuel pump was not priming
I dropped the tank and took apart the fuel sending unit
Put 12 VDC on the pump and it functioned

When the key is on (during the first 2 seconds, no voltage at the fuel sending unit harness, however there are 7 volts at the fuel gauge sensor pin

I jumped the relay (the high current one.30 I believe) to 87
There is 12 VDC at the fuel harness when the pins are jumped
The fuel relay still clicks when the key is just turned on

Ideas would be appreciated
Avatar
Aaronmcd
August 14, 2012.



There is a DARK GREE/Black wire to power the fuel pump, check to see if power goes through it to the pump and check the ground by the DISTRIBUTOR. Do not pull the power distribution center.


Hmac300
Aug 14, 2012.
Ok, so, you mean the 3 pin harness where the fuel pump plugs into?
There was no voltage unless I jumped the fuel pump relay
I'll check the ground tonight


Tiny
Aaronmcd
Aug 15, 2012.
Ok if you have to jump the relay tehre is problem there, either the pcm isn't telling the relay to turn on or the auto shutdown relay isn't sending a signal


Hmac300
Aug 15, 2012.
How would I proceed then?


Tiny
Aaronmcd
Aug 15, 2012.
Well recheck your fuses and see if the fuel pump relay is getting turned on. It's one of the previous answers I gave you. Also check fuse 21 in power dist box, the 96 is wired a little different and this may be closer to that. But it still leads to pcm or auto shutdown relay that turn on the fuel pump relay.


Hmac300
Aug 15, 2012.
Aaronmcd what model jeep is this?Iam trying to find a wire diagram to see whats going on here.


Saturntech9
Aug 15, 2012.
As I said in the first post, it's a 1995 jeep wrangler (YJ) SE (the 4.0L model)

I am going to recheck everything today


Tiny
Aaronmcd
Aug 15, 2012.
When it fails to start, does the MIL illuminates when ignition switch is turned on?


KHLow2008
Aug 21, 2012.
I have this exact same problem. Did you ever come up with a solution? '92 YJ 4.0 no power to the pump with switch on, 7 volts on middle prong of the pigtail at the tank, but can run 12V directly to the pump and will run.


Tiny
Yjfanatic
Oct 13, 2012.
Igniton switch on would only provide power to the fuel pump for a brief period, 2-3 seconds, for priming the system.

The 7 volts is for the sending unit.

Remove the fuel pump relay. Ensure you have battery voltage at terminal # 1. Use a fuse wire to bridge terminals # 1 and # 4 and if fuel pump does not work, you have an open circuit between the relay and fuel pump. Fuelpump circuit works on a rather high current flow and opens in circuits are often due to overheated terminals at connectors.

Btw aaronmcd had tried swapping relays, did you do that? Symptoms and even faults can be similar but the cause or source could be different.


KHLow2008
Oct 13, 2012.
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