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Unread 07-03-2013, 08:02 PM   #1
rusty94yj
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Wrangler YJ Fuel pump issue

Hey I'm new to the forum and new to jeeps. Just picked up a 94 wrangler that's been sitting for 3 years bc "the fuel pump went out". Turns out the fuel pump works fine. when I remove the fuel pump relay and use a jumper lead I can send power to the pump and it runs fine. All fuses are good, all relays are good. Does anyone know of any sensors in the circuit the fuel pump may be reliant on to work properly? Or has anyone run into this before? Thanks for any help. Ps the battery is brand new and when I turn the key the starter cranks just fine, but the fuel pump never primes or pumps when I turn the key to ON.

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Unread 07-04-2013, 01:40 AM   #2
RARECJ8
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just because you can hear the pump does not mean its OK. Can you check the fuel pressure at the fuel rail? This is a critical step to diagnose whats up. Beg, borrow or ??? a gauge and see what is happening when you force run the pump. It screws right onto the schrader valve on fuel rail. Good starting point. I just engineered an entirely new fuel system on t he heep and now know more than i ever want to know about the EFI systems.

good luck
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Unread 07-05-2013, 02:16 PM   #3
rusty94yj
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Good point about the fuel pressure possibly not being up to spec, I will check that, forcibly if needed when I ??? a gauge lol but still te problem stands my fuel pump does not run when the key is turned to on as it should normally. Any sensors I should be looking out for? Thanks for any help
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Unread 07-05-2013, 04:51 PM   #4
RARECJ8
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when the key is turned on, the computer sends a flash signal to run the pump, but only for 1 or 2 seconds then it stops. that is normal. Once the engine is running, it will then kick on all the time, especially if ur running a two line fuel system-- supply and return. i have diagnosed this issue a 100x and the best way to isolate or eliminate the issue is to test the PSI at the fuel rail. Otherwise, you can fret over many things that may not be relevant to the fix.

do you have in tank module or external Airtex style pump?
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Unread 07-05-2013, 08:39 PM   #5
rusty94yj
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Thanks for the reply I will test my fuel pressure as soon as I can get my hands on a gauge. Side note, I did a bunch of electrical tests and here's my findings
I back probed the fuel pump connector key ON and no voltage to the fuel pump.
Relays and fuses are all good.
I pulled the fuel pump relay and jumped the fuel pump from the constant hot and the pump ran ( I spose that circuit is good).
I have battery power at the pump relay from the yellow ignition hot ( I spose that part of the circuit is good).
For funsies I pulled a spark plug and grounded it to the engine turned the key to on and you guessed it, no spark.
Ugh, any ideas? Please don't say ECM
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Unread 07-05-2013, 09:12 PM   #6
rusty94yj
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Also, no engine light when I turn the key to on
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Unread 07-05-2013, 10:05 PM   #7
rusty94yj
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Edit: turned the key to RUN (cranked the starter) and no spark
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