Never starts first try, loses prime

Swiss-cheese TJ-6

Swiss-cheese TJ-6

Swiss cheese because its holy
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Supporting Member
Joined
Jan 20, 2025
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53
Location
North Salt Lake, UT
For the past 3 years, my Jeep has always started on the second or third crank. It starts first try if it was recently running. I suspect a backflow valve of some sort in the fuel tank, which is why it’s losing prime. I’ve been very lazy getting around to fixing it because my tank’s setup makes it difficult to drop for repairs. It’s a 5-6 hour ordeal with a high risk of damaging the tank. I’m finally getting around to fixing it while redoing the rear bodywork and adding a fuel pump access panel. My main question is: which part in the fuel pump assembly typically goes bad and causes this, and is it an individual piece I can buy so I can keep the factory fuel pump or do I need to/ would it be better to replace the whole assembly? Any recommendations for parts brands? My Jeep is a 2002 4.0.
 
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If you turn the key on for a second to hear the pump prime buzz will it fire up? Or do you just hop in and crank away? My point being 99.9% of the aftermarket pumps aren't worth the powder to blow them up IMO. Good on you for the access panel, so carry a second pump assembly when the first china bomb POS dies and your 100 miles from nowhere.
 
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I threw the almost cheapest pump I could put in my 97...a Brute Power from Rock Auto.

It's been almost perfect for a year. The float has stuck twice on hard rock hits to the fuel tank skid but after a couple of minutes of sloshing around it's fixed itself. I also might not have clocked the pump perfectly.

Made it from Oregon to the Rubicon, down the trail. Even ran it out of gas...


-Mac
 
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I al
Gilaguy23 said:
If you turn the key on for a second to hear the pump prime buzz will it fire up? Or do you just hop in and crank away? My point being 99.9% of the aftermarket pumps aren't worth the powder to blow them up IMO. Good on you for the access panel, so carry a second pump assembly when the first china bomb POS dies and your 100 miles from nowhere.
Click to expand...


I always wait for the pump to buzz for a second and stop, but even then it’s usually the second or third crank. If possible I’d rather not get rid of my oem pump just wondering if there’s a valve or something that can be replaced on the pump rather than the whole assembly.
 
My understanding is there’s a check valve in the fuel pump. When the key is turned on, the pump runs for a few seconds to pressurize the fuel rail. If the check valve leaks, the pressure doesn’t hold. Try turning the key to Run (not Start) on / off / on / off / on with a couple second pauses in between. If the check valve is leaky, this should help build fuel pressure so the engine fires when the key is turned to Start.
 
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