RandyQuickXJ

Ok to start it off I have a 98 with a 4L and the previous owned put a fuel pump in it 2 weeks before I bought it and ever since about 6 months ago it takes a second to start it will crank for about 8 seconds before it will start or you hit the key let off and hit it again and it will start right up, put a fuel pressure gauge on it and the second I turn the key off it drops from around 40 to nothing hit the key again and it jumps back up to 40 let it sit for 10 minutes and it doesn't want to start again right away, but if it's cold like 0 degrees it starts fine most of the time gets warmer and it doesnt want to start...is there a check valve somewhere that may be sticky or do I need to just get another fuel pump for it?

Roler

so, there is NO pressure holding at all after shut down? That's pretty pore. The 40 should be around 49 PSI IIRC.
To answer your question: yes, and that valve lives in the fuel pump assembly. And I bet that priming the fuel pump 3 times before starting (key on (not run)-hear the fuel pump prime for 1-2 seconds in the back -key off and repeat that 2-3 times) will improve your cranktimes too.

Airtex fuel pump by any chance?

RandyQuickXJ

Maybe it had like 48 psi I don't remember since I checked it a while back, but idk what fuel pump it has in it now I could figure it out tho...but as soon as I shut the key off it drops down to nothing, and I imagine it gets air in the line and it prevents it from starting right back up

RandyQuickXJ

And also priming it does help also, I'm just annoyed with it and want to fix it, have remote start but I can't use it because it will grind the starter if it doesn't start immediately

Roler

Bad fuel leak back (check valve) could def be the cause. The priming method you can do for ages (been doing it myself), it won't damage anything, until you had enough and replace the pump. The valve itself, like said, is in there and not seperately servicable. Well maybe, but you have the pump out anyway when you do that and dropped the tank. If it's an airtex pump, it could be failing on you already. Bosch and Carter pumps are recommended.

RandyQuickXJ

Alrighty I figured that's what it was but I dont feel like dropping the tank...I'll do a few more tests on it make sure that's what it is

Roler

Post #6 in this thread explains the above. Courtesy of TJ (I really should start keeping these things in a folder haha)

https://www.cherokeeforum.com/f2/lon...8/#post2808999

RandyQuickXJ

Thanks man I was just thinking about that actually...I'll check it out this weekend when I have some time and then figure out what I need

belvedere

Could also be a leaking injector.

RandyQuickXJ

Ok I have a carter pump in there thats about 2.5 years old and i keep researching and people have been having problems with carter fuel pumps so looks like im going bosch after i check n make sure my injectors arent the problem

Roler

Unlikely , with a fuel pressure drop to zero (more a crash) , it doesnt sound like an injector leaking...

RandyQuickXJ

Yeah kind of what I was thinking also but I can check it real quick just for ****s

Roler

Just been thinking....that Carter pump should hold longer than 2.5 yrs (like said, and Airtex pump I would not be counting it would)....apparently there is another check valve, near/in the pressure regulator, like TJ mentioned. However, I'm not sure if that related to pre-update models (before 1997).
It just kinda strange you absolutely hold NO pressure after shut down...it would mean both valves would be failing....(again, if this relates to your model/year).
Any warranty on the pump?

RandyQuickXJ

I don't think so because I didn't buy the pump, but I'll check it today and tell you exactly what it does, how fast it drops I know within 5 minutes it has little to no fuel pressure and as soon as you turn the key off it drops fast...because I know it's suppose to hold 30 psi after 5 minutes and it was wayyyyy below that, and I would rather put a Bosch in it anyhow because I haven't heard one bad thing about them yet

Roler

Apart from them not being continued anymore by Bosch, so I heard.