Help! jeep xj wont stay running

[Frankenjeep4.0]

Long story short i bought an 99 xj, it ran when I got it, sat for two weeks now if it starts it idles for about ten minutes then dies no bogging like it's out of fuel just shuts off, fuel pump cycles but won't start back up and if it does not for very long, also doesn't stay running at first, have to keep the foot in the throttle a little bit to keep it running till it isles by its self, I need a little guidance as to where to start with this issue I know it could be a number of different things I just don't want to start throwing parts at it if it is a common problem that more veteran jeep owners have expierianced. (This is my first jeep) any help is greatly apreiciated.

 

[k-2]

get codes - even if light is off. Scanner is best but key on off trick is better than nothing.

Check fuel pressure with a gauge - then with KOEO observe pressure drop.

Is there a remote starter?

 

[Frankenjeep4.0]

No remite start, and the fuel pump is brand new, also it's not throwing any codes.

 

[k-2]

Auto basic troubleshooting -

Did you SCAN for codes or assume no light no problem ?
FYI - The key trick is a start BUT will not show all codes.

New fuel pump All the more reason to check pressure and check leak own with a gauge...

 

[Frankenjeep4.0]

I tried to check the codes (though there is no light) with no success. Im going to take it to a shop tonight to have them hook there computer up to it, the code reader Ihave doesn't read anything wrong, I also ran the pressure test and came back with just about 38-39psi.

 

[k-2]

we will need to double check that fuel pressure - memory says @50psi ?
Time permitting I will get the book - hopefully someone beats me to that with PSI #s

 

[k-2]

The spec I show is 49psi so new pump... hum not looking so good,

A thought, install fuel pressure gauge. turn key to run pressure will build, record psi, wait after 2seconds pump will stop, watch gauge does it drop? drops Xpsi in 5 min.... let me know.

I will ask again did you scan? Do you have a scanner?

 

[54cj3b]

sounds like the ecm went out

 

[k-2]

why would you suspect ECM ?

Did I miss something? again....

 

[Frankenjeep4.0]

I didn't think it was the ecm, I started it last night moved it probably 100 feet before it died out, I was kinda think maybe it was a crank position sensor or maybe the throttle position sensor, hooked it up to a computer and no codes showed,

 

[k-2]

I was asking 54cj3b - maybe he saw a clue I did not.

PCM is way way down the list of suspects.

Fuel pump and pressure. Is pump staying on after @2 second prime- this is my "guess".

Yes could be ckp watching fuel would be a way to confirm. OR a wave form - I did not think an option for a DIYer.
No to TPS without other reasons to suspect.

Another test would be exhaust backpressue - a vac gauge to check - unlikely to fail without prior symptoms.

 

[JPNinPA]

Clean the TB and IAC. Clean battery cables and connections. Load test the battery.


If it continues to idle with stepping on the throttle it's likely the things I mentioned above.

JPNinPA
Using Jeepz.com app

 

[Frankenjeep4.0]

So after testing the fuel pressure scanning the ecm and finding nothing I went on a whim and replaced the crank postion sensor tonight, fixed my problem instantly!