Jeep runs for 15 mins and dies???

[grand94jeepxj]

I'm at work and don't have the time to search for an answer guys and I need help. The Jeep runs for 15 mim and dies. After it cools it'll run again but shuts off again after about 15 min. Could this be the crank position sensor or maybe the fuel pump? This is not my Jeep, but is one of my employees Jeeps and he's afraid it won't get him home tonight. Any ideas? its an 89 XJ.

[MoparManiac]

my first guess would be the CPS, i've heard of that happening before. After that someone else will have to chime in as I'm not too sure

[ChiXJeff]

It's definitely possible it's the CPS. Heat related failure is one of the failure modes. See if he's got fuel pressure (that'll check the pump) and spark (that'll check the CPS) when it won't run.

[1985xjlaredo]

How hot is it running? That 4.0 will run forever even hot but it might stall if it over heats.

[grand94jeepxj]

Its not running hot. He says its runs till it warms up and the shuts off. I was thinking the CPS but didn't want to steer him wrong.

[jfiscus]

CPS, and get one from the dealer.
Autozone / Advance have been known to sell bad or incorrect CPS's.

[pds84]

Don't know if this will help or not. I used to drive a '75 Duster (Slant Six, 225 c.i. with a 1 bbl Holley) with the same problem. Everything was fine until it heated up, then I'd lose acceleration and finally the engine would die. After much investigation, I discovered a cracked exhaust manifold was letting exhaust instead of fresh air into the combustion mix, and effectively flooding my engine with a too rich mixture. When the metal cooled, the crack was relatively sealed, but when the metal heated up from running, the crack (well, the metal around it) would expand, opening the hole that was causing the problem. It took me the better part of 4 months, but I finally tracked down a new manifold in WV - too bad that car got totaled like....7 months later (bad driver + illegal turn + rain-slicked pavement = totaled car). Regardless, if your co-worker's XJ is carbureted, it might hold some bearing. Fortunately, there are plenty of manifolds out there for XJ owners. Best of luck.