I have to swich my 1991 cherokee on for 20 minutes before i hear the ful pump and than a nother 40 minutes than it starts. what could be the problem?

SOURCE: I have a 1991 jeep

First, check ignition system...cap, rotor, wires & coil. You may have some arcing going on there. If plugs are not recent, take a look at them as well...even if they are good, they can often tell you which cylinders are having a problem (wet with fuel, heavy deposits or just "different" from the rest) You may not hear the fuel pump come on all the time if the pressure in the line is not bleeding down. I would take a look at the relay first (power in & out). If fuel filter is more than 1yr old change that. (routine maintenance regardless of problems) Pressure test system if in doubt. Make sure idle air system is clean and do a quick test on crank sensor (a known problem area). likely something here will get you going.

SOURCE: 93 jeep grand cherokee: won't start when cold.

try replacing the fuel pump relay or swap with another relay from under the hood and see if that makes any difference if it does scrap your relay and get a new one

Steve Allison

• 5569 Answers
• Posted on Sep 07, 2011

SOURCE: 94 grand cherokee. after driving

Your catalytic converter may have disintegrated internally. If the ceramic element in it has crumbled, it will glue together when cooling down and not impede the exhaust discharge for the first minutes but when hot, the broken pieces can gather at the output end and clog it. When you notice the bogging down becoming very noticeable, find a safe place to stop and leave the engine idling.
Listen at the tailpipe to learn if you can hear the 'normal' engine firing noises or if it sounds restricted and sounds more like a hiss than the typical 'throbbing' sound.
If so, then the cat is at fault and needs replacement.
I had this problem years ago and the first sign of trouble was a marked improvement in gasoline mileage, probably due to an initial mild increase in back pressure which the engine seemed to like. As the disease worsened, it fell back drastically and hill-climbing became iffy and coolant temp ran higher than normal.
Frankly, I 'cured' it with a .357 magnum and a couple of rounds into the tailpipe. The whole system was heavy gauge stainless steel and there was only a mild bend from the end to the cat. It didn't hurt the rest of the system but one could occasionally hear a rattle from the shards. ;-) Not legal in some states!