Frustration need help!

1991 4.0l HO manual 4x4. Got in it to drive it today and about a mile from my work the jeep began to stumble and misfire, not bad but noticable. It was fine at high rpms but at low rpms it was misfiring and stumbling. So I parked it and left it for about an hour or so. When back out to start it and it wouldn't start at all now, it turns over but no start. About another hour went by and I went back out and tried to fire it, I turned it over once, no start. Put the pedal on the floor and turned it over and it fired right up. Revved it up and it misfired and stumbled at low rpms again. I got it home and I just went back out to start it and now it wont start at all. Battery seems to be dead, but earlier it was fine??????:dunno: Tried to hook a jumper box up to it and it still wont start. Replaced CPS sensor and it didn't help any, has gas in it, battery terminals and wires are fine, any help would be greatly appreciated...

First thing is to get the starter to crank all the time. Try charging up the battery. Do you have the voltmeter gage on you dash. At any rate, if you have an XJ you need a voltmeter. Do you have one? If not, get one ASAP, and check back in for next steps. We can take you a lot further, but without a known good charged battery, it is a waste of time. Don't really know if a jumper box is worth shit. CPS does not have anything to do with vehicle cranking. Charge battery or try jumper cables from another vehicle. If it cranks, then we have to figure if charging system works.

But I've jumped to a conclusion here. Have you checked the battery connections? Take apart, clean and reassemble. Scotchbrite/sandpaper, cleaning with electrical/brake cleaner, etc., reassemble. The ground connections are equally important. Don't mess with checking the other stuff until the connections are cleaned up.

If your Battery is dead it will run funny..Charge it up an see if it runs better..If it does, then i would have the alt check to make sure it is working right..Clean all your grounds, plus the battery post an cable ends

Two things come to mind. If your IAC is sticking closed, it will try to die when you release the gas pedal. It will also not start (often) if you don't depress the pedal a little at start-up. Normally the IAC will park itself partially open, so you can start without using the pedal any. When you release the pedal during driving, it will open some, so the motor doesn't stall from lack of air.
Second is weak spark, the distributor cap gaps too large (very worn distributor cap), carbon inside the cap allowing the spark to short out, coil or spark plug cables with excessive resistance or a hairline crack in the insulation allowing the spark to ground someplace or water someplace it shouldn't be inside the distributor or the spark plug cable boots. Symptoms are, hard starts, low RPM miss and loosing high RPM (towards the top of the RPM band) the spark kind of breaks down and the motor craps out.
It could be a lot of stuff, but these two are fairly easy checks and fixes. I tend to check out the basics, before I spend money on sensors. Though a marginal CPS, would have also been one of my first guesses.
You have to be carefull when removing the spark plug boots, twist first to break the bond then remove carefully. Pulling on the cables (instead of the boot) can break the conductor inside (over stretching) or the contact on the end can slide into the boot and leave a gap between the contact and the plug end. Same thing at the distributor cap. Spark plug cable pliers aren't expensive, kind of pliers with plastic jaws, they also work well for removing vacuum lines (or even on kitchen appliances to remove rubber hoses with clamps).

Ok besides the battery problem I'm still tring to figure out the stumbling problem. I also noticed that when the Jeep is running it smeels very bad, and the exhaust is getting extremely hot..o2 censor???

89cherokeexj said:

Ok besides the battery problem I'm still tring to figure out the stumbling problem. I also noticed that when the Jeep is running it smeels very bad, and the exhaust is getting extremely hot..o2 censor???

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could be a stopped up cat converter....

try unbolting it so that any exhaust restrictions are removed.

might check the map sensor

how do I check the map sensor and where is it at??

i would also check the fuel pump

89cherokeexj said:

Ok besides the battery problem I'm still tring to figure out the stumbling problem. I also noticed that when the Jeep is running it smeels very bad, and the exhaust is getting extremely hot..o2 censor???

Click to expand...

Fix the battery problems first. And clean the grounds, including the engine to firewall. RENIX models like yours need proper voltage and ground to function properly. Then you can try disconnecting MAP sensor to see if it runs better and hook up a vacuum gage to see if convertor could be blocked. That would show a slowly decreasing vacuum.

i would almost bet the coil is giong out, not uncommon for a '91 especially if it has never been replaced

winterbeater said:

Fix the battery problems first. And clean the grounds, including the engine to firewall. RENIX models like yours need proper voltage and ground to function properly. Then you can try disconnecting MAP sensor to see if it runs better and hook up a vacuum gage to see if convertor could be blocked. That would show a slowly decreasing vacuum.

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1991 is not renix

jneary said:

1991 is not renix

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You are, sir, of course correct. I falsely jumped to the conclusion that 89cherokee was an '89 Cherokee. Reading the post further indicates that he is working on a '91. But I still think he needs to fix his voltage supply before he further diagno$ticizes.

I appreciate all your guys help, I finally got it back after replacing a couple thing. It ended up being the IAC..

What is the IAC, and how do you check it?

fubar XJ said:

What is the IAC, and how do you check it?

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idle air controller, its located on the throttle body.

STILL HAVING THE SAME PROBLEM!!!!!

did you check the map sensor after all

did you check the coil for any visible cracks, you may have to remove it to see them