ok - im still stumped! (pretty long)

ok to refresh.. i bought a 96 xj sport 4.0 auto about 2 months ago. i dont know alot about it yet and its givin me a problem. right after i bought it, i changed all fluids and filters (except trans filter-jeep dealer recommended fluid only).tuned it up as much as advanced auto said that i could (cap,rotor,plugs-zero electrode left, wires,fuel filter-full of brown gas and case rusted out almost,air filter,thermostat and flush, muffler and tailpipe).ran good or better after the tuneup -for 2 weeks. then, started running rough and fuel milage started going south. fuel milage was about 17 when i bought it -now about 14mpg averaged on the tankful. advanced originally sold me "autolite" plugs and i started questioning them so i replaced them with the "recommended" champions - no better. now, sometimes (not sure if rain related or not) when i try to start it, it will either not start without throttle applied- other times, it does start but seems to crank too many times to start,seems to crank slowly,and sometimes "sounds" as if cylinders were full of fluid and engine was being cranked(not sure of technical terms) or kind of like timing was off possibly and firing way before tdc to where it was fighting it. the other night (again, not sure if rain/dampness related), it stalled out two times driving home-fully warmed up and both instances i was cruising at slow speeds and throttle not applied.it seems to be stalling - or- failing to start when no throttle is applied and seems to not matter whether engine is warmed up or not. when i was at advanced, i had them check the charging and starting systems with thier large electronic tester(i was curious since the voltmeter reads low and slow cranking) my battery looks older than the jeep too. they said it seems like i have a weak alternator. could a weak battery or alternator cause the stalling? i do have an exhaust leak up front at the manifold and havent repaired that yet-dont know if its loose or cracked i still have to get to it.when i did the exhaust work,i had the cat off-didnt seem or sound bad to the eye/ear. i could see light through it and no loose rattle inside. also, the exhaust leak in the front is definately more noticable since ive replaced the leaking muffler and tailpipe-which makes sense but my question about that is does that mean that my "off the shelf and physically smaller universal muffler is way too restrictive? it really seems to be forcing ALOT more exhaust out of the front leak.

I doubt the "weak alternator" theory, because low output voltage should cause the engine computer (which contains the voltage regulator) to throw a code. A bad diode might make the alternator behave badly, so it's worth a test. But a weak battery can have an odd effect on running too, and if it's on its last legs it might be a good idea to test it, since winter is coming. Don't trust the dash voltmeter. Test voltage at the battery. For some reason it seems Chrysler electronic systems are sensitive to bad batteries. They don't like the choppy output of the alternator, and if the battery isn't filtering it properly they can behave badly. That is true, by the way, of some of the other electronics. For example, I was experimenting with the rear defrost relay in a non-automotive application (needed a mechanical flip-flop relay for a remote controlled yard light), and found that it won't work at all on unfiltered DC.

The odd starting sounds similar to what I got on my 87 when the distributor was one tooth too far advanced. Once it started it ran fairly well, but it would behave cranking just as you describe. I wouldn't expect this to be the problem, though, if it's developed without your having had the distributor out.

I think if the leak in the manifold gets bad enough it might affect your oxygen sensor reading.

"tuned it up as much as advanced auto said that i could"
They forgot O2 sensor...thats a biggie. I work for autozone...I hear about people at advance getting advice all the time... Anyway, O2 can cause all sorts of problems. Its a regular tune up item that gets over-looked often.

As for the "weak charging" system, that could be causing you problems. My buddy has a 97 RAM 1500, and his was stalling out randomly. And then wouldnt start very well. If you held the gas it would start, run like crap, then die out. I tested it with my ARBST tester at work and everything was "ok", but the battery came up weak. So we changed it and it runs and starts fine 6 months later. Just a suggestion. One thing definetly check your connections at the battery, and the cables. Ive heard of bad connections causing the PCM to randomly go offline and loose memory. Then when it does start back up it needs to "re-learn" things. If the battery looks really old and crappy, go grab a new one. You can get a cheap but still good battery and atleast its a piece of mind.

There are other things it can be too. Sensors are a biggie. CPS, TPS, MAP, and probably a few other. Others may be able to suggest more. I havent run into many sensor problems on my 94 as of yet.

Sounds like you have already replaced a lot of the regular replacment stuff. Its probably something really simple...as usual. Good luck.

Justin

I am guessing the muffler will be ok. From my experience, it seems that a small leak will seem larger if other leaks are fixed. You are probably hearing more noise from that crack in the manifold, because there probably is a little more back pressure than with the leaky muffler. I fought a leak at the manifold/S-pipe fitting for a long time. I finally got everything tight, and it was much quieter than before, but now I have a new loose fitting by the muffler. Back to loud tractor noises. Anyway, I think you are OK on that note.

As for the rough running, I would look very carefully at the CPS. Mine, and probably everyone on this broad's, has giver strange problems when going bad. I had a few very rough starts where it would pop and backfire. After a few re-starts, all was well. Mine also would die on the go. Does yours buck when you hit a bad bump? If it does, I bet your CPS wire has melted through and is shorting out on the manifold. Fire it up and wiggle the CPS wire and connection. See if you can change the way it runs. Be careful, though. I would suggest wearing some welding gloves because the wire runs close to the exhaust manifold, and it will be a hot and cramped space to put your hand. If you are not familiar with the CPS, or the other sensors, do a search for them. This forum is filled with invaluable information on troubleshooting and replacing them. Hope this helps.

any codes?

One of the tricks jeepsters use is to augment the electrical ground system.
run a heavy guage wire from the negative post of the battery to a body
bolt on the front end. be sure to clean off any paint or rust at the body connection.......
this should correct your ammeter reading and make your lights brighter....

thank you to all who have replied. i will try all of these suggestions asap. im not too very familiar with the sensors- but, i am trying to learn. i do not know if any codes have set. can i check them myself on a 1996? and, i do not remember if a bump affects it - but i still will try to wiggle the cps. is wiggling the cps the only way to check it?

I don't know of a way to test the CPS with a voltmeter or other device. Sometimes the connector goes bad, but I think the most common problem is heat related damage to the wire. The CPS sits on the top side of the bell housing and the wire runs between the firewall and the rear of the exhaust manifold. Shine a flashlight down there and look for visible damage to the wire. If you see any, replace the thing. Replacing the CPS requires an assortment of extensions and flex joints and patience. There are only 2 bolts in it. It really isn't too bad of a job with the right combination of tools. I think I did mine in 20 minutes. If I ever do it again, I am going to wrap the whole wire in some type of insulating tape to help prevent heat damage.

The CPS can be checked using an ohmeter for continuity, but I can't remember if it should read as an open circuit or some definite resistance value if it's good. I'm sure someone else knows. Plus, they epitomize the word INTERMITTENT, making it hard to be sure.

thank you to all who have been replying! does anyone know if i am able to check for codes by myself?

DIY code check

Yes, & since yours is a '96, it will be same as mine. I think it is recommended that you drive the truck around a bit beforehand, so the computer will store some recent information. Then:

1) park & shut jeep off

2) REPEAT 3 TIMES WITHIN 5 SECONDS: starting with the key in the "off" position, turn it forward -- NOT to "start" -- but to "on" position (turns on radio, power windows, etc. - auxiliaries) & leave it in the "on" position on the 3rd time [like so: "on" -- "off" -- "on" -- "off" -- "on"]

3) watch your Check Engine Light flash -- it will flash in a series of short flashes followed by longer pauses, and an even longer pause between codes: Code 21 (I think an O2 sensor malfunction) would be *flash* *flash* [short pause] *flash* [then long pause] [then next code or closing code]

For the codes, & more detail, see this webpage (note that different-year XJ's have different procedures): http://www.go.jeep-xj.info/HowtoECUcodes.htm