Ok well here's the story...Got my first Cherokee about 2 weeks ago from a buddy at my fire station knowing some things had to be done to it. Didn't know it would be right away though .

So far I've replaced...water pump, t-stat, temp sending switch/sensor, dist cap, rotor, coil, plugs, map sensor, throttle positioning sensor, air fliter, fuel filter, 1 bottle of injector cleaner, flusher the radiator, changed the oil.

Today it ran fine until it started spittin and sputtin (technical term). It was kind of like it was missing. Then it started to backfire, huge!! So I shut her down. Decided to change out the map sensor and throttle positioning sensor thinking that was the problem. Seemed to work until about 30 minute after driving, back to the same thing! And it seems to do it more at low RPM's and idle... Oh.. and there is no cat on it and I also tried disconnecting the exhaust but it still backfired.

I have good fuel, but I don't think I have good spark for some reason. Took off a plug and turned the key only to see the plug sparking very weak and not very often as I turned the key. Now the coil is new, so could it maybe be the wires? I was also thinking maybe EGR valve but can't find the dumb thing where I thought it would be. I did buy a spool of new vac lines and plan on replacing all the vac hoses tomorrow as some of the lines look pretty old and brittle. Could the timing be off from when it backfired maybe? Maybe it jumped a tooth?

I'm very new to this site, and to my Jeep, so any help is appreciated greatly. If I'm missing any info here, please let me know. I'm sure I'm leaving something out. Thanks in advance.

 

i'd try replacing the wires.. i jsut replaced mine.. to bad you can't get colored ones.. not to expensive at autozone

 

First of all, you dont have an EGR valve since your jeep is not a RENIX.
Buy a universal cat with an O2 sensor bung and put it back on. Not only is not having one illegal and bad for the environment it also messes with the ECU.
Your CPS may be giving out (back of engine, on bellhousing), or the CKP (cam position sensor) which is located somewhere in the distributor and tells the engine which cylinder is firing.

Is your CEL on (it should be, without a cat..)
Pull the codes and post them, Im sure one will be for the CAT, but there might be some others to point us in the right direction too...

 

Thanks for the quick response boys. I'm workin in the ER all night tonight and it's slow so this dang thing is on my mind and haunting me. As far as the codes, the only one that comes up is 55 which from what I've read doesn't mean a whole lot. The exhaust will be getting redone as well along with a new cat. The PO apparently butchered it all up. Hell it's even held up with coat hangers in some spots.
I have heard that the crank sensors are a pain to get to. Is that true? And should I be looking at this before I mess with the exhaust? It sounds fine so if I could wait a few weeks to change it out, I'd much rather wait and spend the $$ on the CPS if needed. Is there a way to check the function of the CPS or is it just a replace kind of thing?
Just for fun tho, I think the very first thing I'm gonna do is get new wires. Better off to start with the cheap stuff before dumping loads at fixes that don't matter.
Again, thanks for the quick responses