MaineXj

Hello all! I have been browsing Cherokeeforum but am really trying to figure an issue out with my Cherokee so I can have it to run in the snow. I have always searched to find answers, but for this I needed to ask. I forewarn you now this is going to be a long post, as I am going to include everything i have already tried with it.

To start, I swapped the motor this summer because the old one had bad rod bearings. It is a 4.0 from a 98 XJ, which is the same year as what I have. The motor has 85,000 miles. I replaced the exhaust/manifold gasket when the motor was put in. 98 XJ, 4.0, AW4, 8.8 w/discs, aussie lockers, 4.10s, rc long arm.. etc.

I overheated the other day and blew a coolant line. The radiator was replaced with the motor swap, but needs to be replaced again because someone threw a rock in front of my jeep while I was going about 50. So that needs to be replaced, I know. Anyways, the day after the overheat, about 30 seconds after I started it, I was pulling in to the garage to rebuild the Johnny joints for my lift. As I was hitting the throttle in the low end to get in the garage, the motor was cutting out, like it stopped getting fuel and/or spark when I hopped it in the low end of the throttle. When I ease in to it, it runs great. Anything past 2000 RPMS it runs strong as hell.

I started off with the basics, and basically, I have replaced almost every sensor and part I can think of that would have anything to do with anything, and I am still having issues. Here is a list of all the things I have replaced in the past 2 days of my diagnostics.

Hooked up a scanner with a laptop diagnostics program, and the 2 codes were for the O2 sensors. They were both reading "high voltage" of 1.000 volts, steady, not moving. I did not have a down stream O2 connected because of the beer can cat That I installed.The upstream was covered in carbon, and one wire was pinched.
Question 1: What does this mean? The 1.000 volt that is usually below one volt, and it is supposed to fluctuate.

So after this, I replaced the upstream O2 sensor, and welded in a bung after the cat for the downstream O2 sensor, and hooked it up. The welds are solid, no leaks. I also replaced a blown 15A fuse under the hood that I had no idea what it went to.

Then I figured, what the hell. Ill try a basic tune up. I put in a new cap, rotor, plugs and wires. The old stuff was corroded, and It deffinatly made it run stronger. The problem actually went away on initial start up, then came back a start up or two later as the motor warmed up.

Keep in mind, almost every time I have added something or changed something (even a fuse) I have disconnected the battery, and hooked the terminals together.

So the tune up was a no go. I then looked else where. My IAC motor is pretty clean, and looks new. It came with the jeep, i think the PO installed it over a year ago when I bought it. It was stock with another motor when I bought it. I figured the IAC was fine, and did not need to be replaced. I left it, but I did screw in the "plunger" or "pintle" as far as it goes. Im not sure if this is good or bad?

So next I was looking at the fuel injectors. I took the fuel rail off, and let all of the injectors (with the o-rings off) in B-12 Chemtool overnight. There was a lot of dirt and grime in there the next day, so I wiped them off, and put the same o-rings on that I had lubed with lucas fuel cleaner, which is more of a lubricant for the fuel system. They are all seated correctly in the manifold / fuel rail, but I can twist the injectors around somewhat easily. How right are these supposed to be in there? Should I be able to twist them? I have new o-rings for them, I just haven't installed them yet.

This still, did nothing. It ran even better (at this point the jeep RUNS great, it just still has an issue with idling slightly rough, and when you go to hit the gas, it wants to just die, and shut off. If you play with the throttle right, you can get it to shut right off.) SO I moved on to the TPS (throttle position sensor). I replaced that with a new one from napa (like 62 friggan' bucks) and to be honest, I think that made it run worse, but it could be me. Anyways, it wasn't that either. Still had the problem.

Finally, I decided to drop the coin for a CPS (crank position censor). I pulled the old one out, and was extremely suprised to see that some of the wires to it had melted, and frayed. It was rediculous. I thought for sure, "Finally, I got this crap figured out! ". So I installed a the new CPS that was 144 dollars at Napa. Checked all the fuses, reset the battery, hooked the battery up and went to turn it over. By the way, my guages never worked or worked off an on until I replaced the CPS. After that, my guages all worked great.

It took a little bit to turn over, and at first it ran great (like every other time I started it after replacing something). Then it went back in to HELL mode, not idling smooth (for a low milage motor, with new sensors etc, it should be idling smooth as ever..) ANd it was still bogging out when I hit the throttle from an idle. After this, I was completely dumbfounded. I tried to seafoam it a little, to clean the carbon out from running rich, and it started knocking from the top end (sounded like the valves) when I started sucking up some of the sea foam through the booster line. I did'nt put much in, and stopped when I head the tapping.

So an hour later, I go to start it up. It no longer knocks, but it only wants to idle at close to 250 RPMs (it sits right at the very first line on the tach). It will go through the RPMS fine, but if I hit the throttle fast, it wants to bog out like it has been doing the whole time. Any ideas on what this bogging could be?

Thanks for any help!! I have thrown so much money at this jeep trying to get it running right so I can throw a new radiator in it, finish up the johnny joints, put my durango steering box in, and run her all winter! I even have some amsoil for it, I just have not put it in yet because of the issues she is having.

NovaTJ

Well, you have said a mouthful! Based on your O2 readings and the carbon you mentioned, the fresh tune-up that lasted for a short while, I'd say you are running rich. You said you did the basics....The basics are fuel, spark, air, and compression. You may have a blown fuel pressure regulator...pull the vacuum line for the regulator and check for the presence of fuel in the vacuum line. Do a manual fuel pressure test. Test your compression...it may have jumped time and now is running rich. I've seen more than my fair share of 4.0L Jeep engines with worn out timing chains. Hows the map sensor??? Map sends barometric pressure readings to the computer for air/fuel ratio strategy. Vacuum leak causing an incorrect baro reading?

Greg

brutalxj

I would say put a real cat in there. Then ur sensors will read right! Without the cat doing what it should the computer won't read right and it'll run like crap and fall flat on it face like yours is doing.

MaineXj

I know im asking for help but I also know what im doing and the cat is real, its not gutted and has internals. It ran for 5-6 months fine with it (bought the cat new). There is no way that is giving me the issue im having.......

brutalxj

The reason I said that was more along the lines that after market cats are crap! That's one of the reasons here in WI they changed the emission laws. A lot of people payed big money to have a shop install them and they just didn't perform. A stock cat has much higher content of valuable metal inside witch is what makes them work. Aftermarket ones use other materials that don't cost as much but also don't work the way they should. U can scrap out ur stock cat and buy a aftermarket cat. That's saying something about quality. Oh and the diff between a high flow cat and an regular aftermarket cat is just the words high flow I have looked threw 2 of them at the same time and there the same thing.
Sorry about the rant.

4jeepers

X2 In some states you cannot install an after-market Cat. They will not pass the visual inspection during a smog test! besides the after-market Cat does not last very long.

MaineXj

its a trail rig, I have a truck I DD. This drives to the trail and back. i dont care about having a super awesome cat on there that im just going to smash up in the rocks anyways. if i wanted a mall crawler i would have bought a wrangler LOL.