Ryan Fairchild

I've recently been having a misfire problem with my 2000 cherokee 4.0. First started having symptoms on a cold startup, where it was running very rough and would buck every so often. Once it got up to temperature, it seemed to smooth out quite a bit but didn't go away. Later that day, on another cold startup, it was again running rough, and began to flash the check engine light. I had no option but to keep driving, but didn't drive far as I only lived 10 minutes away from where I was. Again, once the engine warmed up, it smoothed out but did not completely go away.

Long story short, I replaced the spark plugs, which seemed long overdue (I'm not the first owner, it has 176K on it and had 171K when i bought it). Misfire got better, but didn't disappear. I checked the resistance in the coils and the fuel injectors, all were fine, and then unplugged one injector at a time to see if I could pinpoint the cylinder, but every one seemed to negatively affect the performance. The engine will stall when at idle, and I don't know what else to try.

Any ideas would help, I don't want to pay for a new ECM until I have to. I am pretty good mechanically, but don't have access to real time diagnostics.

Radi

Reading the codes should tell you which cylinder is misfiring. Makes a big difference in troubleshooting if it's just one cylinder, or several.
Stalling at idle- most probably the IAC valve. Clean and/or replace.

Ryan Fairchild

That's one issue I have been having with diagnostics - it hasn't been throwing a code. I do have a code reader, and there isn't a code available. I'll try reading it again, see if there's a code stored in the computer that isn't lighting the MIL. As for the IAC valve, I'll take a look. Thanks

RBLUXJ00

I had the same problem, replaced spark plugs and ignition coil, CEL still came on. We took the fuel injectors out and both 5 & 6 looked pretty bad so we cleaned them and put them back in but CEL came on again. What we've figured out is that my gas tank was the actual problem. We don't have to necessarily get it replaced but we figured out we put too much fuel injector cleaner in it which loosened up the rust in the tank and sent it to the injectors which caused the misfire. So, I guess my question is have you recently treated your fuel? A new filter will probably do it for me. If anything changes I will update.
I forgot to add, we did this about a week and a half ago and the light is still off, didn't get a new filter but I think the bad gas has been eliminated after cleaning the injectors and driving it for a while.

Ryan Fairchild

I have recently treated my fuel, but the misfire was happening before I did that. Being at 176,000 miles, I figure it's probably worth doing a filter anyways. I'll try it, thanks!

Guntar13

2000 xj fuel filter is not serviceable. To change it you have to drop the tank and replace it inside the tank attached to the pump. The first place to check is get a proper diagnostic code from the pcm. Need to know that first. Second is fuel pressure, need a gauge and check it at the rail. Third is make absolutely sure there is not a leak at the intake manifold gasket. I personally would take the throttle body off and clean it all up sparkly in and out including the iac motor; (although I really don't think that's your problem). Get back with us with the DTC and we can start helping better.

Radi

It's flashing the CEL but not setting a code? Is the CEL lit up?

Ryan Fairchild

Sorry for not being clearer about what's going on with the check engine light - it was flashing on a drive home a few days ago before I checked and replaced the spark plugs, all of which were shot. Once I replaced them, the misfire settled out but a code was never stored in the computer, oddly enough. As of right now, the only time it noticeably misfires is at idle, with the occasional, and I mean once every 15 or 20 miles, it bucks mildly. I have been watching it for a CEL to be illuminated, but the light has not come back on since I replaced the plugs. I will check again tonight for any stored codes that did not illuminate the CEL.

robertj

Huh? There is a sock on the fuel pump assembly, but there is a also a fuel filter up on the drivers side of the engine towards the rear near the tank. I am pretty sure I wasn't smoking crack when I changed mine out on my 2000 Cherokee Classic back 5 years ago.

toasterknight

There is no filter in the line from factory on the later models. I know at least 97+ only have the two socks in the tank. If your 01 had one, a PO installed it.

Ryan Fairchild

So I went and read the codes again, and again, there are no codes stored in the computer for anything, let alone a misfire. I did clean my throttle body thoroughly and checked the IAC valve, which seemed to be fine. Another thought is, could it be the fuel pressure regulator? It stalls at idle, hesitates, runs a bit rough and very rough at idle. If this does make sense, where exactly is the regulator? I know it's somewhere on the pump assembly, is it in the tank or on top of the assembly?

RBLUXJ00

It could very well be the regulator. If you remove the vacuum hose that attaches to it and there's gas in it (of course do this while your engine is not running) then you know for sure that your regulator is bad & if there is none in the line, but, when you turn the switch on, fuel drips out of the hose, it is bad as well. There's a couple other symptoms like black smoke coming out of your tailpipe or black spark plugs but you wont always see these. So I would check the vacuum line and go from there because if it is bad it could cause a rough idle. Also, it should be located on top of the assembly, you could probably google where it is located exactly, but I'm almost positive it is on top.

robertj

Crazy, because it is in the same spot on my '96. I guess someone could have added it for some extra protection. Thanks for the info.

Guntar13

Need to check fuel pressure at the rail. Also does your have the heat shield for the injectors installed? There was a recall about this issue from jeep addressing a heat soak issue especially on number 3 injector. The 97+ does not have a fuel return line from the rail hence no regulator that is easily accessible. The only way to check it is to drop the tank.

Ryan Fairchild

So there's three lines coming from the tank going toward the front of the vehicle - the fuel line, the electrical to the pump, and a vacuum line. I'm assuming, unless there's another vacuum line on top of the tank, that is the vacuum line you are referring to. In that case, there is no fuel coming from that line before or after I turned the key on...the car hasn't been started in a few hours, would that make a difference? Or should I run the car for a few minutes, then shut it off and check?