iamdh4

I have a 96 Jeep Cherokee inline 6 4.0L, with a bit of a random misfire. I have just replaced, ignition coil, distributor cap, rotor, spark plugs, and crank shaft position sensor. When my truck broke down earlier in the week (crank shaft position sensor went bad), i did notice that the throttle was sticking a little bit when the truck was off. I wonder if maybe there's a sensor or something on the throttle body that's acting up?

I was driving to work yesterday, it started misfiring i was going about 45mph maybe 1500, to 2,000 rpms. eventually stalled. Started right back up after i gave it some gas. misfired a couple more times the rest of the way, but made it without stalling, and seemed to idle fine when i got to work.

On my way home from work, the first stop light i was sitting at, idle for a minute, it misfired and stalled. Started right back up again. was still waiting at the light died pretty quick again. Started right back up. Got down the rode a few miles to the next light, died at idle. Started back up, and made it all the way home, about 10-25 miles, without stalling(it did misfire a couple of times however).

Any insight would be appreciated. This truck is usually the most reliable car i've driven, I've never had a problem like this before. I hear that the I6 4.0 is a legend of an engine and will run forever. The engine does have a little knock but not very bad, hardly noticable, the engine sounds great at both idle and giving it gas.

I checked the fault codes (I don't have and odb reader, so i used the ignition trick), i got codes (12-43-21-55). 12 being battery was recently disconnected, which i did take the battery cables off recently. 43 is misfire (i already know this), 21 is O2 Sensor (i've been running without this sensor for a while and has never caused a misfire), 55 is end of code readout. Money is a little tight right now, i just droped $160 in her this week (which i had to borrow). I am going to try and get the money together to replace the O2 sensor, maybe the sensor is the problem, and just creating too rich of a fuel mixture or something.

Any suggestions?

Thanks in advance,

Wayne

Edit: I thought that i would add that the misfire doesn't seem that bad maybe a single cylinder misfiring, if driving the truck just jumps a little as if the transmission jumped gears. and at idle you don't feel anything, hardly even hear it. Also my idle rpm's vary between 800 ~ 1200 rpm's

kenjen11

There is a sensor in the throttle body called the idle air control sensor, sometimes it gets dirty from carbon and causes the vehicle to run funny. There is a detailed post ( a write up) on how to clean the IAC on this site that show pictures on how to do it. It would be free to clean and your jeep might need it anyway. That sucks the jeep crapped out two weekends in a row. Once my water pump went out on a friday leaving me and my family stranded, then the next monday the wheel cylinder went out leaving me with out a jeep until I could fix that. There is also another sensor in the throttle body called the throttle position sensor that you might want to look at. If your throttle is sticking it might be throwing this sensor off. Also are your plugs gapped correctly?

iamdh4

Thanks for the heads up i will take a look at it, it ran rough both on the way to work, and back home misfiring maybe about 5 times either way and even multiple times per misfire, and stalled once. i got home and let it idle, it took a little while but it died after i played with the throttle, and let it come back down to idle. it didn't sound like it misfired before it stalled, just shut off by itself, almost as if it just ran out of fuel. So I'm starting to lean twards the pump being bad, i have also already replaced the fuel filter, i checked to see if there was gas in the fuel supply bar to the injectors, and there was, but it seems there was not much gas or presure when i pressed the stem it was pressed in mabe a total of 3-4 and the stream pretty much stoped. I'm gonna try and get a guage hooked up and see if the pump is keeping a constant flow.

Do you know what the fuel pressure reading should be on this model?

I feel bad driving her in the condition she's in but i have to get to work. I'm off tomorrow, so i will check the throttle body out. Maybe that's whats going on, if it is the pump, hopefully she can last one more trip Tuesday is payday and I'll go right over to autozone after work.
Thanks,
Wayne

freegdr

did you replace the o2 sensor it could be causing a mixture problem causing a missfire issue

iamdh4

just cleaned the IAC/Throttle body. The IAC had some pretty bad build up on it. The Throttle body looked alot worse than when i checked it before it started backfiring. Hopefully this will fix the problem.

No I haven't changed the O2 sensor out yet (I get paid tomorrow, plus a little extra cash for a co-workers computer i fixed ) But I ran for a very long time with the sensor not working and never backfired.

Anyway, I'm letting the parts sit out in the sun to dry, will put them back in after while. We'll see how it go's.