I have a 1990 4.0L Cherokee that is having stalling and bucking problems. While driving or coming to a stop the engine would stall, I would hear a slight puff sound and then smell fuel in the engine compartment. At other times, usually on acceleration, the engine would buck. I had the vehicle towed 3-4 times to a shop and they checked the fuel system, the fuel pump (it was bad and replaced), and the fuel system power cleaned. I have had the fuel pump replaced, the CPS replaced, the fuel system(injectors cleaned), and had a rebuilt PCM put in. The intermittent stalling continued and the engine would "buck" on acceleration like I did not know how to drive a manual transmission vehicle. The PCM was taken out and the original replaced (The reason the PCM was replaced was that at times after the engine was turned off the fuel injectors kept firing.) After reading a number of posts on this group, I cleaned the connections on both the Throttle Position Sensor (TPS) and the Input Air Sensor (IAS) on the throttle. Upon restarting the vehicle, the engine stopped stalling in my garage (Yes!) and I was able to drive it without it stalling out for about 5 miles. It did buck a little and a few times the RPM level dropped a little but did not stall. On the drive back home it did not buck at all and the RPM level stayed consistent even at stop lights. I am hoping that the cleaning of the contacts on the TPS and IAS has solved the problem, but I fear that it might be the PCM unit (see note above). Finally, after I had the Fuel Pump replaced, the fuel gauge stopped working, at times it does come back on for a second, (which leads me to think a short, or an electrical (ground) problem. Does the PCM have anything to do with the Fuel Gauge? Should I request the shop that replaced the fuel pump to fix the fuel sender or could this have occured separately. This morning when I drove to work, it was doing it again. The RPM was fluctuating and it stalled once, but I was able to start it rather quickly. I am wondering if I should purchase a new TPS and/or IAS from the dealer or try to get one from a local junkyard. Or I might clean the contacts a little better. Do you have any suggestions on what I should use to clean the contacts. I am also thinking of getting a PCM from the same jyard if I can find my year and manual tranny. Otherwise this has been a great vehicle and I do not want to give up on it! Any other suggestions would be greatly appreciated.

Have you checked the ignition system at all?  Getting good spark all the time?

Could be a bad ICM or coil going out.

Andy

I am having the exact same problem with my 1990 Jeep Cherokee Sport. Also 4.0 I6. I can't smell any fuel leaking though.

What happens to me is virtually exactly what you are describing, with the bucking making me look like I can't drive a stick. I'm the 3rd owner and I've had it for around 5 years or so. Haven't done nearly enough to it as far as maintenance.

My problems are as I accelerate, after the gear (usually 1st or 2nd) is engaged, the bucking occurs, as if I'm still shifting into first and doing a terrible job at it. Once it bucks I open the clutch again and about 50% of the time it feels as though it just drops or falls out of gear. Once I take it out of gear after being in 1st, the RPMs will either hit 0 and stall for a second and either die or sputter back up to 700rpm or so, OR the RPMs will stick around 1700 for 10 seconds give or take. Once it drops back down I can put it in 2nd, assuming I'm still rolling, and then accelerate. At this point I either make it into 3rd with no incident or it bucks again. Usually I can make it to 3rd, but sometimes I experience the "falling out of gear" sensation when I switch.

Also when driving with my foot just barely on the pedal, just enough to maintain current speed, it occasionally "skips" ("buck" is too strong of a descriptor), but does not stall out. It especially does this on the freeway in 4th and 5th gear. Most bumps cause this sensation I've noticed. The closer to being in 1st gear, the worse the bucking or skipping.


This problem has worsened after I replaced the spark plugs, spark plug wires, distributor cap and rotor.

When I bought this from my brother he told me that the fuel pump would eventually need replacing, and I have yet to do so. When I first got it during the hotter times it would hum all the time, but that stopped after a couple years and it only hums occasionally when it's warm out and I'm really low on fuel. I've been told either a fuel pump works or it doesn't.

I am thinking this is fuel delivery problem or maybe a computer problem, but then again, I don't know much of anything about cars..

Any more help is greatly appreciated!!!

Also, I had it test driven by Aamco and they said the clutch is fine and that it's a drive-ability issue. I've noticed that if I give it more gas when I'm shifting that it doesn't want to buck as much. But it feels like I HAVE to give it more gas than I really need to. Even when shifting goes smoothly, I still get the skipping sensation on the freeway and the occasional skip/buck in 3rd gear going over the wrong bumps.