I have a 96 Cherokee and when I drive it everything is fine and dandy tell about 10 mins down the road, then it starts bucking like a bronco nearly dying and backfiring and only running properly under full throttle. When I researched this all signs pointed to the crank position sensor, well I replaced that and it is still acting up. Could this possibly be my computer ?

 

test the sensor. people have been known to get bad CPS as "new". other than that, when was the last tune up?

 

It has new plugs cap and rotor oil radiator water pump but it starts just fine and how do u test the sensor ?

 

I'm having the same problem! Except I haven replaced the cps yet

 

Well I have heard anything from alternator and battery cables which doesn't make since. Also possible would be Tps and map sensor. Once I figure it out I will let you know.

 

In absence of mechanical problems, map sensor, O2 sensor, fuel pressure and vacuum leaks often cause bucking and backfire. Full-throttle most PCM's ignore sensor inputs and revert to open loop temporarily. Sometimes MAP sensor problems become obvious when it's unplugged. Either gets much worse...or it clears up. Leaky vacuum line to the MAP could do it too.

Suspect the PCM last....it's only as good as the sensor data it's fed.

 

I completely agree with everything Radi says. O2 sensor, fuel pressure and vacuum leaks are high on the suspect list here.

Fuel pressure can easily be tested. Rent a gauge from your local parts store; you should have 49 psi at idle.

Oxygen sensors wear out and have a finite lifespan of between 100k and 150k, depending on engine efficiency. If yours are old, replace them with new NTK sensors.

This is not likely to be a computer problem.

 

Front 02 sensor was a code and I ordered new ones but I did not think those could make the car run that bad.

 

What was the exact code? There are lots of codes with oxygen sensor in the description and the devil is in the details. Sometimes the problem is not with the oxygen sensor itself.

 

They can. Runs fine when it's cold, then when closed-loop hits it's like someone threw the jekyll/hyde switch.

 

That's exactly what it is like, and I must have thrown away the code and my jeep is in 100 pieces between me powder coating and doing a basic top end rebuild once I put it back together I will have it scanned again.

 

hey guys so my 98 xj was doing the exact same thing, i reed this and i have already replaced the cps and it and it still did the same thing so i went and got both new oxegen sensors and pulled the battery cables and reset the computer and after about an hour of drive time there has yet to be a hick up right now its idleing outside figured id let it go fer a while but it solved my problem i got a buddy at oriellys and i got each sensor fer 52 bucks normal price is 65 a peice i believe so best of luck.

 

I got the head back today and everything put together except the air box and the bottom bolts on the intake/exhaust and need to put oil in it and see if those new 02 did the trick. Fingers crossed!!!

 

I'm having the same problem as what this post is about. Ive replaced the crankshaft position sensor, positive battery cable, and the o2 sensor. I cant seem to find any vacuum leaks either. Don't know where to go from here but the problem occurs after about 20 minutes of driving.

 

I wish I had the corner on the market for crankshaft position sensors, throttle position sensors, and battery cables.

Edit: I forgot...on oxygen sensors as well.