New 1998 cherokee cuts out from stop.

Just picked up a 1998 Sport 4.0 auto 127k 4x4 and it seems to suffer the double start fuel checkvalve problem. I understand that, but whats got me scratching my head is when you take off from a stop, if you apply throttle slowly its smooth as butter, but if you give it any more than a about an eigth inch on the peddle under 15 mph it will buck and carry on stalling out like the ignition was being turned off... Instant. But if you slowly get above about 15 mph and then floor it, it burns rubber and shifts through the gears like a beautiful truck. Under 15 mph and too much throttle results in it bucking and carring on with muffled backfires out the K&N. Get off the gas for a few seconds and then go slowly after and it runs fine. I figured it was a wire rubbing somewhere but with the engine running I can not get the engine to do anything but run well by shaking the wiring harness and connector ends on the computer and sensors. It just purs.

If it was a wire chaifing I believe it would cut out even more when shifting and applying full or 3/4 throttle.

It seems like as long as you are above 15 mph, instant throttle response and good power. But if you slow down to turn below 15 , or stop and you give it more then it likes it craps out and stumbles.

Have to stay off the gas for at least 4 seconds it seems or it don't "reset".

Going to be doing tune up. Just did oil change, oil gauge is acting weird I'm sure it needs a new sender and I had thought maybe there was a low oil engine cut or something that may have been the issue but even with it unplugged it still acts the same minus an oil pressure gauge.

Such a weird problem, I searched and couldn't find anything like what Is happening. Hoping someone may have answers before I spend money. I know it needs a fuel pump someday here because of the double start when cold. But I don't mind double starting if I can spend that money on an o2 sensor or can of electrical cleaner to spray in the right place. ( lazy in the cold bs weather)

But I have a feeling fuel pressure gauge would show a low pressure at the low rpm ( battery volts?). Seemed to act up with less throttle when headlights, front and rear wipers and defrost on.

Thanks for your time

With engine off: Hook up an analog-type ohmmeter to the Throttle Position Sensor,
and then s-s-slowly open the throttle and s-s-slowly close it. The needle on the
ohmmeter should sweep slowly and evenly: no jitters, no hiccups, and no flat spots.

Dragonslayer said:

With engine off: Hook up an analog-type ohmmeter to the Throttle Position Sensor,
and then s-s-slowly open the throttle and s-s-slowly close it. The needle on the
ohmmeter should sweep slowly and evenly: no jitters, no hiccups, and no flat spots.

Click to expand...

Just picked up a nice analog meter recently, I'll check it out. May have another tsp around to try too if it does act up... I'll get back at ya with what happens.

Thanks

Throttle position sensor is smooth with no dead or flat spots and perfectly in spec.

Trying to do a brake stand with out spinning tires... (applying throttle with no vehicle movement) I can apply throttle smoothly enough to make the back tires break loose. Feels smooth and no hesitation. Throttle response is how it should be. Soon as you go for a test drive, back to the same backfire out the intake crap. I can not make it backfire without vehicle speed.

Motor mounts and tranny mount are fine.

Started cleaning grounds, all the ones under the hood are good.

plug wires

Plug wires are fine, no lightshow at night! Was thinking coil but I can't see it pulling so hard on the highway if the coil was junk.

I keep feeling like this is a low fuel pressure problem so when the woman gets back from the dentist, gonna go get a gauge hooked up and see what it says.

XJR

Well we topped off the gas tank and the problem went away so I have no doubt there is a fuel pump assembly problem. Going to get a pressure reading and the tires balanced. 46 mile trip and couldn't make it actup!

XJR