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A while back I posted about my 98, 4.0 Laredo going into these fits of coughing, spitting, sputtering while at other times it runs good.
175k miles.
Always starts right away, usually idles good.
Usually drives nice at first, biut once under way it goes into a fit of missing and backfiring, bucking and coughing etc. If I stomp the gas to the floor it'll clear right up, rev hard and pull hard. Once I let off it may go back to barely running or it may be fine for a while. This behavior started out showing up once in a while on an average trip of maybe 10 miles. Might do it once might not at all. Has progressively gotten worse. Also to mix things up a bit more, the transmission seems to act up about the same time, by having delayed 2-3 shifts like above 45 mph and sometimes needing to manually do the upshift.
The transmission has been doing this longer than the missing fits with the engine, I assumed it is sticky shift solenoids in the valve body. I do have a cracked exhaust manifold, giving me a fuzzy sounding exhaust. The manifold was cracked when I bought the Jeep and the Jeep has developed this issue long since I bought it. Some one posted a while back about the problem possibly being related to a weak alternator, his explanation sounded plausible so I finally installed a new/rebuilt alternator. It did not change/help/correct the problem I am having.This happens in town at low speeds or out on the highway at cruising speeds. Also, when the engine goes into these fits, the ECM does not throw up any codes. We have even had a scanner hooked up while the engine was having a fit. Nothing. What sensors could be causing this kind of behavior and not throw an engine code? Why will it run good at wide open throttle? How do I find the problem and fix it? The engine rarely stalls when this is going on, even at idle in gear. It will lurch and surge but alwaqys runs.

Please help, please please please...
I am about to my hair out and I ain't got much left.

1998, Laredo Smoothie, Red with Up-Country Suspension Group.
 

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My next guess would be the Crankshaft Position Sensor.. they can get progressively worse over time. If not that, maybe the camshaft position sensor. Possibly one or the other of those components could affect shifting? I know some parts can affect other seemingly unrelated systems. :/ Hope you get this figured out.
 

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found part of problem: O2 upstream sensor

From threads in Jeepforum.com. Folks there suggested O2 sensor gives wrong readings but does not set codes unless readings out of limits. They suggested disconnecting the upstream O2 sensor plug, to see if problems go away. (Doing this causes the check engine light to come on of course.) So I disconnected it and the sputtering, misfiring, loss of power, sucking too much air problem went away completely. So now it is at the dealer getting both O2 sensors replaced. Next I will be looking for solutions to the delayed 2-3 upshift problem and the rough idle problem (IAC? I think I can replace that myself).

Thanks to all.
 

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kennyc thanks for suggestions. I already replaced the camshaft postion sensor while doing a tune up (Champion platinum plugs, new premium wires, new coil, new rotor cap new rotor - set all the plug gaps to .035" and torqued each new plug to 36 Nm). As for the CPS, folks say that the thing wouldn't run or even start if that were bad. (Plus it's down on the transmission bell housing under the car. I'm too old to crawl under there.
 

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final update

The dealer service replaced the upstream O2 sensor. They said the downstream one is not bad and not to replace it until it goes bad. They also puit some kind of additive in the transmission and adjusted the kickdown cable. This seems to have fixed the 2-3 delayed shift problem.

So it's all good and I'm happy. I hope it lasts a while without further repairs.
 
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