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  #1  
Old 09-27-2016, 03:27 PM
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Intermittently rough

So my jeep will sometimes run very rough and the speedo will jump around as well as the gas gauge will act up. It started out by doing it very seldom but now almost every time I drive. I have tried changing the speed sensor. Checking all grounds. Where else should I go now? It will also do this in park

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  #2  
Old 09-27-2016, 09:52 PM
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Re: Intermittently rough

Welcome to the garage.
4.0 engine? What is the gas gauge doing, jumping as well, or going back to 0?
Fuel quantity signal comes from the PCM and the speedometer signal as well. These signals go over the PCI data bus. Any component on this bus could be the problem, but also water ingress in a PCI bus connector. I would start cleaning the connectors on the PCM. A crank position sensor on its way out could also give problems like this, eventhough they mostly cause the engine to stall.
Is there any fault code set in the PCM? You can check with a scanner if available, or by doing the key dance: ignition switch OFF-RUN three times and leave in RUN at the third time. The odometer will show DONE when no faults are set, or the fault code(s).
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Old 09-28-2016, 02:04 AM
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Re: Intermittently rough

Yes it's a 4.0. No codes what so ever. I did unplug the pcm today and checked/cleaned all 3 plugs but haven't tried driving yet. If the cps is on its way out why wouldn't I get a stored when it's acting up? The gas gauge will go to 0 while the speedo jumps with the same pattern as the engine is jumping around. It does have the same characteristics of a crank/ cam position sensor failing. is there a way to know what components share this bus?
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Old 09-28-2016, 02:12 PM
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Re: Intermittently rough

Almost all electronic components use the data bus: PCM, BCM, AC head unit, EVIC, instrument cluster, radio/CD changer, driver door module, passenger door module.
Not always a code will be set when a crank or cam sensor starts failing. But if it intermittently shorts internally, it can make the PCM to short out the data bus. It is really the speedo which is acting up, not the tacho?
It can also be a problem inside the PCM.
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Old 09-28-2016, 07:20 PM
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Re: Intermittently rough

Yes as far as I can tell it's the speedo. I do have a short video clip of it doing it
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Old 09-28-2016, 07:21 PM
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Re: Intermittently rough

I guess I could try replacing the cam and crank sensors
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Old 09-28-2016, 07:22 PM
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Re: Intermittently rough

I also checked and separated all the grounds. I noticed they were all taped extremely tight up against the positives.
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