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Old April 28th, 2012, 07:58
XJ98Jeep's Avatar
XJ98Jeep XJ98Jeep is offline
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help hunting down an electrical gremlin in my 98 xj, I think it's timing

i have a 98 xj with the 4.0 5 speed and whenever water gets up in my cherokee's business (puddles and rain, not wild stream crossings) it will randomly get a really rough idle like it has a huge cam and go from like 400 RPM to 1300 or so.

if I'm driving when it happens it'll just die until I go to WOT which fixes it, sometimes for a week and sometimes for a few minutes. If I give it any throttle it starts popping really loud and i can feel it quite strongly through the accelerator pedal, and it gets worse the more throttle I give it up until WOT.

I replaced the CPS and wrapped the wires in aluminum tape so they didn't melt on the exhaust, but as I'm typing this it's starting to sound like a failing cps sensor.

Any input?

Does the CPS sensor signal get "ignored" when the ECU goes to closed loop for WOT?
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Old April 28th, 2012, 18:24
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Tim_MN Tim_MN is offline
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Re: help hunting down an electrical gremlin in my 98 xj, I think it's timing

I would suspect faulty tune-up parts or other ignition/sensor wires. Perhaps a faulty TPS. Maybe a loose wire plug. Also clean and snug up all the battery wires and ground connections.

What you describe is similar to a short circuit caused by dampness entering cracked or damaged wire insulation. or a faulty TPS. Never heard of a CPS acting that way.
Originally Posted by bimmerjeeper

I spent a few hours researching how to jack up an XJ, but even this is more complex than a normal car.
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Old April 28th, 2012, 19:27
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Matthew Currie Matthew Currie is offline
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Location: Vermont, land of big clay
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Re: help hunting down an electrical gremlin in my 98 xj, I think it's timing

I don't think the system ever ignores the CPS. If the problem is occurring without any codes coming up, I'd look at ignition and fuel supply first. Look for things, in other words, whose malfunction is not likely to throw a code. I am pretty sure a failing CPS, as well as cam position sensor, would. Most sensors will. A TPS giving temporarily false readings but still giving readings might not. Water in the distributor or other wet-ignition issues probably would not unless eventually you got a misfire code, which is not based on a direct reading of the ignition. Fuel supply problems and mechanical malfunction of injectors are not monitored, but electrical firing of injectors is.
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