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Temperamental Jeep

I have a 1997 Jeep Wrangler with the I4 2.5 FI engine with a 5 speed transmission. It has 158k on the clock, does not burn any noticeable amount of oil and typically runs great. In the past year, I have replaced the blocked, corroded radiator and old hoses due to an overheat, New water pump, and t-stat, cracked exhaust manifold with a header due to a leak that had been untreated for about a year, a larger throttle body out of a 4.0, a new exhaust, brake lines, rear disk brake conversion, undercoated with a product called POR-15 and sprayed the inside of the frame with Fluidfilm.

As you can probably tell, I will replace anything that is going bad on this vehicle as is provides me the ability to pull stumps in my back yard, then go to town and buy groceries.

Now for my problem; on moist days, or it seems when started on a hill it loses power. Initially I would get a CE light indicating cyl3 missing so I replaced the cap/wires/rotor/plugs and power did pick up. Recently however, or a couple days after I revamped the ignition system I lost power so badly that the RPM dropped to about 300, and I had to tap the gas to get it any higher. If the gas pedal was held steady it would bog down and mildly backfire. Do keep in mind this is a VERY intermittent problem that occurs about once a week weekly and does not trigger any CE lights…PLEASE HELP AS I AM AT A LOSS

First of all, let me compliment you on an excellent, informative post.

Too bad we don’t see more of them.

Two things come to mind after re-reading your post and those are:
1, you have replaced the throttle body with one of a larger intake capability ( I don’t know if it has any bearing on the air/fuel mix the computer recognizes or not) and:

2, You mentioned you ‘revamped’ the ignition system.

What did you do here?

Thank you!!!, I figure to get an informative response it would require a informative post.

Yes, revamped. I replaced all the typical ignition components that are typically serviced in a tune up. OE plugs, Bosch wires, Cap and Rotor, dielectric greased all connections including the harness connections to the distributer and coil. All of this was in response to the problem. It did help a bit on everyday driveability, as I found some rust on the coil output.

The TB replacement was more of a performance modification, I reused the TPS/Map and Idle air motor off the 2.5 TB. It is a common upgrade and from what I have read should not cause the symptoms described, especially considering the intermittent issues

Let me add that in reading other posts that this is a common problem, and others describe what is happening to me as bucking and popping when the symptoms are occurring.

From what I have read, it is the Crankshaft position sensor, timing or coil. Timing is probably not an issue as it’s controlled by the ECM, that leaves the other two.

I believe I have found a solution and I’m posting to help others here with at least a possibility. It seems as though it was my upstream oxygen sensor. Apparently the O2 wires got nicked upon install and years of road salt and water managed to break down enough of the wire to prevent the O2 heater from fully engaging. This cause the o2 sensor to give an erroneous reading in the transition time from the ECM managed circuit to the external reading circuit during warm up periods. It would also explain the problems during wet periods as well as the wires were shorting enough to cause a running issue but not a check engine light.

Others experiencing this issue should also look at the connector to ensure no corrosion.