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Jeep keeps falling on it's face

camarors8992

camarors8992

NAXJA Forum User
Location
Liverpool, New York
So to speak anyways. My 98 4.0 auto is running weird and thew 4 codes, all of which say the upstream and downstream o2 sensors aren't working properly. I replaced the upstream one last night under warranty, but the CEL is still on and last night I did some driving to see if it fixed the problem/turned the CEL off. Nope, When leaving a light after idling or when I first tired driving after starting it it just backfires, stumbles, no power then straightens out to perfect in seriously a matter of 5 seconds. I drove about 30 miles, and was going to do the same today. Any ideas ? I think it's kind of funny both o2 sensors threw a code at the same time.
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If I am not mistaken, the expensive one is upstream. Replace the second one. Go to H Freight and get an OBDII reader and clear the codes, or disconnect the battery for 15 min to clear them. It will then need to learn everything over but that is OK. If the CEL still comes on, the O2 sensors were symptomatic not root cause.
 
So the real question is are O2 sensors bad or is something else failed and is causing the O2 sensors to see a lean or rich exhaust stream ?

What are/were your exact codes ?

Also, have you inspected the wire plugs and wire harnesses for the O2 sensors. If you have a short circuit in the wires, or a poor connection, the PCM might see this as a faulty O2 sensor instead of as a lack or proper electrical readings.
 
I got P0132, p0135, p0138, and p0141. I inspected the connectors and wiring as far as I could and they seemed fine. I was thinking maybe the first one went bad, and when the jeep started backfiring, running crazy rich, and stumbling maybe the downstream saw this as a failed sensor ?
 
P0132 (M) 1/1 O2 Sensor Shorted To Voltage. Oxygen sensor input voltage maintained above normal operating range.

P0135 (M) 1/1 O2 Sensor Heater Failure. Oxygen sensor heater element malfunction.

P0138 (M) 1/2 O2 Sensor Shorted To Voltage. Oxygen sensor input voltage maintained above normal operating range.

P0141 (M) 1/2 O2 Sensor Heater Failure. Oxygen sensor heater element malfunction


P0132 and P0138 suggest wiring issues.
 
It might not be that bad, just check along the harnesses nearest the sensors, something about them being near driveshafts and hot exhaust pipes tends to result in the insulation doing poorly. I'd bet on a toasty or abraded harness within two feet of the suspect sensors.
 
I've seen other variations but I think it is possible to see these codes if the HEATER circuit is malfunctioning for the oxygen sensors.

There is a fuse for the oxygen sensor heater circuit. I'd check that fuse to be sure it isn't something as simple as it being blown. Will take you all of 1 minute. Simple stuff first.

Let us know what you find.
 
On the Renix XJs the relay nearest the firewall is the oxygen heater relay; check your FSM you could have a bad relay if they are wired similarly.
 
I checked the o2 sensor wiring and it looks clean, no burned, cut, scraped up wires. The connections are clean and more than adequate. I drove it over 100 miles today, it didn't miss a beat.
 
I just checked it, and I couldn't find a labeling showing which fuse that was under the hood. However, I did find a 15amp blown under there, so I'm going to get some replacement fuses now.
 
The oxygen sensor fuse is a 15 amp if memory serves me correctly. Let us know if a new fuse resolves this. Anytime there is a code that references the word HEATER, fuse should be checked.
 
So I did have a blown 15 amp fuse under the hood, and since replacing it, my check engine light has gone away. It still seems like my mileage is a little down though...
 
Do you have E10 fuel?

E10 will rob you of as much as 10 percent of your mileage. Compound that with winter blend AND E10, you can expect as much as a 20 percent loss.
 
I'm having the same problem. I have codes 132, 135, 138, and 141. They all came on at the same time. I went ahead and took out the o2 sensors and cleaned them with some carb cleaner, reset the code, and they came back. I replaced the front o2 sensor and replaced it's relay. (I checked the wiring diagram and all I found were two box 5-pin relays for the o2 sensor, no fuses?) I reset the codes, the CEL came back on after about an hour of operation and it's the same codes. All 4 are back. This tells me it's something else. A mechanic I ran into told me to check the vacuum hoses for a leak. I had already done this visually, but now I'm gonna spray something on there to look a little closer.

Would an intake manifold leak cause this? I recently (500 miles ago) swapped in a reman'd 4.0. I think it's time to tighten all my bolts again and make sure they haven't come loose. A guy at autozone also told me it may be the mass airflow sens, but I don't wanna spend any more money until I know for sure what the problem is.
 
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