Champ04

Hey Everyone.
1998. Cherokee Sport. 4.0L 182K miles.

General issue: Engine sputters during light acceleration.

Check Engine Light code says: O2 sensor issue.

What I've done so far: Replace plugs, O2 sensor, plus two full tank cycles of injector cleaner.

The inner details:
So I've tried to gather as much information as possible to narrow this down. And here is what I've noticed. Whenever the engine has been off, whether it's been 10 minutes or 10 hours, I will experience this sputtering. The key is, it will happen within the first half mile of driving, and then it will disappear and you won't know it ever happened to begin with.
If I'm under light acceleration, such as from a stop light, it will sputter hard and lose power for about 2-3 seconds once I get up around 20mph. If I do nothing, it will clear itself within those few seconds and then be fine. If I goose the gas hard, it will correct itself immediately, and as before, will be fine.
I can drive around town for another hour, with constant stops and accelerations, and it won't have any problems. And it idles fine.

I replaced the upstream O2 sensor and cleared the code. After about 30 miles it popped the O2 code again. I left it like that for the rest of that tank of gas. Then I cleared the code again the last time I filled it up. the CEL hasn't popped back on so far (approx. 35 miles into it). So I'm not sure if the first time it popped back on with the O2 code was a fluke or what it may have been.

I'm trying to work through this logically so that I don't waste a bunch of money replacing parts that don't need replacing. As described above, the symptoms are very specific and easily repeatable. When I leave here today, I expect it will sputter hard before I hit the second stop light from my house, and then be fine.
My best guess at this point is fuel filter. Perhaps a small blockage that gets shifted around once fuel gets flowing???

And then this morning, someone mentioned a loose timing chain. That was something that never even crossed my mind. So, any ideas on how the timing chain my cause this?

Thanks everyone! I've just joined the Cherokee club, so to speak. On my fourth week with this new (to me) vehicle and already addicted.

Champ04

No one has even a guess?

Cheddarnut

There are two O2 sensors, did you do them both?

tjwalker

Please post the specific code number; there are a number of codes related to oxygen sensors. With OBD, the devil is definitely in the details!

Did the check engine light come back on? The strategy for a vehicle with both a code and symptoms is always the same. Follow the code. OBD isn't perfect, but it is awfully darn good at pointing you to the offending circuit.

And related to that, codes with oxygen sensor in the description are NOT always caused by the oxygen sensor. Sometimes they are caused by a condition where the oxygen sensor cannot compensate enough to overcome the faulty condition (exhaust manifold leak, etc.) What brand oxygen sensor did you use for your upstream replacement? NTK is the best as that is original equipment for your 98.

As for your fuel pressure, you should have approximately 49 psi for a 98 4.0, plus or minus 5 psi. The fuel filter is part of the "fuel pump assembly" and is not normally replaced until symptoms/testing point directly towards it. When there is a problem with the fuel pump assembly, I almost always replace the entire assembly, as the gas tank has to come down and I don't like doing things twice. But this is not likely a fuel pump issue.

Follow the code. Always. Post the code and we can go from there.......

Champ04

Thanks for the help guys!

I'm beyond 100 miles since clearing the code and it hasn't popped back on yet.
And I apologize for not listing the exact code. I had the guy read it at my local AutoZone and he's the one that said it was upstream O2 sensor. I wasn't quick thinking enough to write down the actual number. Will definitely do that if it pops again. BTW, I replaced the upstream sensor with a Bosch.

Adding to the specific information.....
Now the the days are warmer I started driving with the windows down. And that has allowed me to notice that there is a distinct gas smell emanating when I'm driving. I didn't notice it while I'm out of the car and it's idling. But it's definitely there while driving.
I'm going to assume that it's coming from the exhaust unless someone suggests another possibility.

The gassy exhaust smell has me thinking Cat Converter and/or downstream O2 sensor. The only thing is, the guy I purchased it from said he has replaced the Cat Converter. I have no reason to doubt him. But I do know the jeep has been off-road quite a bit. So perhaps it's gone bad again.

Also, as I'm not too familiar with these vehicles yet, I can't say for sure, but even with 31" tires mounted, 12 mpg seems low. And that's about what I'm getting.

Thanks again for the help! It is greatly appreciated!

Champ04

Well, I have codes now.

I went and changed out the air filter. And I thought for a moment the problem had been solved. But the CEL light popped back on and here is what it said.....

P1038
(oxygen sensor short to voltage bank 1 sensor 2)
Confirmed
P1035
(Oxygen sensor heater bank 1 sensor 1)
pending

I'm guessing I'm going to have to replace the downstream O2 sensor now as well.
Any insight on what else I will need to do, given these codes?

Thanks!!!

tjwalker

Those are not legit codes. P0138 is legit and P0135 is legit; I think that must be what you have.

I'd start with replacing the downstream oxygen sensor. Use NTK if you can find one; they are OEM for your Jeep. When one oxygen sensor fails, the other is usually not far behind. I replace them in pairs, unless the owner is going to sell the vehicle.

Also be sure that the 15 amp mini fuse for the oxygen sensor heater circuit is good. It's located in the PDC, the black box under the hood.

Champ04

Indeed! Clearly a little dislexic today.

Thanks for the heads up on the proper O2 brand to look for.
I'll report back once the second one is replaced.
Thanks again!

Champ04

Great advice! Thank you!
Checked this first. Blown. Replaced it and everything is running smooth.
Since I've already replaced the upstream O2 I'll do the downstream one as well. Eventually.
But for now, just happy that she's running smoothly.
Thanks again!

tjwalker

Glad I could help. But seriously consider replacing that downstream oxygen sensor with an NTK as it's possible that is what caused the fuse to blow.

Rock on!