98 TJ 2.5 with P0304 code

I just ordered another 23151 via your link, thank you for that, it was a great deal 22.90$ after shipping.

There's a 93 Cherokee with a 2.5 at the local pick n pull, I'm going to swing by after work and take the o2 sensor plug from it so I can eliminate a connection issue.

If anyone has a pin out with wire colors I would truly appreciate it. Again I was careful not to .ix them up but ya never know.
 
PS i do have the FSM here, with the wiring diagram, but they do not have the bk, gry, or 2 wt wires FROM the o2 sensor listed which is key info.
 
Okay, I found a good pinout for the o2, it is what I believe I had done the first time but tomorrow will be when I know for sure if the wiring is good. I grabbed a factory o2 plug out of a Cherokee with a 2.5 so I will solder in an actual plug and eliminate a connection issue with the sensor. Then the new o2 sensor will arrive friday, which will then eliminate my sensor going bad prematurely. Both are #23151

I was doing some reading here in the forum and in others, air leaks somewhere could also be a factor in this fault code (p0171)

I have the intake manifold off and the gasket out..intake manifold has some build up that smells gassy more so on cylinder 3 and 4. the head slots for the intake manifold are the same. The gasket itself had some moisture on it, kinda oily. But mostly it was intact. I have a fresh gasket to put on in the morning after I clean it up.

I have seen a guy doing a smoke test for vacuum leaks with a fluid transfer pump, fittings, and a cigar..I'm going to do that tomorrow as well to eliminate vacuum leaks being the cause.
 
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Well I was hoping between the factory o2 plug i now have, and the new intake/exhaust manifold gasket the issue would be fixed.

If someone can confirm my wiring I would greatly appreciate it.

Black-black/dark green
Gray-Brown/yellow
White-Orange/green
White-Black

I'm done for the day. Tomorrow I will make that smoke tester and check vacuum/air leaks. If that's good I go to leak down test.

I did notice that my muffler is bad, there's a small hole on the front of it. That is after the downstream o2 sensor tho so it shouldn't have anything to do with how it runs,,,,right?
 
Welp, I got a new code..seems the name for this thread is no longer valid.
Still getting pending P0171 code, along with a new code-P0113 air charge temp sensor. Took a look at it, realized the plug wires were not in good shape, and one wire had exposed wiring at the base of the plug. I have a new plug that I will solder in after work, and cross my fingers this is what has caused all these codes. I rented a fuel pressure tester for this evening as well..still haven't done the cigar vacuum check as I am not convinced it is a vacuum issue, but if my fuel pressure is good and the plug doesn't work then that will be next. Then the dreaded leak down test for the final hoo-rah.
 
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Have you pulled the wiring harness and checked for frayed wires?

No I have not pulled the wiring harness. I did however see that the plug for the IAT has loose wires, one is coming out about 1/4 inch, but still connected..I didn't pull too hard in case I rip it out. I did notice on my drive to oreillys for the fuel pressure kit, the rpms did not drop super low and stumble when coming to a stop..this is after I fiddled with the plug, pushed the wires I more and seated the plug back onto the sensor. I have a brand new plug to put in and while I'm in there I'm going to check all the grounds I can find and be sure they are good.

As for the harness, could I find the pin in the pcm plug and check resistance on the ground for that sensor? I am receiving 5.14v to the sensor with key on.
 
Well drove to work this morning without a hitch. So far no CEL.
I replaced the IAT sensor plug, and re-fastened all the grounds and cleaned with a wire brush. The grounds all were tight, so I assume it was that plugbthat was causing problems.

I also did a fuel pressure test. After flipping the key "on" 10x I got about 43lbs, and lost pressure down to 30lbs within a couple minutes.
After a start up and ran for a minute, I got 40lbs, and it did not lower to 30lbs within 5 minutes (service manual guidelines) it stayed at about 35/36lbs after shutting down.
Factory parameters are 44lbs-54lbs. My pump may be on the weak side or filter has some gunk in it, but it is holding pressure so I'll leave it for now.

If anyone is keeping tabs on this, follow the steps backwards and you'll be better off😅

Thank you Tworley and Jerry B. for your advice, and to everyone that watched this post.
 
Sounds like there are issues with wiring and causing the sporadic issues. I think you're fixing them on by one. Also, you're below the specs for the fuel pump (44-54). I think its time to replace it.
 
Following as I had a P0303 code pop on my 2006 2.4L. Brand new plugs, wires, and cap. It drove great, but had a rough idle after sitting for a few seconds. The check engine light would go on and off as well when idling. I need to buy a scanner soon as well instead of running up to Advanced Auto.

I did just swap both O2 sensors this morning and so far so good. We will see if I get any more codes. I'm also waiting on a new TPS, MAP Sensor, and Idle Air Control Valve to get delivered so I can swap them out as well.
 
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Drove to work this morning no problems, no dipping RPMs, no rough idling, no CEL so far.
I replaced that IAT plug, and checked all the grounds I could find and cleaned them up with a wire brush. The grounds were not in bad shape, so I am assuming that plug is what was giving me problems. I guess a faulty IAT can cause the PCM to think it is getting too much/too little air. I tested the resistance of that sensor while at 120°F, and the ohms reading was within specification so I left it alone. (3,600+/- ohms)

I did test the fuel pressure while I was in there as well. Key "ON", give me about 43lbs pressure which lowered down to less than 30lbs in about 2 minutes. After running the engine for a few minutes, I got a steady reading of about 40lbs, and it did not lower to 30lbs within 5 minutes, it stopped at about 35/36lbs. So this is a little low spec is 44 to 54lbs, but the leak down was withing spec. I may have a fuel pump assembly replacement coming down the road. For now I think it's fine. It was a rental fuel tester so it could have been off a little too, not 100% sure.

So all in all I was getting false lean condition information which was triggering P0171, supplamented by the computer by dumping extra fuel, which was causing misfires which gave me P0304. Had I seen the plug sooner I could have saved me some time/money/effort. I'm not bummed tho, I traced it down properly in my opinion by IDing a poor condition intake/exhaust gasket, worn plugs/cap/rotor, a shitty connection for the upstream o2 and replacing with the specified o2 (the one i took out was wrong) and replacing an original 20yr old CPS sensor that was caked in road grime. These are all things that needed to be done anyway.

Next time, I will be sure to start with sensor plug conditions, testing them for proper voltage, and checking all grounds. Then go from there.

Thank you Tworley and Jerry B. for the helpful advice, and thank you to everyone else that watched this post and suffered through my long-windedness. Hope yall learned something (or at least learned what not to do😅) I'll update this thread after a few days of driving as well, just so yall are up to speed.

✌️
 
Following as I had a P0303 code pop on my 2006 2.4L. Brand new plugs, wires, and cap. It drove great, but had a rough idle after sitting for a few seconds. The check engine light would go on and off as well when idling. I need to buy a scanner soon as well instead of running up to Advanced Auto.

I did just swap both O2 sensors this morning and so far so good. We will see if I get any more codes. I'm also waiting on a new TPS, MAP Sensor, and Idle Air Control Valve to get delivered so I can swap them out as well.

Check to be sure all sensors are getting good voltage, test the ones you can further (resistance/signal output) and that there's no intake leaks. I just put a comment on here, but mine was due to a bad plug on the IAT sensor. P0303 is misfire on cylinder 3, there are lots of things can cause that. Start easy, then work your way up.
 
Check to be sure all sensors are getting good voltage, test the ones you can further (resistance/signal output) and that there's no intake leaks. I just put a comment on here, but mine was due to a bad plug on the IAT sensor. P0303 is misfire on cylinder 3, there are lots of things can cause that. Start easy, then work your way up.

Thanks, I'll be sure to check that. The Jeep has 98000 miles on it, so it is time to replace some of this stuff.
 
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