98 TJ 2.5 with P0304 code

tjworley92

tjworley92

New Member
Joined
Aug 30, 2021
Messages
22
Location
Oak Grove, OR
Afternoon gents,

I know this topic has been discussed, and I have read through them but I have some symptoms to go along with it that I have not seen mentioned yet.

As stated in the title, I am having code P0304 (cyl. 4 misfire)
along with some intermittent RPM gremlins. Bear with me now as i try to explain this. Intermittently, The rpms want to hang at about 2k, or sometimes incrementally higher before slowly coming down, as if i have the pedal pushed down, or it is somehow getting more fuel. This has been going on a few months now, but i was under the impression it was me missing shift points. (manual trans.) but it also rises high sometimes on a slight tap of the gas, as if i was trying to rev it up.
Recently, when coming to a stop SOMETIMES the rpms will go way down to the first mark on the gauge, and then kinda find itself and return to normal..either that, or I tap the gas to get it to go back, whichever happens first. It seems to idle ok otherwise, just slightly rough.

Last weekend i got code P0171 (if i remember correctly) which was for upstream O2 sensor. I replaced that with the proper NTG sensor, along with AutoLite AP985 plugs, with new wires and the CEL went away for a few days. The new code, P0304 showed up this morning.

Spark plug #4 looks new still, slight discoloration from heat but looks the same as all the others. they're brand new so wear is extremely minimal. wires are set on good, triple checked. cap and rotor seemed fine, although i may grab a new set and see if that helps. I am going to rent a noid light today and check for a pulse in all injector plugs and verify that is okay along with volts with a multimeter. if that checks out I will pull the fuel rail and check that all injectors are spraying properly (spray pattern/fuel amounts)
If those tests come back good, I will then perform a cylinder leak down test (never done it before) and see what i come up with.

Am I missing anything? Do you guys have any thoughts or additional comments, or other factors i should be considering?
Again, i know this topic has a lot of threads, but I wanted to double check through yall with the accompanied symptoms I am having.

Thank you in advance.
 
minor update: started it up, unplugged injector 4 and it ran rougher than with it plugged in, so the injector must be getting good power? still going to test wiht noid light though to be sure.
Also, it is idling very smooth cold..after fully warmed up, (ex. after driving home 9 miles on freeway) it idles rougher and engine sounds a little clunky. Is this sounding like some sort of engine internal failure? My code reader sais the only fix is cylinder head replacement lol.
 
another update: noid light confirmed injectors voltage is present and pulsing correctly. If i have time tonight im going to swap the injectors around (4 and 1) clear the code, then see if it pops up on another cylinder.
 
  • Like
Reactions: Blondie70
I was getting that same code intermittently until I switched out the crankshaft position sensor with one from NAPA . I was running a duralast one when the code was happening.
 
  • Like
Reactions: Blondie70
Mitchrb1 said:
I was getting that same code intermittently until I switched out the crankshaft position sensor with one from NAPA . I was running a duralast one when the code was happening.
Click to expand...

Hey thank you for the response. I didn't think of that, I've never replaced that sensor in the 7 years I've owned this rig. I'll give it a shot.

This morning I will find out if it is an injector. I swapped #4 for #1 and had the battery unplugged all night. I'll post an update a little later today.
 
Not many people chiming in, but thats okay, its a beaten horse for sure. If anything, it will be some decent steps to read through in diagnosing P0304.

Minor update: no code yet after swapping injectors And resetting PCM. Might just need a few cycles to detect the problem. I'm still having those same running issues so the problem is still there somewhere. I'll check back in soon.
 
Blondie70 said:
I ain't chiming, but I'm watching, cuz I got a 2.5. Wanting to know what happens. Good Luck
Click to expand...

No problem! I'm trying to diagnose it althe best i can and not throw parts at it.
The super low idle/stumble when coming to a stop seems to be getting worse. RPM still wants to occasionally raise really high and hang at 2k before coming down. Highway speeds in neutral, rpm went erratic 3 separate times, fluctuating up and down before lowering. That is new. I did swap the CPS out with an Eichlin from napa..I know it's not Mopar but have heard decent things. After I drive for a bit with the new cps I'll swap it back if this persists.

Just got home, I pulled the spark plugs (hot) now that they've been driven on a while (replaced last weekend)
I'm not a plug guru, so I'm unfamiliar with all the colors and meanings, gonna have to do some research..but here are my plugs. They go from left to right, 4 3 2 1.
Also heres them individually. 4th plug is black and sooty, but dry. 3rd is a little better. 2 and 1 pretty clean.

Also, still no CEL yet after reset.

20230601_184715.jpg


20230601_184227.jpg


20230601_184406.jpg


20230601_184519.jpg


20230601_184654.jpg
 
I have been out tinkering since i got home. Ignition coil resistance on main terminals (plug) is to spec (1.2 ohms) secondary terminal is at 10.3k ohms, spec is 11.3k-15.3k. I will replace that tomorrow with NGK coil.
Also, Upon closer inspection of the distributor cap, posts 3 & 4 have slightly more wear than 1 & 2..I looked at it when I did the plugs, but it looked fine to me so I didn't replace it. I took a bit of sandpaper and cleaned up the contact points to spruce it up a bit and put it back on. I have been reading my FSM and I read that they reccomend replacing it every time you do the plugs..they also said if it MAY be questionable, replace it.

Rookie mistake on my part, if this is the issue I probly deserve to be kicked off the forum lol.
Mine has the aluminum posts, I'm going to find one with the brass/copper colored posts and report back.

🤦‍♂️
 
  • Like
Reactions: tr21triton
If it holds the RPM its caused by the speed sensor and an open/closed throttle position. When slowing, your throttle position is closed but the speed sensor is still sending a signal, the PCM adjusts the IAC to a specific pressure. Once you stop, the PCM then sets the IAC to the normal idle speed. It is perfectly normal.

If it is actually fluctuating though (800-1200 for example), I would start by giving the IAC a real good clean.

Also, some of your issues sound pretty similar to what I went thru some years ago and it was my CAM sensor (also known as the pickup coil assembly) near the oil filter. Are you getting 5V to that? The CAM sensor helps deliver the signal to the CPS sensor. If the sensor is bad, it may be causing your timing to become out of whack.
 
  • Like
Reactions: The4bangertj
tworley said:
If it holds the RPM its caused by the speed sensor and an open/closed throttle position. When slowing, your throttle position is closed but the speed sensor is still sending a signal, the PCM adjusts the IAC to a specific pressure. Once you stop, the PCM then sets the IAC to the normal idle speed. It is perfectly normal.

If it is actually fluctuating though (800-1200 for example), I would start by giving the IAC a real good clean.

Also, some of your issues sound pretty similar to what I went thru some years ago and it was my CAM sensor (also known as the pickup coil assembly) near the oil filter. Are you getting 5V to that? The CAM sensor helps deliver the signal to the CPS sensor. If the sensor is bad, it may be causing your timing to become out of whack.
Click to expand...

@tworley..nice name btw😏

I will give the IAC a good cleaning with a fresh o-ring and new throttle body gasket this evening when I get home, and will report back.

As for the CAM sensor, I will go take a look here in a minute, and report back with those readings as well.

Thank you for the input.
 
tworley said:
Thought the same thing 😅
Click to expand...

Not too often you run into another Worley, let alone another Jeeper Worley!🤝

Okay, 5.16v to the cam sensor plug. Took it off, inspected the bottom, no signs of harsh wear.

I did however receive a CEL!! Never been so happy to get one lol.
P0131 stored, and P0171 pending.
I just replaced the upstream O2 sensor with a NGK 23151 due to P0171 code. Went fine, although the PO had cut the harness plug off to do a crimp connection set up, so I soldered in bullet connectors, heat shrunk, tape, and loomed it.
P0131 is low voltage to bank 1 sensor 1, P0171 is upstream sensor (b1 s1)
When I get home I will remove the Bullet connections, and hard solder the wires together, see if that makes a difference. From my understanding that's not a connection to use standard connectors on other than the factory plug..but it has been working all these years so I re-did it with better quality soldering/connections. I'll fix that and report back again.
 
tjworley92 said:
Not too often you run into another Worley, let alone another Jeeper Worley!🤝

Okay, 5.16v to the cam sensor plug. Took it off, inspected the bottom, no signs of harsh wear.

I did however receive a CEL!! Never been so happy to get one lol.
P0131 stored, and P0171 pending.
I just replaced the upstream O2 sensor with a NGK 23151 due to P0171 code. Went fine, although the PO had cut the harness plug off to do a crimp connection set up, so I soldered in bullet connectors, heat shrunk, tape, and loomed it.
P0131 is low voltage to bank 1 sensor 1, P0171 is upstream sensor (b1 s1)
When I get home I will remove the Bullet connections, and hard solder the wires together, see if that makes a difference. From my understanding that's not a connection to use standard connectors on other than the factory plug..but it has been working all these years so I re-did it with better quality soldering/connections. I'll fix that and report back again.
Click to expand...

P0131(M) 1/1 02 Sensor Shorted To Ground Oxygen sensor input voltage maintained below normal operating range. Sounds like the plugs being cut off is a likely culprit. Also, with the vibrations that a TJ sees you're likely better off with the crimped connections as the solder is likely to crack. A good butt connection would work well there.
P0171(M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor. I'd also bet this is related to your O2 sensor being hacked together by the PO.
 
tworley said:
P0131(M) 1/1 02 Sensor Shorted To Ground Oxygen sensor input voltage maintained below normal operating range. Sounds like the plugs being cut off is a likely culprit. Also, with the vibrations that a TJ sees you're likely better off with the crimped connections as the solder is likely to crack. A good butt connection would work well there.
P0171(M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor. I'd also bet this is related to your O2 sensor being hacked together by the PO.
Click to expand...

I have soldered in bullet connectors now. should I not solder the wires together then? If not, what's the fix?
 
tworley said:
P0131(M) 1/1 02 Sensor Shorted To Ground Oxygen sensor input voltage maintained below normal operating range. Sounds like the plugs being cut off is a likely culprit. Also, with the vibrations that a TJ sees you're likely better off with the crimped connections as the solder is likely to crack. A good butt connection would work well there.
P0171(M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor. I'd also bet this is related to your O2 sensor being hacked together by
Click to expand...

tworley said:
A good butt crimp connector with adhesive heat shrink. I have this bookmarked and they're used by one of the better builders here in the forum. You might be able to find a cheaper alternative somewhere, but this would provide a solid connection.
[URL]https://www.delcity.net/store/Clear-Nylon!Insulated-Butt-Connectors/p_805411.h_805415[/URL]
Click to expand...

Ohh those! Duh lol my bad i was picturing spades in my mind.
Yes, I will grab some quality BUTT connectors and install them tonight.

Thank you for your advice, I will once again report back with the outcome. Maybe I'll take some pics of the process too for shits n gigs
 
  • Like
Reactions: tworley
Well, it almost seems worse now lol no CEL but P0171 is pending.
I did the butt connectors, crimped, heat shrunk, loomed. Cleared the code via tying battery cables together while I did the work. Installed new cap and rotor.
Cold, it sounds fine. Warmed up, it starts getting clunky.

I made a video, maybe this will shed some light. There's 3 short segments, first is exhaust footage upon first start up, then once it was at operating temp I tried to capture the engine noise, 3rd segment I was blipping the throttle, then it goes back to my first exhaust clip..not sure how it got in there, I'm not good at this type of stuff but hopefully there's something useful in there.

Next step is going to have to be cylinder leak down test, correct? If it's a head I need, I just want to know so I can it ordered and get to work on it😅

Anyway here's the link to the video

 
tjworley92 said:
Also, it is idling very smooth cold..after fully warmed up, (ex. after driving home 9 miles on freeway) it idles rougher and engine sounds a little clunky.
Click to expand...
That immediately causes me to suspect your upstream O2 sensor has gone bad. The PCM only uses the upstream O2 sensor to set the air/fuel mixture once the engine has started to warm up. The PCM uses pre-programmed coding to set the air-fuel mixture when the engine is cold which is when your engine runs the smoothest.

I'd replace just the Upstream O2 sensor and the brand used should ONLY be NTK, NGK, or Mopar... all three of those being the same sensor which is made by NTK. Do NOT use a Bosch or aftermarket O2 sensor.

The NTK or NGK p/n you need is 23151 which is at the top of the list at https://www.rockauto.com/en/catalog...13,exhaust+&+emission,oxygen+(o2)+sensor,5132

They only have one of that sensor left in stock so I'd jump on it pretty quick. Maybe other sources too but... The Mopar-branded version of the NTK is p/n 56041212 but it's nearly 10X as much since it is a Mopar. No need to change the downstream O2 sensor which does not affect engine operation, it only monitors the catalytic converter.

P.S. Per Rock Auto's terminology 'Before Catalytic Converter' is another way of saying Upstream O2 sensor which is the one you need. The 'After Catalytic Converter is the Downstream O2 sensor is not the one you need.
 
Thank you for the reply.
I just put in a brand new NTK 23151, that's when I realized the plug was missing and had to splice it In and all this misfire stuff started. Im pretty certain i didnt mix up the wires in the process..but to be sure, do you have the info for which colored jeep wires go to the 2 white, one black and one gray wire?
I noticed in the official o2 sensor thread, they recommend 23151 for 98 only, but 23506 is listed in my year as well. Is that one good to go for 98 2.5?
 
Top Bottom
Back