Easiest way to diagnose misfires?

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ejay

ejay

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Reset codes via scanner and battery.

P0031 and P0051 codes and CEL pop up within a minute of start up. Drove 10 miles. P0031 and P0051 still present. Shut off and got lunch.

Drove another 50 miles at speeds up to 70 MPH. Mostly around 60 MPH. 'CHECK GAUGES' light comes on and and P0135 and P0155 codes pending.

Parked now. Runs fine. Idles fine. No apparent performance issues. Misfire gone but now this O2 sensor issue.

20200118_104406.jpg
 
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ejay

ejay

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Drove it another 50 miles. P0135 and P0155 went from 'pending' to 'confirmed'. 'CHECK GAUGES' light didn't immediately come on upon startup but did eventually return. Still runs fine.

Strangely, my battery voltage indicator dropped by half, then back up to the "about 14" mark several times. Not gradually, either. Went back up a few miles from home and stayed there. Battery without engine on is 12.7 Volts. At idle it is 13.7. Under load (as much as I could give it since I have LEDs) was still 13.7 volts. Had the radio on, amp is on all the time when vehicle is running, had all lights on (offroad lights are disconnected right now) and the CB on.

Below is the live data at idle. Any mechanics in here that could interpret this data a little better than I?

Screenshot_20200118-154118_BlueDriver.jpg
Screenshot_20200118-154110_BlueDriver.jpg
Screenshot_20200118-153852_BlueDriver.jpg
Screenshot_20200118-153850_BlueDriver.jpg
Screenshot_20200118-152017_BlueDriver.jpg
 
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RonT

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Sorry I missed that sale. I paid $8 a pop at Autozone today.

Update:
Coils tested fine last night. All cylinders sparked
Installed the Autolite XP985 plugs gaped at .040. Dielectric grease applied to the contacts. Antiseize in the threads.
Tested the CPS for resistance. None
Started her up.
Still misfiring on cylinder 1 and 5.
Cleared codes
Restarted and idled 'til warm. Got the RPM up a bit. Still misfiring but hasn't thrown the code yet.
Wife not home to watch the kids or I'd test drive. No doubt it would throw P301 & P305 again.
No other codes have been stored.

Any ideas?
Food for thought. Three times now my 05 TJ 4.0L 135,000 miles has acted like it was misfiring. Engine chugs and instrument panel goes flat and CEL comes on. Spent $400 for parts, I did the labor. Replaced plugs, coil bank, cam position sensor and O2 sensors and it didn't fix the issue. Finally the gremlin showed its head. The first time it was a starter control wire that was breaking. The next time I had a corroded headlight connector. The last time my brake fluid level was down. After each of these fixes my so called misfires went away. The codes have only served to steer me in the wrong direction and waste money. I spent pocket change and little time fixing the real problem.
I don't like looking at the CEL light but, now unfortunately I wait for the real problem to surface.
 
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ejay

ejay

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Food for thought. Three times now my 05 TJ 4.0L 135,000 miles has acted like it was misfiring. Engine chugs and instrument panel goes flat and CEL comes on. Spent $400 for parts, I did the labor. Replaced plugs, coil bank, cam position sensor and O2 sensors and it didn't fix the issue. Finally the gremlin showed its head. The first time it was a starter control wire that was breaking. The next time I had a corroded headlight connector. The last time my brake fluid level was down. After each of these fixes my so called misfires went away. The codes have only served to steer me in the wrong direction and waste money. I spent pocket change and little time fixing the real problem.
I don't like looking at the CEL light but, now unfortunately I wait for the real problem to surface.
I'm starting to think that it might very well be an electrical gremlin. That, coupled with items that could probably use a swap like the plugs and injectors.

I ordered new precat O2 sensors. When I install them I'll go through the wiring as a whole. I replaced a few grounds and pos off the battery a while back. Thought i properly clamped the new ends and even had larger gauge wire for a few as well. I'll double check and maybe make sure the contact points are clear of corrosion or rust.
 
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ejay

ejay

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Food for thought. Three times now my 05 TJ 4.0L 135,000 miles has acted like it was misfiring. Engine chugs and instrument panel goes flat and CEL comes on. Spent $400 for parts, I did the labor. Replaced plugs, coil bank, cam position sensor and O2 sensors and it didn't fix the issue. Finally the gremlin showed its head. The first time it was a starter control wire that was breaking. The next time I had a corroded headlight connector. The last time my brake fluid level was down. After each of these fixes my so called misfires went away. The codes have only served to steer me in the wrong direction and waste money. I spent pocket change and little time fixing the real problem.
I don't like looking at the CEL light but, now unfortunately I wait for the real problem to surface.
SMOG is overdue. It's fix the codes or park it, unfortunately. I had hoped my live data would help me trace the problems but alas, not yet.
 

RMETeeJay

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Coolant temp is way too low. If the coolant temp sensor is good, then your thermostat failed. Another sign of a failed thermostat is poor MPG.
 
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ejay

ejay

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Coolant temp is way too low. If the coolant temp sensor is good, then your thermostat failed. Another sign of a failed thermostat is poor MPG.
I saw that too but it's lying. Don't know why. The gauge says just under 210 and the reading was read right after I parked it from the trip. Can't be the thermostat or the sensor if the dash gauge is reading normal I'm guessing.
 

RMETeeJay

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I believe that what the OBD says is what the PCM receives. If the engine was fully warmed up when you took the screenshot, then either that sensor is bad or it has a bad ground.
 
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ejay

ejay

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I believe that what the OBD says is what the PCM receives. If the engine was fully warmed up when you took the screenshot, then either that sensor is bad or it has a bad ground.
Shoot. I just noticed that was freeze frame data. Coolant was that temp when that code first presented. (First startup this morning) Froze all peripheral data at the time the code was thrown.
 

Kawi413p

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I battled an intermittent misfire problem on my 97 with 151k miles for 2 years replacing everything dist cap, wires, etc.
Finally checked timing chain slack at 175k which showed 8 degrees slack.
Replaced timing gears and chain and all misfires gone, period.

View attachment 133860
Was it enough slack to actually hear the chain hitting the cover? What pointed you in the direction of timing chain?
 
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KCsTJ

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Was it enough slack to actually hear the chain hitting the cover? What pointed you in the direction of timing chain?
By coincidence, yes I began hearing a faint metallic tick at idle but could not pinpoint the tick. That was 1 week prior to replacement.

Not until I pulled the cover and saw the gouged snubber holder did I make the connection.
A check engine light for a rich condition actually pushed me to change the gears.
However the two in retrospect are unrelated I later learned.
The engine runs smoother overall since timing gear replacement. Wish i had done it sooner.
 
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ejay

ejay

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So, I replaced the two pre-cat O2 sensors today. (Amazon delivered the new NTK sensors)

Had the battery disconnected all night.

Started up. Same original four codes that were present prior to replacing sensors came back.

Cleared codes, drove it around a few miles. Four codes returned. Cleared again. Drove a little further. Two codes came back. H02S Heater Control Circuit Low Bank 1 Sensor 1 and Bank 2 Sensor 2 P0051 and P0031. O2 Sensor Heater Circuit Bank 1 Sensor 1 and Bank 1 Sensor 2 P0135 and P0155 did not return.

Maybe I need to drive it more? No more light today to look at the electrical connections, grounds, etc.
 

RMETeeJay

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The engine's sensors (including the O2s) use 2 'engine grounds' according to the FSM.

I have the same year as you and looked at the FSM. One of the engine grounds is definitely G105 ('right rear of engine block'). There is a diagram of that ground's location on page 8W - 91 - 20 and If that ground checks out OK, I would think about trying a new/reman PCM.
 
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ejay

ejay

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The engine's sensors (including the O2s) use 2 'engine grounds' according to the FSM.

I have the same year as you and looked at the FSM. One of the engine grounds is definitely G105 ('right rear of engine block'). There is a diagram of that ground's location on page 8W - 91 - 20 and If that ground checks out OK, I would think about trying a new/reman PCM.
You know, in retrospect, I saw a ground strap a few weeks ago (after my misfires started) that had oil on it from an old valve cover gasket leak that I fixed years ago. I hit it with a bunch of brake cleaner. Maybe that screwed up the contact. I don't think it was the same one. Don't see a G105 on that sheet. I do see it on another sheet but it's on the passenger side of the engine.

💡

Son of a bitch! You may have found the gremlin! I have a slight coolant leak from the heater return hose. Years back I put a flush valve in that hose....right above the oil filter. It's been leaking lately. Dripping onto the oil filter, and on the exhaust. Not a whole lot but enough. I think either the plastic valve is deteriorating or the clamps aren't pinching right. It could be dripping on the ground!

Going to investigate this further and report back. I owe you a beer just for the effort. Even if it turns out not to be the gremlin.

ground.PNG

ground2.PNG
 
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ejay

ejay

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Pulled, cleaned, tightened all grounds. Cleaned PCM connections. Cleaned a ton of other terminals with terminal cleaner. Checked the downstream O2 fuse and relay. Checked the upstream ASD relay. Cleared codes. Tried to run it again.

P0031 and P0051 return. Drives fine. Idles fine.

I'm at a loss here. I may have to take her into a professional.
 
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ejay

ejay

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I have the pinouts for what the manual says is 2/1 upstream 4 way and 2/2 upstream 4 way. Reality is, the upstream is 1/1 and 2/1. Bank 1 sensor 1 and Bank 2 sensor 1.

Tested the signals with an OHM meter coming from 1/1 and 2/1 and ending at the PCM harness. Signal is present. (C1 to pins 24 and 26 to O2 harness pins 4. Ground is present. Strangly, though, C3 pin 8 (O2 Sensor 1/1 Heater Control) isn't showing signal to any pin on 1/1 or 2/1.

Pulled the cover off the harness covers over the valve cover and next to the intake. Exposed all joints and looked for breaks, melting, frays, or other damage and found none. Unless I'm wrong, C3 pin 8 should be directly connected to pin 2 of 2/2 harness. Am I wrong here?
 
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ejay

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A miracle has occurred.

After messing with the wiring and looking for a break, fray, cut, burn I put everything back together. I had gone to a local mechanic on Friday who has a good reputation to see if he can track down my issue for me. He agreed and I was supposed to drop the Jeep off on Monday afternoon.

I was getting everything buttoned up today and reconnected the battery. Started it up to get the code stored again in prep for the mechanic. The codes did not return. All indications are that it is ready for smog. I drove it 5 miles and still no codes. All internal tests are done and the Blue Driver indicates that it is ready for smog. Getting signal and voltage from all O2 sensors. Let's hope it lasts long enough to put some more miles on before smog.

Short bus must have heard me speaking to the mechanic.

My conclusion thus far. I have an electrical gremlin in a harness, ground, or in the wiring that can not be seen by visual inspection.
 
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RMETeeJay

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Glad you got it. Make sure to wind it out at high RPMs and that it’s fully warmed up right before the emissions test.