Easiest way to diagnose misfires?

No arc. But again, I'm distributorless.

Took it for a spin around the block. Did not throw a code. Runs a ton better than it did in limp mode with the CEL flashing. Still a rough idle, though so it's not quite right. Not as rough as before but still. I didn't pull the battery so maybe the PCU was compensating and hasn't caught up to the new readings? I'll reset the battery and force it to relearn.
 
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Hooked the battery up and let it idle to let the computer relearn. Still rough. Tested injectors. All have resistance within spec. Probe indicates they are actuating. I can hear them. I even sea foamed a few random vacuum lines. No codes thrown but still a pretty rough idle. Enough for a SMOG guy to wonder what's going on. Any ideas?
 
Anybody? I know this forum gets tired of misfire threads pretty quickly. I'm kind of on the wire here.

I'm going to drive it this weekend and put some miles on before I attempt SMOG. If I don't get a green light I'm going to do a cylinder compression test. What are good numbers? How much +- should they be in range of each other?
 
I'm chasing a P0300 with P0304 flashing CEL at high RPMs, and recently found Service Bulletin 09-003-03 that might be helpful to you.

I recently bought the Jeep, so I don't know how the PO drove it, but I do know that it wasn't his primary vehicle. If he did drive it at low RPMs for short trips, and never wound it up on a regular basis, it's entirely possible that the exhaust valves are carboned up because I only get the CEL when I wind mine up to high RPMs.

Has anyone on here done the entire procedure? I'd like to pull the valve cover and check, but I think I am going to try the Mopar Combustion Chamber Cleaner by itself first, following the instructions in the SB.
 
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RMETeeJay said:
I'm chasing a P0300 with P0304 flashing CEL at high RPMs, and recently found Service Bulletin 09-003-03 that might be helpful to you.

I recently bought the Jeep, so I don't know how the PO drove it, but I do know that it wasn't his primary vehicle. If he did drive it at low RPMs for short trips, and never wound it up on a regular basis, it's entirely possible that the exhaust valves are carboned up because I only get the CEL when I wind mine up to high RPMs.

Has anyone on here done the entire procedure? I'd like to pull the valve cover and check, but I think I am going to try the Mopar Combustion Chamber Cleaner by itself first, following the instructions in the SB.
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When I had my recent misfire issue, I simply pulled the spark plugs. They all were heavily covered in soot. I basically did that procedure with Seafoam instead of the Mopar fluid followed by an Italian tuneup. It seemed to alleviate the issue for a while until I found the catalytic converter had self-destructed.

Pull the spark plugs and check for soot. If they all have comparable amounts of soot, you know it’s a widespread fuel/air/exhaust problem. Only one or two cylinders could indicate a different issue. No soot could eliminate some potential issues.
 
Steel City 06 said:
Pull the spark plugs and check for soot. If they all have comparable amounts of soot, you know it’s a widespread fuel/air/exhaust problem. Only one or two cylinders could indicate a different issue. No soot could eliminate some potential issues.
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As mentioned in my previous post, I just put in new plugs. Didn't solve the issue.
 
ejay said:
Thanks for the input. It has APP985 plugs but they could be swapped out due to condition. Well, I need to determine if I want to spend $50 on really nice spark plugs just to find out that it's the CPS. Then spend another $100 on a Mopar CPS. I did source one on Amazon, though, as I've read (and you mentioned) Mopar is the way to go. 56027865AB. Seems to be the correct part number. I've got until Saturday to fix, clear, and put on another 100 miles. Then smog and register. Don't think I'll make it in time before penalties.

Wouldn't a bad CPS not give you spark? Just like a a bad coil? I have spark on all cylinders. I'll test the resistance on the sensor leads before I commit to buy.
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Pay the DMV then smog it when you can. No penalties that way. If you pay them late you get penalized.
 
Clogged cats won't initially cause misfire, but misfire will kill your cats due to the unburned fuel igniting on the cat media. I had an undiagnosed misfire that didn't throw codes prior to my 1st cat replacement. Replaced the cats and ran fine with intermittent misfire codes. Replacing my coil rail fixed the misfire issue, but not long thereafter, had to replace the cats again due to the previous misfire issues. Everything's running fine now.
 
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LJBean said:
Clogged cats won't initially cause misfire, but misfire will kill your cats due to the unburned fuel igniting on the cat media. I had an undiagnosed misfire that didn't throw codes prior to my 1st cat replacement. Replaced the cats and ran fine with intermittent misfire codes. Replacing my coil rail fixed the misfire issue, but not long thereafter, had to replace the cats again due to the previous misfire issues. Everything's running fine now.
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Did you test the coil rail prior to replacement? I am getting spark on all cylinders. Tested the coil rail by removing it, laying a rod of metal across the leads, placing a long screw into each lead, and grounding the rod. Cranked the engine and saw the spark hit the rod from each lead. Redneck way of doing it but a definate way of letting you know if there is spark.
 
No, I didn't test it. My research suggested coil pack, plugs, or CPS as culprits, and I'd already replaced the plugs. Mopar part is around $200, but you can get one for about 1/3 that price. Here's the one I went with:

Standard Motor Products Coil Pack

I've been running this coil pack for over 3 years with no issues.
 
No go on SMOG. I threw some lacquer thinner in the tank to help clean the cats. I drove around (100 miles) and it idles better. No new misfire codes. But, I'll venture to say running hotter exhaust screwed with the sensors and it threw a P0135 O2 bank 1 sensor 1 heater element 'pending' code that keeps coming back after I try to clear it. SMOG guy says I have to let it cool off and throw some more miles on it and try again.

I'm now at the DMV paying registration. Damn it's busy here.
I'm taking a day off later this week to put some more miles on it after it's cooled.
 
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On my 2002 wrangler the stud at the back engine (driver side) had worn thru the harness and into the wires...since putting an insulator over that stud my P300 codes have stopped. I'm very happy about that... good luck

Picture shows with insulator in place..

IMG_9889.JPG
 
That’s the passenger side what does the driver side look like. Wish I had some advice, I have a persistent P0353 code that Iam chasing down.
 
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