Help! Cylinder 3 misfire code

Luny421 · **Posted:** Sat Apr 29, 2017 10:20 am

Background: took my vehicle in about a month ago for my emissions inspection. Afterwards, it started idling rough when at a stop. Later that night, the check engine light came on and I immediately pulled over and checked the gas cap. Of course, the Rhodes scholar who did my emissions test didn't bother to screw the gas cap back on. I tightened it down, and the rough idle at a stop went away.

I then drove it for a little over a hundred miles and the check engine light was still on. Took it to Advance and when they scanned it, it showed a "cylinder 3 misfire" code. I ordered a coil (Mopar OEM) and spark plug (Denso Platinum TT) from Amazon, but by the time they arrived, the check engine light had gone off.

Fast forward to yesterday, the check engine light came back on. I took it to Advance, they scanned it, "cylinder 3 misfire". Keep in mind, I haven't had any symptoms of a misfire, no rough idling, no loss of power, nothing. I bring it home and swap out the coil and plug then had the code cleared. I drove around trying to reset everything, and after about 50 miles, the check engine light came back on. Scanned it, "cylinder 3 misfire". What should I be looking at next. Thanks in advance for any help or suggestions.

tl;dr - cylinder 3 misfire, changed coil and plug, still showing cylinder 3 misfire, what next? 2008 KK w/ ~96k miles

lfhoward · **Posted:** Sat Apr 29, 2017 12:20 pm

If you've already changed the plug and the coil (and the plug was gapped correctly), the next thing I would check is the fuel injector. For an easy fix you can try running some injector cleaner through a couple tanks of gas and see if it runs any smoother and the light goes away. (I recommend Lucas Fuel Treatment.) For a moderate difficulty test you can try swapping the #3 injector to a different cylinder to see if the code follows it. (I have never worked on the fuel system in my Jeep so that one would be a learning curve for me.)

How's your coolant? All present and accounted for, with no oil in it? And no coolant in the engine oil? A small head gasket leak at #3 could cause loss of compression and misfires but let's try the easier stuff first. Once other causes are ruled out, you could test the compression on the #3 cylinder, but you might need a mechanic for that.

Luny421 · **Posted:** Sat Apr 29, 2017 12:46 pm

Coolant is still the original. Manual says to change it @ 120k, I was planning on coolant flush and water pump & t-stat replace @ 100k. Coolant still looks good, no signs of oil. I just changed the oil @ 95k and no signs of coolant or anything else. I change oil and filter every 5k, and add a can of Royal Purple fuel treatment every other oil change (10k).

I've got a buddy that wrenches around on his Broncos quite a bit, I'll see if an injector swap is something he'd be comfortable tackling, seems a little outside my area of expertise. Maybe someone else here can shed some light on swapping injectors.

Thanks for the suggestions.

Ted15 · **Posted:** Sat Apr 29, 2017 1:58 pm

You might want to replace your plugs with a set from the dealer. Platinum, iridium and copper aftermarket plugs aren't designed for our systems. I put a set of champion copper core in that were recommended and I got the same number 3 misfire code that caused me to replace them in the first place. The code only cleared for a couple hundred miles. I'm on my second set from the dealer and won't use any others. No more misfires, no more engine codes, nothing. I'm around 85000 mikes, the first plug change was about 37000, you're supposed to change them every 35000.
I'd try a set from the dealer first before swapping injectors. :2cents:

Scar0 · **Posted:** Sat Apr 29, 2017 6:02 pm

OEM plugs are NGK, ZFR6F-11G.

Luny421 · **Posted:** Sun Apr 30, 2017 1:14 pm

Scar0 wrote:

OEM plugs are NGK, ZFR6F-11G.

Thanks, just ordered some off amazon.

On a related note, the check engine light turned itself off this morning. I'll change the plugs when they get here and see what happens.

Thanks gents

Scar0 · **Posted:** Sun Apr 30, 2017 10:58 pm

1 trip fault and 3 good trips to reset...
But don't put off getting those Platinum plugs out of there ASAP! They will do nothing but cause problems for you...

Help! Cylinder 3 misfire code

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