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PO306 - Misfire on #6 - With corresponding click through the speakers

2K views 14 replies 6 participants last post by  rep-tile 
#1 ·
So like the title says I'm getting PO306 - Misfire on #6 and when the engine falters there is a corresponding click through the speakers when the radio is on. I haven't had a chance to dig in to it but correct me if my thinking is wrong here that the issue is likely electrical? The spark plugs are due to be changed so I'm going to do that first. Any one have any other ideas for what I should look at?
 
#4 ·
Had a chance to actually work on it today. The new plugs solved the issue. All the gaps were off and cylinder 6 was at .070 which is twice as large as spec. I'm guessing it was arcing to the block causing the misfire and the click through the speakers.
 
#5 ·
Looks like I spoke too soon. It was gone for a bit, but now it's back with a vengeance.

04 with the 4.0

- Miss isn't constant it will hit a few cycles miss one, hit a few, miss a few more, hit one, miss a few more, hit a few
-Ran a bottle of Techron through the last tank full (typically run a bottle through around an oil change)
-Still DTC 0306
-Still getting the pop through the speakers with the radio is on regardless of the volume.
- Doesn't present for the first 30 to 60 second after a cold start
- Misfire is MOSTLY at idle and initial acceleration but occasionally hits when accelerating at speed
- Compression test results (dry) 1. 170, 2. 189, 3. 175, 4. 176, 5. 172, 6.180
- New Spark plugs still look good and are uniform
- Coil pack - tested with multimeter 1 and 6, 2 and 5, 3 and 4 all test at 15.3 ohms.
- All Injectors can be heard opening and closing using a screwdriver against the injector
- Injectors 1, 2 and 6 test at 14.1 +/-.1 ohms (warm engine)
- Disconnecting injector 6 makes the miss constant and still makes the popping noise thru the radio.
- Disconnecting injector 5 or 2 or 1 does make it run noticeably worse

I'm thinking of replacing injector 6. Thoughts? I was really hoping something would be obviously abnormal.
 
#6 ·
Sounds like a grounding issue. Have you checked the known issue of the harness that wraps around the back of the block at the valve cover for holes & general integrity?
It sometimes falls onto the top of a stud & has a hole worn on it. It can cause many issues that are sporadic. Depending on heat, engine movement, moisture, bumps... all sorts of things.
 
#7 · (Edited)
As previous poster mentioned and should have been done while changing the plugs since the packs were off... swap the coil pack and see if it moves to the new cylinder.

e.g. swap it moving it forward by one cylinder on same side will throw a P0304 if it's the coil pack. Costs nothing but a few minutes. Coil packs are dirt cheap also, but do that first.

Also, recheck that you retained the ground strap you may have loose, but it sounds like either a coil pack or a ground strap or both.

Edit: check and see if the coil pack from a 2002 4.7l Durango is the same as what you need. If so just pay shipping and I'll send you this one. Bought it to fix stepdaughters Durango but she got rid of the car. It's a wells c1231 for reference.
 
#8 ·
Rottidog said:
Sounds like a grounding issue. Have you checked the known issue of the harness that wraps around the back of the block at the valve cover for holes & general integrity? It sometimes falls onto the top of a stud & has a hole worn on it. It can cause many issues that are sporadic. Depending on heat, engine movement, moisture, bumps... all sorts of things.
Good point. I'll check the all the engine grounds. Now the ground that goes from the valve cover to the firewall did fall apart like a year ago and I replaced it, well before this issue started, with some 10 gauge wire and circle connectors. Could that be playing a role? Should I get a proper grounding strap? No issues presented when it was broken, for however long that was.
I'll also look at that harness. I had put a bit of hose over that stud, as a prophylactic measure, a few years ago after reading on here how it can cause issues.
 
#15 ·
The 4L is known for injector wiring rubbing against a stud at the rear of the engine. You may want to check for continuity in the wiring for inj 6 from PCM to the injector connector. Unplug the white PCM connector and locate pin #12 (brown/dark blue) and test the resistance against the inj connector with a DVM. It should be closed to none, even when you wiggle the wiring harness.

Now the ground that goes from the valve cover to the firewall did fall apart like a year ago and I replaced it, well before this issue started, with some 10 gauge wire and circle connectors.
The ground strap is specifically designed to reduce engine interference with the stereo, it is not meant as a ground point. The metal mesh it is made of is for shielding. Look up 'Faraday cage', you'll get the idea. Anyhow, if you used regular wire then that's the problem.
 
#9 ·
thor363 said:
As previous poster mentioned and should have been done while changing the plugs since the packs were off... swap the coil pack and see if it moves to the new cylinder. e.g. swap it moving it forward by one cylinder on same side will throw a P0304 if it's the coil pack. Costs nothing but a few minutes. Coil packs are dirt cheap also, but do that first. Also, recheck that you retained the ground strap you may have loose, but it sounds like either a coil pack or a ground strap or both. Edit: check and see if the coil pack from a 2002 4.7l Durango is the same as what you need. If so just pay shipping and I'll send you this one. Bought it to fix stepdaughters Durango but she got rid of the car. It's a wells c1231 for reference.
I wish I could follow that advice about swapping the coil packs. Jeep in their infinite wisdom decided that a single unit, non-serviceable, not cheap coil rail was a great idea.
 
#11 ·
Grounds tested ok. .03 - .00 ohms from the neg batt post to the ground on the rear passenger side of the valve cover, the ground on the passenger side of the engine, alternator and various bolts on the engine.
12.34 volts w/ engine off/ 14.1 w/ engine on from the pos post to the various points listed above.

Checked the wire harness that sneaks around the back of the valve cover. The plastic loom was chewed off by the post but that was already done by the time I put the bit of hose on the post years ago. As best as I could tell the wire's insulation is in good shape and moving it around doesn't have any impact.

I did notice that at startup, the engine ran smoothly until the mechanical fan stopped running full speed after the first 60 seconds or so. Once the fan went to its resting speed the misses started. My question is when the ECM tells the fan to slow down what else does it do?

Rottidog said:
I also have seen in P030X code posts that there can be an issue with fuel getting too hot at the injectors & causing a misfire. I found that after my own GC 4L had a P003 just yesterday. Something to look up perhaps.
That fuel rail does get pretty hot especially when my hand is resting on it as I'm trying to unplug the sixth injector. But I don't think that is my issue. The miss starts with 8a stone cold start before the engine has even gotten a chance to get luke warm.
 
#12 ·
Just trying to think of what else happens other than the obvious. Secondary things etc.
What's going on when it's cold? What happens when it warms up? When the miss-fires happen is it after a specific even like a thermostat opening... those sort of things.
The rotation (twist) of the engine on the engine mounts. Anything electrical get moved much to cause a loose connection, maybe inside insulation a wire has a break that only shows itself when certain heat, movement etc happens?
You said that loom did have damage before. Perhaps a wire inside the insulation got damaged & is just now rearing it's ugly face?
 
#13 ·
move the coil to another cylinder.

Check and recheck all plugs to coils. Noise in the radio is sure sign of an electrical short or floating ground. Since its RPM related, then it most likely ignition related. the plugs was an excellent start and surely contributing.

is the noise there all the time, cold and hot? Before the rough misfire is noted?

Check or swap fuel injectors also from 6 to 4.
 
#14 ·
The other day I picked up a spark tester and put it on 6. I got a couple of sparks but it definitely wasn't consistent. Put it on 1 and it sparked every time. Apparently the continuity/resistance test with a multimeter isn't definitive as to the state of the coil rail's health. New coil rail showed up today, slapped her in and the 4.0 is happy again. Well, happier. Still need to do the RMC so she stops making a mess of my driveway.

Thanks for all the input guys!
 
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