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Discussion Starter #1
Hello all,

I am new here, and I really hope someone can help me. :) I hope this is the right forum.

I have a 2005 Town & Country with 128,000+ miles on it. About 4 months ago, the Check Engine Light came on and it developed a rough idle. Mechanic said it was showing code PO301--misfire on cylinder 1. There was a Technical Service Bulletin from Chrysler on this issue that said to change all the plugs and wires and then reflash the computer. This was all done and the misfire was still there with the Check Engine Light still on.

Mechanic then did the following (not necessarily in this order):
--Measured the idle at which the misfire disappears--it disappears at exactly the same RPM every time (around 1600, I can't remember exactly)
--Swapped out the #1 coil with one from another car that did not have the problem
--Did a smoke test
--Did a compression test of valves 1, 2, 4 and 6
--Visually inspected the valve spring and the rocker arm on the bank of cylinders with cylinders 1, 3, and 5 to make sure they weren't cracked or broken
--Measured the height of the lifters on that same size and the #1 lifter is the same height as 3 and 5
--Checked the crank case positioning sensor
--Replaced all the intake seals and gaskets
--Swapped out the fuel injector on cylinder 1
--Using carb spray, checked for vacuum leaks

After all these tests, he couldn't find anything wrong.

We then brought it to a dealership who said that it was a worn lobe on the camshaft. I disagree (and my mechanic agrees) that this is the problem because the misfire occurs only at idle (and disappears at exactly the same low RPM every time as noted above) and the misfire disappears as soon as I accelerate.

One other notes--this car does NOT have an EGR valve. The hose on the positive crank case ventilation is cracked and I though this could be a potential vacuum leak. But I disconnected it and plugged the intake up to check to see if this affected the misfire problem, but there was no change.

Does anyone have any ideas or suggestions? It drives and feels like a vacuum leak, but we've done everything we can think of to rule that out?

Thanks
 

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You can have someone put a data logger on the car, and monitor the usual suspects in real time. Also when you're driving around.

Did you check for bad wires in the wire harness?
 

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Discussion Starter #3
Thanks for the reply. I'll see if I can find someone with a data logger.

We checked all the wires carefully. If the problem was in the wire harness, wouldn't the misfire appear at all speeds, not just at idle? The misfire goes away when the RPMs rise.
 

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code PO301--misfire on cylinder 1
I would like to know how the engine managment system knows that its cylinder #1. Does that imply an injector issue, a spark issue...how would it know which cylinder is not always firing? I know this probably doesn't help, but it might be good to fully understand.

And by the way...I had a boat engine (inboard 4 cylinder) which suffered a bent valve in one cylinder due to minor water intrusion through the exhaust stream. After that happened, it idled with a "miss", but above idle it ran just fine. After I pulled the head and had a valve job done, it idled and ran fine afterwards. So a valve issue could be the problem. If its not spark, fuel mixture, injector issue...not much left.
 

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When you say it's not misfiring when you accelerate or you're at speed are you reading real-time data on a scanner as you drive or are you just not FEELING it?
 

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I would like to know how the engine managment system knows that its cylinder #1. Does that imply an injector issue, a spark issue...how would it know which cylinder is not always firing? I know this probably doesn't help, but it might be good to fully understand.

And by the way...I had a boat engine (inboard 4 cylinder) which suffered a bent valve in one cylinder due to minor water intrusion through the exhaust stream. After that happened, it idled with a "miss", but above idle it ran just fine. After I pulled the head and had a valve job done, it idled and ran fine afterwards. So a valve issue could be the problem. If its not spark, fuel mixture, injector issue...not much left.
Have you googled it? Plenty of info there.
 

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Discussion Starter #7
@spacecoast
I also would like to know how the system knows that it is cylinder #1, but I haven't been able to find any info on this.

My mechanic looked at the valve with a fiber optic camera and it didn't look bent.

@RIP
Both. I can clearly feel the misfire at idle and as soon as I accelerate, it goes away. And when my mechanic looked at it, the computer showed the misfire up to some number RPM (I forget the exact number--I think 1100), and above that number, the misfire goes away.

Also, yes, I have googled till my fingers bled :). (That's how I ended up here!) We've been trying to diagnose this since the beginning of November. There are threads on this forum and elsewhere on the same problem, but the result was always one of the things we already tested for.
 

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Discussion Starter #8
Update: I took the car out for a longer ride, first time since I brought it to the dealership who said it was a worn cam lobe, and something is different. It now has a more pronounced tick at idle, and under load, I can now hear the tick as well. The misfire still does not appear there under load.
 

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I would check the famous "melted injector harness" issue.

Make sure that the plug wires are going to the right plugs, although this is likely not the issue.

If not, based on what has already been tried, I would guess the ECU is giving you the grief.
 

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Discussion Starter #10
I'll give the harness another look, but I am pretty sure we checked it carefully.

Is there any way to tell if it's the ECU? It was reflashed at one dealership after the initial sparks/wires change, and because of the way they treated me and the fact that they didn't put the sticker on that identified the reflash, I brought it to another dealer. Before he diagnosed the camshaft as being the problem, he checked to make sure that the computer was actually reflashed and and it was. If it was the ECU, wouldn't there be additional problems?
 

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There is another thread here about burned out coil problems. He also has a tic at idle which is characteristic of a shorted ignition high tension circuit. This may be the tic you hear at idle. It would be masked at higher rpms and driving noises.

Look at the engine in the dark to see if you can spot any arcing.

Since you've changed plugs and wires this narrows it down somewhat to a coil.
 

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Re-flashing doesn't fix hardware damage. It could be a wire to the ignition coil, or possibly to the injectors.
 

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If you're ticking and have a bad idle, it could very well be a hydraulic lifter problem. As a test, try something like motor honey or STP, and see if the lifters stay pumped up.

What oil are you running? The lifters in my Mercedes, with 200K miles, would leak down and tick when I ran 0W40 Mobil One. When I ran 1/2 15W50 and 1/2 0W40, no tick.
 

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Update: I took the car out for a longer ride, first time since I brought it to the dealership who said it was a worn cam lobe, and something is different. It now has a more pronounced tick at idle, and under load, I can now hear the tick as well. The misfire still does not appear there under load.
Just a suggestion. maybe your spark plugs are loose? The reason I ask is because my 3.3 had a ticking noise at idle for months with a stumble/misfire at certain speeds and at idle. When I went to change the spark plugs the rear bank plugs were severely loose, Put in new Champion spark plugs and all was well, van drove better than ever and the ticking went away. The spark plugs were my first thought when the ticking started, so check yours it could e loose. Also check your injector harness, the wires might be melted together.
 

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Mostly good suggestions. Please always tell us what engine you have when asking an engine question. Sounds like a V-6 (3.3 or 3.8L?).

The engine controller senses mis-fire based on the spacings of the crank sensor signals. It is hardly exact, so "mis-fire cyl 1" may not be a problem with that cylinder.

I would like you to post a photo of the injector harness above the exhaust cross-over, with the Velcro sheath opened up. So many of us have found crumbly insulation on those brown wires, that we would like to insure you are looking the right place.

A mis-fire in my 3.8L last summer was due to a bad coil pack. Have your mechanic test for that like I did, by clamping a timing light over each spark lead. If he complains that there are no timing marks to flash at, tell him to flash it at his belly. You are just checking if there is spark current to trigger the light in each wire. Two of mine that shared a coil did not cause a flash. I also heard a clicking sound in the coil pack. New coil pack and no more mis-fires.

Replace the spark plugs. A recent mis-fire in my 2.4 L was apparently due to lose plugs (that I installed ~3 yrs ago!). Never had that before. You can also try lowering the gap to ~45 mil. That was a Chrysler TSB for 2.4L turbo owners some years ago, since it is harder to throw a spark at higher cylinder pressure.
 

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Discussion Starter #18
@The_big_dill

We listened to the #1 fuel injector with a stethoscope and could hear it pulse, so it's getting an electrical signal at idle. My concern about the ECU is that I wonder what instructions changed when we reflashed.
 

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@marvinstockman

We've checked the height of the lifters and visually inspected the rocker arms and valve springs. I could try motor honey. My fear is that when I bought the car in June, it already had 5 cans of the stuff in it to disguise the problem!

I use 10W30 synthetic oil. That's a good idea to try some heavier weight oil.
 

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I changed all plugs in August. Then the first thing my mechanic did when we brought it to him in November, was change the spark plug on #1 and check all the other plugs. He also changed all the wires. When we brought it back to our mechanic after the reflash, he double-checked that the #1 plug was working by using a spark tester on #6 to verify that it was working, and then swapped out #1 and #6 and then retested the plug at #6 and that plug was working as well.

We have carefully checked all the wires, but when it stops snowing, I will double-check the entire wiring harness.
 
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