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Discussion Starter #21
@BillGrissom

Sorry! It's a V-6, 3.8L, the model without an EGR.

I agree that the PO301 code might not be really be a problem with cylinder #1. But my mechanic hooked it up to his computer (maybe it's a data logger, as suggested by someone earlier in this thread) and watched the motor in real-time. He could see the misfire on #1 and watched it go away as soon as the RPM increased.

I'll look at the wiring harness when it stops snowing.

The second time we brought the car to my mechanic, he swapped out the coil pack for #1/2 with the coil pack from another 3.8L that happened to be in his shop. The misfire was still in my car and the other car ran fine with my coil pack.

I replaced all spark plugs in August, and my mechanic replaced the #1 plug in November and re-checked all the other plugs. But that's a great idea about closing the gap. We hadn't considered that. I'll give it a try.
 

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Discussion Starter #22
@blknblu

Thanks for this. I will double-check the harness just in case, but I really don't think this is the problem.
 

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Discussion Starter #23
Update: Thanks for all the great suggestions. I will look for sparks at night, try adding thicker oil, look for loose or cross-threaded spark plugs, double-check the wiring harness, check the crank sensor and have my mechanic use his computer to make sure that the problem is with #1, and try closing the gap .005. I'll update after I've done all that. It will be a couple of days at least.
 

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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.
Sounds like a valve train issue..like a lifter, cam lobe, rocker, etc. Perhaps something as simple as tightening the rocker nut.

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!
Ok, just catching up on all the posts....hate to say it but it sure sounds like you have an engine mechnical problem.
 

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I like to be more optimistic and expect simpler things. For some reason some guys right away diagnose major engine catastrophe, never could figure that out?

So many problems turn out to be simple even though they look bad at first. I always remember the time when I was on my honeymoon and the fan belt on my old '40 Buick separated and sounded just like a bad rod/crank bearing. Turned out the separated top ply was hitting the belt cover and making this awful noise. Cost $8 to repair! The car had a sheet metal belt cover just like the chain cover on a bicycle. Sure wish I had that car today, it was a big black 4-dr tank right out of a gangster movie.

Honey is probably not such a good idea in cold weather. Nothing wrong with 10w-40 oil, I'm going to start using it in mine this summer because of high mileage.
 

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Is it possible for a cracked flexplate to interfere with the CKP signal?
Is there a small crack in the intake air runner (aluminum part)?

It is better to find a mechanical who has right tools to trouble shoot electrical problems. A secondary ignition waveform analysis can provide abundant information on misfire. With an oscilloscope and current probe, the fuel control circuit and PCM can be unambiguously identified or excluded.
 

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Here is some interesting info from Chrysler FSM.

NOTE: Anything that affects the speed of the crankshaft can cause a misfire
DTC.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will
shut down that cylinders Injector Control circuit.
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector,
Ign coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
Were any of the above conditions present?
 

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Dumb questions for OP (since I don't see it stated):
What spark plugs are in the motor now? (Champion double platinum or something else)
Were they ALL checked for proper gap? (0.048" to 0.053")
 

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Discussion Starter #29
The upper valve train was all visually inspected. We will delve deeper if we need to get back in there and then we'll check the nuts.
 

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Discussion Starter #31
I will have my mechanic check the flexplate. We did a smoke test on the intake manifold and it's fine.

Re: the oscilloscope--my mechanic has a lot of sophisticated tools, but I will ask him tomorrow specifically about an oscilloscope.

Thanks foe the list of things to check. We have checked all of them except whether the PCM power and ground circuits are corroded. I will ask my mechanic to check tomorrow.
 

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Discussion Starter #32
I don't know for sure, but whatever was spec'd OEM is what we used. I am fairly sure they are not Bosch. However, I will check tomorrow.

Yes, they were all checked for proper gap. I am going try, per another poster's suggestion, to reduce the gap .005.
 

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Its a far fetched idea for plugs to be out of range, I feel like you are missing something simple. I know my plugs worked with the gap two times out of spec and extremely loose, couldn't even tell anything was wrong with the engine.

However, I did see a difference between using Champion plugs and other plugs, these vans are designed with the Champions in mind, so its a good idea to use them.
 

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Discussion Starter #34
Update: No blue sparks at night, no loose or cross-threaded spark plugs, spark plugs are Champion, the gap on the spark plugs is correct, tried tightening the gap on #1 .005, the wiring harness is fine, the crank sensor is fine, the flexplate is not cracked. My mechanic does have an oscilloscope and used it, and the problem is not electrical.

We put in some upper engine cleaner to see if we can burn some carbon off. If that doesn't do it, I think all signs are pointing to the valve train on #1.
 

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Please keep us updated, this is too much of a mystery to let go!!
 

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Discussion Starter #36 (Edited)
@gusc

:) The smiley is for your comment. My car gets :-(

So far, it is not sounding or behaving better. I am now thinking that I will need to decide between an actual diagnosis and fix or a complete engine replacement (because the engine replacement would end up costing less than a (possible) diagnosis and cure). But we do need to drive it 100 miles or so to let the engine cleaner do its thing.

At this point, we are considering putting our 1999 Caravan with 230,000 miles back on the road. The only problem with it is that the AC and heat don't work. Minor issues compared to my current issue!
 

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Have you tried using seafoam my friend?
 

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Please keep us updated, this is too much of a mystery to let go!!
Indeed, esp. since compression test was done on the motor and came up with no issues.
Interesting that the dealer suggested worn cam lobe, there was a report of the problem on here a while back - seemed very odd, perhaps its not that uncommon.
 

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How can a poor valve train result in a miss-fire? Unless the definition of miss-fire has become the word of choice for many related problems...

If we are still referring to the true definition of a miss-fire, then the spark is happening at the wrong time, or not at all. Do it the old fashioned way and pull out the plug, put it in the ignition coil boot and touch it to some metal on the car, do you see a spark at the tip of the plug?

Here is how someone else does it:

http://www.youtube.com/watch?v=ZceAZgZBn9E

If you see a spark, then its a timing issue.

Finally, if you have a miss fire, the fuel being pumped in and out of your cylinder is going to demolish your catalytic converter, so if you can avoid driving while you try to fix this issue, then you can save your catalytic converter.
 

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How can a poor valve train result in a miss-fire? Unless the definition of miss-fire has become the word of choice for many related problems...
MISFIRE = "to have the explosive or propulsive charge fail to ignite at the proper time <the engine misfired>"

Valve train can be the cause by failing to provide the proper fuel:air mixture at the time of ignition (as in failing to purge all/enough of exhaust gasses or not allowing fresh mixture to fill the cylinder) or failing to hold pressure generated by the explosion..
 
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