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My P0304 misfire journey -- suggestions welcome

 
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Old 10 Sep 2014, 09:32 pm
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Default My P0304 misfire journey -- suggestions welcome

My wife's 2010 PT Classic set a P0304 code a couple of weeks ago. The car has 48,000 miles. When the code first set, the misfire was pretty obvious both at idle and driving. I changed the plugs (OE Champions) and wires, checked the coil resistance (good but primary side at limit of spec) and dumped a can of injector cleaner in the tank. The condition improved quite a bit initially but the CEL came back on after a few days -- same code. A couple of days after that, she told me the CEL had come on that day and blinked for a few seconds on a couple of occasions. When I drove the car, the driveability was fine but the idle was rough and the amount of roughness was variable.

At this point I suspected a manifold gasket leak or a bad injector. I took the lower manifold off and took a close look in the intake ports. The valves in cylinders 1-3 were almost perfectly clean, with just a tiny bit of carbon in a couple of spots. Cylinder 4 had one valve that was clean, but the other had a surface layer of carbon over the entire valve head. The carbon buildup pattern in the port was the same as the other three except for the one valve head. The injectors had a fair amount of varnish on them, with #4 being a little worse than the others, so I changed the #4 injector even though all 4 checked OK. The lower manifold gaskets looked pretty good, but there was quite a bit of dirt trapped in the spaces between the manifold and head. After a thorough cleaning of the manifold and head mating surface, I put it back together. I also changed the coolant, the battery (original), cleaned the battery cables, and put injector cleaner in again with a fill up.

The idle roughness was much reduced, but there was still a little when I turned the A/C on, so I verified that the fan is operating correctly. The car now seemed to run great, but after a several mile freeway cruise I got a blinking CEL for a couple of seconds when I stopped at a light. It did not set a hard code. I thought it might be due to IAC position during the relearn, but two days later the same thing happened 3-4 times within a mile after several hours of sitting in full sun on a hot day. It occurred both while driving and idling. Once again, no hard code was set. She drove it home with the AC off with no additional blinking light incidents. I started it after a couple of hours and the idle has definitely degraded again -- the misfire is quite noticeable. I now have it parked until I have time to work on it.

My planned next steps are:

Clean IAC and MAP sensor
Check resistance on the plug wires (despite being new)
Check for a bad plug (despite being new)
Check the condition of the vacuum lines
Check continuity of the injector wiring harness

I also bought 3 injectors and a coil. I generally don't throw parts at a problem, but past experience makes me suspect a heat related intermittent with the coil, so I am going to change it. I'm leaning toward changing the injectors too based on the varnish and dirt mentioned above, plus the fact that the cost for these parts is reasonable at $175 total.

I also want to check the fuel pressure but there is not a Schrader valve on the fuel rail like there is on my '02. Does anyone know the procedure for checking fuel pressure on the later cars?

If none of the above fixes the issue, I think I'm at the point where I need to start hunting for bad/intermittent sensors, harness damage, etc. I'm also considering buying a software package that has full Chrysler diagnostic capability since I own two of these critters... Interesting factoid -- my daughters 80,000 mile 02 LE has always been considerably faster, idled better, and gotten better mileage than the '10.

I should also mention that all code readings have been done with a scan tool -- the Advance Auto Parts store 1/2 mile from my house knows me on a first name basis.

Comments, suggestions, etc, are welcome and encouraged.

TIA
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2010 PT Cruiser Classic -- Deep Water Blue Pearlcoat
2002 PT Cruiser LE -- Deep Cranberry Pearlcoat
2009 Pontiac G8 GT
2000 Honda Civic
1989 Chevrolet Corvette -- original owner, 500 HP 383 build in progress

Last edited by Z51L9889; 10 Sep 2014 at 09:38 pm.
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Old 10 Sep 2014, 09:48 pm
quicksilverdon's Avatar
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Default Re: My P0304 misfire journey -- suggestions welcome

Also check the plug gap - 0.040 is a good starting point.
Spray some staring fluid along intake manifold seams - if idle smooths out, you have an intake manifold gasket problem.
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Old 10 Sep 2014, 10:00 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

Plugs were all gapped to .040 before I installed them.

Good call on the leak check. I was planning to do that anyway but forgot to mention it.
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Old 10 Sep 2014, 10:23 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

If you don't have an intake manifold I would do a compression check on all cylinders to compare with the compression on cylinder #4. I read a post where the exhaust valve had a crack in it causing P0304 but I find it very unlikely with the low miles you have on your PT Cruiser.
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Old 10 Sep 2014, 11:42 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

also check and make sure none of your plug wires are touching each other or anything metal around them , fire the car up at night and look for sparks by the coil , that was my problem I went over everything and it turned out to be my wires touching eachother on 3 and 4 . Good luck
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Old 11 Sep 2014, 06:55 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

Just did an intake leak check with starter fluid. No change in idle. I'll do a compression check tomorrow night.
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Old 11 Sep 2014, 08:33 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

Swap plug wire with other of same length and see if problem moves. You can also swap plugs - all to rule things out.
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nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge."
Isaac Asimov"

'05 Limited Turbo Lite, (Silver, of course)4-wheel ABS, Sunroof, Spoiler. Mods: E&G Classic grill, K&N FIPK, BTG duals, rear lowered 1.5", LED washer lights, $20 catch can, Aoogah horn, Weatherflectors, Sunroof Deflector, Fuzzy Dice, rear logo flames, rear pinstripe graphic, Gen3 Taillights, rear sway bar, hood struts, Strut bar.
Traded in '02 Silver Touring Edition w/87,000 miles
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Old 13 Sep 2014, 04:18 pm
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Default Identified Cause of Problem

I discovered the source of the recurring P0304 code and the flashing CEL. It is an engine mechanical issue, most likely in the head.

I ran a compression test and got the following values (Cyl 1-4): 195; 190; 190; 120. I ran each cylinder twice and got the same values.

I then ran a wet compression test on #4 and still got 120 psi, so the problem is most likely in the head.

The only good thing about this is the fix *should* be covered by Chrysler's powertrain warranty (5 years/ 100000 miles on 2010 vehicles) since the vehicle build date was 12/09 and the car has only 48K miles. We bought the car in 2011 with 10K from a Chrysler dealer and the new car warranty transferred to us, so we should be covered.
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2009 Pontiac G8 GT
2000 Honda Civic
1989 Chevrolet Corvette -- original owner, 500 HP 383 build in progress
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Old 13 Sep 2014, 06:15 pm
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Default Re: Identified Cause of Problem

Quote:
Originally Posted by Z51L9889 View Post
I discovered the source of the recurring P0304 code and the flashing CEL. It is an engine mechanical issue, most likely in the head.

I ran a compression test and got the following values (Cyl 1-4): 195; 190; 190; 120. I ran each cylinder twice and got the same values.

I then ran a wet compression test on #4 and still got 120 psi, so the problem is most likely in the head.

The only good thing about this is the fix *should* be covered by Chrysler's powertrain warranty (5 years/ 100000 miles on 2010 vehicles) since the vehicle build date was 12/09 and the car has only 48K miles. We bought the car in 2011 with 10K from a Chrysler dealer and the new car warranty transferred to us, so we should be covered.
I hope that you can get the issue fixed under the warranty. But in my opinion, if I were you, I would not tell the dealership any of the work/troubleshooting that you have done, just report the DTC and let them do their own troubleshooting. Also, I would not be surprised if they tell you that you need a tune-up first, before they tear into the engine, so be prepared to spend a little money before they cover any warranty repairs, as tune-ups are very rarely covered under any warranty. Good luck!
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Old 13 Sep 2014, 07:25 pm
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Default Re: My P0304 misfire journey -- suggestions welcome

Keep us posted, please.
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nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge."
Isaac Asimov"

'05 Limited Turbo Lite, (Silver, of course)4-wheel ABS, Sunroof, Spoiler. Mods: E&G Classic grill, K&N FIPK, BTG duals, rear lowered 1.5", LED washer lights, $20 catch can, Aoogah horn, Weatherflectors, Sunroof Deflector, Fuzzy Dice, rear logo flames, rear pinstripe graphic, Gen3 Taillights, rear sway bar, hood struts, Strut bar.
Traded in '02 Silver Touring Edition w/87,000 miles
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