Isolating cylinder misfire issue

[Pricejh]

I need some group think here. In another thread (#1 cylinder misfire) I ganged on and started discussing a similar problem. Now, I think that I have gathered enough information to start isolating the issue.

On my '07 Cruiser Touring I've been getting a 304 code (#4 cylinder misfire) for several weeks now. I got a code reader and have been reading and resetting it to try and figure out what is going on. In a nut shell here it is:

I get the check engine light to come on at idle WHEN THE ENGINE IS WARM OR HOT. Usually shortly after start or when at idle. After resetting, I can start the car then drive off. If I don't have to stop or idle the light and code don't come back on...until I slow down at a stop light. Then the light will come on, it will blink for a while, then as I drive away it may go out. It did this several times yesterday.

Today, after resetting this morning, I was able to complete a 150+ mile trip without any codes or lights. After letting the car sit for a couple of hours this evening, I drove over to get some dinner and the caution light came on and stayed on, again.

Also, by keeping the RPMs up slightly, I can keep the caution light from coming on. (Take the car out of gear when pulling up to a stop sign or light.) Tach shows about 600 to 700 RPM when the caution light comes on. Idle is slightly rough, not much, just slightly. Engine is smooth when under way. Power is adequate (for a 4 cyl) and fuel consumption is running between 20 and 24 MPG on the road. Getting about 20 around town.


So, the question for the group is, What component(s) could cause this fault code (#4 cylinder misfire)? I want to take it into a local shop and have them do the work (I am away from home on a temp assignment and won't be home for several months).

[quicksilverdon]

When was last time plugs and wires were done? That's a logical place to start.
Have plugs gapped at 0.040, and buy some good brand name wires - I like Crane wires.
Throw a bottle of Lucas injector cleaner in the gas tank.
Since yours is not a turbo, intake manifold has to come off to change plugs, so have them be sure to carefully look at the intake gaskets (the gaskets can be re-used, but sometimes need replacing if there's an intake leak.

[Pricejh]

Thanks, that is about what i was thinking. I also think that I might replace the coilpack and the gaskets at the same time. That should cover all the bases. I note that anything to do with the ignition components requires pulling the intake. Might as well do it once and be done with it.

[quicksilverdon]

Up to you, but no reason to suspect the coil - when coil starts to go it impacts at least 2 cylinders.

[Chriscokid]

We had the exact same problem on my wife's 05 turbo. Our mechanic mixed up a concoction of cleaners in a pressurized vessel and ran it through the engine and this cleared up the problem. One of those ingredients was Marvel mystery oil. I usually run half quart per tankful every five or six tanks and this keeps it running good. We had already changed the wires and the plugs and our problem remained just like yours. I hope this helps let us know what you end up doing to fix this.

[Pricejh]

Thanks all for the pointers. Left the car in the shop yesterday. Letting them play with it. Defanatley getting new plugs and wires. While they are in there, I'm also getting new timing belt, etc. The car has 85K on it and I expect to put about 5K a month on it over the next few months. The back roads of Appalachia are no place to be left high and dry. This is getting pricey in a hurry. But, I need reliable transportation.

[Puddin]

Currently I have an 04 with 0335(crankshaft) and P0300(multiple cylinder is mis-firing)The 0300 did NOT show up on the Key Dance. I am wonder the same as you about the Coil Pack. The mechanic said the Coil wasnt putting out enough and this could be the reason I have blown through 5 sensors in the last 25,000 miles.
In the OLD DAYS a coil was Bad Or Good. The car DID or DIDNT start. In new cars are there varying degrees of going bad?
Did you replace your coil? How hard was it?

[randyincctx]

Originally Posted by Puddin

Did you replace your coil? How hard was it?

Maybe this might give you a better idea of whether it's within your capabilities......

How To Install Replace Engine Ignition Coil Chrysler PT Cruiser 01-03 1AAuto.com - YouTube

[Pricejh]

Update on the Misfire Issue.

The shop changed the plugs and wires. They also changed out the timing belt, water pump and intake gaskets. They drove it around and there were no codes being thrown. It looked like that had solved the problem. So, I paid for the work and drove off.

That night, the Check Engine Light came on, again. Same code, #4 Cyl Misfire. Back to the shop.

More looking, head scratching and puzzlement. Pulled cylender head and found a burnt #4 exhaust valve. They replaced valve and I got the car back this past Thursday evening. Drove it off and had to make a 150 mile trip that night.

Good News! No lights, no codes, car ran great! UNTIL I was about half way to my destination, still no codes being thrown, but start hearing a gentle tap, tap, tapping under my hood.

Story to be continued in another thread, different problem now.