Engine Misfire

The flashing CEL indicated that the PCM saw a class A misfire... one that could harm the catalytic converter. During thuis type of misfire, enough stray oxygen and unburned fuel is making it down the pipe to overheat a cat in very short order..... without the original codes, a guess is turning into a stab in the dark....

A P030X code is set by the misfire monitor and can be a sign of an ignition problem, a fuel metering problem or a compression problem. Were there any other codes along with the misfire codes from the first scan?

Along with checking the wires for continuity/resistance, we must also inspect the insulation for nicks and abrasions and inside the plug and coil boots for signs of tracking. Similarly, coil towers need to be inspected for signs of carbon tracking. That the problem occured at speed would have me putting the possibility of a vacuum leak on the back burner.... vacuum leaks typically affect things at low rpm or idle. If we had an idea of what the freeze frame data was or where the fuel trims were sitting at the time of the misfire, we could form a better idea of what the conditions were.

#4s running mate is (IIRC) #3... this plug and wire should be checked closely at the same time. One thing to remember about parts stores and free code scans.... there is NO diagnosing going on here..... they scan, you buy parts - capitalism at it's finest.

At this point, there is a real need to know if there were other codes associated with the original misfire codes. Other than that, a compression test and making excrutiatingly sure that the ignition system is indeed OK.... without checking these basics, the possibility of changing many parts needlessly is very real.

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Thanks for your reply Jim. There were no other codes with the first misfire. They were two P030x codes, I just can't remember which cylinders they were for. I've given the spark plug wires a second thorough look and checked the plug in cylinder #3 in addition to #4(the troublesome one), and everything looks good. The wires and plugs are about 9 months/7000 miles old.

I've obtained a gauge with the recommended screw-in spark plug insert to do the compression check. The procedure seems fairly straightforward, but due to the length of the hose on the gauge, is there any other way to do this without needing two people? The chilton manual says something about using a remote starting switch. Also, will a brick on the gas pedal substitute for "setting the throttle to the fully open position?"

In historical posts to this forum, I found lots of references to the coil pack when dealing with misfiring cylinders. I saw a previous post that you (Jim) made to someone that a coil pack resistance can test good and still be defective. If a coil pack gives spark and resistance is in check, is it likely to be defective? Are there any testing methods specifically for the coil pack? Of course, I'll tackle this once I test the engine compression. Thank you for the help.

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I started to write a big long thing about ignitions.... then I had an idea and found this

This shouldgive you some of the basics (it's not hard to grasp but some people insiston making it complicated) and we can answer specific questions from there. If you like, I can give you a "blow by blow" of how I would handle the diagnosis of this type of complaint but there is a lot that rides on the capabilities of the scan tool involved and (very important) the abilities of the tech using the tool to use it to it's best advantage....

Your problem need not be drawn out and complicated and (I hesitate to say this) it may be cheaper to go the expensive route. I spent many years working for both myself and other independents.... I loved the variety of being an "all make" kinda guy but working for a dealer, with the specialized training and equipment, has really turned my head. Sadly, I am only one voice in the wilderness - all I can do is hope that you can find a tech that is enthusiastic about what he does and has a great deal of pride in his end product.

I haven't read the how stuf works article in it's entirety, but the articles I have read, have been better than anything I can cobble up.... Read it and if you have specific questions, I can help....

Thanks for the info Jim. For the archives:

Since my problem was symptomatic of a whole handful of things, I didn't want to go the potentially expensive DIY method of replacing stuff until the problem is fixed. I did a compression test and the engine reported about

160-165 psi on all cylinders. I then decided the problem was ignition related and decided to replace the spark plugs even though the current plugs were about 7000 miles old. Voila! The problem was solved. I used (OE spec according to the guy at the parts counter) autolite double platinums this time round, gapped to the spec of .054 of course. My old one were, apparently crappy, Champion brand plugs. So my recommendation for everyone out there is to stick with autolite double platinums, and don't forget to gap them appropriately. You can find the gap spec on the sticker under the hood. Cheers!

Actually, the champion plugs are very good, in Chrysler vehicles. I recommend the Motorcraft platnum plugs vs. the autolite's. the MC plugs lasted me about 4 years and they looked good enough to just be cleaned, but I swapped 'em out anyway.