ym42

A while ago, at about 100k miles my car threw a P0430 "cat converter below efficiency" code (just one). I changed the spark-plugs to one-piece Champions, thinking a misfire might be a culprit, but the code did not go away. I also went ahead and changed the front o2 sensors, and swapped the rear ones side to side... The code stayed the same... The next thing I noticed was a misfire on cold engine, usually under load and/or more so with AC on, which usually lasted for about a block or two, especially under a hard acceleration. But then it happened one night when I was driving home in a rain, in the middle of the long trip, at highway speeds, again turning off the AC seemed to help a bit and finally it just disappeared. I think I got a code, cylinder 1 misfire... The code went away later. I pulled the plugs again, adjusted the gap smaller, still the same story - misfire when cold. This whole story makes me think of some similar problems with cold starts that other people and I have experience before, when if you start driving immediately while the engine is cold it might stall and even not start for a while or sputter a lot... But what makes me concerned is that this misfire happens at the same cylinder and happened once in a rain on a warm engine. Could it be that one of the coil-packs is going bad? I can try to spray some water on them, or just drive the car with one of the coils disconnected until I figure out which one is at fault... But what makes it even more puzzling is that the misfire is on a passenger side where cylinders 1-4 are while the 0430 code is for the drivers side bank 2 catalyst, which just does not make any sense... The car was fine for 100k miles...

tx_zstang

It all makes sense. The 430 is telling you your driver side cat is going bad, which it probably is with 100k miles. Swapping and changing o2 sensors didnt change anything on that code (and you did the proper things by swapping rear o2 sensors to see if it changed sides). The cat is suspicious at this point.

The cyl1 misfire, try swapping the coil pack with a different cylinder.

Also do a search for misfire issues, as others have had various causes of them.

ym42

Apparently the misfire does not always set a code... I could hear and feel it this morning but it did not set a code... And as soon as the engine warms up after about 3 blocks it is gone...

JimC

On my V6 I had could feel a mis-fire on the highway at cruising. I swapped the plugs, plug wires, coil, and MAF and it was still there. Then I thought maybe a cat was plugged with 183,000 miles on the car. I never had any codes of any kind, but the cats were completely plugged up. We tried blowing compressed air through them and nothing came out and very little air flow.

New cats (well newer, they had 20,000 miles on them) and the mis fire is gone finally.

So with 100,000 on your car and the fact that the mis fire doesn't throw a code for you, I'd check the cats.

ym42

I still have a hard time believing that my cat is shot. This car has 100+k miles but it's all highway... Even now it gets good mpgs and accelerates well ( just beat a Harley to 60 from a stop light:-)... If that cat was plugged I would have problems with higher rpm...

ym42

On the way home I managed to get the code. Cylinder one misfire at around 1000RPM ( i was just accelerating from the parking lot, steady misfire in 5th gear, pressing the pedal to the floor while using the brakes to maintain the speed constant around 55mph. LTFT both banks - 0, STFT +4.2 both banks. Coolant temp +55C ( cold engine ). Will swap the coil to another bank tomorrow... At least I know how to get the code now...

tx_zstang

You could also have a vacuum leak, although the stft at idle would usually be higher (like around +10); check it at idle after the car warms up a little.

Cyl 1 is front-most cylinder on passenger side.

Since you're able to datalog, look at and compare the rear o2 signals.
The P0430 will eventually come up after a few drive cylces if the amplitude of the signal at both top and bottom are near to the front o2 signal wavelengths.

ym42

OK, at least a part of the problem is figured out. This morning, swapped the coils, the same code Cyl 1 misfire, proceeded to swap the spark-plugs. The code followed the plug. What a relief, mixed with anger - I changed them to Champions about two months ago! Glad its not the injector or the cylinder itself.

SCCAGT

And this is why I have been hesitant about using Champions in my car.
I know this remark will get plenty of comments, but, GENERALLY SPEAKING, certain spark plugs do not mix well in certain vehicle brands. ANY GOOD SHOP OR TECH WILL CONFIRM THIS!! A spark plug is not "just" a spark plug.
Champions are used in Chrysler products.
Autolites or Motorcraft in Fords.
AC Delco in GM's
NGK in Japanese cars
Bosch in German cars

Now, I fully realize, the 1 piece Champions were designed for our head design. And that there are plenty of people using them without an issue. These plugs may be an exception to the above list. Its just hard for me to disregard my experience from my shop with spark plugs. Too many times, Champions in Fords have caused a misfire issue 2-3mo later.

A note for our 4.0l V6 brothers. The spark plugs in these engines are DIFFERENT from one side of the engine to the other. Why? because of the positive/negative sides of the coil. If you were to pull these out and look at them, not only are the part#s different on them, you will find the little platinum blob to be on the electrode from one side of the engine. And the other side will have it on the ground side of the plug. For engines with this ignition set-up, a double platinum plug is the preferred replacement to eliminate any goof-up of putting a single platinum on the wrong side. This error will eventually cause a misfire, and necessitate plug replacement again.

tx_zstang

Good to hear it was a plug. Kudos on tracking it down and finding the cause, nicely done!

I too believe certain brands of plugs are best-suited to particular applications, generally speaking.
However, I have run NGK TR6 plugs in my 4.0L v6 and they showed far less wear than the stock ford plugs, which lasted only about 20k miles on the driver side.

I'm running a set of the ngk irridiums for the '08+ head design and 1 heat-range colder, with no misfiring issues so far (I do need to pull them out and check them since it's been a little over a year and 5k miles with numerous track passes).

Sorry, got off topic. But now for the cat issue. As I mentioned, try datalogging both front and rear 02 signals during normal driving after 3-5 minutes of warmup, and compare them.