I have a 2003 Saturn Ion 2.2L that previously was showing a P0300 (Random Misfire Detected) and would randomly drop cylinders/lose power. I worked on a number of fixes including replacing air filter, fuel filter, spark plugs, and using injector cleaner. After accepting it likely wasn't a fuel air mixture issue I replaced the injector module and coil packs. This fixed the code and the car felt like was running great. Shortly after a new problem was found. At stops the car would stutter and at times even stall, forcing me to restart the engine. A terrifying problem in traffic. It now shows a P0420 (catalyst system low efficiency). Anyone have any previous experience with a similar issue?

 

How many miles on car, catalytic converter, and 02 sensors?
How long did you drive it with the missing going on?

 

Try cleaning the throttle body and see what happens.

 

I got this code popping up after a bad coil pack and getting P0300.

Our 03 has just over 210k and as far as I know none of these parts (Upstream, Downstream O2 sensors or Catalytic Converter) have been replaced.

 

A bad (poisoned) end of life REAR O2 sensor will often contribute to falsely accusing the cat of being worn out Happened to me on both my SC2s.
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When you were having more or less constant misfiring, you were dumping raw gas that didn't burn into the catcon -- which is not good for the catcon and shortens its life. At the same time, the front O2 which controls the air/fuel mixture sees the engine as running lean since it's only generating 3/4 the amount of O2. It then increases the pulse width to the injectors to make up for it and richens things back up.

This means you were using fuel (which burned in the cyls) at an accelerated rate while at the same time dumping raw gas to the catcon.

Still have no idea how many miles on car, catcon, and O2 sensors b c you did not answer any of my questions.

I do know that enough raw gas burning in a catcon can actually make it glow orange red while running---and trashing---the catalyst.

Front O2's seem to last 100-120K on average for the S series DOHC's.

Rear O2's last longer. I assume it is because the post cat mix of exhaust components does not foul/poison the Rear O2 as quickly as the raw exhaust fouls the front O2.

Hook up a scanner with real time data logging and watch the two responses. The Rear on average should hang out between 0.4-0.7 (memory failing me)
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Given no other information about the vehicle, I would:
1) Replace the REAR O2 Sensor. The OEM's are made by Denso (for the Ions, I THINK), then put in a box with an AC Delco / GM part # on it. Dig up the Denso part number for the AC Delco part and buy the Denso--costs half of the dealer price. If you choose any other brand, I will have no idea how to guide you as I have had nothing but problems with Bosch O2's in my Saturns. And no universal kit BS either.

2) Clear the code and drive 51 miles.
The catalyst test requires 50 mi (always has for me).
the 51st mile is for you to celebrate or curse, depending on the outcome.

3) If it re-codes with a P0420 AND your front O2 is as old as your rear O2, replace the FRONT O2 - same deal with determining and buying the Denso part. Clear codes and drive 51 miles.

I suggest the front O2 because the catalyst efficiency results are calculated by a numerical comparison between the readings generated by the front and rear O2's. If the efficiency is below a certain value, it throws a P0420.

This can happen if one or both of the O2's are not operating properly, but since the Rear serves as the "reference" (post cat), if your reference is wrong, then all bets are off. Could also be incorrect readings from the front O2.

4) During mile 51, cheer or curse as appropriate. If you are cursing, reattach the realtime data logger and make sure the signals are reasonable.

If you are cursing, you should be. as a catcon is likely in your future.

Walker and others sell a single piece manifold downpipe/flexpipe/cat/ combo -- flanges on both ends. Just need new seals and prob studs
Approx $200
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Ion to S car comparisons are always on thin ice, so take my mileage estimates with a grain of salt.

Tooter -- I find it hard to believe you have 200K+ on an oxygen sensor --I am NOT implying you are being deceitful ---- just that I have a hard time with that. Of course, the engines run cleaner than the mid 90's S cars and the catcon performance has surely improved......so I guess anything is possible.
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I enjoy analyzing 4 month old post issues with vehicles where the OP posted and ran.

Keeps me sharp.
Or wrong.
Either way, I've enjoyed my time on the forum tonight.

 

I didn't want to start new thread.
We bought the car about 3 years ago (1 owner) with 183k on the clock that was a trade-in at a dealer.

Other than a clean CarFax and some previous maintenance included with that, I have no other info on what was done with repairs.

I find it hard to believe the front O2 sensor has that many miles. I normally get just above 100k out of most of them.

 

Honestly, your o2 sensors just might be original... The L61 in the Malibu I had had 136k when I bought it and the sensors clearly appeared to be original, and I never did change them... I agree with Derf, change the rear o2 first, clear the codes, and drive 51 miles... If the code shows itself again, change the front o2, disconnect the battery for half an hour, and then drive the 51 miles...

The reason for the total PCM reset is that after so long on a potentially bad o2, the PCM has fuel trims saved to compensate for the (slowly going) bad sensor, and might run funny with the new sensor, as it'll be reading exhaust gas in an entirely different manner than the old sensor did... The total reset will force it to start from square 1 and immediately learn it over again fresh, instead of slowly scaling the fuel trims back to normal...

IF the cat is bad, which isn't highly likely but possible(we had a 2002 L series with original cat and 262k, fluke maybe?), you can buy a high flow cat(Flowmaster, MagnaFlow, etc) for under $100 and have the exhaust shop weld it in... It MIGHT cause the code to return, but if so, find a spark plug anti-fowler in the proper thread size, drill it out and install in rear o2 bung, and then install o2 in it... Basically, it shields the rear o2 from some of the exhaust gas, which basically tricks it into thinking there's a factory cat in place...

 

Sharing illegal tricks to skirt emissions testing AND pollute the environment? SHAME ON YOU! Ecomodding does NOT give you the right to spread such info.

Not sure the PCM battery disconnect will help much. Because of the nature of the front O2 feedback (quasi real time), I believe the A/F ratio is changed near to the ideal value pretty damn quickly--the injector pulse is shortened as a direct result. Maybe a hard start and some rough idling for 5 min, but I would think all would be well after that.

But it can't hurt.....

 

Not so much an illegal trick(I didn't advise him to gut the cat or replace it with a test pipe), but a way to save on cat replacement and still keep the code away if it decides to come back...

Most high flow cats filter exhaust gas about 99% as effectively as the OEM ones do, and they're much cheaper to buy...

And I learned the anti fowler trick on redline forums...

 

I fixed the problem by replacing the cat with a new one.
I figured after 210k+ miles it was ready for a new one and it seems to like being able to breath....