I have a 2000 protege es with 148k. Shortly after filling my tank today, the car starts stalling out. Feels like it's misfiring. Brought to autozone and there were no codes other than my P0421 (cat) that has been there for a while.

Just changed the spark plugs, pcv, air intake hose, clean MAF sensor before the winter. I thought it was interesting that this happened right after refueling, so I added a bottle of lucas to the tank in case the fuel or fuel tank had contamination.

Any ideas?? About to upload video..

 

Here's the video guys. It doesn't really show how rough the car is running.

 

It seems like a greater than usual amount of moisture is dripping from the muffler. I also noticed my coolant level was low.. Could this be a blown head gasket?

I was hoping it would only be water contamination in the fuel system. This happened very suddenly after refueling.

 

Yes, that sounds bad. You know it could have something to do with the refueling or it could be coincidence. Also it takes a while for the computer to register a code. It is programmed that way.
When was it the last time you changed the spark plugs and wires? I'd be looking at that first.

Consider using ScottyKilmer,s method of cleaning the catalytic converter: When the tank is half full add 1 gal of lacquer thinner (Not Paint thinner!!!) to the fuel and drive for 100 miles or so. That cleans more than the CC, it cleans the whole fuel system and the O2 sensors as well. It may even remove deposits on the valves and in the combustion chamber.

Also read the "Unofficial User's Guide to the Mazda Protege". So yours is a bit younger but is makes no significant difference.

 

Here's Video Tan... talking about Both me and Tan.. have done it with lacquer thinner.

 

Guys - thanks for your replies. I'm familiar with scotty's trick but have yet to try it myself. The car is due for inspection in May and up until this point a long highway drive usually clears the code (P0421) for at least a couple of days.

I took it to my local shop last night and they seemed concerned that there were no codes other than P0421 getting thrown.. The shop manager even entertained the idea that somehow diesel got put in the tank.. The mechanic ended up revving the **** out of the car and the problem went away. We let it run for 10 mins, cool down for a while and retested. No sign of the problem. The shop manager took it for a test ride and I tagged along. He drove by the pump I had used earlier in the day -- there was no diesel pump next to it. (I was out of it that morning but not THAT out of it)..

When I asked him what he wanted for his time he shook his head. I ended up tipping the mechanic $20. They have always been fair and honest to me. His advice to me was to take the car "up to New Hampshire" (roughly 40-50mi) and back at 80mph. Took it for a highway drive today and still no issues.

 

It seems to be fixed. If you use non-ethanol fuel then you may have had a drop of water entering the fuel line.

I once wanted the fuel filter in a vehicle replaced and the shop owner said: "Tan! (actually, he used my real first name) you don't need to replace it. That filter is really separating the water and nothing else. But since they mix this much ethanol in the fuel you won't have that trouble!" I haven't replaced a fuel filter in any of my vehicles since. That is in Iowa, in other regions they may not adding ethanol as much.

Anyway, motor on!

 

Sounds like some water in your fuel. Just to be safe, buy some fuel additive that disperses water in your gas tank so it will be burned with the gas. If you keep the tank less than half full most of the time, water will condense in the tank and over time it will make its way into the fuel system. Those little short plug wires to the COP's can also cause intermittant rough engine. The most common cause of low water level is a leaking hose or leaking hose clamp connection, not a blown head gasket. If your oil level is where it should be and has not increased, it is doubtful your head gasket is blown. Fill the coolant reservoir tank to the line, and let the car idle for a good while to heat up and build pressure with the car parked over a dry spot, then look for a drip puddle. Usually it is the large hose at the bottom radiator connection that drips a little if the clamp is not tight or the hose is not pushed forward enough on the radiator hose flange.

 

Thought i'd post this interesting but good comment i came across about catalytic converter cleaners:
"To the people complaining it didn't work and giving it one star. Most of you are clearly don't understand what this product is for. If you have a 1 year old catalytic converter in your car, then something is wrong with your engine management or you are burning oil. If your engine is burning oil, or if the cat has lost the platinum, palladium, and rhodium that covers the ceramic honeycomb inside then this won't fix it. This only fixes dirty converters, if the catalyst is missing inside, it's not going to work. Also, if the light goes off and then comes back on, again, your car probably runs horribly and you don't even realize it. Catalytic converters don't generally fail on most vehicles unless something is wrong with your car, you're probably just trying to fix the symptom. So, if you clean the oil/carbon out of the converter, but your engine still runs like crap it's just going to get dirty again and not catalyze. This is a last ditch effort at not replacing the cat."

Don't like lacquer thinner, try these:

 

just for info. i tried that cataclean thing. it did not do anything to my car. and the bottle costs around 29 dollars. scratch that one. i dont know about the other products. i can only recommend **** that i use or used and i used that cata clean stuff. it was a waste of money.