Intermittant Miss and OBD Code 0303

[SPUD54]

Engine has been running fine for a year sinced purchased used. Drive all highway miles. Just turned over 200,000 miles. Two weeks ago however, started running rough and up came 303 code for #3 misfire. Took to mechanic who replaced wires, plugs, and air filter. Wires had been arching.

Ran fine for a week, then started again. Checked code (same 303) and cleared code. Car ran fine for another week, then started up again this morning. Same code.

I'm hearing coil pack from other forums but no other real definite answer. Not sure why car runs great for a week, then suddenly starts missing. Then after a code reset runs fine for another week. Wouldn't this occur constantly.

There was a heavy dew this morning and the time before was a heavy rain. Car was only driven about a block both times before this started happening. Any clues???

[65comet]

Please list the year and engine. That could help if a certain one gives that code under specific circumstances. Whenever I get a code related to a single cylinder ignition, if it is possible for that year and engine I will swap the coil pack and anything else possible with the cylinder next to it. (that is remove everything from them to do a total switch, not just pull one end of a wire off one to move to the other) Then if the code changes to that next cylinder I know what the problem is. If it doesn't change, then I start looking at other possibilities like a controller, ECM, bad cylinder, bad sensor, etc.

[SPUD54]

2002 3.0L (Basic engine, no frills).

[shorod]

Welcome to the forum, SPUD54!

Further following 65Comet's lead, he didn't specifically mention the fuel injector as one of the "anything else possible" items, but I would suggest moving that as well. Swapping fuel injectors around may require pulling the upper intake manifold, and if it does, that would be a good time to give it a close inspection for evidence of a vacuum leak due to a bad gasket, a crack, or possibly even a hole melted through it.

Do you even notice the vehicle running roughly or does the code just appear with no apparent symptoms? Do you have a scan tool that will allow you to monitor the oxygen sensor voltages or short term and long term fuel trim values in datastream?

-Rod

[SPUD54]

Here's the latest. Car is now parked. Did get it home yesterday. Ran rough with no guts going uphill. I did check the PCV valve pipe as described in another recent post by frenchrl. Mine has same issue so that will be replaced. When inspecting this, I noticed that the windshield washer tube was split and leaking fluid. Not sure when this happened but yesterday I used the washer several times before leaving the house and the car started acting up immediately after using the washer. I believe that line is directly over the offending cylinder (passenger side).

I know that sounds ludicrous but that's the way it went down. But no recovery this time. The car is not showing a knocking type running, just plain rough. Idles fine and at the engine compartment there is no particular noise or sparks (looked at it at night). But the exhaust has a lumbering sound.

I have no tools other than a code meter. I just spent $180 on new plugs, wires, and air filter. And, I just put over $3,000 in a used engine for my son's Focus and other repairs to our other two cars. So I am not wanting to start throwing parts at the issue. The mechanic will look at it for free and so probably that will be my next step. I just don't want to get involved with a dealership right yet.

The mechanic and I have been discussing the suggestions shown here and he is aware of the potential problems. If anyone has any other ideas, it would be appreciated. Otherwise we'll continue looking at the suggestions already given.

Thanks to all.

[libraflo]

I have a 2002 Taurus SES with standard V6 Vulcan engine and had a very similar problem. It may have been the same code. It indicated a misfire on cylinder #3. The most likely suspects were spark plug, spark plug wire, coil, fuel injector, and other things in that order. Changed spark plug and still had problem. Checked ignition wire with meter and decided it was probably OK. Added fuel injector to fuel and still no change. Engine loped on start up and ran rough but cleared up and ran fine after a couple of minutes. Check engine light was on. Changed to shell gas and added fuel injector cleaner again and about 3 weeks later check engine light went out and engine seems to be OK the last month. I think the problem was a dirty fuel injector. Suggest adding fuel injector cleaner and using a good quality brand gas and see if this helps.