No mufflers for 2 days, now misfiring??

[WildBoxer]

(Mods: If this is in the wrong forum, I apologize, please feel free to move.)

 

Okay guys, this is puzzling me. The car is a 2005 Legacy 2.5i Limited Wagon.

 

I noticed my exhaust had been getting louder recently, so I checked it out and discovered that the gaskets between the muffler and Y-pipe are pretty much falling apart.

 

I took everything apart to get at the gaskets and discovered how rusted the flanges are, so wound up taking the mufflers off the car to clean everything so I would get a nice solid fit when I put everything back together. It wound up raining all weekend while my car sat outside with no mufflers on it.

 

So, this morning I go to move the car so that I can take my truck to work. I start her up, and it's running really rough, the CEL starts flashing, which I know indicates a misfire. I had to take it around the block to park it in my driveway, and by the time I get there, the misfiring stops, but now the CEL is on solid, and now the CRUISE is flashing.

 

Could this be caused by water getting into my exhaust from the heavy rain, possibly gunking up my rear O2? The ends of the Y-pipe are turned upwards, but being under the car, I can't see how that much water could get into them. I was wondering if it was just the moisture exposure in general, from sitting out in a heavy rainstorm with no mufflers....?

 

IDK. The whole thing seems strange, but it can't be a coincidence that this happened while the exhaust was removed. I plan to get the codes pulled sometime this afternoon as long as I can get it to Autozone without it misfiring again.

 

In the meantime, any ideas....???

[WildBoxer]

I pulled the codes today and got 2 readings for the same code:

 

P0303 - Cylinder # 3 Misfire Detected.

 

I cleared the codes, and reset the CEL. I restarted the car, and CRUISE stopped blinking. Then I started the car a few minutes later and it wouldn't start until the second try.

 

The funny thing is, I was driving it around all day in the torrential downpours we were getting around here. I didn't have any more issues starting it, and it never misfired or anything, so I'm still curious as to what may have caused it. It makes me wonder if if was even related to the muffler removal.

 

I'm going to run some fuel injector cleaner through it. It probably won't do anything, but I've got a bottle of Techron in the garage, so I guess it can't hurt to try.

 

Hopefully I will not have any more trouble. And the mufflers will be repaired and back on the car by the end of the week.

[gotsflat4love]

Well, I am not sure about the code, but what I can chime in about it the rought start about clearing the codes. I cleared my CEL and had the same issue. I think the ECU has to relearn itself once cleared. I drove around for about 10 min and it started and ran fine.

[TSiWRX]

The car "re-learns" - in a fashion apparent to the driver (there's tons of other stuff going on, but you won't see it, unless you're datalogging) - idle after such a "reset," and also, after such a reset, the TPS resets, which is why if you try to crank her over immediately, it either won't start, or will struggle to do so.

 

The former will simply get better with a bit of time and miles.

 

The latter, the next time you reset the ECU, simply turn the key to "ON," let the gauge-sweep cycle (or do a count of 3-Mississippi), turn the key back to "OFF," and then try to crank her over.

 

As to the CEL/misfire....

 

I honestly don't know why that would happen. The moisture theory I don't quite buy - but heck, I suppose it's possible that it (i.e. driving through such downpours and standing water) could've messed with things in a number of different ways.

 

Hopefully, now that you've reset, it'll just go away, and never come back.

[WildBoxer]

I'm not totally sold on the moisture theory, either. It was just too big of a coincidence to ignore. A few years ago I had a recurring issue with my '99 VR6 GTI doing the same thing if I started it in wet weather. It threw a CEL for a misfire, I would clear it, and then it would do it again the next time I drove it in heavy rain. Of course, the cruise control still worked while the CEL was on...

 

It turned out to be a cracked distributor that was causing the issue, so it was misfiring due to lack of spark. Anyone familiar with VW's will remember that was one of a few notorious problems with MK3's. I checked over the ignition system as soon as I remembered about my GTI, but didn't find anything.

 

Also, I never thought about how clearing the CEL might affect immediate startup. I've done it plenty of times before in other cars, but never had that happen. It makes sense, though.

 

The weird thing was that it just sat in front of my house for two days during the heavy rain - I didn't even drive it. Then when I started it the following day in drier weather, it started misfiring right at startup.

 

Who knows what it was, but since I cleared the codes it's been fine. I also ran some fuel injector cleaner through it on the next fill-up, just in case. The next major service that I do, I may have the fuel injectors checked out to see if there's any clogging going on.

[TSiWRX]

^ Hey, all we can do is keep our fingers crossed!

 

Indeed, this car was the first, for many of us, where its ECU-reset/startup behavior caught many off-guard. If you searched the archives of .com, look back at '05-'06, and you'll see a lot of people getting caught-out by this little trick.