Misfire - Bad Fuel?

I realize that there are dozens of threads about rough idles, but I still have questions and feel the need to vent. After about 20K miles, my car started to shake at warm idle. Not a rough idle, but a noticable shake. The shake is fairly minor occurs at irregular intervals usually a few seconds apart. It's bad enough that passengers can feel it.

 

Last week I got a CEL. I took it to the dealership and they diagnosed a misfire. They checked the plug from the cylinder that was causing the problem and noticed it was fouled. They cleaned it up and put it back in. They also said something about switching some injectors around. They reset the ECU and gave it back to me. They said the problem was bad fuel which isn't covered under warranty and charged me $160 for the service.

 

I use 93 octane Shell V-power fuel exclusively. I have their credit card, so I save 5%. Otherwise I probably wouldn't bother. Given that, I find it very unlikely that bad fuel is the cause of the problem.

 

After getting the car back with the ECU reset, the car idled smooth as glass. It was under 1/4 tank when I took it in, so I went to a Mobile station and filled it up, again with 93 octane fuel.

 

It's been a couple days now and the shake is back. I know some people call this a rough idle and say it's normal, and indeed it seems like a ton of people have it, but it's not a consistant roughness. It's fine for a few seconds, then a shake, then fine again. Over and over. A rough idle should be rough consistantly. It really feels like continuous misfires.

 

So any opinions on this. Is the shake normal and the misfire unrelated? Could it actually be a fuel problem? My WRX didn't shake like this and if this car can idle smooth for the first 20K miles, and after an ECU reset, then start shaking again, is this normal?

Mine turned out to be a bad injector. Took the dealership 3 months to figure this out, and that was only after SOA finally sent an engineer to have a look.

 

The problem more than likely is one of your injectors is getting stuck and needs to be replaced. Injector and coil-pack.

 

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I had misfires (on top of the usual Subaru rough idle), but no CEL, and had to replace all 4 injectors to get rid of the misfiring. This was at only 17K miles.

+1 for bad fuel injector ... I have had 4 go bad .. but not all at once ..

Just had one my fuel injectors go at 25,000. Luckily they diagnosed it as the problem and fixed pretty quickly under warranty

Just took the wagon in for this occasional rough idle symptom, it's at just over 36k, of course, and no CEL or code in the ECU. The dealership said bad gas, which I doubt, so now I'll keep an injector checkup in mind. Thanks.

Alrighty. I'm in the middle of troubleshooting my own misfire issue and wanted to lay out what I've done so far.

 

1st, its an 05 LGT with ~76k miles on it. Started throwing misfire codes on cylinders 1 & 3. Replaced plugs and it seemed to improve a bit, but cylinder 3 started throwing misfires again semi regularly.

 

Note, when I changed the plugs cyl 2 and 4 (driver side) looked pretty good, but cyl 1 and 3 looked a little sooty and smelled STRONGLY of fuel.

 

Since I've replaced the plugs, and I'm just getting a cyl 3 misfire now, I was thinking of swapping the #3 injector with the #4 injector (one I've never had a code for) and seeing if the problem moves. This should tell me pretty quick if it is an injector problem right?

 

Does the fuel smell on those 2 plugs give any clue? Could it be a fuel rail issue? Wires? Anyone had an issue with coil caps?

 

Anyway. Just looking for some experienced advice. I'm starting to think its an injector issue, but I want a way to narrow it down on my own since I'm out of warranty.

 

thanks,

csl

Cslewis- i'm having a similar issue, although i don't have as many miles. I am considering swapping injectors around, let me know how that goes for you.

sgeorge, I will let you know. I would just like some feedback from someone that's more of a gear-head than I as to whether swapping the injectors for troubleshooting purposes is a good idea.

 

Also I'm interested to hear comment on whether anyone else has noticed the strong fuel smell on the plugs of misfiring cylinders. Also, what does that mean? Does it maybe indicate that we aren't getting enough fire in the cylinder to burn all the fuel, or does it mean the injector is swamping it with too much fuel??

 

-csl

I changed the plugs and swapped the possible bad injector to another cylinder. No check engine light yet.. I give it another day and then i bet it comes back. Pulls so much harder..

 

P.S. before you swap the injector bleed the pressure off....i forgot to and anything i drank for about an hour tasted like gas.

sgeorge, did you ever get another CEL? IF so did you find a bad injector?

ever think about the cam shaft?

Yeah, i got another CEL the day after thanksgiving and then another one last friday. Both cyl 4 misfires. I dropped off my car last friday and the subaru dealership has had it for a week and has no idea what is wrong. Look here.. http://legacygt.com/forums/showthread.php?t=76919

So if Subaru says bad gas is not covered, when is Subaru going to open gas stations world-wide so we can use Subaru approved fuel?

I just had a misfire in #4 at 39K, dealership changed out the injector under warranty with no charge or hassles (tossed in a free bulb too!). The "bad fuel" cop-out says to me that you need to take it somewhere else next time.

when you had your misfires, did it continually misfire, or was it just a couple times?