Was accelerating to 35 mph and all of the sudden heard a loud bang from under the hood ,then a lot of bad smelling exhaust. Pulled over, popped the hood ...nothing leaking just nasty noise from behind the engine. CEL started to flash...waiting for tow truck. Currently at dealer. Will know in a few days. Anybody have any ideas?

 

Probably your downpipe, if you have stock maybe the flex pipe bursted open

 

CEL flashing is odd, that's usually only from a misfire, unless it blew the flexpipe right off and it went very rich due to loss of accurate feedback from the O2 sensor.

Let us know what happened when you find out.

 

Well flashing CEL tells me its something with his cat so its not getting the correct reading so the pcm is thinking cat damage could be happening so CEL starts to flash. so if his flex pipe popped that would probably cause it, it sure sounds like he did

 

No mods other than an K&N filter.

 

It was a misfire....the spark plug blew out., so they are putting a helicoil in it and 4 new spark plugs. I have until the end of may til I get my new Subaru Legacy. They said it will cost $494.67. More than 3/4 of it is labor.... If they have to send the head out to be fixed its $2,600. SO hopefully it will hold until the end of May.

 

How does a flashing CEL indicate a cat problem? You should probably learn a bit more about that.

I see you post a lot in the problems/service section, and a lot of your replies are just guesses. I'm sure people appreciate the help, but sometimes it's better to stay quiet than give wrong information. I'm a master tech and do this for a living, and still if I don't know what's wrong I will say so.

 

That explains the noise and misfire then. That sucks.

Who changed the plugs last on the car? I've only ever seen that happen when a plug was cross threaded or not installed properly somehow, only seen it once on a local LSJ ('04 IRL), the helicoil repair can be very permanent if done properly and the head is not opened up larger than the size of the re-thread drill bit.

The labor is a bit steep but it's to be expected at a dealership. The repair should hold permanently so I wouldn't worry about it.

 

Thank you.

 

How is it a guess? If a cel is flashing it means the cat could get damaged thats all the goverment cares about and if i dont know i dont post and say i dont know also im in the field yes i dont know everything yet but the tips i do give is because ive learned about it at school. I guess your the master for everything and everyone else is wrong. My bad

 

Because a flashing MIL means misfires detected over specified threshold.
It is usually ignition related.

It does not flash for a bad cat or cat related problem. Misfires can cause damage to the cat tho.

 

Thats what i meant i guess i didnt explain myself well enough but its flashing because the cat could get damaged due to a misfire. But **** that teaches me to give help to other. Also said that since he said a pop was heard and exhaust smell, i mentioned what it seemed to me to be the problem bit without opening the hood and doing proper diagnostics, everything anyone mentions is just a guess to some extent. Also like he said its rare to see a spark plug pop out

 

blinking CEL is always indicative of misfire. random at that...probably p0300.

 

Don't get defensive. You say you're in school, look at it like a learning experience.

You say you didn't have all the info, yet you gave a strong opinion. Read my reply, I said it would be highly unusual for just a flex pipe to cause a CEL but I didn't disagree because based on his description it was a possibility. You tried to give him a 100% answer with 25% of the information, that's just not possible. Try to consider all the options before answering, like an ASE test question.

The only reason I bring it up, is that I see more and more false information in this forum as the owner base gets younger. This isn't directed at you, but more people just google things and post answers like they know what they are talking about, and it clouds up people's judgement. I was trying to help a guy with a P0171 code in a thread, there was 4 or 5 bad recommendations by the time I got there, just people pulling the trigger on incomplete info, resulting in the customer throwing parts at a car without solving the issue. I work with techs that diag cars like that, it's not necessary if you understand why the systems work the way they do and what the car is trying to do with that system.

 

MIL flashing means there is something happening that would cause the car to fail emissions right now, I believe the threshold is a 50% increase over baseline but that could be wrong, the standard has changed since it's inception.

Pretty much the only way that happens on a modern auto is when there is no combustion/misfire.

The problem with that is you can have a misfire from a multitude of reasons, lack of spark, mistimed spark/fuel, loss of compression, etc. All very different causes of the same fault, all will only set a p0300 or possibly a cyl specific 301-304 if it happens enough and the car can narrow it down.

 

I usually check sparkplugs, wires, injectors, maf or any other senors in that area. when its 301+ its a lot better than 300. random. fml.

 

Yeah the cyl specific ones make it much easier, but they can be wrong also, particularly on certain engines where the CKP resolution just isn't good enough. I've seen cases where it's off by one cyl on it's code, or cases where I have a dead coil and the car still can't figure out which one isn't working on it's own. A good scanner and a cylinder contribution check works wonders on the useless Ford misfire detection.

For sure always a good idea to check the basics if you are the one doing it. I'll say, in my years of doing it, i've only seen a spark plug CAUSE a misfire once. Even if the plugs are shitty, modern ignition systems are hot enough to fire them anyway 99.99% of the time. Unless it's a Kia.

 

Its just seemed like a attack to me, but yes i agree with you, and i wasnt 100% on it i said it seems to me thats the problem but im not saying go check your downpipe because thats your problem. If it sounded that way well i do apologize, i try to help on what i feel most comfortable helping i dont have much experience yet as i started not even knowing how to do a oil change or change plugs and ive come a long way. I still need to learn alot more for sure but i think more constructive tips instead of putting people down would help alot, and if im wrong i dont mind getting corrected, thats the way we learn

 

It wasn't putting you down, just constructive criticism. We all learn somewhere, I was working on cars when I was in middle school at my dad's shop, and I still learn something new all the time. Think like a doctor, does a doctor just tell you what might be wrong with you right off the bat? Don't they ask questions, test things, check you out, and then offer an educated opinion? Hold yourself to the same standard. The world is full of half-ass mechanics, be better than that, it will be appreciated by your customers more than you will ever know.

 

Yup and i agree but thats the problem you have the person in front in our case the vehicle, in the case we see here we dont and the info given by the op suggested that to me, of course if i had the car i would see thats not the case and i would start the diagnosis on something else. Im learning the stuff by the book so by no way im half-assed in the field, if i wanted half-assed i would of gone directly to a independent shop and start work. But for sure i mean if im wrong at something ill rather someone let me know than keep making the same mistake, but to me there are way of telling people they are wrong, had that happen while i was learning English (still learning) so it just bothers me when someone takes that approach.

 

Wow that got away quick.....anyway I changed the plugs at 50K and have 97,700 on the odometer now. SO 40k+ miles after the spark plugs. I took my time with them, didn't rush at all. maybe one wasn't fitted properly. Service tech gave me hell because they were not AC Delco plugs. Plus, end of next month my 2015 Subaru Legacy will be in and Cobalt goes bye bye.

 

Js....when I read your post about why you thought the cell was flashing I said wtf in my head.. ( it's flashing because because damage to the cat could happen. Lol what?

 

Lol yeah i didnt explain myself in great detail had all that info in my head just couldnt put it in writing i guess ohh well it in the past now

 

Yeah that's makes no sense

 

U can just buy an entirely new head for cheaper with everything in it.