Re: My First check engine light

The car is almost 12 years old with 47,000 miles so perhaps I'm due. It's never had a major service, just the fluid type of stuff - I was waiting till it hit 50,000 miles for the major service.

I was driving by an AutoZone on my way home after the light came on and I dropped in to get their free diagnostic check. The error codes came back P0300 Random misfire detected in Cylinders 1.2 and 3. So my first thoughts are plugs and/or coils - but here's the puzzling part:

The car is running as smooth now as it did when it was new! No rough idle, it pulls strong and hard through the entire rev band - it doesn't exhibit any of the symptoms I'd expect with fouled plugs or cracked coils!

Can it be the AutoZone equipment is just a POS and it's really something else that caused the CEL

Thanks,

Ed

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

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Ed fromTampa ( formerly Long Island)
The car is almost 12 years old with 47,000 miles so perhaps I'm due. It's never had a major service, just the fluid type of stuff - I was waiting till it hit 50,000 miles for the major service.

I was driving by an AutoZone on my way home after the light came on and I dropped in to get their free diagnostic check. The error codes came back P0300 Random misfire detected in Cylinders 1.2 and 3. So my first thoughts are plugs and/or coils - but here's the puzzling part:

The car is running as smooth now as it did when it was new! No rough idle, it pulls strong and hard through the entire rev band - it doesn't exhibit any of the symptoms I'd expect with fouled plugs or cracked coils!

Can it be the AutoZone equipment is just a POS and it's really something else that caused the CEL

Thanks,

Ed

The number of times my 2002 Boxster has turned on the CEL due to misfires is just maybe 2 times. But even though this is very rare event the engine never manifested any signs of any engine problems. So, based on my experience I don't think AutoZone code reader is a POS.

One time I recall the Boxster CEL came on due to misfires was when it turned from warm/dry to cool/damp and I let the car sit a few days with no use. I attributed the misfires to dampness affecting the coils.

However, while I have replaced the plugs a number of times the coils are original. So the coils aren't real bad. And it has been a very wet winter here and the Boxster is out in it every day/night and has not misfired once.

I notice you were formerly in Long Island. Now did you drive the car in/around the Long Island area? In bad weather? I have noticed -- noticed this some years back (first with cars in the UK) -- that cars that spend time in areas of bad weather, rainy/wet/damp weather, or snow/icy weather, have more coil problems than those that spend time in nicer weather. Even with just 47K miles your car could be manifesting the early signs/first signs of bad coils due to exposure.

Are the plugs original? While they may not have the required number of miles that would warrant replacement they should be replaced on time. Time can affect the plugs from combustion gases being forced into the plug/head threads and this forms a corrosive compounds that can interfere with the electrical operation of the plug. (There is a risk this corrosion can ruin head threads, too.)

Could be engine deposits too. (Back when my Boxster misfired I remember I was using discount gasoline because gas prices were so frickin high then.)

You might try a bottle of Techron. One bottle treats IIRC 20 gallons. I just dump a bottle in the tank and fill the tank up with gasoline. The rule is if you notice any improvement to repeat the treatment when the tank with the 1st bottle of Techron added gets low. The recommendation is to change the oil/filter after using Techron.

Or you can just switch to -- if available to you -- Chevron gasoline. I did nearly 2 years ago and after a couple of tanks I noticed the engine running better. Kind of a surprised me as I was running a pretty good gasoline -- Shell V-Power -- before I switched to Chevron.

It's past due for a major tune, so it's probably best I get it done.

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue



Edited 1 time(s). Last edit at 01/13/2017 08:58AM by Ed fromTampa ( formerly Long Island). (view changes)

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Ed fromTampa ( formerly Long Island)
It's past due for a major tune, so it's probably best I get it done.

Misfires can sometimes be rather inconsistent. As I mentioned in an earlier post my Boxster has misfired once maybe twice -- at cold start never once warmed up -- and I did nothing and the misfires never returned.

Misfires limited to just one bank are interesting.

My first thought is cylinders 1, 2 and 3 are located on the passenger side of the engine and this side gets exposed to more splash since most of the time in bad weather that's the side that has the most standing water or an accumulation of snow/slush. So if you drove the car in bad weather the coils on that side could be suffering because of it.

I have come across this at least once I can recall -- another owner's Boxster -- and the culprit proved to be the MAF. But I would not replace the MAF in your car without much more evidence it is required.

Another possible explanation though thankfully this is rare is a VarioCam solenoid/actuator is acting up on one bank. But my limited experience with a failed solenoid/actuator -- with just one (and hopefully that is all I ever experience) -- is the engine manifested misbehavior: An up and down idle speed and rough idle. There were no misfires, no CEL in fact, but a pending code that pointed to the VarioCam system. But the tech told me that misfires can arise as the DME adjusts the fueling to get the O2 sensor reading it expects and because the VarioCam solenoid/actuator is the problem will not get the O2 reading it expects before it has adjusted the fueling to the point misfires occur.

Still if the plugs are original and if the tech thinks the coils are due -- or even if you just want to throw coils at the symptom -- that's not a bad idea. As I mentioned I've never changed the coils in the Boxster. I've changed the plugs a number of times and afterwards the engine never really felt any better. I'm not arguing against changing the plugs just making you aware there may not be any improvement from the engine.

OTOH, I did have the plugs and coils replaced in my 996 Turbo -- throwing parts at its occasional cold misfire problem -- and when I got the car back the engine ran noticably better. This even though the plugs were 10K miles from when they were due to be replaced again. The coils were original but there were never any misfires at any other times and the car has not been exposed to very much bad weather at all. The tech reported the coils looked to be in pretty good shape, too.

Marc, the car has rarely been out in the rain and never out in the snow! And since the issue is limited to one bank I'm inclined to agree with JM. I'm still not confident that the AutoZone reading is accurate. I'm bringing it to a "real" mechanic who's got the corrrect equipment on Monday - we'll see what he says!

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

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Ed fromTampa ( formerly Long Island)
Marc, the car has rarely been out in the rain and never out in the snow! And since the issue is limited to one bank I'm inclined to agree with JM. I'm still not confident that the AutoZone reading is accurate. I'm bringing it to a "real" mechanic who's got the corrrect equipment on Monday - we'll see what he says!

Ok. With very limited exposure to bad weather, the elements, likely the coils are ok.

Those error codes are pretty run of the mill, that is they are part of the basic OBD2 error code database. Hard to imagine AutoZone would have a code reader that mis-read those error codes.

Regardless, I have no problem with you seeking a professional's opinion. You want to be sure before you do anything.

The code is the code, and an error would likely return nothing or garbage.

I suspect that your car is made because you keep it shut in during the winter and when its wet, and is getting its revenge :-)

thoughts- fouled plugs (how?), poor gas (why not all cyl?), coils (they do fail),

I'd so some sleuthing and ask "what is common to one bank but not the other"? Cam timing for one.

G

Grant

gee-lenahan-at-gee-mail-dot-com

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grant
The code is the code, and an error would likely return nothing or garbage.

I suspect that your car is made because you keep it shut in during the winter and when its wet, and is getting its revenge :-)

thoughts- fouled plugs (how?), poor gas (why not all cyl?), coils (they do fail),

I'd so some sleuthing and ask "what is common to one bank but not the other"? Cam timing for one.

G

Well, it took 12 years to get mad(e)

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

Grant

gee-lenahan-at-gee-mail-dot-com

The P0300 only triggers if there are misfires from several cylinders, which means you could get P0301-6, P1313-9, P1585.

P0300
P0301
P0302
P0303

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

somebody might correct me, but If it is all one bank, it is less likely plugs and coils.

Since the problem is happening on all cylinders on on bank, it is much more likely to be a problem with a bank-specific component.

- O2 sensors (can swap to diagnose)
- Air intake leak (both sides of manifold are subject to leaks - gasket or rubber tube)
- Fuel bank (see below)
- Camshaft position sensor or tensioner

I would start by double-checking all of the codes. Depending on the codes I would run some Techron Fuel System Cleaner -- not their "fuel injector cleaner" -- through the system and see if the problem persists. As always put the cleaner in on an empty tank then refill and drive.

It doesn't like the nice warm weather down there Ed.

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

It's fine!

The initial review did show the faults but once they were cleared they did not reappear. Fuel mixture was fine, no leaks, tensioner OK, coils & plugs OK,. belts and hoses OK. Bottom line, the car is running fine!

I'm replacing the plugs since it's time; having a 4 wheel alignment (it's a bit off, but nothing major); Oil & Filter; and brake fluid flush and it should be good for another "few" years. I think it just wanted some attention.

Thanks to all for your thoughts on the issue.

Best,

Ed

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue

Quote
Ed fromTampa ( formerly Long Island)
It's fine!

The initial review did show the faults but once they were cleared they did not reappear. Fuel mixture was fine, no leaks, tensioner OK, coils & plugs OK,. belts and hoses OK. Bottom line, the car is running fine!

I'm replacing the plugs since it's time; having a 4 wheel alignment (it's a bit off, but nothing major); Oil & Filter; and brake fluid flush and it should be good for another "few" years. I think it just wanted some attention.

Thanks to all for your thoughts on the issue.

Best,

Ed

Good. And thanks for the update.

Hi Ed,

Which mechanic did you use to diagnose and tune up your Box? I'm in Tampa and just purchased a new to me 2004 S SE.

Thanks
Al

Al,

I take it to:

[www.rennenimports.com]

Very pleased with the service.

PM me if you want to get together for a drive.

Ed

Ed from Long Island (Tampa)
05S Cobalt/Blue/Blue