'07 Cobalt Bad engine misfire

First I would like to that everyone in advance. I am new to this forum and just need a little advice. Have an '07 Cobalt 2.2 with 28k miles. At about 27k miles it started to miss a little at idle when it got up to operating temp. Then just recently the miss became very bad and finally got a P0300 code which is engine misfire. I checked the spark plugs and they are white indicating that the motor is running lean. A friend told me there is a TSB that states you have to change all the injectors and reprogram the computer. The vehicle is not under warranty because it is a rebuilt title. (Roof damage from a tree falling on it) so nothing that would affect the motor.

Any ideas other than that TSB ? I just want to see some opinions before I go through the expenditure.

Thanks in advance,
Eric

Are you positive there's no water in the fuel tank? I've seen random misfires (P0300) caused by that. A vacuum leak will also cause a 300, as well as a MAF or MAP sensor issue. It's possible all 4 fuel injectors are fouled beyond repair also.

Joel

Are you positive there's no water in the fuel tank? I've seen random misfires (P0300) caused by that. A vacuum leak will also cause a 300, as well as a MAF or MAP sensor issue. It's possible all 4 fuel injectors are fouled beyond repair also.


Joel

Thanks for the response. How can I tell if there is water in there ? I've gone through maybe 20 tank fills since it had the problem. Should I add a water remover to the tank and clear the code to see what happens ?

It wouldn't hurt, but like you say, with that many fillups, it's not likely your problem. If it is water, you'll notice wet-ish sparkplugs and they won't smell strongly of gasoline.

It wouldn't hurt, but like you say, with that many fillups, it's not likely your problem. If it is water, you'll notice wet-ish sparkplugs and they won't smell strongly of gasoline.

The plugs are dry and the electrode and end are white. Lean for sure.

Does it start up and run perfectly fine when cold?

Does it start up and run perfectly fine when cold?

Yes it does. Everything is fine when it's cold.

Yes it does. Everything is fine when it's cold.

It sounds to me that once the ECU jumps from open to closed loop mode and needs to read off all your sensors (O2, MAF, IAT, etc...), something is causing the fuel trim to fall too lean. You'll only go into closed loop when the engine is up to temp, not near full throttle or under heavy load. R U sure you don't have any other codes?

Joel

It sounds to me that once the ECU jumps from open to closed loop mode and needs to read off all your sensors (O2, MAF, IAT, etc...), something is causing the fuel trim to fall too lean. You'll only go into closed loop when the engine is up to temp, not near full throttle or under heavy load. R U sure you don't have any other codes?

Joel


Yep. Just reran the scanner to make sure and I'm getting just the one code.

After that, I started the motor and it runs great. Wierd huh ?

If you let the scanner go to the point it reset the code, the ECM has now been cleared of all it's 'learned' variables. You'll run in open loop mode now for something like 50miles or a bunch of start- warm up - stop cycles. Not a bad thing, you just don't want to do this and then take the vehicle in for a safety/smog inspection. It won't pass while in open loop mode. Honestly though, I'd pop the top half of the aircleaner housing off, unplug the connection to the MAF, spray it out really good with spray MAF cleaner or spray electronics cleaner and see if the issue stops.

Joel

If you let the scanner go to the point it reset the code, the ECM has now been cleared of all it's 'learned' variables. You'll run in open loop mode now for something like 50miles or a bunch of start- warm up - stop cycles. Not a bad thing, you just don't want to do this and then take the vehicle in for a safety/smog inspection. It won't pass while in open loop mode. Honestly though, I'd pop the top half of the aircleaner housing off, unplug the connection to the MAF, spray it out really good with spray MAF cleaner or spray electronics cleaner and see if the issue stops.

Joel

Tried cleaning the MAF, adding a water additive, and a fuel injector cleaning. Nothing. Same thing. But again, it only happens when the motor gets warm. I think you are on to something with the open and closed loop computer thing but I can't pinpoint what sensor is making the car run lean. Not getting any other codes.

Man that is frustrating!:banghead: Still just the P0300 / random misfire code? Is it possible for you could get ahold of a more advanced scanner that will give you pending and/or manufacturer specific codes? The <$300 readers just give you generic OBDII codes. Only other thing I could think of is swap MAFs with another ~2007 Ecotec 2.2 to see if the problem goes away. *ahem*.. maybe rent a 2008.. (wink-wink.. nudge..nudge). The MAF could be bad. O2 sensors don't jerk the fuel trim around enough to cause misfires, so I'd rule them out. Also can't see all 4 coil-overs being bad to cause random misfires.

Joel

Man that is frustrating!:banghead: Still just the P0300 / random misfire code? Is it possible for you could get ahold of a more advanced scanner that will give you pending and/or manufacturer specific codes? The <$300 readers just give you generic OBDII codes. Only other thing I could think of is swap MAFs with another ~2007 Ecotec 2.2 to see if the problem goes away. *ahem*.. maybe rent a 2008.. (wink-wink.. nudge..nudge). The MAF could be bad. O2 sensors don't jerk the fuel trim around enough to cause misfires, so I'd rule them out. Also can't see all 4 coil-overs being bad to cause random misfires.


Joel

Let me see what I can do to get someone to loan me a better scanner or just pay someone for the diagnostic. I'm with you on the coil comment because the spark plugs are white. It's obviously fuel related and not the coils. What do you think about the TSB that states that you have to replace all 4 injectors & reprogram the computer ?

I don't have a lot of faith in the replace all four injectors deal. The only thing that would ruin all 4 simultaneously would be some serious contamination in the fuel (plugged/clogged/dirty injectors). Other than that, like the coils, all 4 wouldn't go bad at the same time. Low pressure at the fuel rail could cause a lean condition, but why it only happens when warm is a mystery to me.

Joel

Can your scanner read some data such as operating temperature and O2 sensor switching. You really need a scan of various data to pin point what is going on.

Have you checked fuel pressure while the engine is running and hot and see if it's in spec? You can check the injector resistances. That won't fully diagnosis the injectors though. You have to have more equipment to do that.


I wouldn't overlook that the TSB might be the fix. This might be a case where you need to take it to a good dealer and have a diagnosis ran. A lot of places can do it for under $90. If they say you need to complete the TSB, that willl cost a small fortune there. You can get new injectors are Ebay pretty cheap usually and put them in. Then if necessary you can later take it to the dealer to have to the PCM calibration updated. Normally you don't have to update the PCM when you replace injectors but this car might have a problem with the original calibration.

Depending on what kind of deal you get on the injectors the injectors, diagnosis and reprogramming could be around $300 vs. $800+ if the dealer installed injectors and did all the work.

what engine and rpo code do you have? does your reader show what cylinder is misfiring. does your engine light flash?

I have an '07 Ion with the same engine that just developed the same issue. It has 60K on it, and has been perfect until now. I will likely take it to the dealership next week if it continues. I will let everyone know what they say if I do. Like yours, it only happens once at operating temperature, it isn't bad enough to cause a stall but is definitely a miss fire.

map-02 sensors are your biggest decision makers in fuel trim when closed loop is entered.first you need to find out if it does it immediately as soon as closed loop is on and which sensor is reading wrong.I putting my money on the map sensor.an easy way to check is get the baro reading from a known good car and yours using the scanner.both car need to be in same area and readings should be about the same.I have seen readings .1 inhg off cause the car to run like poop.

Very very bad news. My Ion just got diagnosed with a bad injector. Itself, easy fix, but it seems the misfire is coming from ruined valve seats, etc due to how lean the injector made the cylinder run. Bad compression too, only 85 psi, other cylinders are 175. I am waiting for a call back to see if drying out the engine helps the compression or if I need a valve job in addition to the $700 injector and plug replacement. With 60K on the '07, warranty won't cover it. They are looking to see if the Cali emission warranty will. Has anyone else had these issues with the Ecotec?

The mechanic mentioned I should change all 4 injectors as they have been having 'issues'

... With 60K on the '07, warranty won't cover it. They are looking to see if the Cali emission warranty will. Has anyone else had these issues with the Ecotec?

The mechanic mentioned I should change all 4 injectors as they have been having 'issues'

Oh khrap that's right.. Saturn doesn't have the 5yr/100K powertrain warranty like Chevy does for 2007+. If it did, low compression would warrant major engine work. Yanking the cylinder head to do valve work has got to be a major job for the Ecotec given the chain driven DOHCs. Not cheap nor easy. I'd keep speaking with Service Advisers, making phone calls, etc.. You should be able to get GM to goodwill some of the cost. I would NOT expect it to be covered 100% given the ~2.5yrs and 60Kmi, but with some persistence (calm and cool), I bet they come through even in today's state.

Joel

Thanks for the info Joel. My 07 is covered by the 5yr/100K BUT...because it was caused by an injector, which is not powertrain, technically it would not be covered. As luck would have it, and very very good luck, the injector is covered by the emissions 5yr/150K california/massachusetts PZEV coverage and then the rest covered by they powertrain. Saturn went way out of their way to help me with this to my surprise given the state of GM right now. They even gave me a rental. An '08 Malibu which I am very impressed with. You are right about the amount of work involved, it will be at least 16 hours of labor and about 3 days!

Oh sweet!! I didn't think Saturn had the 5/100 warranty. GREAT! Unless you were driving around with a blatant misfire long term on that cylinder due to the injector issue, I think most would cover this with some general persuasion. I've never heard anything but good with respect to Saturn service! What were your initial symptoms? Did you have them for a long time? Just trying to get a feel for this so we could hopefully ward-off issues for others.

Joel

Honestly, up until last week, no symptoms at all. With all the time I spend in this car, I would think I would have noticed something like that. As soon as it started misfiring, the engine light came on. It was not a bad misfire, just enough to cause a rough idle, nothing that would elude to the extent of this damage. Even the mechanic was surprised the engine was so smooth with the huge compression difference. Like my mechanic said, they are noticing 'issues' with these injectors, so beware!

Yet another update....
The heat in the cylinder caused the valve seats to miss shape. They sent the head out to get tapped but it was so bad that they ended up getting a new cylinder head complete with new valves, etc. I should have the car back tonight. GM is concerned that ethanol levels in the fuel might be partly to blame!

GM is concerned that ethanol levels in the fuel might be partly to blame!


Thanks to the goverment regulations I think starting sometime in '08 all fuel now has about 10% ethanol. Ethanol requires a richer A/F ratio. So a PCM tht's not calibrated for primarily 10% ethanol gasoline mix might run a little leaner than it should. What a lean mixture does is cause higher exhaust temperatures and higher exhaust valve, valve seat and cylinder head tempatures. I think the ethanol was just adding to the problem of the bad injector(s) which was the main problem. So the ethanol could be poartly to blame. The later PCM calibrations probably take into account the ethanol mix.

Thanks to the goverment regulations I think starting sometime in '08 all fuel now has about 10% ethanol. Ethanol requires a richer A/F ratio. So a PCM tht's not calibrated for primarily 10% ethanol gasoline mix might run a little leaner than it should. What a lean mixture does is cause higher exhaust temperatures and higher exhaust valve, valve seat and cylinder head tempatures. I think the ethanol was just adding to the problem of the bad injector(s) which was the main problem. So the ethanol could be poartly to blame. The later PCM calibrations probably take into account the ethanol mix.

Ethanol does not make the engine run lean. The ethanol oxygenates the fuel which makes the O2 sensors read leaner which enriches the mixture. You can see the difference looking at the fuel trim, but that means the PCM is correcting for it.

For the OPs problem, the coil assembly is an extremely common failure on these engines. Ignition module is also common. What kind of spark plugs are in it?

Ethanol does not make the engine run lean. The ethanol oxygenates the fuel which makes the O2 sensors read leaner which enriches the mixture.
You can see the difference looking at the fuel trim, but that means the PCM is correcting for it.


Well your saying the same thing that ethanol does run leaner and needs a richer mixture but saying the PCM will automatically compesate in open loop. But first off the engine is not always in open loop, during warm up and power enrichment it is not. Power enrichment is most critical. The thing is ethanol has a slightly different lambda or A/F ratio value than gasoline does. There are limits to what the O2 sensor can correct for and is why the base calibration and fuel delivery has to be rich enough for the fuel mix used to begin with.



For the OPs problem, the coil assembly is an extremely common failure on these engines. Ignition module is also common. What kind of spark plugs are in it?

An ignition misfire would not have overheated the engine. Possibly the catalyst. The O2 sensor thinks an ignition miss is the same thing as a lean misfire from an injector. But anyway some people posted about TSB's about the injectors and PCM calibration.

That's what LTFT is for, in open loop and PE the PCM goes off what the engine was doing recently. We're talking about stoichiometric being (I believe) 12.x:1 for ethanol (and here we're mixing it 10%) opposed to 14.7:1 for gasoline, so I doubt there'd be a significant difference. My '86 carbureted truck runs just fine on 10% ethanol, and has with no problems (or re-jetting) for over 90k miles that I've had it.

I must have missed where the OP's engine overheated. The only overheating I remembered was the Saturn, but I'm not reading through all that again.

That's what LTFT is for, in open loop and PE the PCM goes off what the engine was doing recently. We're talking about stoichiometric being (I believe) 12.x:1 for ethanol (and here we're mixing it 10%) opposed to 14.7:1 for gasoline, so I doubt there'd be a significant difference. My '86 carbureted truck runs just fine on 10% ethanol, and has with no problems (or re-jetting) for over 90k miles that I've had it.

Yeah but again the LTFT applies to operating ranges and conditions that are similar to the one at closed loop. I think it's mostly telling you how much the fuel trim was leaned or enrichen to maintain lambda at the operating condition of closed loop. It will compesate some for power enrichment maybe or trim some through out the operating ranges, but it's still going to be slightly too lean outside those ranges. Ethanol has a stoichiometric of 9. If you do the math the the AFR will be off by .5 or so. This doesn't sound like much but at power enrichment/near WOT where it matters for engine overheating. That might not sound like much but if for some reason you are at 13.5 or so with straight gas, this ethanol can tip the ratio too lean.

If you hook a wide band tuning tool up for tuning purposes you'll see that power enrichment A/F ratio will vary dpening on the level 0-10% of ethanol in the fuel while closed loop stays at lamda, which may be 14.3 for this gasohol instead of 14.7. This happen in reality to tuners.

I'm not saying it's a big difference but it can aggravate a lean condition al ready there like dirty injectors. You hve less room for error. The O2 sensor can't fully compesate for everything, cars lean miss all the time although an O2 sensor is better with small changes.

I must have missed where the OP's engine overheated. The only overheating I remembered was the Saturn, but I'm not reading through all that again.

I don't know that the OP engine overheated and I'm not reading through all of it again either. I'm just saying the OP has a similar engine and problem as the same TSBs and problem the Saturn had.

Yeah but again the LTFT applies to operating ranges and conditions that are similar to the one at closed loop. I think it's mostly telling you how much the fuel trim was leaned or enrichen to maintain lambda at the operating condition of closed loop. It will compesate some for power enrichment maybe or trim some through out the operating ranges, but it's still going to be slightly too lean outside those ranges. Ethanol has a stoichiometric of 9. If you do the math the the AFR will be off by .5 or so. This doesn't sound like much but at power enrichment/near WOT where it matters for engine overheating. That might not sound like much but if for some reason you are at 13.5 or so with straight gas, this ethanol can tip the ratio too lean.

In closed loop and PE the PCM is programmed to run a bit rich to provide some safety margin... if you snap the throttle and watch the upstream O2 sensors, they go .9xV (and generally stay there until the throttle is released) I have never had the chance to play with a wideband sensor (but I'm adding one to the Cavalier soon, want to be sure I'm OK before I really get into the boost :)), so all I know is "rich", it may be 14.4:1 at WOT, I really don't know there.

I think you're backwards on the AF ratio, 13.5 is pretty rich. First number is air, less air=more gas=rich.

In closed loop and PE the PCM is programmed to run a bit rich to provide some safety margin... if you snap the throttle and watch the upstream O2 sensors, they go .9xV (and generally stay there until the throttle is released) I have never had the chance to play with a wideband sensor (but I'm adding one to the Cavalier soon, want to be sure I'm OK before I really get into the boost :)), so all I know is "rich", it may be 14.4:1 at WOT, I really don't know there.

I think you're backwards on the AF ratio, 13.5 is pretty rich. First number is air, less air=more gas=rich.

The O2 sensors will probably max V at 14.2. That's the nature of narrow band O2S, they make a big jump when you get away from stoichiometric. I know the first number is the air and higher the ratio the leaner, lower the ratio richer. Power enrichment and WOT is usually tuned around 12.8-13.3. It's suppose to be richer at heavy load. If you are in the 14's or higher than about 13.5 not only are you losing power but that's too lean for high engine load and risking damaging the engine. Yeah, a wideband tool like the Innovate is an easy and affordable way to go and is almost a neccessity to get the tune right. I'd like to have a 5 or 6 gas analyzer too. That's what the manufacture engineers use.

Ah, ok, I thought you meant 13.5 was a little lean for cruising conditions. I gotcha now. I was told that 14.7 is OK until you get into boost. I didn't have to tune anything on my supercharger, it was done with a PCM recalibration that came with the kit from GMPP. Tuners could talk circles around me all day. I'm working to change that tho :)

Jezzus-H... you guys got me all paranoid with the E10 now.:uhoh: I gotta think it's mostly a non-issue though. I know in the Buffalo NY area, almost all of our stations have sold nothing but "up to 10% ethanol" for about 20yrs now. It's nothing new for us, nor have I ever had a fuel related concern. Maybe I'm lucky!

Joel

Jezzus-H... you guys got me all paranoid with the E10 now.:uhoh: I gotta think it's mostly a non-issue though. I know in the Buffalo NY area, almost all of our stations have sold nothing but "up to 10% ethanol" for about 20yrs now. It's nothing new for us, nor have I ever had a fuel related concern. Maybe I'm lucky!

Joel

It's not really a big deal, it's if your car is switching between regular gas and E10 stations AND you have a fuel deliver problem like a dirty injector it gives you less margin for error for leaning out. If your always getting E10 then like J-ri said your PCM LTFT will mostly compensate for it.

Gotcha. That makes sense. I've never had a fuel injector issue that I know of, but I'm wondering if adding a fuel system cleaner like Chevron Techron concentrate a few times a year would be a good thing. I used to use that and 'experimented' with a product called "Fuel Power" and used Lucas fuel system treatment years ago. Kinda gave up on'em. Never really saw a benefit for my usage.

Joel

Gotcha. That makes sense. I've never had a fuel injector issue that I know of, but I'm wondering if adding a fuel system cleaner like Chevron Techron concentrate a few times a year would be a good thing. I used to use that and 'experimented' with a product called "Fuel Power" and used Lucas fuel system treatment years ago. Kinda gave up on'em. Never really saw a benefit for my usage.

Joel

I think it's a good idea to add Techron fuel system cleaner a few times a year. When you're using the fuel cleaner the idea is not so much noticing a difference as keeping your engine running smooth and your injectors from clogging up and causing misfires. Fuel should have a minimum amount of cleaning additives, but some brands and locations do not have enough. Also so engines and injectors are more susceptibl;e to deposits than others. Maybe you use good gas in your area or you car has a good injector design, but I think it's a good idea to use Techron a few times a year. It won't hurt and it's cheap insurance. I've had to clean my injectors on the rail and replace clogged injectors before, so I use Shell gas now and add Techron occassionally.