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Discussion Starter #1
When doing any merging,passing right at 5,200 rpm my cel starts flashing. I've checked n changed plugs. moved ignition coils n tried fuel system treatment. For now I just don't go near 5,000 rpm n I still get 30mpg n No Other codes. I'm stumped. any help suggestions? Thanks.
 

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Discussion Starter #3
Sometimes 3. Sometimes a random multiple. allready did compression test. .

---------- Post added at 10:50 AM ---------- Previous post was at 10:27 AM ----------

Thanks for the info. i will try the compression test again with somebody. 1st results may be off as i hooked up gauge n tried to start car. right before it almost started i stopped got out n looked at gauge. All readings were at 130 psi.
 

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Levee
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What are the specific codes given?
 

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Discussion Starter #5
P0303 n sometimes P0300.
 

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P0300 is a multiple misfire. P0303 is kind of misleading on the Cobalt because the ECM throws this out when it doesn't know what the problem is. Does your reader show misfire counts? If you have a P0303 with no misfire counts on cylinder 3 this means you have an O² sensor going out of limit, usually sensor #1 upstream. It leans out the engine and you get misfire, actually you get no fire because there is not enough gas. So all this to say my guess is on the first O² sensor but I'm no mechanic.
 

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To verify it in fact is the o2 sensor, swap #3 coil pack with another one. If the misfire changes cylinders, its a coil pack. If the misfire is still there, swap #3 injector with another. If misfire follows, replace injector. If misfire doesnt follow, id go with coby and get a new o2 sensor. After every step, delete your code so its a fresh code popping back up
 

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Discussion Starter #8
Thanks for the advice. On way home I checked and misfire was on 3. Counts were 148. Not enough to set the cel just save a pending code. I will try swapping injectors 1st later in the week. thanks again for the input every body. i just gotta drive for MPG not MPH.

---------- Post added at 03:52 PM ---------- Previous post was at 03:29 PM ----------

Just to recap. swapped coil 3 to 4. Misfire stayed on 3. Not always p0303. Sometimes p0300 n cylinders 1 and 4 would have the highest misses. but usually its p0303. Cel flashes then goes out. No CEL on. It shows a pending code n after a drive or 2 gone. when driven in old man mode n checking mis fire counts every thing normal. Thanks again for the input from every body on the forum.
 

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You're probably running out of fuel at high rpm. Fuel filter or maybe even fuel pump.
 

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not all of them do, mine sadly does.
 

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Discussion Starter #14
I probally should have mentioned the kn typhoon intake that WAS on the car when I had CEL issues. Now the complete Stock Set up is back on n I have driven 100 miles I havnt been able to replicate the issue. I'm glad my Cobalt isn't Broken but I'm mad at myself for not suspecting the intake sooner.
 

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Levee
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Probably the MAF was out of calibration with the new intake, thus not reading the proper amount of air and not giving the right amount of fuel.
 

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Discussion Starter #16
With my scan tool hooked up I still have a pending code p0300 random misfire.. but the cel hasn't flashed at me yet. The misfire counts have went down also. I'm really feelin dumb right now. The only problem with my Cobalt is the owner! I still have limited power train coverage til Oct. I was bout to pay GM dealer to look at my car! No need for that. problem solved for now. thanks again to everybody for their input.

---------- Post added at 02:59 AM ---------- Previous post was at 02:55 AM ----------

N the kn typhoon was on for 10,000 miles! No problems b4 The intake. none since back to stock. quiet n quick better than loud n slow!
 

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Discussion Starter #17
Problem still ongoing. I thought it was fixed and had a quick decision to make when merging n sure enough at 5,500 rpm in 3rd CEL flashing. Luckily for me I'm old n can drive like Captian Slow when need be. GM Customer Service is working with me to get me in a Dealership ASAP since I have time left on my limited powertrain warranty. Once the Pros figure it out I will let the forum know what was wrong with my Cobalt.
 

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Levee
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I'm still saying MAF
 

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Discussion Starter #19
I cleaned the maf with maf sensor cleaner when i put the stock set up back on. using stock paper filter also.
 

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Discussion Starter #20
Just an update. on may 16,2014 I reluctantly took my cobalt to Miller n Sons Chevy,Buick. WORST EXPERIENCE EVER. THE TECHS JOY RODE NOT ROAD TESTED MY CAR FOR 45 MILES N THEN SAY THERE IS NOTHING WRONG WITH MY CAR. THEY CHARGEC ME $85 N SAID IF THERE WAS A PROBLEM TRY REPLACING INJECTOR 3. I HAD TO ASK IF IT WAS COVERED UNDER 100K WARRANTY. NOPE BUT FOR $235 THEY COULD DO IT. I SAID NO THANKS. I GOT 1 AT PEP BOYS FOR $46. THEN THEY FORGOT TO RE INSTALL MY ENGINE COVER N GAVE ME GRIEF WHEN I WANTED IT BACK. TI
ME TO START BUYIN FORDS! I WAS A LOYAL GM CUSTOMER EVEN AFTER THE 57 CENTS THEY WOULDNT SPEND MAKING THE IGNITION KEY WORK BETTER!
 
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