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Thread: P0300 - Misfire, Gas-y smell, extremely rough idle

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    P0300 - Misfire, Gas-y smell, extremely rough idle

    Hello all,

    I'll cut right to it, for the past 3 weeks i've been experiencing off and on P0300 misfires. Symptoms are when driving(when the engine is normal) it'll sputter for a second, come back to normal for a few miles, then drop to 2 or 3 cylinders with a flashing CEL. Things I've thought it was/replaced:

    - Spark Plugs (replaced with 4 new AC Delco, gapped)
    - Bad gas/clogged injector (ran prem with 2 tanks so far of fuel Lucas Oil fuel injector cleaner)
    - Air Filter (replaced)
    - Ignition Control Module (Replaced with a BWD brand ICM)
    - Coil pack (tested, seems to be working fine)
    On this note, im not sure the CP is the issue as i thought those only worked or didn't, not intermittently work/fail.

    Last couple of fixed have left me with no errors for a week or so, with it coming right back.
    After the ICM, car ran fine for a week then yesterday it ran hard and bad again, misfired. Each time i have the code checked its always P0300 with no other codes. Granted, i was not able to check it this last time as i was not close enough to an auto parts store and wanted to get my car home. Then today, heres what happened and what i tried:

    Started car up, rough idle/misfiring again. Smelled gas within 30 seconds. Shutcar off, disconnected negative term from battery for 15 minutes, reconnected and started car. Same thing, flashing cel and smell of gas. So heres what i tried:

    - Took off fuel rail (which involved disconnecting the coolant return, vacuum line from intake to valve cover(breather? not really sure what thats called, please verify!), throttle body and vacuum line from TB to another unknown valve on driver side of engine. Has a green screw-on cab and vacuum lines, assume its like a secondary air as i dont think ecotecs have a EGR or user serviceable PCV. De-preassureized fuel system by turning car over and pulling the fuel pump relay and cracking the gas cap.


    - popped out fuel rail w/ injectors attatched and noticed that the inlets for the injectors was dirty with gunk as was the the button of the injectors (tho, the holes were as far as i can tell spotless). So i also took off my intake mani and used some CRC throttle body/intake manifold cleaner and cleaned area really well as well as used a rag to clean out the injector ports.

    - for each injector, tested for resistance with an Ohm meter test. All injectors were at 14.5 ohms. Then i took a little dab of that fuel injector cleaner and put it directly on the outlets of each injector, let sit 10 minutes.

    - Reassembled everything, double checked everything, put key in and waited 15 seconds for pump to pressurize system and turned over. First start the car died out immediately, was not until 3 tries later it at least managed to run. But it was running exactly the same as before.

    - Pulled off the ICM, hooked a volt meter up to pins 1 and 3 (with the grouping of 3 pins on the left and pin 4 on the right, not at the same time!). One clip ran to positive on fuse box, negative ran to pin 1 or 3 on the ICM. I cranked it to make sure the ICM was actually outputting a signal, it was tho i dont remember what the readings were but they were both the same.

    - took the injector wiring harness completely off and tested for resistance across each wire with a meter, got 1.5ish across all the wires(there was a 3-wire connector to some kind of sensor with a single torx screw here as well, no idea what that is, please confirm!).

    - Other things i've tried in no particular order:
    - cleaned MAF with electirc parts cleaner
    - cleaned throttle body
    - inspected spark plugs for burned/blackness
    - tested resistance on spark plugs
    - reseated/cleaned plug boots and gooped with spark plug grease.

    After doing all that, car is still idling rough(a bit rougher than before, actually), flashing CEL. I'm out of ideas and resources on this one. Instead of looking around for more ideas that will lead be down hours more of troubleshooting, decided asking here was a far better options. Sorry for the Encyclopedia of a post! I just wanted to list all the steps ive taken thus far.

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    Very few of us left. Hate to do this but......
    http://www.ecotecforum.com/forums/sh...e-Issues-Only)

    You have done a very good job of trying to find the problem! With all that has been done it only leaves me with O2(could be but don't think so) or the one thing that people forget: coolant temp sensor. When going bad it will tell the computer that the coolant is colder than it is. As it gets worse the problem gets worse(too much fuel).
    Basic guy with basic answers here. I'll be watching, but may not be much help.
    More humans=more problems
    Don't worry nothing will be done until it's too late, there is money to be made.
    Maximum profit and overpopulation will ruin all the major economies.

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    SkrillBilly (06-03-2016)

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    Very few of us left. Hate to do this but......
    http://www.ecotecforum.com/forums/sh...e-Issues-Only)

    You have done a very good job of trying to find the problem! With all that has been done it only leaves me with O2(could be but don't think so) or the one thing that people forget: coolant temp sensor. When going bad it will tell the computer that the coolant is colder than it is. As it gets worse the problem gets worse(too much fuel).
    Basic guy with basic answers here. I'll be watching, but may not be much help.
    nogo04cav Quoted Post
    Thanks for the reply, i never even thought about the sensors. But heres a bit of an update for you. Today i decided i wanted to test the coilpack outside of the car, and maybe do it when im not dripping in sweat from being in direct, 85 degree and humid sun light. So i pulled it off and tested again. Heres what i got when measuring with a volt meter(with the setting the Vm was tested on):

    20K was tested on the bottom of the coil pack, touching 1 to 4 and 2 to 3, and 200 was read touching the top-side where the ICM connects, pins 1 to 2 and 2 to 3.

    Coil pack 1:
    20K: 4.39
    200: 100.1 - 98.8 (never got stable beyond that)

    Coilpack 2:
    20K: 4.43
    200: 1.5 (stable)

    I'm not 100 sure here, but that big of a difference tells me that my CP is bad. Im sure there are some other in-car tests i can do but im pretty sure that means my CP is dead. Would you come to the same conclusion?

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    I'm more of a DIS coil guy and those numbers are a bit low to me, but would point my finger at the #1 pack. One thing I've learned on DIS is that when a coil goes out and it goes out again after replacement the ICM is bad. With these cars I'm still learning.

    something found:


    Models: 2002-2005 Chevrolet Cavalier

    2005-2006 Chevrolet Cobalt

    2006-2006 Chevrolet HHR

    2004-2006 Chevrolet Malibu

    2004-2005 Chevrolet Malibu Classic

    2002-2004 Oldsmobile Alero

    2007 Pontiac G5

    2002-2005 Pontiac Grand Am

    2005-2006 Pontiac Pursuit (Canada Only)

    2002-2005 Pontiac Sunfire

    2003-2006 Saturn Ion

    2004-2005 Saturn L Series

    2002-2006 Saturn Vue

    with 2.2L Engine (VIN D or F - RPO L61)




    --------------------------------------------------------------------------------

    This PI Supercedes To Remove 2007 Model Year. Please Discard PIP3433C


    --------------------------------------------------------------------------------

    The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

    Condition/Concern:
    Some customers may comment on a severe engine misfire and a SES Light. Upon inspection, DTCs P0300 - P0304 may be found due to misfires on cylinders 1 and 4 or cylinders 2 and 3.

    Recommendation/Instructions:
    If this concern is encountered, inspect circuits 406 (IC Control for 2/3 Coil) and 423 (IC Control for 1/4 Coil) for an intermittent short to ground or poor connection on either end. Depending on the model, these circuits may short on the AC lines near the AC compressor, on the transmission mount, or on the transmission lines where they enter the transmission. If there is no problem found with these circuits, inspect the ignition control module ground to ensure that it is clean and tight.

    If there is no problem found after performing the suggestions above and the SI diagnostics lead to ignition module replacement, replace the ignition module as directed but also replace all of the spark plugs and clean the ignition module ground to possibly prevent future ignition module damage.

    Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

    GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

    WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


    © 2008 General Motors Corporation. All rights reserved.
    More humans=more problems
    Don't worry nothing will be done until it's too late, there is money to be made.
    Maximum profit and overpopulation will ruin all the major economies.

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    Hear you on the heat. Got some work to do on the DD car this weekend(same as last weekend). After going nuts and changing everything that would or could cause a fuel cut it came down to the coolant temp sensor(that is why I said that).
    Shame some of the major players here are gone or don't show up often. They would have you all fixed up by now.

    As you read there is a main ground that could cause all sorts of problems and does a lot of the time. That one is on the drivers side of the engine and looks like a huge bare wire.
    Last edited by nogo04cav; 06-03-2016 at 07:18 PM.
    More humans=more problems
    Don't worry nothing will be done until it's too late, there is money to be made.
    Maximum profit and overpopulation will ruin all the major economies.

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