P0300 CEL - Multiple Misfire Detected?!

[JLangevin]

Any idea on this code and what to look for? The light came on but no difference in performance or anything. When the light came on, I felt an initial retardation in timing but as fast as it happened, everything went back to normal. The wires and plugs are new. They are the NGK plugs and I forget which wires, but none the less, I did not feel anything at all. When I pulled the code on my OBDII reader, I cleared it and after about 10 miles of city driving, it hasnt come back. This isnt the first time it did this, the other time the code cleared itself before I could pull it.

It was about 105*F and cruising at 70mph and no boost when the CEL came on... so what do I do from here. So far, there is no break down.

 

[JLangevin]

Anyone?

 

[PieEyedPiper]

Same thing here dude, and no I've got no clue.
It;s been suggested that the CAs is bad but I think that's unlikely.

 

[JLangevin]

Does your car run funny? Mine doesnt. It did it again to me today, Immediately pulled the code. P0300 again. Both times I was on the freeway with the AC on just crusing, not even boosting. Today was a little cooler, was only 100*f, but Im not certain the heat has anything to do with it. Temp in the car was a little below half way mark.

So do you keep clearing the code or do you just leave it? I would hate for the code to mask something that really goes wrong. My question here that no one seems to be able to answer is which sensor exactly is sending the CEL signal to the ECU? Anyone?

 

[KScivic]

Plugs, wires, and/or coil...

 

[JLangevin]

As I stated, the plugs and wires are new. Will the coil send a signal to the ECU that would throw a code?

 

[BISHILVR]

The crank sensor can go bad and cause this code.

 

[verytalonted]

Any one else????

 

[JLangevin]

I have noticed one thing... Has anyone else noticed that there is a serious rise in the number is P0300 posts since the summer temps started rising? We should look into how the outside temps could play into all this.... I mean, my car isnt overheating, but its been 100*f+ outside since this code started. But as stated in another thread, turning off the car and restarting it, always cleared the stumbling. Today, it actually went without giving the code, so tomorrow it will for sure...

I wonder if it IS the CAS, mine is stock with 149K miles.

 

[grnchevyz]

alright, I had the same issue, changed coils, plugs, wires, nothing.

Changed MAF and boom fixed...try that

 

[PieEyedPiper]

alright, I had the same issue, changed coils, plugs, wires, nothing.

Changed MAF and boom fixed...try that

Interesting, what led you to the MAF? How did you aquire one? and are you still running a 7bolt?





EDIT: I don't think that heat is the issue here. At least not for me. Rain or cold or hot or sun, still throws the code.
Also the OP claims he gets no ill effects from the code? Kind of strange. While the car still operates and is capable of increasing speed, it does so with a lot less power and a TONNE more vibrations. I'm pretty sure the car skips spark fires, or runs on only 2 cylinders when this occurs. Everything goes back to normal, however, once you let the engine wind down to idle and then pop it back into 5th.

 

[grnchevyz]

I think I might have typoed...I changed the Mass Airflow Sensor as my intake had a breach in it and just used a friends in the interim. Got rid of all my misfire codes.

Yes I still run 7-bolt.

Sorry bout the confusion WTF

 

[PieEyedPiper]

Oh now worries, I didnt even realize you and I both said MAF instead of MAS, I knew what you meant.

What do you mean a breach in your intake? I'd just like to look into this MAS replacement since I too have a misfiring 7bolt.
Maybe my barometric sensor is screwed, that is the only thing in a MAS I can think of that relates to how a misfire is detected.

 

[grnchevyz]

The rubber gasket between the MAF and the MAF adapter was broken giving me a major leak. Just for the heck of it I unplugged it today and misfires came back, plugged it back in and gone they were

Not sure about the barometric sensor but it definitely was the MAF that caused all my misfires.

 

[donmagicjuan]

Any idea on this code and what to look for? The light came on but no difference in performance or anything. When the light came on, I felt an initial retardation in timing but as fast as it happened, everything went back to normal. The wires and plugs are new. They are the NGK plugs and I forget which wires, but none the less, I did not feel anything at all. When I pulled the code on my OBDII reader, I cleared it and after about 10 miles of city driving, it hasnt come back. This isnt the first time it did this, the other time the code cleared itself before I could pull it.

It was about 105*F and cruising at 70mph and no boost when the CEL came on... so what do I do from here. So far, there is no break down.

Are you certain that your spark plugs are gapped correctly? Also, are you running a colder heat range than the manufacturer's recommendation? If you're getting the code under prolonged light load conditions, it's likely that your plugs are not sufficiently burning off deposits, which would lead to a misfire condition. I would positively eliminate the things you most recently changed before running off on a wild goose chase. Since I switched from the stock heat range to one colder, I've thrown the occasional P0300 during extended idling.

 

[zippyshoe]

As I stated, the plugs and wires are new. Will the coil send a signal to the ECU that would throw a code?

A failing coilpack could produce a weak spark at one or more cylinders, which could then cause a misfire. It may be worthwhile to test your coilpack.

 

[Fayt]

I have this code too, but my problem is much worse. I misfire/backfire every once in a while. When I cruise, one or two of my cylinders will shut off, causing my car to vibrate and lose a lot of power. Once I push the clutch in, let it go to the idle RPM, then let the clutch out though its fine. As long as I don't cruise at a steady throttle position, it doesn't happen.
New NGK6ES gapped correctly.
New MSD 8.5 wires.
Not sure on the coilpack... I'll test it once I figure out how to.

 

[zippyshoe]

I have this code too, but my problem is much worse. I misfire/backfire every once in a while. When I cruise, one or two of my cylinders will shut off, causing my car to vibrate and lose a lot of power. Once I push the clutch in, let it go to the idle RPM, then let the clutch out though its fine. As long as I don't cruise at a steady throttle position, it doesn't happen.
New NGK6ES gapped correctly.
New MSD 8.5 wires.
Not sure on the coilpack... I'll test it once I figure out how to.

Testing the coilpack is very straightforward. Disconnect all ignition wires from the coilpack and disconnect the ignition transistor from the coilpack. Using a multimeter set to measure resistance (kohms/ohms), measure resistance between the two leftmost ignition wire terminals. Then measure resistance between the two rightmost ignition wire terminals. In both cases, you should measure between 11.3 kohms and 15.3 kohms. Then go to the connector for the ignition transistor and measure resistance between pins 1 and 3. Then measure between pins 2 and 3. In both cases, you should measure between 0.7 and 0.86 ohms. Check out page 16-57 of the service manual for more details.

 

[DiamondStarM]

Im in the same boat as Fayt. I have a p0302 Random Misfire Cylinder 2, sometimes it comes up as Injector Circuit Malfunction Cylinder 2. I have a new CAS, NGK plugs gapped correctly, new Accel ThunderSport wires, Ive switched Injectors to see if my problem moves to a different cylinder, ran fuel system cleaner, tested and switched coil packs.

When I get the problem I first see my A/F gauge freak out and light up like crazy, then then CEL goes on then cylinder 2 cuts out and the car runs bad. If I push in the clutch and let the RPMs drop for a second then cylinder 2 comes back and the A/F gauge cycles like normal but the CEL stays on until I clear it. Usually only happens at highway speeds when maintaining a consistant speed for a little while.

Im curious about this MAS idea and also how would I test the injector controller/resistor pack or whatever it is that controls the positive side of the injectors?

edit: Also my vacuum has been a little shakey at idle since this started happening.

 

[grnchevyz]

I just wanted to confirm that changing the MAS in both my cases fixed the P0300 issue. We even went as far as putting the "bad" MAS on a good non-misfiring car and threw a P0300, replaced back with the good one and boom...gone.

Just thought I'd drop this to confirm that a bad MAS will cause a P0300.

 

[DiamondStarM]

hmmm, i wonder if a bad MAS will cause a P0301, P0302, P0303 or P0304 (misfire detected in each cylinder respectivly) my issue is a P0302 and if I can find a local willing to trade me for a week Ill have to give this a try

 

[Artago]

I just wanted to confirm that changing the MAS in both my cases fixed the P0300 issue. We even went as far as putting the "bad" MAS on a good non-misfiring car and threw a P0300, replaced back with the good one and boom...gone.

Just thought I'd drop this to confirm that a bad MAS will cause a P0300.

Thanks for the info. Can anyone confirm this?

Thanks,

Tom

 

[Project2G]

Hope this helps..

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[Artago]

Hope this helps..

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Sure does Thanks

 

[hobbystocker]

i have been told that you can change the power transistor in some causes, and i have been told that it will fix the problem.