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P0300 Random Misfire Random Misfire

#1 User is offline   Mechanic98 

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  Posted 15 October 2008 - 02:29 PM

Hey Everyone. I have a problem with my 2001 Firebird 3.8 V6. I have a random misfire going on.

I had a problem with an ignition coil about a month ago. I replaced it with another coil that I had from another pontiac. It stopped Misfiring at that time. So, I figured that I fixed it. Then about a week ago, it started doing the same thing. I then replaced the coil with another coil that I had. I replaced that, and it seemed to work. Then the next day, it started misfiring again. So, I tried yet... one more coil... and it didn't work. So, I decided to look into it further...

This is what I have done so far.

I have changed the Plugs/wires, checked the EGR valve, Camshaft Pos Sensor, MAF sensor, Checked the Ignition Control Module, checked for Vacuum Leaks and any wires that might need replacing, Checked all the Engine and PCM, Sensor Grounds... etc. I'm missing something. Any ideas would sure be helpful. Thank you

Ron
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#2 User is offline   tonka 

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Posted 15 October 2008 - 02:40 PM

Try replaceing the altinater, thats what was wrong with mine. And i took it to 6 mechanics to try and fix the prolem (befor I knew it was the alt.) and 5 of them said dont bring it back. I did not take it to a dealer though, they are a bunch of rip offs. And Yes, I replaced all three coil packs, new wires, crank. pos. sensor, all the O2 Sensors, and other things thatI cant remember.

Have you had it scanned with a computer?
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#3 User is offline   Crispy 

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Posted 15 October 2008 - 02:41 PM

Make sure your injectors are clean, possibly a clogged fuel filter, also check the catalytic converter.

How did you check your maf, CPS, and egr?

Make sure your plugs are in and gapped correctly, make sure your wires are on snug and in going to the correct coil in the right place for proper firing order.

Which coil is giving you problems, and was it the same coil both times? Does it miss all the time, or on acceleration, deceleration, or only when the car gets up to temperature?
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#4 User is offline   Mechanic98 

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Posted 15 October 2008 - 06:43 PM

Hm, never would think of the alternator... At this point, I would try almost anything. I'll look into that tomorrow....

As far as the EGR, MAF, and CPS, I actually changed them. Tried them, then returned them... Shhhh don't tell the auto parts place that... lol They don't like installed items...

Plugs are gapped properly to specifications and installed correctly. Plugs are attached well along with dielectric grease. Might check on the fuel filter as well,. I should go ahead and replace it anyways. As many miles I put on the car...

Coil update... I have now, replaced all the coils.

As far as the misfire, it does it all the time, from startup to acceleration, to cruising speed, the slowing down, to idle.. It does it constantly.
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#5 User is offline   FBN Firebird Nation 

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Posted 15 October 2008 - 06:57 PM

You might also want to check the fuel pressure, evap system, and fuel injectors.
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#6 User is offline   Mechanic98 

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Posted 20 October 2008 - 10:46 AM

I did an injector coil test and they all checked out fine. I checked the evap for any leaks etc. didn't see any. I"m going to get a hold of a fuel pressure tester from somewhere and see what happens. Might be the sending unit of pressure regulator... I'm running out of options...
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#7 User is offline   FBN Firebird Nation 

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Posted 20 October 2008 - 11:43 AM

You are running out of options and possibilities, which is a good thing since you are narrowing down the possibilities.
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#8 User is offline   Mechanic98 

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Posted 21 October 2008 - 08:39 AM

Yup, I hope to narrow it down to one thing, and that be it... lol Only so many things left... oh well... guess it needs to be done... Off I go to test something else... lol thanks for the support
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#9 User is offline   Mechanic98 

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Posted 22 October 2008 - 08:20 AM

FIXED!!!! It ended up being a BAD ignition coil that I put on. What is the chance that two in a row can be bad?? lol anyways... It is all fixed and running like a champ again... woo hoo.. Thanks for the help guys. I'm so glad to have this taken care of.
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#10 User is offline   FBN Firebird Nation 

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Posted 22 October 2008 - 08:40 AM

Excellent news Ron, and thanks for the update.
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#11 User is offline   tonka 

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Posted 22 October 2008 - 03:56 PM

Nice job man!!
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#12 User is offline   Mechanic98 

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Posted 22 October 2008 - 04:04 PM

Thanks for the help guys :waitasec:... I'm so glad now that it is working... lol

This post has been edited by Mechanic98: 22 October 2008 - 04:04 PM

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#13 User is offline   vilem 

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Posted 14 May 2013 - 11:28 AM

this is why I love the internet. I bought a 1997 firebird trans am 5.7 last night. it has the p0300 code on it. I actually got a ignition coil with it so im gona try that first before I start making my knuckles bleed with those plugs. iv read a lot about these p0300 and everyone writes they do the spark plug change and wire check and its always something else it seems. hope this fixes my problem. but I haven't felt it misfire, it runs like a champ. only 1700 because the ac was out and im in Florida
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#14 User is offline   Injuneer 

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Posted 14 May 2013 - 12:25 PM

Welcome to Firebird Nation!

Is the engine "stock"? If it's got an aggressive aftermarket camshaft, it can set misfire codes, even if it's not misfiring. The misfires are detected by the crank position sensor readings, to a problem there (e.g. loose reluctor gear, gear hitting timing cover) can cause a misfire code. It can even cause a code to set if you hit a large pothole or drive on rough roads.

The advantage of OBD-II is that if you have a scanner with "Advanced Parameter" capabilities, you can access the misfire count by individual cylinder. That will tell you if its really a "random" misfire, or if it's primarily one or two cylinders. One of our members has written OBD-II scanning software that you can download for free. I believe it has the advanced parameters capabilites.

http://www.firebirdn...anner-software/

Before starting to randomly replace parts, try to pull the misfire count by cylinder.
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#15 User is offline   GaryDoug 

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Posted 14 May 2013 - 01:14 PM

Yes, it does have the misfires-by-cylinder. This screenshot is showing a V6 which does not have cylinders 7 and 8. That's why it says "not supported". Download the "...GmEnhanced" version.


Those parameters are also available in the Android app "Torque", in the extended PID data set (free). That would require a Bluetooth adapter.

Attached File(s)


This post has been edited by GaryDoug: 14 May 2013 - 01:24 PM

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