P0300 Random Misfire Random Misfire
Posted 15 October 2008 - 02:29 PM
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
Posted 15 October 2008 - 02:40 PM
Have you had it scanned with a computer?
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Bought it back, Now sitting in my field of projects. Its time will come and it will live again
Posted 15 October 2008 - 02:41 PM
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?
1985 Monte Carlo SS - Restoration in Progress
Hang together, or we'll surely hang apart.
1980 Trans Am 400, 1995 Trans Am 355, 2001 Firebird V6, 1991 Trans Am 350, 1979 Trans Am 301
Posted 15 October 2008 - 06:43 PM
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.
Posted 20 October 2008 - 10:46 AM
Posted 22 October 2008 - 08:20 AM
Posted 14 May 2013 - 11:28 AM
Posted 14 May 2013 - 12:25 PM
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.
Before starting to randomly replace parts, try to pull the misfire count by cylinder.
381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor
Posted 14 May 2013 - 01:14 PM
Those parameters are also available in the Android app "Torque", in the extended PID data set (free). That would require a Bluetooth adapter.
Screenshot - 3_3_2013 , 10_07_59 PM-1.png (42.66K)
Number of downloads: 5
This post has been edited by GaryDoug: 14 May 2013 - 01:24 PM
1998 Trans Am - LS1/A4 - all stock and almost all original - one owner - driven daily