Random misfire...code 300 and still needing help!
Thread Starter
Staging Lane
Joined: Jun 2003
Posts: 77
Likes: 0
Random misfire...code 300 and still needing help! I was wondering if anyone has an idea of what i shoudl focus on in attempting to figure out my misfire issue. The motor seems to misfire after the first minute of running on. The only time it doesnt misfire is at WOT. I pulled the codes and came up with several codes, of which one was a code 300 and the others were emissions related as i havent tuned my PCM to reflect that i had eliminated the emissions control devices (EVAP, EGR, after cat O2s, etc). I have checked and replaced the plugs and wires. I will check the springs this weekend but what other areas should i check out when focusing on eliminating the misfire? Any help would be greatly appreciated!! 
have you recently changed the cam, oil pump, replaced the pcm, or done any work to the bottom end? If so, you probably just need to do a CASE relearn. EFILive, HPT, and a Tech2 and do this.
Robert - Tech2 will cost you an arm, leg, first born, and 6 pints of blood. 
Tech2 is what the dealerships uses to access the PCM. It's a cool device, but not the most cost effecient if you are not making a living using it. You need to look at www.efilive.com or www.hptuners.com. Both EFILive and HPT can do the CASE relearn. If those software's are not in your budget, you should hit your regional forum and see if anyone with EFILive or HPT can do this for you.
Adlashwa - I think you're problem may be solved. Just as a side note, if your cam has a lot of overlap, the CASE relearn won't necessarily cure the misfire code - nature of the beast. After I installed my motor, I had misfires like crazy (viewed with EFILive). I did the case relearn and the misfire counts went way down, but were still high enough to throw a code. I had to modify the tune to ignore misfires at low RPM.
Tech2 is what the dealerships uses to access the PCM. It's a cool device, but not the most cost effecient if you are not making a living using it. You need to look at www.efilive.com or www.hptuners.com. Both EFILive and HPT can do the CASE relearn. If those software's are not in your budget, you should hit your regional forum and see if anyone with EFILive or HPT can do this for you.Adlashwa - I think you're problem may be solved. Just as a side note, if your cam has a lot of overlap, the CASE relearn won't necessarily cure the misfire code - nature of the beast. After I installed my motor, I had misfires like crazy (viewed with EFILive). I did the case relearn and the misfire counts went way down, but were still high enough to throw a code. I had to modify the tune to ignore misfires at low RPM.
Crank Angle Sensor E(i can't remember off the top of my head).
There is a reluctor ring on the Crank that is read by the PCM to know the crank position. The relearn procedure (activate the relearn, rev up to ~4-4800 RPM, let off when the fuel cuts off, turn car off for 15 seconds) allows the PCM to remap the crank.
There is a reluctor ring on the Crank that is read by the PCM to know the crank position. The relearn procedure (activate the relearn, rev up to ~4-4800 RPM, let off when the fuel cuts off, turn car off for 15 seconds) allows the PCM to remap the crank.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
On The Tree
Joined: Jan 2004
Posts: 152
Likes: 0
From: Buffalo, NY
From the HPTuners Help File:
CASE Learn: To use the CASE learn function please follow these steps:
Put the vehicle into park (auto) or neutral (manual).
Turn off all accessories and A/C.
Apply the parking brake.
Press the brake pedal. Keep the brake pedal depressed during the entire procedure.
Press Begin.
Gradually rev the vehicle to fuel cutoff (around 4000-5000 RPM's) over a period of about 4 seconds. When fuel cuts out, immediately release the throttle.
Allow the engine to come back to an idle.
Turn the ignition off for at least 15 seconds. This step is required for the VCM to store the newly learned configuration
CASE Learn: To use the CASE learn function please follow these steps:
Put the vehicle into park (auto) or neutral (manual).
Turn off all accessories and A/C.
Apply the parking brake.
Press the brake pedal. Keep the brake pedal depressed during the entire procedure.
Press Begin.
Gradually rev the vehicle to fuel cutoff (around 4000-5000 RPM's) over a period of about 4 seconds. When fuel cuts out, immediately release the throttle.
Allow the engine to come back to an idle.
Turn the ignition off for at least 15 seconds. This step is required for the VCM to store the newly learned configuration
TECH Veteran
Joined: Aug 2002
Posts: 4,055
Likes: 1
From: Hartsdale, NY
I recently had similar PO300 issues. I replaced the plugs and wires with no help. Since your motor is stumbling, I would consider changing the cam sensor and crank shaft sensors since it may be having diffuculty finding TDC.
The cam sensor is in back of the manifold near the firewall and the crank sensor is above the starter motor.
After I changed both, the car ran great.
The cam sensor is in back of the manifold near the firewall and the crank sensor is above the starter motor.
After I changed both, the car ran great.
Staging Lane
Joined: Aug 2005
Posts: 94
Likes: 0
I thought it was normal to get the p0300 random misfire codes with an aftermarket cam???
I got them about every other day after my cam install, yet the car ran perfectly. Si I just disabled that code from throwing an SES light.
Also, when do you need to do a CASE relearn, is that anytime you have the engine apart, such as cam install ??
I got them about every other day after my cam install, yet the car ran perfectly. Si I just disabled that code from throwing an SES light.
Also, when do you need to do a CASE relearn, is that anytime you have the engine apart, such as cam install ??
TECH Veteran
Joined: Aug 2002
Posts: 4,055
Likes: 1
From: Hartsdale, NY
I'm not a case-learn expert but I thought it is done after you mess with the crank shaft/crank sensor relationship (e.g, rebuilding/replacing the crank with its stationary reluctor, changing the motor, or changing the crank sensor.)
It is not needed for cam sensor changing I think.
It is not needed for cam sensor changing I think.
