Random Misfire Code (P0300) but I am not sure it is really missing.

[scottyielding]

I am new to tuning so please forgive me if my questions are remedial or may even sound stupid to some of you.

I have a 2002 LS1 that has been stroked (383), heads, cam exhaust ect... I can list the specs if needed. I had it running decent but changed a few items and know I am having an issue.

I changed injectors, coils, throttle body, intake and MAF sensor. now the car sets P0300 for random misfire. It may have been doing it before but I do not think so. I have not driven this car in about a year. The car idles fine and does not seem to have a misfire but the computer says that it does. I am showing random misfires on every cylinder (according to GMs scan tool) but just 1-5 times pre cycle. On #6 I am showing 25-50 per cycle. This is at idle. If I raise the RPM to 1000-1200 I only show misfires on #6 and it is only 10-20 per cycle then. I thought it might be a coil at first but if it is a coil I would expect it to get worse at higher RPMs and my coils are almost impossible to access or I would just swap one. I did swap the plug to a different cylinder but nothing changed.

I don't really think the car has a misfire and I know the tune is WAY off at this point but I am hesitant to start tuning the car if i might actual have an issue. I say all of this to ask this question. If the tune is way off can it cause a false reading of a misfire? Please give me your advise and keep in mind I am a novice to tuning but I have been playing with cars for over 25 years.

[kevin87turbot]

I am new to tuning so please forgive me if my questions are remedial or may even sound stupid to some of you.

I have a 2002 LS1 that has been stroked (383), heads, cam exhaust ect... I can list the specs if needed. I had it running decent but changed a few items and know I am having an issue.

I changed injectors, coils, throttle body, intake and MAF sensor. now the car sets P0300 for random misfire. It may have been doing it before but I do not think so. I have not driven this car in about a year. The car idles fine and does not seem to have a misfire but the computer says that it does. I am showing random misfires on every cylinder (according to GMs scan tool) but just 1-5 times pre cycle. On #6 I am showing 25-50 per cycle. This is at idle. If I raise the RPM to 1000-1200 I only show misfires on #6 and it is only 10-20 per cycle then. I thought it might be a coil at first but if it is a coil I would expect it to get worse at higher RPMs and my coils are almost impossible to access or I would just swap one. I did swap the plug to a different cylinder but nothing changed.

I don't really think the car has a misfire and I know the tune is WAY off at this point but I am hesitant to start tuning the car if i might actual have an issue. I say all of this to ask this question. If the tune is way off can it cause a false reading of a misfire? Please give me your advise and keep in mind I am a novice to tuning but I have been playing with cars for over 25 years.

When tuning an engine with a big cam, you always have to desensitize or disable the misfire counter tables in the tune. If you don't, you'll see false misfire data. If you're unsure if they have been desensitized, just compare it to the stock tune file. If you'd like to post your file, we could take a look at it and make recommendations.

[2xLS1]

Stock misfire detection routine is looking for smooth rotation of the crank reluctor like a stock cam with a small duration large LSA will produce. Just about any aftermarket cam that has any lope is going to show up as random misfires at idle. It is common to either desensitize the misfire tables or completely disable idle misfire detection depending on how large an aftermarket cam is.

[scottyielding]

When tuning an engine with a big cam, you always have to desensitize or disable the misfire counter tables in the tune. If you don't, you'll see false misfire data. If you're unsure if they have been desensitized, just compare it to the stock tune file. If you'd like to post your file, we could take a look at it and make recommendations.

Thank you, I will check that. I assumed it would be something simple. It that does not help I will post the file an see if I can get some more help.

[scottyielding]

Stock misfire detection routine is looking for smooth rotation of the crank reluctor like a stock cam with a small duration large LSA will produce. Just about any aftermarket cam that has any lope is going to show up as random misfires at idle. It is common to either desensitize the misfire tables or completely disable idle misfire detection depending on how large an aftermarket cam is.

The cam is a TSP 233/239 .600"/.600"