P0300 on pretty much Stock 4.8

[frankmarroquin]

My truck is a 03 Silverado with a 4.8... It is pretty much stock except for a 4500 PI Converter and Borla XR1 I recently added. By the way it does still have the CATS and stock manifolds. It drove perfectly fine after the in stalls but then i noticed my CEL on after while but it wasnt blinking. The problem there was that I had forgot to re connect B2S1 Oxygen Sensor. OK after a day or two I finally reconnected the sensor cause it had finally dried up outside. Right then is when it started driving bad... What I first noticed from the Scanner is that B2S1 Stayed all the way up and LTB2 stays all the way down in the negatives.

I have already replaced the Spark Plugs and the 02 sensor but I was thinking maybe could be the Cats??? Looked perfect when removed and it doesnt give a bad odor as some usually do when they going bad.

Funny thing is if I go to "Closed Loop", "Fuel Trim Learn" and set them to on and switch them to off as well as delete the DTC's my truck drives perfectly fine and everything works as should but as soon as I turn off my truck I need to redo this again. You guys have any ideas? Ill post up the Scan as soon as my truck does it again because its like a kid at the doctor... Get better as soon as you get to the office. My truck misfires then I just connect the MPVI and it starts to work fine.

[frankmarroquin]

Here are my scans

[frankmarroquin]

Cylinders 2,4,6 & 8 are all mis firing... But if I press "Reset Fuel Trims" it smoothes out. Any ideas guys?

*Update... Weird thing is the driver side CAT is Really Hot but the Pass Side Warm to where I can actually keep my hand on it.

[Sherminator]

Pull the plugs on bank 2 and see what they look like. Looks like you may have burnt up the bank 2 cat.

[frankmarroquin]

The plugs on the pass side were dark... Like they were burned. Solution to this I can just hollow the cat out right? Its for track purposes only... Test and tune

[Sherminator]

Take a look down at the cat once you pull if off the header, I'd suspect a plugged or melted cat. If that is the case, gut both sides. The plugs shouldn't be black, just a slight tan brown.

[frankmarroquin]

This is what one person on ls1 tech told me... What you think

ITs the torque converter...* you need to disable misfire detection.* The torque conveter weighs less and the computer dosen't know how to calculate for it.* Do a seach for converter randomly unlock

[vortec]

Correct it's the torque converter.

[Sherminator]

So tell me how does it effect the fuel trims on just one bank? and the bank that had the O2 sensor unplugged for a bit. I could see misfire issues on both banks but one is interesting to me.

[frankmarroquin]

Not sure what the problem was but I hollowed both cats and turned of the misfire.... ill post the link that I followed. Thanks for you alls help

[Sherminator]

So gutting the cats cleared up the misfire?

[frankmarroquin]

Yes

[04colyZQ8]

I also have code PO300 random miss fire. I have a 4.8L with LS2 intake, 06 SSR throttle body, and long tube headers high flow cats, cold air intake, SSR mass air flow sensor LS2 knock sensors, LS1 flywheel and Zo6 clutch disk, LUK pressure plate. 06 SSR manual transmission tune, and 06 SSR E40 PCM. I also am getting P0172 and P0175 rich codes it runs like crap black soot and lots of water out the exhaust. It seems to really stumble when letting out the clutch starting and stopping, it is constantly missing so bad that the check engine light is flashing? Is this mechanical or a tune issue where to start?

[04colyZQ8]

I replaced the #2 spark plug, made a big difference the code went away, but now it is back again, not enough to cause the light to flash, but enough to set the code!

replaced O2 sensors, now I get P0134 PO154 seems to take to long to warm up, and the close to open loop transssion be adjusted?

[frankmarroquin]

My problem was that I just needed to tune out the Misfire detection...

[04colyZQ8]

Same here desensitized the knock sensors alot and listened for real knock seems fine now, hope it isn't knocking cause they wont trip any thing the way there are now!

[domestic rice]

This is what one person on ls1 tech told me... What you think

ITs the torque converter...* you need to disable misfire detection.* The torque conveter weighs less and the computer dosen't know how to calculate for it.* Do a seach for converter randomly unlock

As in just go under the engine diagnostics and select "no error reported" or is there somewhere else u need to do this?

[04colyZQ8]

As in just go under the engine diagnostics and select "no error reported" or is there somewhere else u need to do this?

Well I am probobably going to turn mine back on for protection as the tuner really messed up the tunr RG motorsports. My trims are between -20 and 20 %

I think if it is tuned within 3 -3 % t will no longer go lean, and knock.

That being said, you can try to desntitze them go to engine spark knock and try doubling the intetial leval and min level or times them by a factor of 1.5

This may set a code it did for me, said knock sensor low voltage and knock senor bank 2 low inout I then set those to no error reported. I think this is sorta a bandaid fix, but anyway you can try it.