Ok, quick run down of the car. I have a 2001 Z I rebuilt the engine with stock pistons, rods and crank. I installed ported 243 heads, headers and a Stealth 2 cam. I cranked the car and to my surprise the car ran great with no tuning. It idled fine and pulled real hard.

Well after driving it for 3 weeks I decided to install true dual exhaust. At first the car ran fine then it started to misfire badly under light acceration and just cruising. I can put the pedal to the floor and it instantly clears up and pulls just as hard as before. I checked for DTC's and got P0155 and P0300. Anybody have any ideas or know where I should start?

 

You have a code for a bad O2 Sensor heater on your primary passenger side that could be causing it. Also check the standard stuff IE make sure your MAF and IAT sensors are clean with MAF spray and pull your plugs, look for cracks, and check your wires. You really need to get it tuned with all those mods you have, I ran lean after my LT and catback. I'd make sure all your other stuff is good to go then if you have to put in a new O2 sensor.

 

Would a bad O2 cause the car to misfire and throw the P0300 code? Its wierd because the misfire comes and goes and completely disappears at full throttle.

 

light trottle miss could be a vaacum leak
or lean missfire look for exhaust leaks before the O2s
the heater code in of itself is not likely to be your problem
in the way it runs

 

Yea, a lazy/going out 02 will let the computer think its running lean and dump more gas in so you get your misfire.. I have seen that before on my 04 silverado... I was able to use EFIlive and see how the 02's were switching, which confirmed the bad one. Put a new one it and eveything went away..

Also, a few weeks back I had just a p0300 code on my 07 Silverado.. I took it in and the dealer said I had a broken exhaust valve spring.

 

my car is doin the exact same thing after header install. few days after the install somehow my o2 extension came unhooked, and when i hooked it back up it started doing it instantly. so tht basically narrows it down.

 

you may need to desensitize the misfire code with that cam. it seems making it 3-5 times less sensitive at low rpms usually cures the problems with a cam. if it is actually missing then you may have other problems as well.