latley when it rains out my engine starts to missfire and stumble and backfire like its running on 4 cylenders but if i give it full throttle it runs on all 8. get the car back home and start it up next day when its dry out, and its running fine take it for a drive and the motor breaks up only for like 10 seconds but its fine after that (no ses light or no bad readings on gages) the other night i was on the parkway and it was raining and then it started acting up again for a while and then the ses light came on and the problem stopped 2 mins later the ses light went off and the problem happend again. drove the car home and the ses light never came back on next day i drove the car when it was dry out and no problems but it acted up for like 10 seconds again and then it was fine. i may have a slight missfire that i may not notice while i dont have any problems with the car but im not sure?

since i had the new motor put in this is what is new (2000miles currently)
30lb svo injectors
new stock plugs
fairley new msd wires
new opti from summit
2yr old bosch o2 sensors that i extended for the lt headers
madz28 tune
stock fp (can be monitored on gage)
all emisions are fully functional like egr and air pump just have cat delete.

thanks Frank

 

Best place to start would be to get it scanned to see why the SES light came on - the code should still be stored in the PCM.

Something's getting wet.... ignition wires and Opti are a good possibility. Check for corrosion on all the plug wire terminals, coil wire terminals, Opti connector terminals, etc. Could also be a problem with your O2 sensor extensions not sealed well and getting wet.

But why guess.... get it scanned.

 

My free ram air mod made my car do the exact same thing when it was raining fairly hard....the exhaust had a louder sound to it as well for short periods of time. I think it was just drawing too much moisture up through the little scoop directly under the air filter.

After I removed the free ram air mod, problem solved.

 

Sounds like my opti when it went, but get it scanned first.

 

I had the EXACT same symptoms on my car... The problem was that the o2 extensions that i made were getting wet when i drove over water.... So i ordered the extensions and BAM problem solved..... give it a shot...

 

the fact it goes away when you go WOT.. lead's me to believe the 02's are acting up... Check the wiring like mentioned above... If the wiring check's out.. I'd replace the 02's and go from there...

 

check the coil terminal for corrosion

 

i am going to have it scanned tommorow and keep you guys updated i will go over the o2s and wiring as well as coil wires and opti wires tommorow as well. thanks for all the replys

 

Update!

had the car scanned and it pulled up code dtc 65 which is like rich condition
my mechanic said that at the time it read like over 1157 mv when the other side was reading 137 mv or something like that and now the right side was currently reading somewhere in the 300 mv range. im not sure what they are supposed to be reading normally but i am going to get the correct o2 sensor extensions and new ac delco o2 sensors and see if that helps because he said that with a right side being so high, that it mostlikeley is shorting out becuase i extended them on my own.

 

An exhaust leak will cause similiar problems.

 

well i put in new ac delco o2 sensors with caspers electronics o2 sensor extensions and the problem is now gone. i wonder if i get better gas mileage now. lol

thanks guys for all the help