Last weekend finally installed my slp headers and y pipe on the 305. Car was running like a champ prior to the installation. After we installed everything, put the plugs, wires, etc back in, i took it for a drive. It pops and misfires under heavy load, and the idle is up and down. Ive checked all the wires with a timing light, plugs look ok (less than a month old), 12v at the injectors, no codes, new O2 sensor, all of the injectors have a good ohm value (except #3, but it was like that before), new PCV valve. Ive been messing with it all week and im at my wits end. Any ideas?

 

try the old o2?

 

Sounds like either a couple wires crossed up or possibly a vacuum leak. I'ld double check #s 5&7, very easy to get those ones mixed up. If it ran good before, it's most likely something you did during the header install. It really sounds like crossed wires, recheck your firing order...it's 1 8 4 3 6 5 7 2.

 

UPDATE......no crossed wires. Used a laser pyrometer and the #1,2,3,4,5,6,8 cylinders were all reading between 535 and 635 degrees. #7 was at 400, so i put a new plug and nothing changed. The TPS was staying at a constant .55v with the engine going through surges. The O2 sensor climbed up to about .7mv with the engine running about 10 minutes. Dropped the computer and found a tan/white wire just barely holding on by about 2-3 strands of copper. Repaired that with no changes to the problem. My Haynes manual doesnt show a wire like that, so I dont know. Also found out it has a Hypertech 128842 installed. Going to see a buddy with a datalogger in an hour, so hopefully ww'll see something. Driving me crazy, this is my daily driver.

 

Try removing the hypertech chip and see if it runs better. I had a jet chip that made my car run like a terd, went back to stock and runs great.Just a thought.