sjdf10112

I have a 99 trans am with the ls1. I have long tube headers. CAI granatelli MAF ORY slp loudmouth 2.
Air delete egr delete. No tune
I have the following codes. And I realize most of the codes are from my emissions delete and running on factory tune.
P0140-o2
P0512-o2
P0160-o2
p0300-random/multiple mis
p1637-L circuit?
p0405-egr
P0418-smog

intermittent #6 & #8 misfire heavily when they miss they mis at same time. I can start my car and about 2 mins after it will start missing horribly. This morning when it started to mess up I killed it right away and restarted it and it ran fine the whole 10 mile drive to work. Please help. I've changed pugs wires and checked my coil packs

LS1MCSS

iTrader: (18)

This a tuning question. See if you can get a moderator to move it to the correct section and you will get some answers.

03Sssnake

iTrader: (20)

Did you just install the headers, anything else change?
P0160 and P0140 are the down stream O2s, expected without tuning them out and should not cause a misfire
P0512 is "Start Switch Circuit"
P1637 is related to your alternator, to the "L" terminal. Check the connections and wires for damage
You can ignore the smog and egr ones, should not cause the car to miss. I would also plug the stock MAF back in, and/or unplug the Grantelli MAF and see how the car runs, it will run with the MAF unplugged.
Also make sure your plug wires/boots are not touching any of the header primaries, that will definitely cause random misfire. I have shot myself in the dick on that one and ruined new MSD wires...
When you installed the wires, did you get two clicks at the coil and one click at the plug?

Paul Bell

iTrader: (9)

SJDF10112, welcome to LS1tech!

You'll do better with this over here.

sjdf10112

@03Sssnake. I'vehad the headers on for about 6 months . And just now having problems. I recently discovered that when it goes into the misfire deal if kill it and immediately recrank it it runs fine. I think it's something to do with computer. Please help.