Car wont run now!
Thread Starter
Teching In
Joined: Jun 2010
Posts: 42
Likes: 0
From: Enid, OK
Car wont run now! Alright guys, so here is the rundown and I think I may have really screwed up. I got my new TDP tranny, stage 3 diamond clutch, and tick m/c put in saturday. I drove it last night and part of today open header then put the exhaust back on when i got a chance today. Now here is the problem, it has been tuned in the past not stock, has a 230/230 comp cam in it. It threw the check engine light on my way to the shop to put on the exhaust, so i unhooked the batter while installing exhaust and then went to eat, came back, hooked battery back up and started the car. Now it will not run! It surges from about 850rpm down to 200 and back up if it doesnt die, and constantly dies when driving and coming to a stop. It is an M6. So here is my real question now, since I unhooked my battery for that amount of time to clear the code, could that have wiped out my tune? 
Staging Lane
Joined: Nov 2009
Posts: 77
Likes: 0
From: The End of My Rope
I'm almost damn certain that a tune is stored data in the computer. Even unhooking the battery will not erase the code that was generated. It'll clear your light, but will still be stored. Just happened on my pig, I unhooked the battery to change my plugs (had to pull the starter), my SES light was on. When I got done a few hours later, I re-connected everything and my light was off. Code still popped up on my scanner, and would've stayed there until I erased it. Even then, a computer that is more hi-tech than my Actron (such as the dealer's) may still be able to pull it up, not sure...
But to answer your question, I've NEVER heard of a tune being erased by leaving a battery disconnected. And in attempt to shed some light on your situation, I had the exact same thing happen to me, regarding your idle condition. The back cylinder on the passenger side (Gen I & II it would be #8, can't remember the Gen III), I had a helluva time getting the wire to snap onto the coil. I thought I had it. Got everything bolted back up, and it barely wanted to idle or even rev. I put it in gear to pull it forward into the garage a little more, and it died out. I knew it was that wire. Un-bolted the EGR tube off again, 20 minutes of fighting and scratches on my forearm, and I got it to snap in place. Good to go.
Just sayin'....
But to answer your question, I've NEVER heard of a tune being erased by leaving a battery disconnected. And in attempt to shed some light on your situation, I had the exact same thing happen to me, regarding your idle condition. The back cylinder on the passenger side (Gen I & II it would be #8, can't remember the Gen III), I had a helluva time getting the wire to snap onto the coil. I thought I had it. Got everything bolted back up, and it barely wanted to idle or even rev. I put it in gear to pull it forward into the garage a little more, and it died out. I knew it was that wire. Un-bolted the EGR tube off again, 20 minutes of fighting and scratches on my forearm, and I got it to snap in place. Good to go.
Just sayin'....
Disconnecting power for a while does, however, clear out the Long Term Fuel Trim data which can make poorly-tuned engines run badly until they're warmed up and running in Closed Loop again.
