Ive got a 99 A4 vert with an ls6 with dart 205s and mti R1 cam. lately when i floor it and it gets up to the redline of 7000 it dies and then when i try to start it , it idles rough and smells like fuel and dies. when i try to rev it to clear it out it acts as if the throttle is not hooked to the engin(i know it is drive by wire) the only way that i had been able to get it to run after a stall is to try until i could get it revving to about 6000 rpm then it runs like normal. yesterday it died eveytime i had it at redline. I noticed that after a stall when i would go to start it that if i held the key in the start position as if i was going to keep cranking that it would idle and run fine but as soon as i let it go into the normal run position it would be rough and die. I thought maybe it was some kind of theft deterent system failing so i used my other key(in case the micro chip in the usual key was bad) and the first time i ran it to red line it stall as usual. The car was fine for 6 months with the ls6 in it so its not something that happened with the new engine..any ideas? Im not sure what to try next but the fact that it runs normal if i hold the key in the start position might shed some light from a more experienced person. thanks in advance for any help...Ps I checked and its not throwing any codes thanks, Normand

 

If your smelling gas, it sounds like the motor is dumping too much fuel and is soaking ther plugs which would cause the car to continue to die, and idle rough. Until the gas is burned off the plugs and the plugs get hot, which at 6,000 RPM that will do it. I would pul a pliug and take a look. If it smells like gas, and is wet the plugs are garbage. You might have a tuning issue.

 

the only thing about the plugs being fouled is that if i hold the key in the start position it will run as if nothing is wrong. maybe the key cylinder switch is messed up? Im not sure if thats even possible.

 

I was hoping a GM tech would have run into this problem before. Any other ideas? Thanks

 

I agree with the above post, pull your plugs and look at them.

You say that there are no codes, just to make sure, you did it this way, right?

https://www.corvetteforum.com/techti...D=26&TopicID=1

 

i pulled alot of codes. only one was current but right now the car runs until i floor it. Ill list some codes and if anyone can tell something let me know
P 1518 h
P 1571 h
P 1626 h this one has to do with theft deterent and thats kinda what it acts like to me
P 0410 c
C 1245h
u 1096h
u 1064h
u 1040h
u 1088h
u 1255h
u 1016h
b 2283h
b 2285h
b 2263h
b 2265h

if anyone can help ,please chime in . Thanks in advance

 

Clear all the codes in manual diagnostics and see what happens then.

The P1518 also may be a problem, this is the PCM to TAC module serial data.

Once you clear the codes exit out of diagnostics and then get back in to make sure that all of them are gone.

 

The '99 has a redline of 6K and its set in the PCM. At that RPM, fuel will be cutoff. How it does that I don't have a clue and the ramifications to that fuel cutoff action. You can manually change the redline cutoff but will need software, interface and a laptop.

 

the car was dyno tuned over a year ago when i put the ls6 in it and the rev limiter is now 7100. I did find something today.. the header to x pipe connection had lost some bolts so i know there was a leak after the first O2 sensors and before the second set of sensors. I think that my second set is desensitized or tuned out with the dyno tune because I dont run cats. I ran it alittle bit ago and it seems better. I'm wondering if the leak has been there so long that the pcm richened the fuel up and now I have to wait a few more cycles for it to return back to the way it was. If any other codes seem bad on my list let me know. I keep everyone posted on whether this cures the problem. Thanks everyone.

 

Assuming you're at WOT when you hit 7000 rpm, your O2 sensors should have nothing to do with this problem.

 

well i ran it through the gears a few times last night and it never stalled. somehow the exhaust leak must have screwed with the A\F enought for the computer to make a drastic change. Hopefully if anyone else has this problem this will give a possible cause to look for. Ill keep u posted on if the problem shows again in the future