Driver Error? Time for another Tune?
Thread Starter
Racer
Joined: Dec 2004
Posts: 427
Likes: 0
From: Albuquerque New Mexico
Driver Error? Time for another Tune?
Hey guys, here's head scratcher for ya'
The car:
1996 LT4 Procharger
Air to Air intercooler
Forged motor, FAST stand alone fuel management.
Here's the situation, sometimes when I WOT up to redline and then hop off the throttle, the engine shuts down. If I try to start it right away, it catches and then shuts off. If I leave it for about a minute, it catches and sings it's pretty tune as if nothing ever happened. Any thoughts on why this is happening?
The car:
1996 LT4 Procharger
Air to Air intercooler
Forged motor, FAST stand alone fuel management.
Here's the situation, sometimes when I WOT up to redline and then hop off the throttle, the engine shuts down. If I try to start it right away, it catches and then shuts off. If I leave it for about a minute, it catches and sings it's pretty tune as if nothing ever happened. Any thoughts on why this is happening?
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
drochau,
Look at the base VE table. Review your values from 4K-6.5K at the lower right of the table. Even though low values in the lower right prevent the proverbial "pops" in the exhaust, if you go too lean, the car will shut off while moving. I target 12.2 AFR at the lower levels, and achieve that with a slightly higher 50-60 VE. It will run in the 40s, but seems happier in the higher ranges.
What target AFR are you running at max boost (and what is the boost)?
Aaron
Look at the base VE table. Review your values from 4K-6.5K at the lower right of the table. Even though low values in the lower right prevent the proverbial "pops" in the exhaust, if you go too lean, the car will shut off while moving. I target 12.2 AFR at the lower levels, and achieve that with a slightly higher 50-60 VE. It will run in the 40s, but seems happier in the higher ranges.
What target AFR are you running at max boost (and what is the boost)?
Aaron
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
So you're saying that the engine actually dies, as in, you coast over to the side of the road? If thats the case I couldn't see being a tuning problem, especially if you can't start it again right away. Do you have any kind of wideband or EGT feedback into the system? You might want to disable it and try it again, or just monitor it closely.
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Tuning can cause what he is describing, as a very lean tune can "snuff" the flame. A lot of tuners will go lean under high vacuum situations (i.e just off idle, low RPM, low load, etc), but when that is combined with higher RPM, the situation can cause the car to die.
As he is running FAST, I'm sure he is running a wbO2, and as such will find that under high vacuum, his desired AFR will be closer to stoichometric vs staying a bit rich. I do not think disabling the wbO2 is a good idea, though I do recommend max of +20%/-5% on the upper two rows of the VE table in a 2 bar set-up (4 rows in a 3 bar set-up), which will not solve this issue, as he is dealing with the bottom right in the VE table.
Let's see what drochau returns with regarding desired/actual AFR.
Aaron
As he is running FAST, I'm sure he is running a wbO2, and as such will find that under high vacuum, his desired AFR will be closer to stoichometric vs staying a bit rich. I do not think disabling the wbO2 is a good idea, though I do recommend max of +20%/-5% on the upper two rows of the VE table in a 2 bar set-up (4 rows in a 3 bar set-up), which will not solve this issue, as he is dealing with the bottom right in the VE table.
Let's see what drochau returns with regarding desired/actual AFR.
Aaron
Thread Starter
Racer
Joined: Dec 2004
Posts: 427
Likes: 0
From: Albuquerque New Mexico
Sorry
Sorry about the dely folks. I shredded the belt at the supercharger on saturday and I won't get the car back until at least tommorow morning. I'll be back with the data tables tommorow night though.
On an unrelated note, the damn ac pulley is what shredded the belt...so I'm deleting the son of a gun
. Guess mother nature will be providing the cool air for me now.
-Dave
P.S. I don't have the a/f tables on me, but I did check out the last dynotune. It looks like my leanest period happens right around 3900 rpm at 11.81 so I'm a little rich as when the RPM hits 6k I'm a fat 12.74. When I get the car back I'll check out the tables and see what it is set for at vaccum.
On an unrelated note, the damn ac pulley is what shredded the belt...so I'm deleting the son of a gun
. Guess mother nature will be providing the cool air for me now.-Dave
P.S. I don't have the a/f tables on me, but I did check out the last dynotune. It looks like my leanest period happens right around 3900 rpm at 11.81 so I'm a little rich as when the RPM hits 6k I'm a fat 12.74. When I get the car back I'll check out the tables and see what it is set for at vaccum.
Last edited by drochau; May 2, 2005 at 07:33 PM.
Safety Car
Joined: Apr 2001
Posts: 3,525
Likes: 2
From: Houston TX
Originally Posted by drochau
It looks like my leanest period happens right around 3900 rpm at 11.81 so I'm a little rich as when the RPM hits 6k I'm a fat 12.74.
It may be that it is already lean, and then goes to high vacuum and the target AFR is very lean.
Look at the tables and let us know.
Aaron
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Thread Starter
Racer
Joined: Dec 2004
Posts: 427
Likes: 0
From: Albuquerque New Mexico
Good Call
hahha, noob mistake. Guess this is why my wrench work is done with my wallet! I get it now, air/fuel ratio not the other way around. Anyway, car should be back tommorow I'll let you all know what's going down.