Join Date: Feb 2009
Location: Largo, FL 33774
Changing the computer will not make a difference. The difference between computers is the chip. The headers may give the computer enough erroneous information that it thinks the mixture is too rich, and lean it out. stabbing the gas pedal could allow the computer to get the mixture info to keep the mixture a little richer at idle. You could redo the wire from the O2 sensor to see if it makes a difference. The fact that it is not throwing a code, implies that all of the sensors are doing their job, and the issue is with a non-monitored system. Fuel would be my first direction. As to what it is doing, you can not monitor the fuel pressure unless you install a fuel line from a 91, 92, or 93 Fleetwood (91 and 92 with an LO3/5) that has a Schrader valve port. Other than the fuel check, using a heated O2 sensor (because you changed its location) is the only other item that I would suspect causing the stalling. The long tube headers set up a resonant frequency pressure wave in the pipe to extract gasses from the cylinder head. If that frequency causes the O2 sensor to have an exhaust pulse hit it at a time when it is showing a rich mixture, the computer may lean the mixture at the injector. It may not be enough to trip the CEL, but enough to lean the mixture to the point where it stalls. This is all speculation, but I can not check the specifics. You might consider having a garage put it on a computer to verify the information sent by the sensors.
1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html