[XfireZ51]

Originally Posted by tpepmeie

Jeff,
Boy do I know what you are talking about. I was totally perplexed by this for several years on my modified '91. Several "little" things can help, but not totally eliminate this. For what it's worth, my pristine stock 7000-mile 93 does the same thing. I am (almost) convinced that this is something all LT5's experience. My personal view is that it is a function of the lengthy inlet tract behind the throttle blades, and the plenum volume. There is surely an inertial "lag" of the airflow from when the throttle is cracked to when the engine responds, but I can't get my head around the engineering explanation.

Some things that help, but don't totally eliminate the phenomenon:

1) Denso IT-22 plugs, or equivalent, gapped at no more than 0.040" AC Rapidfires seem to contribute to a sag, in my experience.

2) properly adjusted TPS sensor, and throttle blades. I like less than 15 IAC counts at idle.

3) extensively re-worked Delta TPS, and Delta MAP Acceleration enrichment and some other values in the calibration.

This sag clearly shows up as a lean spike on a wideband O2 trace. The task, therefore is to get the fueling to respond quicker to the initial tip-in. But not too much fuel as to cause a rich bog after the tip-in. It will try your patience to get it just right.

Short answer... you're not alone. It is just something to live with unless you want to spend hours working with the calibration to improve it.

Todd

Todd,

Do the Delta TPS/MAP AE have any "lag filters" or coefficients? How about the VAFPR? EBL has them which allows you to adjust how quickly these params will react to the changes. Shortening the lag improved throttle response significantly. I would think that the fuel would arrive sooner than the airflow given that the injector is closer to the valve than the TB. By that logic I wouldn't expect to see a lean spike. But as you described the stumble is caused by AFR leaning out.