Tuning '94 chev Suburban Big Block

[rsicard]

With the injectors firing every 2nd DRP (TBI mode) the Pulse width of the now 8 injectors (especially if you upgraded to the 29#/hr units) becomes very low. This is a result of the PCM commanding an injector pulse every 2nd DRP and essentially overfueling at idle and part throttle. Once the fueling is expanded to an injector pulse once every 4th DRP the injector pulse width is restored to a more tolerable level , resulting in a cleaner idle and an easier transition to tune from idle to off idle.

Pin 56 on the Memcal is the cylinder select pin , depending on what the voltage is at on pin 56 it controls what fuel mode is selected.

There is a chart somewhere on this site , I think by 1Project2Many , that describes what fueling mode is selected by what voltage is seen on pin 56. I will try to search it out if I get a minute.

Hope this helps.

TOM

Switching from the 2nd DRP to the 4th DRP should lean out both the on-idle and off-idle operation of the engine. Is this correct? Please advise. Thanks.