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.

[rsicard]

Forget my last post. I understand what is going on.

[rsicard]

Mod'd the 16197427 ECU. Put jumps across the two current sense resistors. Also put a jumper on the Memcal per the photo from HP tuners. Installed the ECU in the Suburban and started it up. Wow does it run shitty. Shut down the truck, removed the ECU, opened it up and removed the Memcal jumper, re-installed it in the Suburban. Ah, back to running smooth. Don't know the pin layout of the Memcal so I will stay away from jumpering it for now. Set up TunerPro RT to record BLM values at idle and off idle. Open loop at idle, it fills the BLM cells with 128. Set up TP to record off idle BLMs. Ran the Suburban for several miles to warm it up, varied the speed, RPMs, gears to fill in as much of the off idle BLM cells as possible. Then came back and parked at the house. Went back to idle BLM map, varied throttle to fill in as much BLM cells as possible. Captured all with MS Excel spreadsheet.