since the TBI ecm is only 160 buad does that mean that it only adjusts the engine about every second? I know with the winaldl cable that is about as frequent as I get readings.

 

Mike,

Not exactly. The baud rate is for ALDL communications, so you'll only get limited updates about operation, sensor parameters, etc.

The oscillator for the CPU is a 4.712MHz crystal. The time base is a x/4 divider, so the CPU is actually clocked at just under 1.2MHz. This is clocking speed, not I/O scan speed. That is done on about every 1,000 operations, or 12,000 times per second. This also doesn't mean the I/O tables are updated at that rate, just scanned for status. Actual writing to the output data table occurs about every 24,000 scans, or 60+ times per second. Of course, this all depends on the length of the program. Since most older ECMs for TBI have a 32K EPROM and don't use all of the available words, and considering an 8-bit wide data bus, the processor can execute the entire program in somewhat over 12,000 clocks (read, compute, write) or at the slowest, about 120 times per second. Most are faster due to shorter programs. That is why we hear the IAC stepper motor "cogging" open or closed at about 40-60Hz (times per second) when in operation. The same is true for the M/C solenoid on CCC engines, EGR solenoid duty cycle, EVAP purge, etc. This is also why an older ECM can be limited to about 6,500 RPM, since the injectors can't be pulsed at a rate that will keep up with the engine speed at much more than that.

So despite the slower communications rate, your engine is under pretty tight control.