Yeah it is 160 baud, but how in the world does it work? I know it reads off the serial data. I am guessing I need the caddy 4.5 ECM? My guess is that it is using Injector pulsewidth, speed, engine RPM to calculate the data? Anybody have a clue?

 

TBI ECMs that drive a MPG display output a 5 byte data stream (typically, this is all in general). Once the AB terminals are shorted (or 10K?) the ECM then outputs the standard diagnostic ALDL stream.

The MPG display stream has four bytes of interest: injector flow constant, accumulated distance pulses, accumulated injector pulses (2 bytes). These three terms are used to calculate the MPG, and distance traveled.

The accumulated distance pulses are incremented each time a VSS pulses occures. So for a 2000PPM VSS the miles traveled is accumulated distance pulses / 2000.

The accumulated injector pulses is the total time the injectors have been open.

Both of these terms count up and roll back over to 0. This needs to be tracked in the MPG display box.

RBob.

 

You lost me on the 5 byte data output? Would that be a standard TBI ecm? I know the older vettes had a similar setup as well. Any easy way to get the 7747 or the 8746 to spit the required information out the serial data stream? I know the patch that modifies the data output on moates.net. Maybe I am better off using the 4.5 caddy TBI and ECM. That would also integrate my cruise control into the ECM as well??? Any known hacks for the cadillac TBI ecms?

 

Just picked up the parts. I have the cadillac ECM, the cadillac BCM and the fuel data display. I also have harness clippings from everything. I will be incorporating the cadillac BCM into the van as well. That way I can have all the features offered in that year model as well. Theres alot of them. I also have the haynes manual for the car as well. The serial data goes from the ECM, to the BCM, then the BCM runs the display. Would the conversion values be stored in the ECM or the BCM. I know they used several different engines in these cars 4.1 TBI, 4.5 TBI, and 4.9 PFI. Apparently the BCM is the same but the ECMs are different. I am thinking the ECM is feeding the BCM the data you stated, the BCM translates it, and the fuel data module displays it.

Now I only need to find .ECU file for the ECM, if one exists? Even a partial one would help? Maybe just the injector constant, VE tables, and spark tables?